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C++ 1: Introduction to C++ - O`Reilly School of Technology

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1. F Save and run it and observe the output OBSERVE Result is 1 You might be asking yourself why we can t use the equality operator to check to see if two strings are the same Let s try itto see how it might work include lt cstring gt include lt iostream gt int main char strif Steve char str2 Steve if strl str2 std cout lt lt Same lt lt std endl gt cout lt lt Not the same lt lt std endl return 0 F Save and run it and observe the output OBSERVE Why is this The two strings obviously have the same value Using our mailbox metaphor the equality operator checks to see if the two mailboxes are the same like if they have the same serial number it doesn t check their contents This fails because the mailboxes are notthe same Tips Converting C Strings to C Style Strings You can convert from C style strings to C style strings and vice versa To get a C style string from a C style string use the c_str function You can assign a C style string to a C style string Try it include lt iostream gt int main i char name Sam The name for this example char other Toa Another name char c style 4 New variable to hold C string slat setring cpp Style cpp style name Assigning to a Ct t style string SGCttaLIincpy ic Style cop Style c str 1 Copy C string to a varias std cout lt
2. I have T lt lt CLASS SIZE lt lt Y students in my class lt lt std end 1 return 0 F Save and run it If you typed everything correctly you will see the following What happens if the program tries to change the value of CLASS_SIZE Try it include lt iostream gt int main conet int CLASS SIZE 20 Stas scout lt lt TI Dave T lt lt CLAS OIAR lt lt T studentie 1m my class lt lt std send 1 CLASS SIZE 35 Std scour lt lt Now I have lt lt CLASS SIZE lt lt students in my class lt lt std endl return 0 Save your code This time your program won t compile because you are trying to change a constant F Build of configuration Debug for t project constants const int CLASS SIZE 20 std cout lt lt I have T lt lt assignment of read only variable CLASS SIE std cout lt lt Mow I have e Internal Builder is used for build ec g O0 g3 Wall fmessaqe length 0 oconstants a Constants cpp Constants cpp In function int returni mainii Conatants cpp 9 error assignment of read only variable CLASS SIZE Build error oceurred build is stopped Time consumed 6807 ms If your number is going to change in the middle of a program run like this it shouldn t be defined as a constant To fix this problem you d need to remove the word const from the variable declaration and change
3. OBSERVE Hello World My name is Steve Our output appears on two lines because we used std endl Another way to make the output appear on two lines is to use the special escaped character n Modify hello cpp as shown include lt iostream gt int main std cout lt lt Hell World lt lt n std cout lt lt My name is Steve lt lt n return 0 O Save your program and run it The output looks identical to the last run OBSERVE Hello World My name is Steve n is called an escape character The backslash escapes from the regular interpretation of keyboard characters to begin a special multi character sequence indicating a special character In this case it s a newline or end of line the equivalent of pressing the Enter key For more information see the glossary s description of the escape character But the escape character is the old fashioned way to printa newline The more modern practice is to use the special symbol std endl There is a subtle difference between n and std endl the std endl symbol causes a buffer flush which makes sure the output appears immediately The n is not required to flush the buffer although on most systems it does We cover buffering and flushing in more detail in later C courses What Goes On Under the Hood Eclipse is a type of tool called an IDE or Integrated Development Environment This sort of tool is a wrapper around many o
4. Le 1L gt 12 return il return i2 int main int i 1 int jJ Z3 Std cout lt lt Max 1s lt lt max 1 J J lt lt std return 0 F Save your program you ll see this error e Build of configuration Debug for project int max const int il const int 12 Var pass ttt i d assignment of read only parameter il if iil gt iZ ttt Internal Builder 18 used for build kaw er return 1i1 g O0 g Wall c fmessage length 0 return iz j OVAD pPaSS o0 Var pass cpp i VWar pass cpp In function int maxfint int VAE pass cpp 6 error assignment of read only int main parameter il Build error occurred build is stopped int i 1 Code that attempts to change the value of a constant parameter results in a compile time error In this case the code i1 99 is the offender References References let different variables point to the same underlying value It is like having a two sided mailbox the postal worker opens the box on one side to deposit mail and you open the box on the other side to retrieve it Both doors point to the same contents Let s take a deeper look at references Change your code as shown tinclude lt iostream gt int amp max eens int amp il eerste int amp 12 fa e 11 gt 12 return il return 12 int main int 1 1 int J 23 Std cout lt lt Max 1s lt lt max 1 J lt lt std return 0 O
5. Properties for exp expression iol x type Filter text C C Build t e 2 Project References RunjDebug Settings Builder Setting Behaviour i Task Repository Build settings M Stop on First build error Use parallel build Use optimal jobs number f Use paralleljobs 1 Workbench Build Behavior Workbench build type d I Build on resource save Auto build Note See Workbench automatic build preference M Build Incremental build W Clean Restore Defaults Apply Now in the exp expression project select File New Source File and enter information as shown New Source File Ox Create a new source File C Source Folder exp expression Browse Source File exp expression cppl Configure Template Default C source template Editing and Running Your Program Open your exp expression cpp file and enter the following code we ll omit the automatic comments from now on to save space include lt iostream gt int main std cout lt lt The answer is lt lt 1 2 4 lt lt std endl return 0 F Save your source file then in the editor window for exp expression cpp right click and select Run as Local C Application or select exp expression cpp in the Package Explorer and click the F icon in the toolbar You ll see this output OBSERVE The answer is 12 The computer evaluated or calculated the answ
6. include lt iostream gt int main std cout lt lt The answer is lt lt 1 2 4 return 0 F Save and run it You ll see this OBSERVE The answer 1812 Do you see a problem in this code That s right we need a space between is and the answer Add the space as shown we use an underscore here to represent the space include lt iostream gt int main Sta scout lt lt The answer 126 lt lt 1 2 gt d return 0 F Save and run it Hmm There s still a problem See if you can spotit We ll add another output statement as shown in blue below to help illuminate the problem include lt iostream gt int main std cout lt lt The answer is lt lt 1 2 4 std cout lt lt The answer still is lt lt 1 2 4 return 0 O Save and run it The outputlooks like this OBSERVE The answer is 12The answer still is 12 Any additional output statements will be appended to the end of this one You need to add a newline at the end of the output line Edit the program as shown include lt iostream gt int main std cout lt lt The answer is lt lt 1 2 4 lt lt std endl std cout lt lt The answer still is lt lt 1 2 4 lt lt std endl return 0 F Save and run itto make sure thatthe problem has been corrected We covered a lotin this lesson We went over expressions integers and float
7. loop int temp 1 A local variable to play around with Staitcout lt lt global 16 T lt lt global lt lt std endl std cout lt lt temp is lt lt temp lt lt std endl qlobal rT Leni Almost useless comment return 0 F Save and run it and observe the output Output of var types globa Mmi Il temp is 1 Globalis 2 temp is 1 global is 3 temp is 1 The value of temp never changes but why The answer scope Let s take a closer look atthe life cycle of temp var types cpp include lt iostream gt int global 1 Global variable to play around with int main e IOC A loop counter moe lose 0p loose lt Se Flloce int temp 1 A local variable to play around with Stele colle lt lt YellcloeJk aks Y lt lt ellcloet lt lt steele seiniolily Sec Cout lt lt hemp ahs e lt lt eeo lt lt ste endl Teo Popa temp Almost useless comment return 0 The variable is created by the line int temp 1 It then is incremented by the line temp so its value is 2 Itthen is destroyed just after the line Almost useless comment So itnow has no value because it doesn t exist The for loop starts another loop The variable is born again with the line int temp 13 It s important to remember that the scope oftemp is local and the storage class is temporary We can make a local variable permanent by putting the keyword s
8. Multiple markers at this line eg city ciby was not declared in this scope unused variable city lt lt Std endl The compiler is telling us that city isn t defined but we did define it didn t we Not quite The variable city has a local scope Scope is the portion of a program in which the variable is known city only exists within the curly brace block enclosing it not outside of it Compare this to the state variable It also has a local scope but its enclosing braces include the entire program Is the state variable accessible from the middle of our program Let s see Change your program tinclude lt iostream gt int main std string state Texas std cout lt lt State 1 is lt lt state lt lt std endl SLaOSsString city Austin Std scout lt lt City is lt lt city lt lt std endl std cout lt lt State 2 is lt lt state lt lt std endl F Save and run it You ll see OBSERVE Starte vil is Texas Cits Io Au tin Starte 2 is Texas Though we added a block in braces and a local variable to our list of variables state is still within the scope ofthe program Now let s see if we can access state AFTER the block in braces Change your program include lt iostream gt int main std string state Texas std cout lt lt State 1 is lt lt state lt lt std endl std string City Austin
9. for x 0 x lt CLASS SIZE x x 1 total total students x In English this loop might be written this way for x starting at zero while xis less than CLASS_ SIZE xis incremented by one after we add each student value to the total Since x starts atzero and our CLASS _SIZE is 5 the code total total students x will run five times with x having the values 0 1 2 3 and 4 A for loop typically has these parts OBSERVE for Initialization Test Increment body of loop In our loop e x 0 is the initialization code Arrays start at zero so x must start at zero as well e x lt CLASS_ SIZE is the test code Our array only has the number of elements 5 specified by CLASS_SIZE but the indexes start at 0 so the last index will be 4 therefore we want to stop looping before xis equal to CLASS_ SIZE e x x 1is the increment code x will increase by one after each iteration e total total students x is the body of loop code which updates the total To really see what the for loop is doing let s add some code to show the values of x and total inside the loop while it s running include lt iostream gt int main const int CLASS SIZE 57 int x float average OF average of the items Q0 float total 0 0 the total of the data items float students CLASS SIZE 34 0 27 0 46 5 82 0 22 data to average a nd total f
10. students x std cout lt lt Studentsix lt lt x lt lt lt lt students x lt lt total lt lt to tal lt lt std endl average total CLASS SIZE std cout lt lt Total lt lt total lt lt Average lt lt average lt lt std endl return 0 Save the file No error or warnings will be generated because the computer assumes you know what you are doing and has not checked to make sure you are staying within the bounds of the students array What happens when you try to run the program Run it to find out F Your program may run and it may crash If it runs you might see output like this OBSERVE Students Students Students Students x 34 tOTals 34 x E x Students x Xx Xx x ex Ze total T 6 il AO eee EOC Omi S28 jeOwe lls Ike 5 227 total 25 oe eC nme a Soetoro oD Ota 4 S08 Oe secs S210 s 2 4307 Oral 564 7 Students Students Students Students Co O CO SS WWD FS Stcucents x Students x 10 3 21401le 039 total 564 7 Students x 11 5 95261le 039 total 564 7 Students x 12 1129 4 total 1129 4 Students x 13 0 total 1129 4 Students x 14 1 96182e 044 total 1129 4 rotal 2I1 5 Average 21 153 KO See the junk added atthe end Your specific output may look different C didn t check to make sure you were staying within the bounds of your array and happily went on with the program Itis like trying to get mail o
11. 0 test retains the value originally assigned to it We learned a lot about variables and types in this lesson In the next lesson we ll learn how to store many values ofthe same data type using arrays See you then E a a D Copyright 1998 2013 O Reilly Media Inc This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information Arrays and For Loops C 1 Introduction to C Lesson 4 Using Arrays So far we ve only learned basic data types and every datum had a name But Suppose we want to calculate the average grade for twenty students in a class It s a lot of work to define twenty different variables one for each number OBSERVE Hane lt Sisueleioe Il A number we are going to average ine otudent A number we are going to average int studento A number we are going to average AM Wot Goring EO Wweite eur che whole ching int student20 A number we are going to average Arrays allow us to define a set of data like a group of mailboxes at an apartment building Compare this to a regular variable one that isn t an array it is like a mailbox outside of a single house A regular non array variable is justa single part of your computer s memory butan array is a chunk of continuous memory locations Here is how we d declare an array to store the same se
12. Compare with d Replace with d Preferences Exclude From build Build Configurations d Make targets d Remove From Context Et GlE Shife Dovn Note To run a program you can also select itin the Package Explorer and click the Run icon 2 in the toolbar at the top of the screen In the future we ll use that icon when we wantto run the program A Console window appears containing the output from your program terminated hello world exe CMC Local Application w tworkspaceth x k Ex Ele A E ri 2 hello cpp Hello World 3 q created on May 3 2010 5 Luthor smiller 6 r TF hello cpp m T 10 created on Deg 15 2009 iij Author miller la ls include lt iostream lint maini 15 std cout lt lt Hello World lt lt std endl 16 return O 1 is Excellent You ve run your first C program Now let s screw it up We re doing that on purpose now so we ll know what it looks like and how to fix it when we screw up our programs later by accident Modify hello cpp as shown below include lt iostream gt int main standard cout lt lt Hello World lt lt std endl return 0 Note We omit the header comments from some of our examples in order to save space In your real programs you should always include descriptive comments Save your file File Save all Ared icon appears on the left side of the panel near the line you just changed If you
13. Let s try an example Edit c string cpp as shown include lt cstring gt include lt iostream gt int main char name 25 Short name with plenty of space std cout lt lt Size is lt lt sizeof name lt lt std endl std strncpy name Joe sizeof name std cout lt lt Name is now lt lt name lt lt std endl std strncat name Smith sizeof name std strlen name 1 name sizeof name 1 0O std cout lt lt Name is now lt lt name lt lt std endl return 0 F Save and run it and observe the output OBSERVE Size ae 25 Name is now Joe Neame is now Joe Smith Success Comparing Strings The C style string comparison function is std strcmp Ittakes two parameters OBSERVE std strcmp stringl string2 It returns e O ifthe strings are equal e Apositive value ifthe first character that does not match has a greater value in string1 than in string2 e A negative value if the first character that does not match has a greater value in string2 than in string1 Let s see how it works Create a compare c project and assign itto yourC 1_Lessons working set Then create a program named compare c cpp as shown include lt cstring gt include lt iostream gt int main char strif Steve char str2 Steven int result BUI teCrcmpisli ri SDr std cout lt lt Result is lt lt result lt lt std endl return 0
14. O0 g3 Wall c Imessaqe length o0 oc string o g string cpp return Q 40 string cpp In function int maini 4C string cpp 6 error ISO C forbids assignment of arrays Build error occurred build is stopped Time consumed 625 ms This error is generated because C strings require the programmer to worry about memory and do extra work when copying them Think of the mailbox analogy from the array lesson here we created a mailbox with three slots containing the values S a and m Using name Joe is like buying a new mailbox with three slots and trying to shove the new mailbox with slots J o and e where the old mailbox is still hanging Instead of trying to smash one mailbox in place of another we must manually open each slot and copy the contents from the new to the old This is done using the strncpy function see the reference information at colusplus com Note this reference uses an old header file string h instead of the current one cstring This function has three parameters strncpy Syntax std strncpy destination source size destination is where the data is to be put source is the source of the data and size is the maximum number of characters to putin the destination Before we can use strncpy we need to get out our tape measure an operator named sizeof sizeof returns the size of something in char units If we use iton a C style string it will return the maxim
15. The std cout functionality is defined in iostream so in order to use std cout we have to include iostream in our program Edit the program as shown include lt iostream gt bipedia Lie int main L 2 d return 0 When you compile the program you ll notice a warning triangle next to the line that contains the expression Look in the Console panel to see the text associated with the warning er fmessage length 0 oexp expression a int maini EXpP expression cpp exXp expression cpp In function int waint Eexp expression cpp 9 warning return Oj Statement has no effect g oexp expression amp xe EXP EXPression c Build complete for project exp expression Time consumed 516 m s The warning reminds us that our expression doesn t really do anything we do not output its results or save them anywhere F Save and run it The output window contains absolutely nothing In particular it does not contain the result of the calculation The line 1 2 4 tells C to compute the value of the expression but nothing more It doesn t store the result anywhere doesn t make a decision based on the result and doesn t output it C just computes the answer and then throws it away This is perfectly legal but pretty strange so strange that the compiler issues a warning when you build it That s why you got the no effect warning Let s fix the program by editing itas shown
16. lt The name if lt lt name lt lt T and other is lt lt other lt lt std en stds tcour lt lt cpp style as a C style string is lt lt o style lt lt stditend return 0 In this example we 1 Copied a C style string to a C style string using direct assignment cpp style name 2 Copied a C string to a C style string using c str and std strncpy F Save and run it and observe the output To us the results look the same OBSERVE The name is Sam and other is Joe Coo style as aa Cosivie Slicing a8 Sein Unsafe String Functions Many people don t use the string copy design pattern we provided and thus buffer overflow problems occur in many programs Instead they use the function std strcpy The standard form of this function is Unsafe Use of strcpy jf WaASeie De ino wise std strcpy destination source Where destination is where the data will be copied into and source is the string to copy Paranoid programmers will ask themselves What happens if the source is bigger that the destination The strcpy function does not check length and if the source is too big it will happily write random memory corrupting your program j xe Y o 5 2 O om O Q s o 3 D a Y Q r Z lt Q O Q fe C lt In the style guide we recommend that you not use the strcpy function In the real world you might encounter le
17. std string name std cout lt lt Enter your name std cin gt gt name std cout lt lt You typed lt lt name lt lt std endl return 0 F Save and run it Enter a first name a space and a last name separated by a space and press Enter You see something like OBSERVE Enter your name Jimi Hendrix you cypel Jimi The program only reads the first name You probably know Jimi by his first name but that won t work for everyone But all is notlost The solution is to use the standard function std getline The general form of this function is getline syntax std getline input stream string The input stream is the source of the data in our case it s std cin Change your reading program as shown tinclude lt iostream gt int main std string name std cout lt lt Enter your name std getline std cin name std cout lt lt You typed lt lt name lt lt std endl return 0 O Save and run it again Enter the first and last name and press Enter This time the resultis much better OBSERVE Enter your name Jimi Hendrix You typed Jimi Hendrix std getline reads a full line up to and including the end of line character The result minus the end of line is stored in the string Reading Integers std cin and the gt gt operator work for all sorts of variables including integers Edit your reading program as shown tinclude lt
18. 1 to 2 and multiply the result by 3 and get 6 2 Increment the FIRST current_size from 2 to 3 and multiply the result by 5and get 15 3 Add the results from steps 1 and 2 together and get 21 So which result is right They both are The C standard allows for this ambiguity That s one of the reasons the style guide prohibits this type of coding We want to make the code safer and more reliable You should never use the increment and decrement operators inside another expression especially an assignment statement But some people do so it s important to know how they work The prefix increment x operator increments the variable and returns the result after incrementing The postfix increment x operator increments the variable and returns the result bef ore incrementing The mnemonic use is that if you see the first then C increments first then returns the value If you see the value first C returns the value first then increments it Now let s rewrite our program so it does one thing ata time with no side effects include lt iostream gt int main int total size Total so far int current size Count of the numbers int first termy 77 foe first term int second term for second term total size U current Size 1 current size 1 tiret term Current size J current aize 17 Second term current size Jj TCA S125 Tire tern rerna Cery Stds regut lt lt C
19. 854 775 808 to 9 223 372 036 854 775 807 This is the difference between 32 bit 16 bit and 64 bit integers Unless you are interested in the technical details regarding the physical storage of integers within your computer s processor you don t need to remember the difference between bit sizes and number ranges Instead remember there are different ways to store this data and remember to use the constants we saw earlier such as INT_MAX Think ofa variable as a box You can puta single integer in it and you can look in it and see what s in it Let s look at this in action Create a project named assign exp in yourC 1_ Lessons working set and a program named assign exp cpp that contains the following code Put in the regular heading comments include lt iostream gt int main int play An integer to play around with play 5 Std scout lt lt The value of play is T lt lt play lt lt std endl return 0 F Save and run it This program assigns the variable play a single value and then uses itin an output You ll see the results OBSERVE The value of play 13 5 The program stores 5 in the variable named play and then displays that value to you Variables can change values as programs execute and play is no exception Let s see how the value of play changes as the program executes Change your program as shown include lt iostream gt int main int play An integer to play around wi
20. Eria first Joyce last Kilmer full first last Cl e Ql 7 a Stat tcout lt lt My substring ie lt Tull eubserrt4 5 lt lt aces rencl return 0 O Save and run it You will see the following output My substring 1s 2 Kill Let s take a look at the substr code rull substr 4 5 The 4 is the position ofthe starting character for the substring in this case the e in Joyce The 5 is the length of the substring in this example the program returns the characters e space K i and I If you omit the second number a different substring is returned Try it include lt iostream gt include lt string gt int main std string first First name stdristring lasti Last name std istring full The full name first Joyce last Kilmer full first last std cout lt lt My substring is T lt lt full subastr 47 3 lt lt std return 0 O Save and run it This time you will see OBSERVE My substring is e Kilmer C also has a function to tell you how many characters are in a string It s called length let s try it include lt iostream gt include lt string gt int main std string first First name Storestring last Last name std string full The full name first Joyce last Kilmer full first last stdircout lt lt My name has lt l
21. File Select File New C Project enter the information and click Finish as shown C Project de Create C project of selected type Project name exp expression M Use default location Location VWworkspace exp expression Browse Project type Toolchains J i Executable Empty Project xL C C Tool Chain 2 i Hello World C Project H E Shared Library H E Static Library 5 gt Executable xL C C oo Static Library xl C C lt gt Shared Library L C C H E Makefile project M Show project types and toolchains only if they are supported on the platform If you are prompted to change the perspective check the Remember my decision box and click No Open Associated Perspective This kind of project is associated with the ClC perspective Do you want At to open this perspective now M Remember my decision e Assign the C 1_Lessons working set to the exp expression project right click the project select Assign Working Sets and assign the working set as shown Working Set Assignments ojx Select working sets for exp expression C I Python Lessons O I Pythonz Community C I Pythonz_Handback Deselect All LIL Phar Heres Select All HE lw Show only Package Explorer working sets Configure In the Package Explorer right click the exp expression project select Properties and set the Build properties as shown
22. Increments total size 2 Assigns the value of total_ size to current_size This is bad programming style because it makes the code harder to read Two short operations are much easier to maintain and understand than one complex one There is another problem with side effects Change your program as shown include lt iostream gt int main int total size Total so far int current size Count of the numbers total eize U current Sige 1 total size f current Size 9 Ftcurrent size 3 std 2CouL lt lt Current Size lt lt Current size lt lt SCdriendl stdescour lt lt Total Size lt lt Total size lt lt stditendl return 0 F Save and run it Once again the output may surprise you OBSERVE Current olz o TOCE ze ie The code total size current size 5 current size 3 tells C to 1 Increment current_size and multiply the result by 5 2 Increment current_size and multiply the result by 3 3 Add the results from steps 1 and 2 together There is no rule that tells C which step step 1 or step 2 to execute first Depending on the compiler the execution order could 1 Increment the FIRST current_size from 1 to 2 and multiply the result by 5 and get 10 2 Increment the SECOND current_size and multiply the result by 3 and get9 3 Add the results from steps 1 and 2 together and get 19 Or it could 1 Increment the SECOND current_size from
23. Line Delimiters To d Per Other Ctrl N Print Ctrl F Switch Workspace d Re a Oe a A A O yet 1 Note f C Project isn ton the menu then the perspective hasn t been set properly Click the down arrow i next to the Red Leaficon and then select C Due to limitations in the GNU tools all project names and file names should consist of only letters Note digits and underscores Do not use punctuation or spaces in a name It confuses the tools and causes things to break For Project Type select Executable Empty Project Under Toolchains select MiniGW GCC the default Then click Finish C Project gt Create C project of selected type Crojectname hello word J mame hello world Use default location Location Vowworkspace hello world Browse Project type Ming Glee ee Hello World C Project gt Shared Library H E Static Library lt gt Executable xL CIC m Static LibrarysL C C on Shared Library XL C C H E Makefile project Iw Show project types and toolchains only if they are supported on the platform If you are prompted to open the C perspective check the Remember my decision box and click No Open Associated Perspective x This kind of project is associated with the ClC perspective Do you want ey to open this perspective now M Remember my decision New projects are added by default to the Other Projects working set To help keep your pr
24. PYTHON C etc Most of the perspectives look similar but subtle changes may be present under the hood so it s best to use the perspective designed specifically for each course For this course select C 05T Java Eclipse Platform File Edit Navigate Search Run Project Window Help a POO TTE Start Page 5 b To select the perspective for this course click the down arrow next to the red leaf and then select C To reset the perspective click the red leaf O SCHOOL oj TECHNOLOGY gt My Start Page Steve Miller s Start Page Okay now that you understand the basic structure of an OST course you re ready to enter and run code Writing Your First Program We want you to see a working C program as soon as possible so we ll resist the urge to explain too much for this first program while you re creating and running it Let s get going we ll fill you in on the details later To start your project select File New C Project as shown here C C Eclipse SDK File Edit Refactor Navigate Search Project Run Window Help ce C Project Alt Shirt h F amp e Open File fey C Project Clase erly N Project Close Al irb Shift rh Convert to a CfC Make Project Save atris Source Folder Save Oe Folder Save All brl Shitt 5 Source File Revert Ci Header File ct z T File From Template Reman re G Class Refresh FS Example Convert
25. TJ 2 196 T lt lt J lt lt sCdirendl return 0 F Save and run it You ll see Sure enough the reference returned by max i j which pointed to the same place as j was changed to zero Const Return Values In the last example we could assign a value to the reference returned by max i j To keep this from happening let s change the function so it returns a const reference include lt iostream gt const int amp max int il int amp 12 if il gt i2 return return i2 11 7 main int i 1 ine J 2 std cout lt lt Max 195 T lt lt max 1 max i j 0 lt lt std endl Assigning a reference stdiicout lt lt J 1 as lt lt J lt lt std endl Sstds cour lt lt J 2 16 lt lt J lt lt std endl return 0 Once you save your file you will notice that we can no longer assign a value to max Because itis a constant we can only retrieve the result not change it e ee Internal Builder is used for build FEET g 00 g3 Wall c fmessage length 0 OVar pass o var pass cpp VWar pass cpp In function War pass cppil read only location Build error occurred Huild is stopped Time consumed 655 me int maint Error assignment of Problems with Reference Returns hu wL L i S a return iiz int main i int i I int j 2 atd cout lt lt Max is lt lt max ii j lt l
26. The classic Hello World program Prints out the message and that s all Usage Run it and get the message This is another way to comment a single line include lt iostream gt int main std cout lt lt Hello World lt lt std endl return 0 Save and run it to verify that it still works as expected The User Manual Are we finished Not yet a program isn t any good if no one knows how to use it so we ll write a user manual for every program You may wonder how to go about writing a manual for such a short program For a short program we just write a short manual To create your manual select the hello_world project and then select File New Other In the New File Wizard select General File Name your file manual txt Now write the manual Run the program see the message The Test Plan Finally the program needs a test plan Our test plan should have these attributes e Itshould testas much ofthe program as is feasible e lItmustlista precise setof steps to follow ambiguous instructions lead to results that cannot be reproduced e Its results must be observable e lItmustlead to a clearly observable pass fail result For example a test plan that says Play around with the software and see if you can break it is a vague and therefore pretty bad test plan First the term Play around is not precise Different people could play around in different ways Second what happ
27. are two quite different things There is still a lot of legacy code out there that uses C style strings As a programmer in the real world you will see this type of string and have to deal with it So let s start with an experimental C style string program Create a project named c string assign it to your C 1 Lessons working set and create a program c string cpp containing the following tine luide lt Loestreanc gt int main char name PO Fs The name for this example Std cout lt lt The name is T lt lt name lt lt std end gt return 0 This assigns the value Sam to a C string name which can be output to std cout F Save and run it and observe the output include lt iostream gt int main char namel FL a tm 10 42 The name for this example char other J To te i Another name with an error std cout lt lt The name is lt lt name lt lt T and other is T lt lt other lt lt std endl return 0 F Save and run it and observe the output OBSERVE The name is Sam and other is Joew Your actual output might differ from this exam ple in fact it might even look normal This is another situation where the behavior is undefined If you do not put an end of string marker 0 in your C style string itis anybody s guess what will occur Remember when we accidentally used an array element we weren t supposed to use What happened Because the
28. can change your for loop to accomplish this as well tinclude lt iostream gt int main int total J Tatal s far int count Count of the numbers int number A number to read total 0 Lor ee std cout lt lt Enter a number gt std cin gt gt number Skip all negative numbers if number lt 0 std cout lt lt Negative numbers don t count lt lt std endl continue if number 0 std cout lt lt I guess you want to end the list lt lt std endl break total number std cout lt lt The new total is lt lt total lt lt std endl std cout lt lt The grand total as lt lt total lt lt std endl return 0 F Save and run it It will continue until you enter a zero Earlier we discussed the sections ofa for loop OBSERVE for Initialization Test Increment body of loop The initialization test and increment sections are all optional Only the semicolons are required For Loop Misuse The goal of programming is to be as clear and correct as possible However some people think it s to use as few characters as possible hope you never have to debug their code One of the tricks they have is to put the comma operator into a for statement Coding Horror for twos 0 threes 0 twos lt 100 twos 2 threes 3 The comma operator can be used to string two C stat
29. don t count lt lt std endl continue if number 0j std cout lt lt I guess you want to end the list lt lt std endl break total number std cout lt lt The new total 1s lt lt total lt lt std endl gtd cout lt lt The grand total is T lt lt total lt lt std endl return 0 F Save and run it Enter a few positive numbers a negative number and finally a zero You ll see something like this OBSERVE Enter a number 1 The new total as i Enter a number 1 The new total is 2 Enter a number 1 The new total is 3 Enter a number 1 The new total is 4 Enter a number 1 The new total is 5 Pimker a numbers 5 Negative numbers don t count Enter a number 9 The new total is 14 Enter a number U I guess you want to end the list The grand total is 14 When the program encounters a negative number itoutputs a message and then runs continue This skips the rest of the for loop and goes on to the next number When you enter a zero the program outputs a message and then runs break which completely exits the for loop and outputs the grand total Instead of using continue and break you could have accomplished similar results by using if statements and perhaps another variable but continue and break make the loop much easier to understand Suppose you wantto allow users to enter as many numbers as they want and only quit the program when they enter a zero You
30. endl at a lt lt aedi endl Array to play around with is lt lt kiI0 lt lt std endl A single array element is just like a single variable so by default C passes by value Const Parameters Let s now produce a program with a function that returns the maximum of two integers Start a new project named max and assign itto your C 1_Lessons working set Create a source file named max cpp as shown inelude lt iostream gt Function comments int Mextint al int izj if 11 gt i12 return il return 12 int main int i 12 int J Aa std cout lt lt Max ig T lt lt Max i lt lt std return 0 F Save and run it You ll see Notice that the values ofi1 and i2 are never changed in the max function Given the nature of the function they never should be changed But what if someone decided to change the parameter Edit the program as shown include lt iostream gt Function comments int Max ant il int 12 il 99 if il gt i2 return il return i2 int main int i 1 int Jj 23 stdiicout lt lt Max is T lt lt max 1 J lt lt std return 0 The function should not change the value of the parameters To help ensure that the parameters don t change put the modifier const in front of them Edit your program as shown include lt iostream gt int max const int il const int 12 il 99
31. lt The answer is lt lt 1 0 3 lt lt std endl return 0 F Save and run it and read over your results Try 1 3 0 as well Now that you ve seen how mixed mode arithmetic will affect your programs avoid using itifatall possible For now that may be difficult but later we ll learn about casing which will let us explicitly tell the compiler which types of numbers and therefore operations to use Dividing by Zero We cannot divide anything by zero that operation isn t defined and the expression has no meaning So what happens if we tell the computer to divide by zero Modify your program to compute a new expression that divides by zero as shown include lt iostream gt int main std cout lt lt Divida lt lt 1 0 lt lt std endl return 0 Save your program and ignore the warning message F Run itand observe that it terminates with this message exp expression exe Application Error E4 The exception Integer division by zero Oxc0000094 occurred in the application at location Ox0040141d Click on OK to terminate the program Click on CANCEL to debug the program Cancel The computer can t handle this type of math so the program stops with a warning Click OK to end the program But what happens when you divide by zero with a floating point number Try it and find out edit your program below as shown include lt iostream gt int main Std scout lt lt Dav
32. resides The for statement is special in that you can declare the loop variable rightinside the for itself Edit var types cpp as shown include lt iostream gt int global 1 Global variable to play around with int main irtee heee counters for int loop 0 loop lt 37 ttloop int temp 1 A local variable to play around with static int perm 1 A local permanent variable to play with std cout lt lt loop is lt lt loop lt lt std endl std cout lt lt global is T lt lt global lt lt std endl std cout lt lt temp is lt lt temp lt lt std endl std cout lt lt perm is lt lt perm lt lt std endl o Lobe temp perm Almost useless comment return 0 F Save and run it You ll see OBSERVE loop io 10 globalki temp is 1 perm is 1 Toop als Ih globali 2 temp is 1 perm is 2 oopis globalis gt temp is 1 perm is 3 In this case the loop variable has a scope ofthe entire body ofthe for loop Hidden Variables Now we ll discuss hidden variables First let s see them in action Create a program called hidden cpp and type in the program below hidden A very good demonstration of what not to do More of a puzzle than a useful program a include lt iostream gt int main int var Ze int b var hi ScCorrcouL lt lt Ta var Gl is T lt lt a var lt lt etdi rendi Stidi cout l
33. return 0 F Save and run it You should see the Fibonacci sequence a a e e e e e int main ILI old number 0 previous Fibonacci number UE current number 1 current Fibonacci number E next number next number in the series Stud Cout old number Output firt number while current number lt 100 std cout lt lt current number lt lt next number current number old number old number current number current number next number std cout lt lt std endl return 0 From the formula for Fibonacci numbers we know the starting values and that the next number is the sum ofthe previous old and current numbers so we created variables for the old_number setto 0 the current_number setto 1 and next_number which we ll set in our loop The first Fibonacci number is 0 the initial value of old_number so we ll just output it before we start the loop But rather than print 0 we ll use the variable so if we ever ant to change it we only need to change it in one place in the program We wantto continue looping while the number is less than 100 so we can add a while loop to our program Inside the while loop we display the current number then add the old and current numbers to get the value of the next number Now to move the sequence along we shift the values move the current_number value to old_number and the next_number value to current_number before the
34. std endl std cout lt lt State 2 is lt lt state lt lt std endl std cout lt lt Country p2 is lt lt gountry lt lt std endl std cout lt lt State 3 is lt lt state lt lt std endl std cout lt lt Country 3 is lt lt country lt lt std sendi return 0 F Save and run it You ll see OBSERVE State 1 is Texas Country 1 is USA City as PUI 1c aig State 2 is Texas Country 2 is USA State 3 is Texas Counery to ie Usk In the city you can see the state and the country In the state you can see the country but not the city In the country you can t see the state or city It s an imperfect anaology but it s okay for the purpose of illustration right Storage Class The storage class ofa variable can be permanent or temporary The local variables we ve defined are temporary They are created when they are declared and disappear when their enclosing block ends Global variables are permanent They are created and initialized when the program starts and are not destroyed until the program ends Let s create a quick program to take a look at this situation Create a project named var types and assign it to the C 1_Lessons working set In the new project create a program named var types cpp as shown include lt iostream gt int global 1 Global variable to play around with int main int loop A loop counter for loop 0 loop lt 3
35. to assign a constant of one type such as boolean to another such as integer Here are the conversions that occur when mixing types Result Expression Conversion type type 1 for true O for false not guaranteed by the standard but everyone know ofimplements it integer boolean that way The character whose character number is the number being assigned This depends on the char integer character seton your system For mostsystems this is ASCII so assigning ch 65 makes ch an A ASCII character number 65 Integer after truncation Note If the value of the floatis bigger than the maximum size the integer float integer can handle the integer will get the maximum value The numeric value of the character in the current character set The numeric value of the character in the current character set Ifthe number 0 zero the boolean variable gets false If non zero the value true is boolean Numeric assigned Let s try this Change your program as shown tinclude lt iostream gt int main bool flag Boolean to play around with flag true Set it to true float test flag will this work flag false std cout lt lt Flag is lt lt flag lt lt stad std cout lt lt Test is lt lt test lt lt std return 0 F Save and run it Your program happily stores the boolean value 1 from flag into test Also note that even when the value of flag changes to false
36. to find bugs caused by bad index values CHECK YOUR CODE We covered a lotin this lesson We learned how to use arrays and how to loop over arrays using for loops In the nextlesson we ll learn about another type of variable strings See you then La Copyright 1998 2013 O Reilly Media Inc This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information C Strings C 1 Introduction to C Lesson 5 Strings in C Strings are sequences of characters you can use in a computer program There are two basic ways to use strings the newer C style strings which we will learn about in this lesson and older C Style strings that we will review in the next lesson To use C strings we need to include lt string gt atthe top of our programs We can then declare a string with a statement like OBSERVE std string variableName comment Let s see how this works Create a project named string assign itto the C 1_Lessons working set create a source file named string cpp and enter the following code include lt Lostrean include lt string gt int main std string first First name Bios etring last Last name first Joyce last Kilmer std cout lt lt My name is lt irst lt lt T lt lt last lt lt std tendl return 0 Replace we
37. to variables as return values but when you do need to use them be very careful about what you are doing You made it In the next lesson we ll discuss your final project for the course Good luck a This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information Final Project C 1 Introduction to C Lesson 13 Putting It All Together At this point we ve learned enough to create your very own program from scratch Assignment To start create a projectnamed final_project assigned to yourC 1_Homework working set with a source file named final_project cpp Your assignment is to create a program that will count the number of words in a file Itis up to you to define whata word is hello is a word But what about high five is that one word or two And how about something like ground_point Some programmers might consider that one word and others think it was two Did you consider something like O Reilly Whatever you decide to consider a word document your decision in a file named requirements txt The specification is as exact a description as you can get of what the program is going to do Sometimes you don t know how a program is going to end up until you start coding In that case you start with a preliminary specification and refine itas you go on At the end of coding the spe
38. width Sealine Goulcz Cleves SALAS The other is something called CamelCase OBSERVE boxWidih Porn C oUnt dataSize In practice there s nota lot of difference in the readability of the two styles but there is a great benefit to picking one style and sticking to it The style guide for this course requires you to use the underscore style Variable Definitions A variable definition consists of three parts OBSERVE type name Comment explaining the variable The comment is not optional at least notin this course The reason is that a program is a set of instructions to the computer that uses a unique to that program vocabulary mean if you see a variable named center_point in code the first question you are going to ask yourself is Center of what By commenting every variable declaration you produce a mini dictionary describing every specialized word variable you use in your program It makes understanding the program much easier Variable Types Integer The C keyword for the integer type is int Glossary integer int A integer variable declaration looks like this OBSERVE int x example variable The int declaration tells C to declare an integer variable using the optimal size of an integer for the machine On most machines this allows numbers from 2147483647 to 2147483648 to be used On some older systems this is just 32767 to 32768 and on some newer systems it s 9 223 372 036
39. you type lt itadds a gt And after you enter the line that contains int main Eclipse automatically indents the next line by four spaces and adds the closing bracket on the following line Eclipse is your friend and does its best to help whenever it can Select File Save All to save your file C C hello hello cpp Eclipse SDK File Edit Refactor Navigate Search Project Run Window Mer AlE SHiFE K F Open File Close krl Close All Cerl ShiFk yy e Save Ctrl 5 lal Save SS Ctrl ShiFE 5 Congratulations you ve just written your first C program Now let s run it In the editor window for your hello cpp program right click and select Run as Local C Application 1 al 2 hello cpp lt 2 Undo Typing Ctrl 2 a o Revert File 4 created on Me Gave Chrl4 5 oi Author ay bl 77 Open Declaration Fa TY Open Type Hierarchy F4 5 hello cpp Open Call Hierarchy Ctrl Alt H Quick Outline Ctrl o 10 Created on DE auick Type Hierarchy Ctrl T 11 ae Explore Macro Expansion Ctrlt ne i Toggle SourcefHeader Ctrl Tab lshinclude lt 1ostr ean Alt Shift i l4int maini i 15 std cout lt lt Gut Etrit 16 return Qj Copy trl Li Paste Ctrl 16 Quick Fix Ctrl 1 Source d Refactor d Declarations d References d Search Text Show LaSTNode in DOM view E 1 Local C C Application Debug s OO i Glean Selected File s Build Selected File s Run Configurations Team d
40. your brain absorb the new information thoroughly Taking your time helps to maintain a relaxed positive approach It also gives you the chance to try new things and learn more than you otherwise would if you blew through all of the coursework too quickly e Experiment Wander from the path often and explore the possibilities We can t anticipate all of your questions and ideas so it s up to you to experiment and create on your own Your instructor will help if you go completely off the rails e Accept guidance but don t depend on it Try to solve problems on your own Going from misunderstanding to understanding is the best way to acquire a new skill Part of what you re learning is problem solving Of course you can always contact your instructor for hints when you need them e Use all available resources In real life problem solving you aren t bound by false limitations in OST courses you are free to use any resources at your disposal to solve problems you encounter the Internet reference books and online help are all fair game e Have fun Relax keep practicing and don t be afraid to make mistakes Your instructor will keep you atit until you ve mastered the skill We want you to get that satisfied I m so cool did it feeling And you ll have some projects to show off when you re done Lesson Format We ll try out lots of examples in each lesson We ll have you write code look at code and edit existing code The code will b
41. 0 F Save and run your program You ll see the value of x change One of the mostcommon uses of these shortcuts is in for loops Let s take a look include lt iostream gt int main ine z Of Jf to play for x 0 x lt 25 x t atdi scout lt lt Ss 16 lt lt amp lt lt Sle ttendl return 0 F Save and run it You ll see o JAIA WNEF O XxX X x x x xX xX x x x x x x xX x x x x x xX x x xX xX x We can use to have our loop skip by five instead include lt iostream gt int main int x 0 to play for x 0 x lt 25 7 std cout lt lt x is lt lt x lt lt std return 0 F Save and run it See the difference For Loops It turns out the for loop has a few more tricks Suppose we wanted to write a program to add several numbers but no more than ten We don t want to include any negative numbers and if we encounter a zero we will know our listis done We can make this happen with two shortcuts continue and break Clear your program and type the following include lt iostream gt int main int total j7 Total s far int count Count of the numbers int number A number to read total 0 Tor count OF count lt 10 eounT std cout lt lt Enter a number std cin gt gt number Skip all negative numbers if number lt 0 std cout lt lt Negative numbers
42. 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information
43. Assembly code is machine dependent In other words the assembly language for an Intel x86 compatible processor such as the Intel Core 2 Duo or Intel Pentium is entirely different from the assembly code for the iPhone s ARM processor Fortunately all this complexity is hidden from you and you can ignore it most of the time Butsometimes you may need to take a peek under the hood to deal with any bugs you encounter along the way Finishing the Program Our program although syntactically and logically correct is not complete because it only contains the default comments produced by Eclipse A commentis text in the program that tells people reading the program what s going on Comments are not read by the computer and although itis possible to write a program with no comments in it we will notdo so in this course Professional programming means creating professional quality programs with comments even if that program is Hello World All of your programs should begin with a comment block that contains these sections e The lesson and project number so the instructor knows which question you re answering e Adescription section that describes what the program is supposed to do e Ausage section Comments begin with and end with Comments can also begin with and go to the end of the line Our program needs a set of comments Modify hello cpp as shown Lesson 1 Example 1 Or Assignment 1 for programs you turn in Description
44. BSERVE Siccls 2 0uU lt lt Seclicsenw Z2 lt lt isceiceciom Colic F Save and run it This time you ll see a beautifully formatted table OBSERVE TceracLon oloa current next lt 1007 T za l l ces e e ee es l 2 e 4 3 6 q 8 9 0 IL hb The output shows how variables are saved for the next trip around the while loop By the tenth iteration we have the first Fibonacci number stored in current_number thatis greater than or equal to 100 so the program stops You ve added some extremely helpful tools to your C tool kit In the next lesson we ll discuss the scope of our variables See you then El xl D This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information Scope C 1 Introduction to C Lesson 10 What is Scope Up to this point we ve used very basic variable declarations We ve declared variables at the top of our programs and used them throughout the entire program In other words all variables existed through the entire program In this lesson we ll see how to create variables that exist for only a portion of the program We ll start with a short program Create a project named var exp and assign it to your C 1_Lessons working set In this new project create a program named var exp cpp as shown include lt iostream gt int mai
45. C 1 Introduction to C PDF Lesson 1 Introduction Learning C History of C About Eclipse Perspectives and the Red Leaf Icon Writing Your First Program What Does It All Mean Adding to Our Program What Goes On Under the Hood Finishing the Program The User Manual The Test Plan A Few More Notes Lesson 2 Expressions Mathematical Expressions Creating the Project and File Editing and Running Your Program Types of Numbers Floating Point vs Integer Division Dividing by Zero Limits on Numbers Common Problems Lesson 3 Variables Basic Programs Variables Variable Definitions Variable Types Integer Variable Types Floating Point Variable Types Characters Escape Characters Wide Characters Boolean Mixing Types Lesson 4 Arrays and For Loops Using Arrays The const Modifier Our first array for loops Array Safety Lesson 5 C Strings Strings in C Characters in strings Other Functions Lesson 6 C Style Strings What is a C Style String Concatenation of C Style Strings Comparing Strings Tips Converting C Strings to C Style Strings Unsafe String Functions The future of strc and strcat Comparisons to other types C Strings vs Arrays of Characters C Style vs C Style Lesson 7 Reading Data and if Reading Strings Reading Integers if Statements if Abuse Equality or Assignment Blocks Conditional Shortcuts Lesson 8 Shortcuts Operators For Loops For Loop
46. Misuse Side Effects Lesson 9 While Loops while break and continue Fibonacci numbers Lesson 10 Scope What is Scope Global Variables Storage Class for Loop Scope Hidden Variables Lesson 11 Functions What is a Function Our First Function Void Functions and Array Parameters Function Overloading Default Parameters Lesson 12 Parameters and Return Types Passing Parameters Pass by Value Array Parameters Const Parameters References Const Return Values Problems with Reference Returns Lesson 13 Final Project Putting It All Together Assignment Code Design Agile Development Coding Notes Testing Revisions Copyright 1998 2013 O Reilly Media Inc This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information Introduction C 1 Introduction to C Lesson 1 Welcome to the O Reilly School of Technology s C course We re glad you ve decided to go on this ride with us and learn C programming By the time you finish the course we re confident that you ll have firm grasp on this really practical programming language If you ve already taken an O Reilly School of Technology OST course you re familiar with the useractive approach to learning I s an approach where you the user will be active You ll learn by doing building live programs testing them and then experimenting with them han
47. PAaSS GxXEG War pass a Build complete for project var pass Time consumed 1462 ms ant main The compiler warns you that you are returning a reference to a local variable This is reminding you that the variable result will be destroyed when max returns This is like removing your mailbox from the wall the postal worker can t put anything into the box and you can t either So what does the reference generated by the return statement refer to Absolutely nothing The value referenced is notin scope so itis notlegal to reference it This is yet another area of undefined behavior in C Your program might work just fine or it could crash or it could cause strange and mysterious data errors When a reference refers to something thatis no longer in scope it s called a dangling reference You can t legally return a reference to a local variable from inside a function Now let s try another experiment with our program Edit the program so thatit uses expressions as parameters to max include lt iostream gt eorst int amp max int amp il int amp 12 TESA ee 1l gt 12 return il return 12 main int i 1 inc a int answer answer max itl jtl std cout lt lt Max is lt lt answer lt lt std endl return 0 This program too has a dangling reference that is hard to spot but the compiler won t let it by LJ Leal Save it and you ll see Build of c
48. Save and run it you ll see the original message again Now let s add a new variable I which is a reference to j We ll then zero this reference which should cause i to be zeroed Change the code as shown tinclude lt iostream gt int amp max int amp il int amp i2 Le ak gt 12 return il return 12 main int i 1 int j 2 std cout lt lt Max 16 lt lt Imex 1 7 lt lt stdiiendi inte 1 4 1 now refers to 7 L 0 Since 1 is j J is now zero Std scout lt lt J 1328 lt lt q lt lt rds send Btdrrcour lt lt 2 18 lt lt 7 lt lt stditendl return 0 O Save and run it Sure enough and i both point to the same place and i ends up being setto 0 OBSERVE Max ss 2 j 1 is 0 j 2 is 0 This is because our latest and greatest max function returns a reference to i Because it s a reference we can use iton the eft side of the equals sign as well as the right Make the changes indicated in the program to remove the reference k and replace it with the reference max i j include lt iostream gt int amp max int amp il int amp i2 Le 1l gt 12 return il return i2 int main int i 1 ine J 2 Std cour lt lt Max is T x lt max i lt lt std endl teks 0 Assigning a reference std cout lt lt 7 1 us lt lt 7 lt lt std sendl Sstdescoun lt lt
49. The language was also designed not to getin the way of the programmer In other words if he wanted to do something stupid it let him C is a procedural language The data and instructions are kept separate Ten years after its invention people realized that they could make better programs if they combined data and the instructions that operated on the data into one thing called an objector class In 1980 Bjarne Stroustrup started working on a new language called C with classes The goal of the language was to bring classes to C while not breaking existing C code or at least not breaking it too badly This language would become C About Eclipse We re using an Integrated Development Environment IDE called Eclipse It s the program filling up your screen right now IDEs assist programmers by performing many of the tasks that need to be done repetitively IDEs can also help to edit and debug code and organize projects Perspectives and the Red Leaf Icon The Ellipse plug in for Eclipse developed by the O Reilly School of Technology adds an icon to the toolbar in Eclipse This icon is your panic button Eclipse is versatile and lets you move things like views and toolbars If you ever get confused and want to return to the default perspective window layout the Red Leaf icon is the most efficient way to do that You can also change perspectives by clicking the drop down arrow beside the icon and then clicking a series name JAVA
50. a of the first triangle is 5 Excellent Suppose you now want to calculate area for two more triangles Extend your program as shown include lt iostream gt int main float width float height float area width 5 0 height 2 0 area width height std cout lt lt Area of the width 3 8 height 5 9 area width height std cout lt lt Area of the width 2 38 height 1 6 area width height std cout lt lt Area of the return 0 O Save and run the program You ll see Area of the first triangle is 2303 first triangle is lt lt area lt lt std endl all second triangle is lt lt area lt lt std endl Mall third triangle is lt lt area lt lt std endl 5 Area of the second triangle is 11 21 Area of the third triangle is Zee In our program we have lines of code that repeat area width height 2 0 std cout lt lt Area Of the nth triangle ws lt lt area lt lt sed Let s take those lines of code and turn them into a function Edit your program include lt iostream gt triangle compute the area of a triangle Parameters width the width of the triangle height the height of the triangle ReCUrLnS the area of the triangle FF SF MB HN F float triangle float width float height float area width height 2 0 return area main float width float hei
51. al to zero Much better You made it In the next lesson we will shift gears and discuss some shortcuts that are common in C programs See you then a gt D Copyright 1998 2013 O Reilly Media Inc A This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information Shortcuts C 1 Introduction to C Lesson 8 There are many different ways to accomplish the same task in C Some code patterns occur very often so the developers of C and C have included shortcuts that can make code shorter and easier to understand Operators Consider the following operation Incrementing a Variable s Value This code pattern occurs frequently in C and other languages so the makers of C added a shortcut operator to the language Incrementing with a Shortcut lt x 5g Other shortcut operators are Longhand Shortcut a a b a b azan fen Let s experiment with some shortcut operators Start a new project named shortcut and assign it to your C Lessons working set In the new project create a source file named shortcut cpp include lt iostream gt int main int x 0 to play Scatscour lt x is lt lt x lt lt Sta endl X 3 Poot reout x Te 19 z lt 4 Stet ecru Xtt std cout lt lt Tk 26 lt lt 2 lt lt Btatrencl return
52. ards third return 0 F Save and run it You ll see this slightly different result OBSERVE The area of the triangle is 5 The area of the second triangle is 11 21 The area of the third triangle is 2 24 The first time we call print_it with only one parameter and C runs the correct print_it function that accepts one parameter the second one in the program The next two times we call it with two parameters and C runs the correct function that accepts two parameters the first one in the program C keeps track of this by using function signatures A function signature is the combination of the function name return data type parameter data types and names In our program there are actually four functions 1 float triangle double width double height 2 void print_it float area char whatl 3 void print_it float area 4 int main In C the function name and parameters must be unique In other words you cannot define two separate functions like this 1 void print_it float area 2 int print_it float area Default Parameters C lets you define functions with default parameters For example you could decide that triangles have a default height of 2 0 You can add a small bit of code to the parameter list to specify this OBSERVE float triangle float width float height 2 0 To see this change in action edit your program include lt iostream gt j gt triangle Compu
53. ariable Variable Types Characters The character char data type stores a single character To be more specific it stores a single character from the ASCII character set This character set provides for the letters a z upper and lower case the digits 0 9 a set of punctuation characters and special control characters Glossary ASCII Character Set Control characters are not printed but instead control how the output appears on the screen Character constants are enclosed in single quotes A B Create a char play project assign it to the C 1_Lessons working set and in it create char play cpp as shown include lt iostream gt int main char chl First play character char ch2 Second play character char ch3 Third play character chi A ch2 B Chia Cre std cout lt lt The characters are lt lt chl lt lt ch2 lt lt ch3 lt lt std endl return 0 include lt iostream gt int main char chl First play character char ch2 Second play character char ch3 Third play character chl A ch2 B ch3 CDEF std cout lt lt The characters are lt lt chi lt lt ch2 lt lt ch3 lt lt std return 0 See the warning This is the first indication that something isn t quite correct ttt Internal Builder is used for uild TATE g O0 g Wall c fmessage length 0 ochar play oa char chi First Char ch2 S
54. ation Error x UI The instruction at Ox00401 42c referenced memory ak Ox002306F0 The memory could not be written Click on OK to terminate the program Click on CANCEL to debug the program concel_ C did not check to make sure your array index of 500 was valid Instead that line executed and crashed your program In C when you try to access or write something you are not supposed to access any of these things might happen e your program could crash e your computer could crash depending on the operating system e your program could run and calculate things incorrectly e your program could run normally only to crash later perhaps waiting until it s shipped to 10 000 customers when it suddenly decides to wipe out all their important data If you remember the good old days of computers and operating systems MS DOS Windows 95 and MacOS 7 to name a few you probably remember bugs in applications that could crash the entire computer Those bugs were often array problems just like this In some other languages you might not need to worry so much about checking your array indices In C you do Ina future course we will discuss ways to double check your programs to make sure you are accessing arrays correctly In the real world almostno one checks the array indices before using them to access an array Instead i Note they run without checking and spend millions of dollars later to debug the strange and hard
55. ber A number we are going to check std cout lt lt Enter a number std cin gt gt number if number 100 std cout lt lt number lt lt is one hundred lt lt std else std cout lt lt number lt lt is not one hundred lt lt std endl return 0 F Save and run it and enter 25 You ll see OBSERVE Enter a number 25 POORA Try itwith other numbers 0 25 150 No matter what you type the computer thinks you entered 100 This is because we didn t use the equality operat or instead we changed the value of number In other words this line OBSERVE if number 100 was essentially interpreted as OBSERVE number 100 if number 0 This sortof error can be tricky to spot An easy way to avoid this issue is to always place constants on the left side of the comparison Change your code to the following include lt iostream gt int main int number A number we are going to check std cout lt lt Enter a number std cin gt gt number 100 number std cout lt lt number lt lt T is one hundred lt lt std endl else std cout lt lt number lt lt is not one hundred lt lt std endl return 0 umber atd gout lt lt numbe This error indicates you are trying to change the value of 100 to whatever is stored in number but 100 isn ta variable so y
56. ber A number we are going to check std cout lt lt Enter a number Std scin gt gt number if 50 lt number 7 ir 1 if 100 number if 2 std cout lt lt number lt lt is one hundred lt lt std endl else else 1 std cout lt lt number lt lt is not so big lt lt stca tendl else else 2 stotfcout lt lt number lt lt is 777 lt lt std endl return 0 Confused You should be Without braces and proper indentation itis very hard to figure out what exactly will happen in this program Which else goes with which if Possible answers include e if 1 goes with else 1 e if 2 goes with else 1 e if 1 goes with else 2 e lf you don t write code like this you won t have to worry about silly questions like this The correct answer is number 4 You need to know this so you can debug other people s code People who value compact code over readability understandability and safety However since we find readability understandability and safety valuable and we write good code we will never write code like this Some people tell you to always use for the statements affected by an if The Perl language i Note requires it We considered this but decided that for the most part letting the programmer decide whether or a single statementis clearer i Conditional Shortcuts If statements also let you take shortcuts in the conditional test In the C wor
57. cification should be detailed enough that you can use it as a user guide Create a file named spec txt and write your specification in it Code Design The design is a general outline of how you are going to create your program The design for this word count program should be fairly short A good paragraph describing the general operation of the code should do it Create a file named design txt and enter your design Agile Development Years ago there was programming technique called fast prototyping Today ithas been renamed agile development Basically it means that you create the smallest working program you can Test it enhance it and repeat until you get what you want The idea is that you start with a working copy and build a working program on top ofthat That way you have a working program to see where you are and to give you an idea of what the computer can do This lets you refine your specification as you learn more about what s happening with your system In this case there are three stages that we go through in our development 1 Make a program that reads a character at a time counting nothing 2 Make the program count characters 3 Change the program to count words Coding Notes To help you get started the following is code that will read each character from a file called input txt and will output it It uses fstream ineclude lt iostream gt tinclude lt fstrean gt int mein 4 Soar Gy std ifstrea
58. cout lt lt The grand total is lt lt total lt lt std endl return 0 F Save and run it Enter the numbers 5 10 15 20 and 1 you should see your program stop OBSERVE Enter a number 5 The new total is 5 Enter a number 10 The new total is 15 Enter a number 15 The new total is 30 Enter a number 20 The new total is 50 Enter a number 1 The new total is 51 The grand total is 50 Fibonacci numbers The Fibonacci numbers are numbers in a sequence starting with 0 1 where each subsequent number is the sum of the previous two Fibonacci Number Calculations and so on Thus the first Fibonacci numbers are 0 1 1 2 3 5 8 and 13 Yes 1 is in there twice We can use a while loop to calculate the sequence of Fibonacci numbers less than 100 Create a new project named fib and assign itto yourC 1_ Lessons working set and in that project create a source file named fib cpp as shown cincluide lt iostream gt int main int old number previous Fibonacci number int current number current Fibonacci number int next number next number in Che Series start things out old number 0 Current number 1 std cout lt lt 0 7 7 Output first number while current number lt 100 SLa icCoul lt lt current mumber lt lt 7 next number current number old number old number current number current number next number gtd 00E lt lt gidi iendlj
59. de lt string gt int main std string first First name Sede etring last Last name Std string Tull The full name Char Iirst initial The first initial first Joyce last Kilmer full first last first initial first 0 Assigns first initial the value J std cout lt lt My rirst initial i9 Y lt lt Tiret Initial lt lt sta rend return 0 F Save and run it and observe the output OBSERVE Why riro e nitra e This syntax might remind you ofan array This is because a string is just like an array of characters There is a problem here the index is not checked in this operation So if the index is out of range the expression returns an undefined value In other words this operation is not safe and you know how we feel about safety Fortunately there is another way of getting the character the at function Change the program as shown include lt iostream gt include lt string gt int main std string first First name std string last Last name std string Tull The full name char first initial The first initial first Joyce last Kilmer full first T Last first initial first at 0 Assigns first initial the value J This is the safe way of doing this Std Oout lt lt My 21rst Inicial 19 lt lt irot IMiC al lt lt sed rendi return 0 F Save and run it You ll see the same output a
60. ds on Learning with O Reilly School of Technology Courses As with every O Reilly School of Technology course we ll take the useractive approach to learning This means that you the user will be active You ll learn by doing building live programs testing them and experimenting with them hands on To learn a new skill or technology you have to experiment The more you experiment the more you learn Our system is designed to maximize experimentation and help you earn to learn a new skill We ll program as much as possible to be sure that the principles sink in and stay with you Each time we discuss a new concept you ll put it into code and see what YOU can do with it On occasion we ll even give you code that doesn t work so you can see common mistakes and how to recover from them Making mistakes is actually another good way to learn Here are some tips for using O Reilly School or Technology courses effectively e Type the code Resist the temptation to cutand paste the example code we give you Typing the code actually gives you a feel for the programming task Then play around with the examples to find out what else you can make them do and to check your understanding It s highly unlikely you ll break anything by experimentation If you do break something that s an indication to us that we need to improve our system e Take your time Learning takes time Rushing can have negative effects on your progress Slow down and let
61. e characters we want to display on the console This is followed by lt lt again which sends whatever follows it to the output stream on the left and the symbol std endl The std endl symbol tells C to output an end of line character The statement ends with a semicolon Next we have the return line return 0 which tells C to end the program and return a status of 0 to the operating system You ll learn more about the return statement later but for now all you need to know is that inside main itends the program A return code of 0 indicates a normal exit Codes 1 255 typically indicate that the program exited abnormally the bigger the number the bigger the problem Again the statement ends with a semicolon At the very end we have a closing brace This ends the block of code that started at the brace just after the main line Adding to Our Program Now let s say we want to output another line of text To do that we can add another line to output an additional message Edit your program as shown using your own name instead of Steve include lt iostream gt int main std cout lt lt Hello World lt lt std endl std cout lt lt My name is Steve lt lt std endl return 0 F Save your file then run it by right clicking in hello cpp in the editor window and choosing Run as Local C Application alternatively you could click the Run icon in the toolbar You ll see this output
62. e 3 8 5 9 std cout lt lt Area of the second triangle is lt lt area lt lt std endl area triangle 2 8 1 6 std cout lt lt Area of the third triangle is lt lt area lt lt std endl return 0 F Save and run it You ll see the same outputas before OBSERVE Area of the first triangle is 5 Area of the second triangle is 11 21 Area of the third triangle is 2 24 For each triangle calculated we replaced three lines of code with one We re making progress Do you another area where we could save a few lines of code Void Functions and Array Parameters In our program we could also add code to the triangle function to display the message like OBSERVE float triangle float width float height float area width height 2 0 std cout lt lt Area of the triangle is lt lt area lt lt std endl return area This message would be a side effect of the triangle function A function has a side effect if it outputs messages modifies files or otherwise performs some action besides returning a value Generally speaking side effects are nota good idea Instead let s create a separate function to output the message Change your program include lt iostream gt triangle compute the area of a triangle Parameters width the width of the triangle height the height of the triangle FF HF F Returns the area of the triangle EJ floa
63. e presented in boxes that will indicate what needs to be done to the code inside Whenever you see white boxes like the one below you ll type the contents into the editor window to try the example yourself The CODE TO TYPE bar on top of the white box contains directions for you to follow White boxes like this contain code for you to try out type into a file to run If you have already written some of the code new code for you to add looks like this If we want you to remove existing code the code to remove wttttecokt kent We may run programs and do some other activities in a terminal session in the operating system or other command line environment These will be shown like this The plain black text that we present in these INTERACTIVE boxes is provided by the system not for you to type The commands we want you to type look lik e this Code and information presented in a gray OBSERVE box is for you to inspectand absorb This information is often color coded and followed by text explaining the code in detail OBSERVE Gray Observe boxes like this contain information usually code specifics for you to observe The paragraph s that follow may provide addition details on information that was highlighted in the Observe box We ll also set especially pertinent information apart in Note boxes Learning C C is the workhorse language of the programming world It s used for many different applications from
64. econd char ch3 Third char play cpp ichar play cpp l6 11 warning ulti character character constant et aed S ae che H mulki characker characker constant std cout lt lt The return 0 g oachar play exe char play a Build complete for project char play Time consumed i422 ms F Try running the program You ll see something like OBSERVE The characters are ABF Looks like the computer wasn t happy with our CDEF character so itdropped CDE without telling us Warnings exist for a reason don t ignore them Escape Characters There is a special character the backslash which is used to specify characters that cannot be typed inside single quotes easily such as tab t and newline n In these cases the backslash escapes from normal rendering oftand n allowing you to represent tabs and newlines in program output Some of the escape characters are Edit the program below replacing the value we assign to ch2 as shown include lt iostream gt int main char chl First play character char ch2 Second play character char ch3 Third play character chil KATI aha rn oi i gt std cout lt lt The characters are lt lt chl lt lt ch2 lt lt ch3 lt lt std endl return 0 F Save and run it and observe the output OBSERVE The characters are A Now let s try something a little different Change the value of c
65. ements together and have the compiler treat them as one Do not use it All it really does is make it easy to write bad code In this case we have two initialization statements twos 0 and threes 0 Because of the comma operator C does not object to them both being inside a for initialization The same holds true for the increment section Two statements have been stuffed into a place where only one should go What this loop is supposed to do is to count up two variables twos by 2 and threes by 3 all in one loop What it really does is to cause good programmers to curse the people who think they are being clever by writing such code Side Effects A side effect is an effect that occurs in addition to the main effect of a statement C allows you to use the and operators inside other expressions Let s take a look Clear your program and enter the following include lt iostream gt int main int total size Total so far int current size Count of the numbers total size current size c rrent size 7 lotal S126 gtdiicont lt lt Current Sizet T lt lt ourrent size lt 4 stdirendi std Court lt lt Ttotal piz T lt lt total Size lt lt Stay send return 0 Do you know whatthe program will do F Save and run it The results may surprise you OBSERVE Corrent SILAS 6 coe Siwees 6 This is bad code The line current_size total_size does two things in this order 1
66. ens if someone breaks the software Can he do it again Often the answer to this question is no Third the term break is not defined If the system crashes that certainly is a break But what if it merely draws something that looks odd Is that odd drawing a feature or a bug Now we ll write our clear brief and excellent test plan Create a file called fest txt then type in the code as shown 1 Run the program 2 Observe the message Hello World Yes Pass No Fail A Few More Notes We recommend that you use the Save All menu option to save your work this will save everything you have opened and it can prevent problems when running your programs while you re working on them Do not put spaces or other special characters in file names Limit yourself to a combination of letters digits underscores _ and dashes This helps to avoid problems with the tool set being used When you create a new source file it always contains the standard header including the file name date and your name You should replace those elements with more detailed and specific information about your program Remember when using the O Reilly sandbox system that Red Leaf icon is your emergency button It will restore your screen to the original layout amp OST Java Eclipse SDK Mil E3 File Edit Navigate Search Project Run Window Help Ka s wt O Q 2Bee ss FY OST Java as Fics Resource ss T a r T T D o O
67. er to the expression 1 2 4 which is 12 and showed you the results So how did the parentheses affect the answer I m glad you asked Let s remove them and see what happens edit your code as shown include lt iostream gt int main std cout lt lt The answer is lt lt 1 24 4 lt lt std endl return 0 O Save and run your program This time the answer is different OBSERVE The answer is 9 The computer reads the expression 1 2 4 from left to right but it also follows the Order of Operations 1 exponents and roots 2 multiplication and division 3 addition and subtraction Multiplication occurs before addition so the computer actually does this e 2 4 8 e 1 8 9 You can change the Order of Operations by using parentheses In the first example we used parentheses to force addition to occur before multiplication Types of Numbers There are two major types of numbers in C integers and floating point You might also hear about a complex type but that type isn t actually built into the language Integers also known as whole numbers have no fractional value For example these are all integers OBSERVE 1 324290 42 999 37 Floating point numbers contain a fractional part For example OBSERVE T2739 14 8 37 0 The last number presents a key concept 37 0 is a floating point number Even though the fractional partis 0 its presence after the decimal point mak
68. es 37 0 a floating point number The number 37 is an integer Note When writing floating point numbers always include a decimal point It tells anyone reading your code that you intend the value to be floating point So 1 0 is good and 1 is bad 0 0 is good 0 is bad Floating point numbers can also contain an optional exponent For example OBSERVE Poo ES This tells C thatthe value of the number is 13 33 x 10 Floating Point vs Integer Division Editexp expression cpp to compute and print the value of the expression 1 3 as shown include lt iostream gt int main std cout lt lt The answer is lt lt 1 3 lt lt std endl return 0 O Save and run it then read the output OBSERVE The answer is 0 When C does integer division the resultis an integer it truncates any fractional part of the result Now editexp expression cpp again as shown include lt iostream gt int main std cout lt lt The answer is lt lt 1 0 3 0 lt lt std endl return 0 F Save and run it and look over the output OBSERVE The answer is 0 333333 When C sees thatthe arguments are floating point numbers it performs floating point division and gives floating point results But what if one number is floating point and the other is an integer Let s give that a try Modify exp expression cpp as shown include lt iostream gt int main std cout lt
69. es in one statement Change assign exp cpp as shown include lt iostream gt int main int play 2 An integer to play around with std cout lt lt At first the value of play is lt lt play lt lt std endl play 5 std cout lt lt The value of play is lt lt play lt lt std endl play 399 std cout lt lt Finally the value of play is lt lt play lt lt std endl return 0 F Save and run it You should see the following output OBSERVE At first the value of play is 2 The value of play is 5 Himealily ene vale er play as 999 Variable Types Floating Point The int is just one of C s built in types Another major type is the floating point number Here s an example ofa typical floating point float declaration and use Create a project named float play assign itto the C 1_Lessons working set and in it create a float play cpp program as shown include lt iostream gt int main Floating point variable declaration float area 5 2 3 5 Area of a rectangle std cout lt lt The area is lt lt area lt lt std endl return 0 F Save and run it You should see the following result OBSERVE The area is 18 2 Here we saved a step we declared a variable named area and assigned it the value of the expression 5 2 3 5 all in a single line of code C does the math it evaluates the expression and assigns 18 2 to the area v
70. ety so you do not cause any buffer overflows C style strings are more efficient that C style strings However as a practical matter most Efficiency programs are not CPU limited so efficiency makes little difference in a program Safety does and that s where C style strings win If you are interacting directly with an operating system like Windows or Linux you will find that OS many of the lower level operating system functions raw read and others use C style Interaction strings as arguments This means that if you pass data from one part of the OS to another C style strings are more efficient Have you had enough of strings yet In our next lesson we ll finally move on from output to input and we ll start learning how to make decisions in our programs See you there a x El D This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information Reading Data and if C 1 Introduction to C Lesson 7 Reading Strings In earlier lessons we used std cout to output data to the console If we want to read data in from the console we can use surprise st d cin Let s look ata short program that demonstrates the use of std cin Create a project named reading assign it to the C 1 Lessons working set then type a reading cpp program in it as shown tincliude lt iostream gt int main
71. gacy code containing strcpy a lot of code still uses this function So what should you do when you see it Ideally to make the program safe replace all strcpy functions with strncpy but any time you change a program there is risk for example you may not make the change correctly If the code is working even if itis messy the best thing to do is to eave it alone Unless there is a bug in the program that forces you to rewrite the code leave working code alone There are two times you would want to upgrade strcpy to the C string strncpy design pattern The firstis if you are changing the code anyway Always leave code better than when you found it The second is when you are trying to track down a memory corruption bug in this case the change might fix the bug Another unsafe function is std strcat It performs much the same function as std strcepy except that it does concatenation instead of copying Std strcat unsafe J UlIieette Wo inner wise std strcat destination source This function adds the source string to the end of the destination with no regard for the size of the destination The future of strcpy and strcat People have done all sorts of things to get around the limitations of strcpy and strcat for years Currently the OpenBSD folks have devised new functions stricpy and stricat designed to overcome the safety problems with strcpy and strcat respectively However the
72. ght float area width 5 0 height 2 0 area width height 2 0 std cout lt lt Area of the first triangle is lt lt area lt lt std endl width 3 8 height 5 9 area width height 2 0 std cout lt lt Area of the second triangle is lt lt area lt lt std endl width 2 8 height 1 6 area width height 2 0 std cout lt lt Area of the third triangle is lt lt area lt lt std endl return 0 Let s take a closer look at the triangle function OBSERVE float triangle float width float height float area width height 2 0 return area The first line specifies the return type name and parameters of the function Our function named triangle will return a float value It requires two parameters the firstis afloat named width the second is afloat named height After calculating the area the function returns it Now that we ve defined our function let s update our program to call it include lt iostream gt triangle compute the area of a triangle Parameters width the width of the triangle height the height of the triangle Returns the area of the triangle FF FF F HF float triangle float width float height float area width height 2 0 return area area triangle 5 0 2 0 std cout lt lt Area of the first triangle is lt lt area lt lt std endl area triangl
73. h2 to b the backspace as shown below include lt iostream gt int main char chl First play character char ch2 Second play character char ch3 Third play character chi IAT ehz mbps cho C3 std cout lt lt The characters are lt lt chl lt lt ch2 lt lt ch3 lt lt std endl return 0 F Save and run it and observe the output OBSERVE The characters are AOC The display probably doesn t look correct depending on how your computer handles the backspace character you might see anything from AC to A some funny character and then Wide Characters The char type suffers from the fact that it cannot deal with international alphabets To help solve this problem the wide character wchar type was created While the char type defines 256 characters wchar defines 65536 However there are languages such as Chinese Japanese Farsi Hebrew and many others that contain even more than 65536 characters To display characters from those languages a character encoding system called Unicode was created Support for wide and Unicode characters is dependent on the compiler and operating system that you are using We ll discuss this in a future lesson Boolean The boolean type bool can have the value true which is also one or 1 or false which is also zero or 0 Create a project named play bool assign the C 1_Lessons working set to it and create the program file play bo
74. high end graphics systems to embedded processing Chances are you already own two or three computers running C programs only they aren t called computers they re called cell phones GPS systems cameras or DVD players Our course is designed to teach you how to do real world practical programming As such it will teach not only the best practices when it comes to design and coding but also how to deal with the worst practices that seem to seep into many of the programs out there in the real world For this course we will use the Advanced O Reilly Learning Sandbox This system allows you notonly to read the lessons but to interact with the examples You are encouraged to experiment and try new things all within the environment of your O Reilly Learning Sandbox Of course in the real world you ll make mistakes Typing in a program finding that it s broken and sweating over it until 2 o clock in the morning only to find you ve made a small mistake is another way of learning We hope you will rarely need to use this method of learning History of C C was born in 1970 when two programmers wanted a high level language for a machine they were working on They designed a language similar to an old language they had been using called B In the programming tradition of keeping things simple they named their language C C was a good language for its day It ran on very limited hardware 4mhz 64K memory and did a pretty good job
75. i Note andcalltriangle a function because it does return a value C just has one construct a function Our function does not have a return statement because itisn t required inside a void function Let s add it and revise our program to call print_it include lt iostream gt x triangle Compute the area Or a triangle Parameters i width the width of the triangle height the height of the triangle BECUS i the area Of the triangle float triangle float width float height float area width height 2 0 return area x print 1E output a message Parameters i area the area of the triangle what the name of the triangle void print it float area char what std cout lt lt The area of the lt lt what lt lt triangle is lt lt area lt lt std e ndl returni int main float area Area of a triangle area triangle 5 0 2 0 ste cout lt lt Aree of ehe 1st ttrencgie s lt area ste tend Print 2 lares Tiret area triangle 3 8 5 9 std eent lt lt res of the second tstrenegte _ s l eee lt lt ste ere Print i area second area triangle 2 8 1 6 std eent hrena ehehe print iLlarea rthird ji return 0 0 Save and run it You ll see the same output again OBSERVE The area of the first triangle is 5 The area of the second triangle is 11 21 The area of the th
76. ide lt lt t 070 lt lt std endl return 0 F Save and run it You ll see output like OBSERVE Divide alee The floating point format used by basic Intel compatible processors has special numbers defined for error conditions such as inf inf and NaN nota number This is processor dependent and although almost all modern processors now use this standard format some don t Results on those computers could be different SO now you may be wondering why integer division by zero crashes your program while floating point division by zero does not This is by design Intel compatible processors have been used for decades and at first could only perform integer arithmetic Floating point arithmetic was handled separately and thus it continues to generate different errors Instead of worrying about the differences in error handling itis better not to generate the error in the first place In future lessons we ll learn how to make sure our programs work correctly Stay tuned Limits on Numbers Suppose you have an old eight digit calculator You type in the number 99 999 999 and then add 1 to it The result is a nine digit number which the calculator can t display So the calculator displays ERROR There are similar limits to the numbers in C Unfortunately these are not hard limits They can vary depending on the processor type compiler and operating system C has a file named climits that defines the li
77. ing hidden variables whenever possible That s because if you say something like And here print the value of a_var someone has to ask you Which a_var There s enough confusion in the programing world now without us adding more You made it In the next lesson we will put scope to work with functions Stay tuned This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information Functions C 1 Introduction to C Lesson 11 What is a Function In prior lessons Our programs were fairly short Repetition so far has been limited to for and while loops In this lesson we ll learn how to use functions to organize frequently used code A function is like a black box you provide the box with some parameters and it returns the result Our First Function Let s suppose we wantto compute the area ofa right triangle the formula is area base height 2 Create a project named triangle and assign it to yourC 1_ Lessons working set In the new project create a source file named triangle cpp as shown include lt iostream gt int main float width float height float area width 5 0 height 2 0 area width height 2 0 std cout lt lt Area of the first triangle is lt lt area lt lt std endl return 0 O Save and run the program You ll see OBSERVE Are
78. ing point numbers Now you re ready to tackle the next lesson where we ll discuss program structure and variables See you there a gt D Copyright 1998 2013 O Reilly Media Inc This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons orq licenses by sa 3 0 leqalcode for more information Variables C 1 Introduction to C Lesson 3 Basic Programs We have to walk before we can run so we re going to learn to program for now in a subset of the C language Our basic program structure is OBSERVE File heading comments include directives int main data declarations executable statements return 0 In some books and code examples the data declarations are placed before the int main line In these i lessons they come after it At this stage for the types of programs we can currently write either order will Note work We ll learn the difference between the two types of declarations later Itis easier to use Eclipse if you put the data declarations just after the first brace The include directives data declarations and executable statements sections are optional so the shortest possible C program would have all three sections omitted OBSERVE int main return 0 Such a program may appear to be useless but it s actually a standard Linux Unix command true It s used in shell scri
79. iostream gt int main ant value OG a value to double std cout lt lt Enter a value stditcin gt gt value std cout lt lt Twice lt lt value lt lt is lt lt value 2 lt lt std endl return 0 F Save and run it then click in the console window type 123 and press Enter You will see OBSERVE Entrer a value 123 Twice 123 16 246 Let s look atthis code more closely Observe reading cpp include Io trean int main ine vyv nao o a e wo oae std cout lt lt Enter a value std cin gt gt value std cout lt lt Twice lt lt value lt lt T Iis lt lt value 2 lt lt std endl return 0 Back in the first lesson we learned that the lt lt operator means to put whatever s on the right into whatever s on the left Since we are using std cin and want to get data from the console we use gt gt to go the other direction and get whatever s on the right from whatever s on the left In our case we get data from std cin and put itin the variable named value Also look at the line std cout lt lt Enter a value Notice that there s no std endl at the end We omitted this deliberately to make this output line a prompt In real world programming paranoia is part of the job So one question you need to ask atthis pointis What happens if type something that isn ta number Let s try it Run your program again enter Ji
80. ir effort has not made it into the Standard yet For more information see strlco py in Wikipedia Comparisons to other types C Strings vs Arrays of Characters C style strings and arrays of characters are two different things An array of characters is of fixed length and contains no markers or other special characters In other words char name 50 contains 50 characters of any type no more or less Note In a character array the null character 0 need not be present it s just another character with no special meaning A C style string is built on the character array type It states that you have an array of characters with an end of string marker 0 to end it So null 0 cannot be part of the string So all C style strings are arrays of characters but all arrays of characters are not C style strings Let s try an example Edit yourcompare c cpp program as shown include lt cstring gt include lt iostream gt int main ehar state 2 1 C A Sta reout lt lt This probably looks Tunny lt lt stats slats cout lt state lt Sstdy renal std cout lt lt This looks better T lt lt std endl Stottcout lt lt state lt lt starel lt lt etdssend gt return 0 You mightlook at the state declaration and think itis an error that it should be char state 3 in order to reserve one character for the end of string But this is nota mistake state is nota C sty
81. ird triangle is 2 24 Function Overloading Our print_it function works fine but what if we didn t always wantto pass the second parameter In C we can overload a function which means that we can have two or more different functions with the same name and different parameters Let s define a new print_it with only one parameter instead of two Edit your program as shown include lt iostream gt J gt triangle compute the area Of 2 triangle Parameters j width the width of the triangle height the height of the triangle Returns 2 the area of the triangle float triangle float width float height float area width height 2 0 return area x print 1E output 4 message Parameters i area the area of the triangle what the name of the triangle k void print it float area char what std cout lt lt The area of the lt lt what lt lt triangle is lt lt area lt lt std e ndl return fs print it output a message without the what Parameters ji area the area of the triangle a v id print it float area std cout lt lt The area of the triangle is lt lt area lt lt std endl return int main float area Area of a triangle area triangle 5 0 2 0 Prine 10 dareag sa area triangle 3 8 5 9 print it area second area triangle 2 8 1 6 print IC
82. items float students CLASS SIZE 34 0 27 0 46 5 82 0 22 data to av erage and total total students 0O students 1 students 2 students 3 students 4 average total CLASS SIZE std cout lt lt Total lt lt total lt lt Average lt lt average lt lt std endl return 0 F Save and run it You should see the same results as before Our code so far looks good but our total calculation is a bit unwieldy because we ll have to change the formula each time we change the CLASS_ SIZE Let s see how we can fix that for loops We can have the computer calculate the total for us after all itknows how big CLASS_SIZE is To do this we can use a for loop which executes a block of code a specified number of times Change your program as shown include lt iostream gt int main Const int CLASS Size 5 int xj float average 0 0 average of the items float total 0 0 the total of the data items float students CLASS SIZE 34 0 27 0 46 5 82 0 22 data to average a nd total X lt CLASS sick 7 x xX 1 total total students x average total CLASS SIZE std cout lt lt Total lt lt total lt lt Average lt lt average lt lt std endl return 0 F Save and run it You should see the same output as before OBSERVE Metal 211 5 Average 4273 So how does the for loop work Take a look at the code OBSERVE
83. ld 0 is false and anything else is true With this in mind people have devised shortcuts such as the following tinclude lt iostream gt int main int number A number we are going to check std cout lt lt Enter a number std cin gt gt number if number std cout lt lt number lt lt 1s zero lt lt std else sto scout lt lt number lt lt is not zero lt lt std endl return 0 The is the logical negation operator it adds a not to the condition The conditional statement in this program might read like if not number which is pretty confusing O Save and run the program Enter 0 zero you ll see this OBSERVE Enter a number 0 OQ iS Zzero If you enter a non zero number even 25 you ll see the following OBSERVE Enter a number 25 25 18 NOU Zero This code is not good because it isn t clear exactly whatis going on Instead be explicit with your if statements Change your program as shown include lt iostream gt int main int number A number we are going to check std cout lt lt Enter a number std cin gt gt number if 0 number std cout lt lt number lt lt is not zero lt lt std endl else std cout lt lt number lt lt is zero lt lt std endl return 0 This program is clearer the condition reads if number is not equ
84. le string it s a character array Itholds two characters No more no less there are no one character state name abbreviations F Save and run it and observe the output Generally you ll see something like OBSERVE Tais joncoloclolly eOk runny CA y This looks better CA When you use std cout lt lt state lt lt C will assumes that state is a C style string it s not It will then look for the end of string marker there is none and write the state abbreviation followed by some random garbage You must write a character array one character ata time Writing a Character Array std cout lt lt Sins ice lt lt statel lt lt std endl The bottom line You can write outa C style string using lt lt but not a character array C Style vs C Style There are advantages and disadvantages to using each type of string c strings can store any length string auto matically You must explicitly declare the ra maximum size of C style strings The memory used by C style strings is precisely controlled They do not grow or shrink depending on what data you putinto them C style strings manage their own memory They can grow and shrink They can also use memory in Surprising ways if you are not careful Almostall of the operations you can use on C style strings are safe Almostall of the Operations operations you can use on C style strings can be dangerous You must be very careful about saf
85. ll use Joyce Kilmer in the examples but you should replace Joyce and Kilmer with any names you like As you can see string constants are enclosed in double quotes Remember that character constants are enclosed in single quotes It might help to remember that one tick is for a single character and multiple ticks for multiple characters strings F Save and run the program You ll see something like OBSERVE My name is Joyce Kilmer Excellent So far strings work exactly like any other variable such as an int or float We learned how to add two numbers in a previous lesson You can perform a similar operation on strings using the plus operator you can concatenate two strings To see how this works change your program as shown include lt iostream gt include lt string gt int main std string first First name std string last Last name std istring full The full name first your first name last your last name Lull Firet m Last std cout lt lt My name is lt lt full lt lt std endl return 0 F Save and run it You ll see the same output In this program we concatenated the two variables first and last with the space in between What if we tried to concatenate Joyce a space and Kilmer directly Change your program as shown include lt iostream gt include lt string gt int main std string first First name
86. llo o hello cpp Vhello cpp In function int main ihello cpp 3 error expected initializer before lt lt token Build error occurred build is stopped Time consumed 609 me So what happened Eclipse flags errors with an x error icon Ideally itappears on the line where you made the mistake but sometimes like now it doesn t However in this case you do see a small yellow box containing a question mark on the int main line Eclipse s internal parser detected an error on this line and flagged it that way When Eclipse flags errors in your program you still might need to do some investigative work to find and fix them and it s a good idea to check the lines of code surrounding the flagged ones as well Fix the problem in hello cpp by removing the misplaced int then save your work What Does It All Mean Let s take a closer look at the program to see how it works OBSERVE hello cpp include lt iostream gt int main std cout lt lt Hello World lt lt std endl return 0 The firstline is include lt iostream gt This include line tells C I m going to use your standard streaming I O package iostream The compiler brings in the definitions of the items for this package The next line int main is the start of the code for your program The main function is special in C itis the first function that C executes We ll get into function definitions later for now yo
87. m Back Refresh Fie Googe O To reset the screen click the red leaf O REILLY Ox My Start Page Steve eee ta ele Java pbs anil TECHNOLOGY Congratulations You have created your first C program and completed lesson 1 of the course In the next lesson we ll investigate expressions See you there a D Copyright 1998 2013 O Reilly Media Inc This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information Expressions C 1 Introduction to C Lesson 2 Glad to see you re back In this lesson we ll learn to use mathematical expressions in C Mathematical Expressions C understands these operations Addition a Subtraction Multiplication Modulus remainder after division We can combine these operations with numbers into an expression to do useful lots of really useful work Let s get going and try an example to see how these operators work Start a new project and name it exp expression Assign itto the C 1_Lessons working set Then create a new source file in the new exp expression project and name itexp expression cpp Now create the project and source file You can see a graphical representation of this procedure in the next section But if you feel comfortable with the process so far go ahead and skip to the following section Creating the Project and
88. m myfile input txt Make sure the file can be read from if imyfile is open While we have not reached the end of file EOF while myfile eof c myfile get Slot oot lt lt o myfile close else std cout lt lt Unable to open file return U Create a file named input txt in your project add some appropriate text to it and then save and run this code to see how it works Your program will prompt for user input instead of using a file Testing Testing comes next Write up a test plan for your program named test txt Take care to test all major components of your program would suggest that you create a file named input txt containing the input that you want to use for testing the program To actually test the program 1 Open the input txt file 2 Select Edit Select All 3 Select Edit Copy 4 Run the program 5 Click in the console and select Edit Paste to paste the test file s contents into your program s input 6 Type Ctrl Z to signal end of file Revisions Your program counts words Think of how you might want to enhance it Create a file named rev txt containing the wish list for your new program Then be thankful that you ve reached the end of the lesson and you don t have to implement any of those revisions When you finish hand in your project GOOD LUCK This work is licensed under a Creative Commons Attribution ShareAlike 3
89. mailbox in the name string F Save and run it This time you ll see OBSERVE Size as 4 Name is now Joe Name is now Ste We only see the first three characters of Steve because name is only big enough to contain four characters Ste plus the null character Believe it or not changing the size of C style strings is notas straightforward as you might expect That topic will be covered in a future course Concatenation of C Style Strings In the last lesson we covered the length function for C style strings The function std strlen returns the length ofa C style string In other words it returns the number of characters actually in the string as opposed to sizeof which returns the capacity The function to perform concatenation of C style strings is std strncat Unlike concatenation of C strings concatenation of C style strings requires some planning to make sure you don t overflow any buffers The function takes three parameters OBSERVE std strncat destination source size You must carefully calculate size in order to make sure you don t overflow the destination The easiest way to do this is to always use the following code Concatenation Design Pattern std strncat destination source sizeof dest std strlen dest 1 destinati o nioi xe Glesie dla cic t ie ee ee On The calculation for the size parameter for std strncat works like this Std strlen destination
90. message Launch failed Binary not found Itisn t possible to set this flag as the default But just in case you need to refresh your memory on occasion we ve provided a checklist of the steps you need to take in order to start a project Okay we re ready to create our program Find the hello_world projectin the C 1_ Lessons working set and select it then select File New Source File Ee I Ce ee aa Fr Projec Elle Java H E javal 2 Delete Do pa Move H E Java Rename Remove From Gonbesxt e g Import ey Export po t Ex I re A 4 Project Open in Mew Window Fa Ecore Diagram Lei Ecore Tools Project File File from Template C5 Folder 4 SOL File br AlE Shift Bown Class hi Header File a a Gi Source File 62 Source Folder Enter the name hello cpp and click Finish New Source File io Source Folder hello_world Browse Source File hello cppl Configure Create a new source file Template Default C source template The new file hello cpp appears with a short header containing the filename the date and your name In hello cpp add code as shown below hello cpp Created on Dec 15 2009 Author smiller a include lt iostream gt int main std cout lt lt Hello World lt lt std endl return 0 As you type you ll notice that the system auto matically completes certain items For instance when
91. mi Hendrix and press Enter This time you ll see the following OBSERVE Enter a value Jimi Hendrix Twice O0 is Q When you try to assign an inappropriate type of data to the value variable it doesn t change if Statements Now that we can read data we are going to create a program that reads a number and tells you if it s even Create a project named if assign itto yourC 1 Lessons working set In that project create a program named if cpp as shown if Show the use of the if statement In this case the program will tell you if a number is even or odd Usage Run the program Type in a number when prompted Get the answer FF amp SF S amp S SS amp S S E SS tincluide lt iostream gt int main int number A number we are going to check std cout lt lt Enter a number Sta scin gt gt number if number 2 0 std cout lt lt number lt lt is even lt lt std endl return 0 F Save and run the program Enter an even number like 8 You will see the following output OBSERVE Enter a number 8 8 is even If you enter an odd number like 7 you won t see any output at all How does the if statement work The key line is if Statement in Use if number 2 0 This says to C compute the value of the expression number 2 The is the modulus operator it calculates the remainder after division If the value is equal
92. mits on its basic types We ll include this file and then add some code to use it Edit yourexp expression cpp program as shown include lt iostream gt finclude lt climits gt int main std cout lt lt INT Max lt INT MX lt lt std 2endl return 0 F Save and run it You ll see this OBSERVE INT MAX 2147483647 This example uses the C style constant for the integer limit The pure C way of doing this is to include the header file lt limits gt Then you can get the maximum integer with the expression Note std numeric_limits lt int gt max We used the C method because it s shorter Also to understand the expression std numeric_limits lt int gt max you need to understand classes static member functions templates and template specialization all concepts we will cover in a future course Let s see what happens when we go past the limit Change the program as shown include lt iostream gt include lt climits gt int main Std cout lt lt INT MAX L M lt lt INT MAX IL lt lt sStd 2endl return 0 Based on the last execution of the program we might expect to see the number 214748 3648 O Run it Instead we see OBSERVE INT MAX 1 2147483648 This is called overflow Iit occurs when a number becomes too big or too small to fit into its type in this case integer C does not check for overflow and will not warn you when it occurs You won t encoun
93. n std string state Texas std cout lt lt State is lt lt state lt lt std endl return 0 F Save and run this program As you might expect you will see the following output OBSERVE State is Texas Now edit the program as shown include lt iostream gt int main std string state Texas std cout lt lt State is lt lt state lt lt std endl return 0 include lt iostream gt int main std string state Texas std cout lt lt State 1 is lt lt state lt lt std endl std string city Austin atd icout lt lt City 1g lt lt City lt lt std endl return 0 F Save and run it You ll see OBSERVE State 1 is Texas City Tean aio Edit the program again as shown include lt iostream gt int main std string state Texas std cout lt lt State 1 is lt lt state lt lt std endl std string city Austin std cout lt lt City 15 lt lt city lt lt stditend atd rcout lt lt City F216 lt lt city lt lt stdrtendi return 0 LJ Leal Save your program this time you ll notice an error l include lt iostream gt 2 zint main i 4 5 std i sCrCcing State Texas 6 std cout lt lt State 1 is lt lt state lt lt std endl T i m std string city Austin std cont lt City 13 T lt lt City lt etd iiendli
94. n in this lesson In the next lesson we ll continue our discussion of parameters and types Stay tuned La Copyright 1998 2013 O Reilly Media Inc This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information Parameters and Return Types C 1 Introduction to C Lesson 12 Welcome back In the last lesson we discussed functions and learned how to write our own functions with parameters In this lesson we ll explain just how parameters work Passing Parameters C provides many ways of passing parameters to functions Knowing what choices you have and how to use them is key to writing good C code Pass by Value Let s start with a short program Create a project named var pass and assign itto yourC 1_Lessons working set In the new project create a program named var pass cpp as shown tinclide lt lostrean gt void test int a std cout lt lt test a is T lt lt a lt lt Ste tendcl a 5 Star 2coui lt lt testi A ae T lt lt A lt lt ardi rend int main ine ij Variable to play around with i 23 test i Scatter lt Nain 2 ae lt lt 42 lt lt stditendl return 0 F Save and run the program and observe the outp
95. next calculation Finally we do a little housekeeping Our program outputs everything on a single line so we add an end of line character after the loop finishes Excellent To get a better idea how Fibonacci numbers and while loops work let s add some cout statements Add the colorized code include lt iostream gt include lt iomanip gt int main int old number 0 Previous Fibonacci number int current number 1 current Fibonacci number int next number next number in the series int iteration count 1 atd gout lt Iteration olda current next lt 10U07T lt lt eta while current number lt 100 gtdiicout lt lt Sto te617 2 lt Iireration count stdicout lt lt std rsetw 14 lt lt old number skd icout lt lt gtdirserr 7 lt lt purrent munder next number current number old number old number current number Current number next number gcd cout lt lt Sstciteetwis lt lt next number if current number lt 100 stds ico lt lt FT else Stat cour lt lt T F Stic ttcou lt lt sto senda iteration Count iteration count 413 std cout lt lt std endl return 0 We included iomanip specifically the std setw function to help format our output This function sets the padded width of the next item in the cout chain For example the following code ensures that iteration_code is outputas exactly two characters O
96. ojects organized we ll move them to the C 1_Lessons working set Find the hello_world project in the Other Projects set right click it and select Assign Working Sets In the dialog box that appears check the box for C 1_Lessons and click OK Working Set Assignments a x Select working sets For hello_world C d C 1 Community Select All C 1z C 1_Handback J C Homework J C4 1_Lessons He Deselect All M Show only Package Explorer working sets Configure Now we ll set up the project s building behavior Right click the hello_world project again and then select Properties Select C C Build then click the Behavior tab Check the Build on resource save Auto build box and click OK Properties for hello_world _ OR C C Build O F type Filter text Project References 7 Run Debug Settings 5 Server Task Repository Task Tags H validation Builder Setting Behaviour Build settings M Stop on First build error Use parallel build Use optimal jobs number f Use paralleljobs 1 Workbench Build Behavior Workbench build type V Build on resource save Auto build Mote See Workbench automatic build preference M Build Incremental build W Clean Restore Defaults Apply You will need to do this for every project you create If you don t when you try to run programs from the project you ll see this
97. ol cpp as shown include lt iostream gt int main bool flag Boolean to play around with flag true Set it to true atdrrcout lt lt Flag is T lt lt ilag lt lt sfc renal flag false Set it to false etarscour lt lt Flag ig lt lt flag lt lt startendi flag 1 1 is the test for equality operator expression is true stat cout lt lt Flag 1s lt lt flag lt lt stditendli return 0 0 Save and run it You should see the following output OBSERVE The computer printed the underlying values for flag as it was set to true then false then true Originally C did not have a boolean type so people defined their own As a result you may see things like BOOL BOOLEAN Bool TRUE and FALSE in older books or code Be aware that these are local non standard items Now the question comes up What should do about legacy types in my code The best answer is if the code works leave italone You could waste a lot of time and effort trying to improve working code and bring it up to current standards merely to make it do whatit already does If you do have to go in and change something and bringing the types up to date will not cause too much trouble by all means do so But don t change anything just for the sake of changing it Mixing Types C is very flexible when it comes to mixing types If it can figure out a conversion it will silently allow you
98. onfiguration Debug for project War pass t t if fil gt 12 return ili e e Internal Builder is used for build return iz teat g 00 g3 Wall c fmessage length o0 OVar pass o0 var pass cpp war pass cpp In function int maint war pass cppiil error invalid initialization of non const reference of type int Crom a temporary of type int int main i i int i 1 int j ag War pass cppi4 error in passing argument 1 int answer of int waxfintse ints Build error occurred build if stopped Time consumed 609 me Btd i cout lt lt Max is lt lt answer lt lt std endl return Oj When a function expects a reference parameter such as max the compiler performs a number of operations behind the scenes 1 It creates a temporary variable and assigns it the value of the expression 2 It performs the function call 3 It destroys the temporary variable So the code the compiler generates looks something like The compiler s version of max cpp sin ade ostren ints max Inte Il Int i ite i return il recurcn L2 p main inc i aie J int answer int tmpl i 1 int tmp2 j 1 7 answer max tmpl1 tmp2 At this point answer is a reference to tmp2 At this point tmp2 does not exist srt cole lt lt 6 Max is Y lt lt answer lt lt Stele senals return 0 You will rarely need to use references
99. or x 0 7 amp lt CLADO SIZE F x xX a 1 total total students x Sctastcour lt lt Students x Y lt x lt lt Ja lt lt students x lt lt 2 total lt lt to lt lt std endl average total CLASS SIZE std cout lt lt Total lt lt total lt lt Average lt lt average lt lt std endl return 0 F Save and run it and observe the output OBSERVE Students Students x 34 total 34 x aO totaler ol x lt doo told le lOS x Soy CoCa la o Students Students Students x 7 total 2I Potal Ales Average 412 3 A for loop can really make short work ofa big list Suppose our class size grows to ten We can quickly update our program to handle this simply by updating CLASS_ SIZE and entering values for the additional students Update your program as shown Remember arrays are zero based so we are adding students 5 through 9 include lt iostream gt int main const Int CLASS SIZE 107 int x Us float average 0 0 average of the items tloat total 0 0 the total of the data items float students ChASS SIZE 340 2707 40 5 62 0 22 Tsd 9 9 Dls 900 45 8 F 7 data to avera ge and total for x 0 7 X lt CLASS SIZE 7 x X 1 total total students x std cout lt lt Students x lt lt x lt lt lt lt students x lt lt total tal lt lt std endl ave
100. ou cannot do that sort of assignment Fix the error by using the equality o perator tinclude lt iostream gt int main int number A number we are going to check std cout lt lt Enter a number Std scin gt gt number if 100 number std cout lt lt number lt lt is one hundred lt lt std cout lt lt number lt lt is not one hundred lt lt std endl return 0 Blocks C allows you to write if statements in a compact way Change your program as shown include lt iostream gt int main int number A number we are going to check std cout lt lt Enter a number std cin gt gt number if 100 number std cout lt lt number lt lt is one hundred lt lt std cout lt lt number lt lt is not one hundred lt lt std endl return 0 i Save and run your program a few times with different numbers You will see this program works just like the prior version The if statement does not require you to use braces it executes the statement immediately following the if or else OBSERVE if conditional test Code to execute when conditional test is true else Optional Code to execute when conditional test is false You do not need t o have an else This can be very problematic though Change your program as shown including spaces include lt iostream gt int main int num
101. pting as a command that always returns a good status 0 to the currently running script Variables A variable is a bit of your computer s memory like a box in which you can puta single item of data We must declare variables before we use them In order to declare a variable C needs two pieces of information the name and the type what the box is called and what type of box itis In order to pass this course you ll need to add a third piece of information Acomment explaining what the variable is used for A variable name begins with a letter upper or lower case or an underscore _ then continues with any combination of letters underscores or digits It cannot be the same as any C keyword For example these are legal variable names OBSERVE box width Pe Lie eomnite today whatever Point dataField These are not legal variable names OBSERVE stime h Beine wath ra cise alte box top Contains hyphen Variable names are usually lower case size full_size or mostly lower case Size FullSize fullSize Constants are usually given upper case only names PI MAX_INT Nothing in the language forces you to follow this convention but if you choose to ignore it don t be surprised ifa mob of angry maintenance programmers shows up outside your door with torches and pitchforks Style Note There are two major ways of constructing variable names The first is separating words with underscores OBSERVE box
102. put the mouse pointer on the icon you ll see this message Fi Package Explorer Build hello_world lH include lt iostream gt S El ft a ris Zint maini project hello world unused variable cout gt cout was not declared in this scope standard has nok been declared wee Internal Builder is used for build eA g O0 g3 Wall c fmessage length 0 ohello o hello cpp thello cpp In function int main Vhello cpp 3 error standard has not been declared thello cpp 3 error cout was not declared in this scope thello cpp 3 warning unused variable cout Build error aceurred build if stopped Time consumed 656 ms This tells you that something bad happened In particular the compiler can t figure out what the symbol standard means Fix the problem by changing standard back to std then save the file The red icon should go away Now let s create a new problem for ourselves Modify hello cpp below as shown include lt iostream gt int main int std cout lt lt Hello World lt lt std endl return 0 Save the file You ll see an x error icon on the the std cout line C Build hello_world i include lt iostream gt a zint mainii i int T OU 26 Hello World oe bai Endl e e Build of configuration Debug for return 0 project hello world eee Tee Jnternal Builder is used for build tity g O0 g3 Wall c fmessage length 0 ohe
103. rage total CLASS SIZE std cout lt lt Total lt lt total lt lt Average lt lt average lt lt std endl return 0 F Save and run it See how we didn t have to change the rest of the program it just worked Your output should look like this OBSERVE Students Students Students Students 34 total 34 Students x ZIPs e ees e l A Gre O7 toral 10 or e E S 22 otal alas or S e S e Domo Er O e Ios a Students Oiler Total eae Students On were lls S205 3 Students x Gls 43 8 tortal 564 Total 564 7 Average 56 47 Students x Students xX co CS WWD PS x x Array Safety C makes it easy to store a lot of information in an array What happens if you make a mistake like accidentally loop over too many array elements Edit the program as shown RR KKK KK KKK KK KK KK KK KK KKK KK KK KK KK KK KK KK WARNING In order to see what happens when we violate the rules this program del iberately overflows an array RR KKK KK KKK KK KK KK KK KK KK KK KK KKK KK kK KK KKK include lt iostream gt int main conet Int CLASS SIAE 10 int x 0 float average 0 average of the items is float total 0 0 Z7 the total of the data items float students CLASS SIZE 34 0 27 0 42625 8260 22 727 3 3549 91 2 90 0 43 8 by 7 7 data to averag e and total for x 0 gt x lt 18 x 1 77 OOPS total total
104. re was no end of string marker C did not stop at the end of other It continued to write out characters from random memory until it actually found an end of string character C allows for even more compact initialization using double quotes Let s use it to fix the error tinclude lt iostream gt int main dhar neme 119 at Tmp PLO ts The name for this example char other Joe Another name with an error std cout lt lt The name is lt lt name lt lt and other is lt lt other lt lt std endl return 0 This form of initialization creates an array four characters long and assigns it four character values the fourth and last being the end of string character O Save and run it and observe the output You cannot assign a value to an existing C style string This is because a C string is an array and you cannot change its value like you can with other variables Try it include lt iostream gt int main char name Sam The name for this example l l name Joe Will this work std cout lt lt The name is lt lt name lt lt anc ethe gt i o ll other std endl return 0 When you save this file you will see an error ttt Build of configuration Debug for project char name Sam C Strling Ft 150 C forbids assignment of arrays ttrt Tnhternal Builder is used for build ttt std cout lt lt The na g
105. s before Why ae iro e ae aa Now just for fun change the line that gets the first initial to attempt to grab character 99 an illegal index as shown below include lt iostream gt include lt string gt int main Std tscring first First name std string last Last name Sta2 sering full The full name char first initial The first initial first Joyce last Kilmer full first FT last first initial first at 99 Assigns first initial the value J This i s the safe way of doing this std cout lt lt My Tirst initial i T lt lt first initial lt lt std endl return 0 0 Save and run it You ll see the following on the console This application has requested the Runtime to terminate it in an unusual way Please contact the application s support team for more information The program can t access the 99th character in the string so it threw in the towel This isn t quite a crash but it isn ta good way to end your program Other Functions One of the more common things to do with a string is to extract a substring for example some substrings of the fullname Joyce Kilmer are Joyce e Ki and Kilmer C strings let you take substrings using the substr function Let s try it include lt iostream gt include lt string gt int main std string first First name std string last Last name sca tstrang Tull The full name Sheet he
106. se variables are the same thing As a result any change to b is a change to i Using the mailbox analogy again passing by reference is like putting the original letter in the mailbox so the recipient the function can look at and potentially change it Array Parameters Now let s see how functions work with arrays We ll add an array parameter to our program include lt iostream gt void test int k std cout lt lt test lt lt k 0 lt lt std endl k 0 7 std cout lt lt test lt lt k 0 lt lt std endl int main int k 3 10 20 Array to play around with test k std cout lt lt main lt lt k 0 lt lt std endl return 0 F Save and run it You ll see OBSERVE test k 0 is 10 is 7 is 7 test k 0 main k 0 Notice that the value of k 0 is changed even though we didn t use the amp reference operator That s because arrays are automatically passed by reference In fact there is no way to make them pass by value What happens if you pass k 0 to a function instead Let s try it tinclude lt iostream gt void test int a std cout lt lt test a is a 5 std cout lt lt test a as int main int k 3 10 20 30 test k 0 std cout lt lt main return 0 k 0 F Save and run it You ll see OBSERVE a ais 10 a is 5 kiOl is 10 test test main ez a lt lt std
107. sraetcouc lt lt City 19 T lt lt city lt lt std sendi std cout lt lt State 2 is lt lt state lt lt std endl Sidi scout lt lt State Fs is T lt lt state lt lt std endl return 0 F Save and run it You ll see OBSERVE Stare gil is Texas Cat as Asie aia Starte 2 18 Texas State 3 is Texas Global Variables Like their geographical counterparts you re in the state when you re in the city but you re not necessarily in the city when you re in the state In our example the state variable is actually a local variable It exists only inside the curly braces that enclose it butit s still available within other braces nested in those braces Right now that happens to be our entire program but we will deal with more complex programs in the next few lessons A variable that exists outside of main and in fact exists everywhere is called a global variable std cout for example is a global variable It exists before main starts and after it ends Let s declare our own global variable named country Edit your program as shown include lt iostream gt std string country USA A global variable int main std string state Texas std cout lt lt State 1 is lt lt state lt lt std endl std cout lt lt Country F1 is lt lt country lt lt std endl SLO string City Austin std cou t lt lt City 15 lt lt city lt lt
108. std string last Last name Stds string Tuil The full name first Joyce last Kilmer full Joyces Kilmer Std cout lt lt My name is lt lt full lt lt std endl return 0 Oops Looks like C isn t happy with us It gives the following error g 00 g3 Wall c fmessage length 0 ostring a first teve string cpp last oualline string cpp In function int operator mainfi std cout lt lt My name is lt lt full lt lt std endl return 0 string cppi le error invalid operands of types const char 6 and const charf e to binary operator t Build error occurred build is stopped Time consumed F16 ms This is because ofthe way the concatenate operator is defined There must be a std string on atleast one side of the Change your program to fix this problem include lt iostream gt include lt string gt int main std string first First name std string last Last name std string full The full name first Joyce last Kilmer fii 1 1 iirst W LAJ Kilmer std cout lt lt My name is lt lt full lt lt std endl return 0 F Save and run it you ll see the same results as before Characters in strings You can access any character in the string using the subscript operator Change string cpp as shown tinclude lt iostream gt inclu
109. t f ll length lt lt characters in it lt xstdi endl return 0 O Save and run it Sure enough it counts the characters including spaces In the next lesson we will learn more about strings and discuss C Strings See you then ac Copyright 1998 2013 O Reilly Media Inc This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons org licenses by sa 3 0 legalcode for more information C Style Strings C 1 Introduction to C Lesson 6 What is a C Style String In the last lesson we learned about C strings There is an additional different type of string the C style string C style strings are the primary string type of the C language Since C is a superset of C ittoo has use C style strings In previous lessons we examined characters and arrays a C style string is essentially an array of characters with the special character null 0 at the end Since C style strings are arrays they have a fixed maximum length Dynamic strings are possible but they require the programmer to manually manage memory a process thatis full of pitfalls and gotchas Many security problems and bugs refer to buffer o verflows which are typically errors with C style strings that result in memory corruption There are many who believe that you should never have a C style string in a C program Unfortunately should and the real world
110. t lt Th var el aS lt D var lt lt stditendl lt lt gtdiiendli int a var d Std rcout lt lt Ta var 2 is T lt a var lt std rendl otdi ceo x Th var ge ip Tas D var x std icndl lt lt ptdr iondl staitacut lt lt g war 7s 16 lt lt a var lt lt gidi rend etd scout lt lt bp var Fo ig T lt lt b var lt lt stdiiendly return 0 F Save and run it You ll see OBSERVE Itlooks like a_var switched values in the middle of the program to 3 and then back to 2 But did it Not quite So what s happening Let s start by looking at the scope of b_var since we haven t played any games with it Scope ofb_var int main AINE el Wee int b var std cout lt lt a var 1 is lt lt a var lt lt std endl std cout lt lt b var 1 is lt lt b var lt lt std endl lt lt std endl int a var 3 std cout lt lt a var 2 is lt lt a_var lt lt std endl std cout lt lt b var 2 is lt lt b var lt lt std endl lt lt std endl std cout lt lt a var 3 is lt lt a var lt lt std endl std cout lt lt b var 3 is lt lt b var lt lt std endl return 0 b_var s scope includes all of the code shown in green Now we ll show the scope ofint a_var 3 we need to say int a_var 3 to identify the variable instead of a_var because there are two a_var variables This confusion should provide a clue as to
111. t name lt lt std endl return 0 F Save and run it This time you ll see something like this OBSERVE Size ig 4 Name is now Joe Name is now Stev a The output from your program may be slightly different see how Steve wasn t copied correctly and the output contains extra characters We used the sizeof operator to compute the maximum number of characters that can be stored in the variable name This included the null character Steve is six characters Steve plus the end of string character If the source string has fewer characters than the size of the array then std strncpy copies the string and adds an end of string 0 to the end But since the source is bigger here it copies size s number of characters and does not append the end of string So in order to make things work we must do so ourselves include lt cstring gt include lt iostream gt int main char name 4 Short name std cout lt lt Size is lt lt sizeof name lt lt std endl std strncpy name Joe sizeof name std cout lt lt Name is now lt lt name lt lt std endl std strncpy name Steve sizeof name nate Sizeot name 1 0 std cout lt lt Name is now lt lt name lt lt std return 0 Since sizeof name is 4 in our example sizeof name 1 will be 3 Remember arrays and C style strings which are arrays of characters are zero based so 3 is the last
112. t std endl i assignment of read only locationp pS het BL aE rt Assigning e rererence std cout lt lt j 1 is lt lt j lt lt std endl std cout lt lt j 2 is lt lt j lt lt std endl return Oj Returning a reference as an int has its benefits but it can be very tricky to use Let s change our code so that max assigns the result to a local variable and returns that variable instead include lt iostream gt eorst int amp max int amp il int amp 12 int result Which one to use if il gt iz result il else result LaS This is a bad thing to do return result main int 1 1 ane J 3 std cout lt lt Max is T x lt max i lt lt std endl max i j 0 Assigning a reference stds icour lt lt 1 ae T lt lt 2 lt lt Std tendls return 0 LJ Leal Save it you ll see a warning ff Function comments ints max iints il ints iz Build of configuration Debug for project Var pass eee Internal Builder is used for build reference to local variable result returnedje to use eeE if fil gt 12 g 00 g3 Wall c fmessagqe length 0 result il 0ov ar pass 0 vVar pass cpp else vVar pass c cpp In function ints max iint result le intej VAE pass cpp 7 warning reference to local variable result returned f This is a bad thing to do return resulti g OVAL
113. t not by humans The object file contains only the code for executing the task that you wrote In the case of hello_ world that code uses std cout to write outa message The definition of std cout is notin your object file instead itis part of a standard library This library contains generally useful definitions like std cout and lots of other things The library itself is just a bunch of object files packaged together into one file something like a zip file but different The linker takes your object file and the object files in the library and produces an executable program Here s a graphical representation of what it does Source a Linker Executable File exe cpp Library With some compilers you may not see object files because they delete object files after the link step With the GNU compiler the compilation process is actually accomplished by multiple programs The first thing g does to your program is pass it through a program called the pre processor This program takes care of things like the include directive We cover lots more about this program in the next C course The next stage turns the high level C code into low level assembly code In high level code one statement can result in many machine instructions being created to process that statement In assembly language there s one statement per instruction Also high level languages are machine independent or they are supposed to be
114. t of numbers OBSERVE int students 20 The numbers we are going to average The elements of the array are students 0 through students 19 You might expect them to be 1 through 20 butin C array element numbering starts at 0 The numbers 0O 1 or 19 are indexes to the array The const Modifier Our class might always have twenty students in it but what if it changes say to 35 We would have to go through our program find all of the 20 values relating to our students array and change them manually to 35 This process is error prone after all there may be occurrences of 20 unrelated to the number of students that we don t want to change Good programming practice dictates that we specify the size of our class in one place as a variable and then use that variable rather than the literal number in our program Since our class size doesn t change very often we can tell C that the variable is a constant The const modifier defines a variable actually a constant whose value cannot be changed by the program when it s running C C style conventions call for the names of constants to be all upper case for example const int CLASS_SIZE 35 How do constants work Let s find out Start a new project named constants assign itto the C 1 Lessons working set and in it create a new source file named constants cpp as shown include lt iostream gt int main const int CLASS GIZE 20 Std 2cout lt lt
115. t triangle float width float height float area width height 2 0 return area print it output a message Parameters area the area of the triangle what the name of the triangle void print it float area char what std cout lt lt The area of the lt lt what lt lt triangle is lt lt area lt lt std e int main float area Area of a triangle area triangle 5 0 2 0 std cout lt lt Area of the first triangle is lt lt area lt lt std endl area triangle 3 8 5 9 std cout lt lt Area of the second triangle is lt lt area lt lt std endl area triangle 2 8 1 6 std cout lt lt Area of the third triangle is lt lt area lt lt std endl return 0 Let s take a closer look at print_it OBSERVE void print it float area char what std cout lt lt Ihe area of the lt lt what lt lt triangle is T lt lt area lt lt std e This function named print_it returns void which means nothing in C In other words our function does notreturn any value Ithas two parameters a float named area anda C Style string named what a character array named what The character array parameter has no dimension That is because the dimension is determined by the code that calls the print_it as you will see shortly Some other languages might call print_it a procedure because it does not return a value
116. tal so far int number A number to read total Q while true std cout lt lt Enter a number std cin gt gt number Skip all negative numbers if number lt 0 std cout lt lt Negative numbers don t count lt lt std endl continue if number 0 std cout lt lt I guess you want to end the list lt lt std endl break total number std cout lt lt The new total is lt lt total lt lt std endl Statscour lt lt The grand total is lt lt total lt lt std send return 0 F Save and run your program You ll soon notice it runs exactly the same as the for loop we used before right down to the continue and break statements Suppose we want our program to run until we enter a zero OR our grand total is greater than 50 We can alter the condition in our loop to accomplish this include lt iostream gt int main int total j Total So far int number A number to read total 0 while total lt 50 std cout lt lt Enter a number gt std cin gt gt number Skip all negative numbers if number lt 0 std cout lt lt Negative numbers don t count lt lt std endl continue if number 4 std cout lt lt I guess you want to end the list lt lt std endl break total number std cout lt lt The new total is lt lt total lt lt std endl std
117. tatic in front of it Edit your program as shown include lt iostream gt int global 1 Global variable to play around with int main int Loop A loop counter for loop 0 loop lt 37 47tloop int temp 1 A local variable to play around with static int perm 1 A local permanent variable to play with Std scout lt lt qlobal is lt lt global lt lt std endl std cout lt lt temp is lt lt temp lt lt std endl std cout lt lt perm is lt lt perm lt lt std endl qlobal temp perm Almost useless comment return 0 O Now save and run it again and observe the output Output of var types glopa mie temp is 1 perm is 1 global i Z2 temp is 1 perm is 2 global is gt temp is 1 perm is 3 The storage class of perm is permanent Itis created and initialized when the program is created and that means thatitis initialized once Every time through the loop itis incremented by one unlike temp which is re initialized every time through the loop On the other hand the variable perm always stays around The static keyword is the most overloaded keyword in C It has many different meanings Note depending on where you use it For local variables it changes the storage class to permanent i We will examine its other uses as they arise for Loop Scope In general the scope ofa local variable is restricted to the block in which it
118. te the area orl a triangle Parameters i width the width of the triangle height the height of the triangle BECUS i the area of the triangle float triangle float width float height 2 0 float area width height 2 0 return area x print 1E output a message Parameters i area the area of the triangle what the name of the triangle void print it float area char what std cout lt lt The area of the lt lt what lt lt triangle is lt lt area lt lt std e ndl return void print it float area std cout lt lt The area of the triangle is lt lt area lt lt std return int main float area Area of a triangle area triangle 5 072 print 1ti area area triangle 3 8 5 9 pene tt tarea second area triangle 2 8 1 6 print 1t area third return 0 F Save and run it You ll see the same results as before OBSERVE The area of the first triangle is 5 The area of the second triangle is 11 21 The area of the third triangle is 2 24 If we DO provide a height the function uses it otehrwise it uses the default 2 0 i Using default parameters hides information and can make programs confusing While i WARNING you may encounter default parameters in existing programs you would be wise to avoid i using them in new programs i We covered a lot of informatio
119. ter this problem too often but if you do now you ll be able to recognize and correct it Okay now let s see what happens when we have a floating point overflow Because of the way floating point numbers are stored and computed it s hard to specify an exact maximum number But the expression below will definitely give you an overflow so go ahead and add it to your program as shown include lt iostream gt include lt climits gt int main std cout lt lt Float lt lt 9E399 9E399 lt lt std endl return 0 F Run it You ll see the special floating point number inf the floating system gives you some indication that an overflow occurred Common Problems There are some common warnings and errors that you may encounter when working with C We ll experiment with some ofthem by making a few mistakes on purpose Change your program as shown E E include lt climits gt int main std cout lt lt The answer is lt lt 1 2 4 return 0 C flags this line with an error message because it doesn t recognize std cout eee INTEEHaAL SULLAEr 13 used Lor build ETET g g Wall c message length oexp expression o EXp expression cpp exp expression cpp In function int ma amp infi Ld int main i return Oj EXP Expression cpp 9 error cout is not a member of std Build error occurred build is Stopped Time consumed 156 ms
120. th Sta cour lt lt AL first the value of play is lt play lt lt std trendl play 5 std cout lt lt The value of play is lt lt play lt lt std endl play 3299 std cout lt lt Finally the value of play is lt lt play lt lt std endl return 0 0 Save and run it You should see the following output OBSERVE At first the value of play is 0 The value of play is 5 Einally the valus of play us 999 If we stepped through the program we d see the value of play after each line is executed We might see the following int play undefined std cout lt lt At first the value of play is lt lt play lt lt std endl undefined std cout lt lt The value of play is lt lt play lt lt std endl play 999 std cout lt lt The value of play is lt lt play lt lt std endl return 0 BUT WAIT This table shows that the initial value of play is undefined but the output shows that it was 0 Before we assign play a value for the first ttme before the play 5 line its value is not known and cannot be assumed to be anything With this specific computer compiler and execution the value happened to be 0 A different computer compiler or execution could produce any other result such as 100 900 or 2147483648 The bottom line dont assume your variable has a value before you give it a value In C you can declare and initialize variabl
121. the variable name to an appropriate style forexample class size You should use named constants to specify the dimensions of arrays for example int students CLASS_ SIZE Good programming style dictates that you should always use named constants in this way In other words the dimension specification of an array should never be just a number like 20 Our first array Now let s look at arrays in action Create a new project named average assign it to the C t 1_Lessons working set and in it create average cpp as shown tinclude lt iostream gt int main Gonet Ane CLA o SLAE 57 float average OF average of the items 0 float total 0 0 the total of the data items float students CLASS SIZE data to average and total students 0 34 students 1 27 students 2 46 students 3 82 students 4 22 total students 0 students 1 students 2 students 3 students 4 average total CLASS SIZE std cout lt lt Total lt lt total lt lt Average lt lt average lt lt std endl return 0 F Save and run it You should see the following result Remember how we could declare a variable and set its value atthe same time You can also do that for arrays using braces Change your program as shown include lt iostream gt int main Const int CLASS SIZE oF float average 0 0 average of the items float total O02 the total of the data
122. ther tools The idea of the IDE is to hide the other tools and give you a single system in which to work Butas a professional you ll need to know what goes on under the hood to make the most effective use of all the tools available When your project is built Eclipse figures out what needs to be done to make your programs executable auto matically This comes in handy for many types of programs including our small hello world project Tools like Visual Studio work much the same way Some programs use other builder tools to make them automatically executable in the C C world a program called make is a common tool for that In java Ant is a popular tool for that task Both of those tools require programmers to specify a set of rules or targets that describe how a program will be built To convert your code into computer instructions Eclipse uses the GNU g compiler This program takes your source code cpp file and turns itinto an executable To do this itneeds to run a series of programs The firstis the actual C compiler Its job is to take the human readable source code and turn it into an object file 0 file You can see the object file created by the compiler Switch to the Package Explorer tab then expand the Debug folder Inside that folder you ll see hello o among other things If you try to open hello o you won tfind anything useful this file contains computer code The object file is readable by the computer bu
123. to zero the program executes the statements in the following block enclosed in curly braces if statements have the following structure OBSERVE conditional test Code to execute when conditional test is true else Code to execute when conditional test is false You do not need to have an else There are other comparison operators you can use in if statements and elsewhere jp i fiora Let s try a different comparison Change your program as shown ti nclude lt iostream gt int main int number A number we are going to check std cout lt lt Enter a number std cin gt gt number if number gt 100 SLdi cout lt lt number lt lt te big lt lt etdisendl else etaricoul lt lt number lt lt 16 not eo big lt lt td rendl return 0 In this program we changed our conditional test slightly and added an else clause F Save and run it Enter 250 you will see OBSERVE Enter a number 250 DORT DIa If you enter a smaller number like 250 you ll see the other message instead OBSERVE Enter a number 250 250 is mor So 5G if Abuse Equality or Assignment In our first example of the if statement we used the equality operator to see ifa number was even or not What would happen if you used a single instead Try it tinclude lt iostream gt int main int num
124. u just need to know that this special line starts the program The curly brace indicates the start of the body of the code Code enclosed in braces is called a block In this program we have one block of statements and they make up the body of the main function In later lessons we ll learn how to use multiple blocks of code The next line contains std cout lt lt Hello World lt lt std endl which is a C executable statement It tells C to printa message You ll notice that the line starts with four spaces C doesn t care how many spaces you use to starta line but good programming style dictates that you use one level of indentation for each level of logic Here we indented four spaces for each set of braces we have nested We chose to indent four spaces as a standard because it s easy to read and we needed a standard for this course Let s break the std cout statement down into components The first item std cout is the name ofa predefined variable that is used by C to write to the standard output the console In the Eclipse programming environment console output shows up in a window atthe bottom ofthe screen The std cout variable is one of the items brought in by the include lt iostream gt statement The operator lt lt tells C to take what follows it and send it somewhere else in this case to the output std cout Nextin our code we have the string Hello World This is a literal string containing th
125. um number of characters that can be stored in the string This is very important because our strings mailboxes are fixed in size If we try to copy too many characters from our new mailbox to the old bad things could happen Copying too many characters is yet another way to overflow the buffer and possibly cause the program to crash Let s see an example Edit c string cpp as shown include lt cstring gt include lt iostream gt int main char name 4 Short name std cout lt lt Size is Y lt lt sizeort name lt lt std endl std strncpy name Joe sizeof name std cout lt lt Name is now lt lt name lt lt std endl return 0 F Save and run it You ll see OBSERVE S ze i5 4 Name is now Joe You might be wondering why you see Size is 4 after all Joe is only three letters long The fourth character is the end of string 0 null character Remember this character is required so you must take it into account What happens when we try to copy a larger string into a smaller variable Let s try it include lt cstring gt include lt iostream gt int main char name 4 Short name std cout lt lt Size is lt lt sizeof name lt lt std endl std strncpy name Joe sizeof name std cout lt lt Name is now lt lt name lt lt std endl std strncpy name Steve sizeof name std cout lt lt Name is now lt l
126. urrent size T lt lt Current size lt lt std endl Stade scout lt lt total size T lt lt Total siz lt lt std send return 0 This program is a little longer than the last but itis very clear what is happening F Save and run it You ll see OBSERVE Current GLASs S POr Salen Ie We covered a lotin this lesson In the next we will examine another loop we can use in our programs while loops See you then a gt D Copyright 1998 2013 O Reilly Media Inc This work is licensed under a Creative Commons Attribution ShareAlike 3 0 Unported License See http creativecommons orq licenses by sa 3 0 leqalcode for more information While Loops C 1 Introduction to C Lesson 9 while break and continue Welcome back In the previous lessons we have used for loops to do some repetitive work In this lesson we ll learn about while loops another way to do repetitive work The basic form of the while loop is while Syntax while condition statement In the last lesson we used an empty for loop that would let us input as many numbers as we wanted and give us the grand total after we entered a zero We can do the same thing using a while loop instead Start a new project named while and assign itto the C 1_Lessons working set In the new project create a new file named while cpp as shown include lt iostream gt int main int total To
127. ut Output of var pass teste a is 2 Tests a 18S 5 marne ab 18 2 We passed i as a parameter to test where itwas labeled a We changed the value ofa inside test but that change did not make its way back to i Why did this happen It happened because the parameters to the test function were passed by value Internally C copies the values of any variables passed by value and passes the copy to the function Any changes to this copy will not be reflected in the calling procedure This is the default way C passes parameters to functions Remember when we discussed how variables were like mailboxes Passing by value is like making photocopies of your mail then putting the copies in the mailbox the function keeping the originals safe C lets you pass by reference as well using the reference amp operator Edit your program as shown include lt iostream gt void test int amp b std cout lt lt test b is lt lt b lt lt std endl b 6 std cout lt lt test b is lt lt b lt lt std endl Variable to play around with i is lt i lt lt std endl return 0 F Save and run it You see Output of var pass IGS See b is 2 test bis 6 main i is 6 In this program i passed by reference so the test function changed its value main I is 6 With pass by reference C makes the parameter b a reference to main s local variable i A reference means that the
128. ut of 15 mailboxes when only 10 physical mailboxes existin your apartment building What happens if we try to write to an array location outside of CLASS_ SIZE Try it RR KKK KKK KKK KK KK KKK KK KK KK KR KKK KK KKK KK KK WARNING In order to see what happens when we violate the rules this program del iberately overflows an array RR KKK KK KKK KK KK KK KK KK KK KK KK KKK KK KK KK KK 7 nclude lt iostream gt int main conet Int CLASS SIAE 10 int x Us 0 0 average of the items 0 03 the total of the data items CLASS SIZE 0 46 5 82 0 22 72 3 55 9 91 2 90 0 43 8 7 data to averag float average float total float students 2 34 0 e and total students 500 500 0 for x 0 x lt 15 x x 41 OOPS total total students x std cout lt lt x lt lt x lt students s lt lt students x lt lt total lt lt to lt lt std endl average total CLASS SIZE std cout lt lt Total lt lt total lt lt Average lt lt average lt lt std endl return 0 Save the file Once again no error or warnings are generated because the computer assumes you know what you are doing and has not checked to make sure you are staying within the bounds ofthe students array What happens when you try to run the program F Run itto find out Your program will crash and give an error like this average exe Applic
129. why hidden variables are a bad thing Here s the scope of int a_var 3 Scope ofa_var 3 int main WINE el Welle ALINE o Ve siecle o lt lt Me wen Gill as lt lt a a a Siecle 3COuE lt lt dS were Gil as 4 lt lt 19 wee lt lt eiccleseincll lt lt sizcl sein int a var 3 std cout lt lt a var 2 is lt lt a var lt lt std endl std cout lt lt b var 2 is lt lt b var lt lt std endl lt lt std endl j E a Gd as lt lt a wee a a seela sou lt lt Ms were aS ae 4 K amp lt lo wee lt lt siecle 2einell 5 return 0 Now let s add int a_var 2 to the mix Scope of a_var 2 and a_var 3 int main int a var int b var std cout lt lt a var 1 is lt lt a var lt lt std endl std cout lt lt b var 1 is lt lt b var lt lt std endl lt lt std endl int a var 3 std cout lt lt a var 2 is lt lt a var lt lt std endl std cout lt lt b var 2 is lt lt b var lt lt std endl lt lt std endl std cout lt lt a var 3 is lt lt a var lt lt std endl std cout lt lt b var 3 is lt lt b var lt lt std endl return 0 Because a_var 3 has the innermost scope where itis defined it hides a_var 2 in the middle of the program Thus the scope for a_var 2 has a hole in it In other words the declaration of a_var 3 hides a_var 2 in the dark red area Avoid us

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