INTRODUCTION TO PROGRAMMING
Contents
1. INTRODUCTION T O PROGRAMMING Problem Solving Concepts Flowcharting and Programming Languages It is the inte nt of this manual to provide an introduction to computer programming and to the programming language BASIC Beginners All Purpose Symbolic Instruction Code BASIC is a popular programming language especially for new programmers and casual compute communicating r users Its conversational nature makes with computers natural simple and straightforward Its use of near English words and mathematical expressions gi ves the coding a familiar appearance Also its original design to teach the casual user how to program makes it a good language to learn first For those of you with computer operations experience this course is intended to provide a transition from operations into programming It will introduce concepts of programming that apply to other languages as well as BAS IC For those of you with programming experience it will provide a review of programming concepts and introduce the capabiliti processing wh introduction t computers Whe the capabiliti write a progra es of BASIC and its syntax For those not in data o have a computer available it will pro vide an O a programming language available on most n you complete the course you should understand es and syntax of the BASIC language a2. fig 1 6 Don t worry about complete understanding just look at the instructions with the flowchart to get an idea of what coded instructions look like You will have to have specific information about the computer you are to use and how the language is implemented on that particular computer The computer manufacturers provide these specifics in their user s manual Get a copy and study it before you begin to code To you but they may prevent your program from running Once coding is completed the program must be debugged and tested prior to implementation Debugging Errors caused by faulty logic and coding mistakes are referred to as bugs Finding and correcting these mistakes and errors that prevent the program from running and producing correct output is called debugging Rarely do complex programs run to completion on the first attempt Often time spent debugging and testing equals or exceeds the time spent in program coding This is particularly true if insufficient time was spent on problem definition and logic development Some common mistakes which cause program bugs are mistakes in coding punctuation incorrect operation codes transposed characters keying errors and failure to provide a sequence of instructions a program path needed to process certain conditions To reduce the number of errors you will want to carefully check the coding sheets before they are turned in fo
3. again If the YES branch is taken the INPUT OUTPUT operation is performed merrtute PROCESSING AND O PROCESS a3 1966 pace ca CARD Ne X gt OFFLINE STORAGE AUXILIARY INPUT AND OR OUTPUT conranws To USA STANDARDS OPERATION py in DISPLAY OUTPUT Y C FLOW FLOW ONLINE STORAGE Figure 1 3 Flowchart Template FLOWCHART WORKSHEET The Flowchart Worksheet is a means of standardizing documentation It provides space for drawing programming flowcharts and contains an area for identification of the job including application procedure date and page numbers fig 1 4 You may find it helpful when you develop flowcharts If you don t have this form available a plain piece of paper will do Constructing a Flowchart There is no best way to construct a flowchart There is no way to standardize problem solution Flowcharting and programming techniques are often unique and conform to the individual s own methods or direction of problem solution This manual will show an example of developing a programming flowchart It is not the intent to say this is the best way rather it is one way to do it By following this text example you should grasp the idea of solving problems through flowchart construction As you gain experience and familiarity with a computer system these ideas will serve as a foundation In order to develop a flowchart you must first know what pro
4. correct habits and procedures since this will prevent later difficulties in pro gram preparation Whether you are working with a systems analyst a customer or solving a problem of your own it is extremely important that you have a thorough understanding of the problem Every aspect of the problem must be defined What is the problem What information or data is needed Where and how will the information be obtained What is the desired output Starting with only a portion of the information or an incomplete definition will result in having to constantly alter what has been done to accommodate the additional facts as they become available It is easier and more efficient to begin programming after all of the necessary information is understood Once you have a thorough understanding of the problem the next step is flowcharting FLOWCHARTING Flowcharting is one method of pictorially representing a procedural step by step solution to a problem before you actually start to write the computer instructions required to produce the desired results Flowcharts use different shaped symbols connected by one way arrows to represent operations data flow equipment and so forth There are two types of flowcharts system data flowcharts and programming flowcharts A system data flowchart defines the major phases of the processing as well as the various data media used It shows the relationship of numerous
5. processing decision input output terminal flow lines and connector symbol All flowcharts may be initially constructed using only these fundamental symbols as a rough outline to work from Each symbol corresponds to one of the functions of a computer and specifies the instruction s to be performed by the computer The contents of these symbols are called statements Samples of these fundamental symbols definitions examples and explanations of their uses are shown in figure 1 2 GRAPHIC SYMBOLS Within a flowchart graphic symbols are used to specify arithmetic operations and relational conditions The following are commonly used arithmetic and relational symbols plus add minus subtract multiply divide H plus or minus equal to gt greater than lt less than gt greater than or equal to lt less than or equal to not equal to gt not greater than not less than YES or Y Yes NO or N No TRUE or T True FALSE or F False FLOWCHARTING TEMPLATE To aid in drawing the flowcharting symbols you may use a flowcharting template Figure 1 3 shows a template containing the standard symbol cutouts A template is usually made of plastic with the symbols cut out to allow tracing the outline PROCESS SYMBOL is used to represent general processing functions not represented by other symbols It depicts the process of operations resulting in a change o
6. ant the computer to do The next step is to code a program that can be translated by a computer into a set of instructions it can execute This step is called program coding PROGRAM CODING It is important to remember program coding is not the first step of programming Too often we have a tendency to start coding too soon As we discussed earlier there is a great deal of planning and preparation to be done prior to sitting down to code the computer instructions to solve a problem For the example amortization problem fig 1 5 we have analyzed the specifications in terms of 1 the output desired 2 the operations and procedures required to produce the output and 3 the input data needed In conjunction with this analysis we have developed a programming flowchart which outlines the procedures for taking the input data and processing it into usable output You are now ready to code the instructions that will control the computer during processing This requires that you know a programming language Before getting into the specific programming language called BASIC it may be helpful to have a greater understanding of programming languages in general All programming languages are composed of instructions that enable the computer to process a particular application or perform a particular function Instructions The instruction is the fundamental element in progra
7. ata movement arithmetic logic and transfer of control Input output instructions are used to communicate between I O devices and the central processor Data movement instructions are used for copying data from one storage location to another and for rearranging and changing of data elements in some prescribed manner Arithmetic instructions permit addition subtraction multiplication and division They are common in all digital computers Logic instructions allow comparison between variables or between variables and constants Transfer of control instructions are of two types conditional or unconditional Conditional transfer instructions are used to branch or change the sequence of program control depending on the outcome of the comparison If the out come of a comparison is true control is transferred to a specific statement number if it proves false processing continues sequentially through the program Unconditional transfer instructions are used to change the sequence of program control to a specified program statement regardless of any condition Programming Languages Programmers must use a language that can be understood by the computer There are several methods that can achieve human computer communication For example let us assume the computer only understands French and the programmer speaks English The question arises How are we to commun
8. blem you are to solve It is then your job to study the problem definition and develop a flowchart to show the logic steps and sequence of steps the computer is to execute in order to solve the problem As an example suppose you have taken a short term second mortgage on a new home and you want to determine what your real costs will be the amount of interest the amount to be applied to principal and the final payment at the end of the three year loan period r 3 i i t Lawn ad Figure 1 4 Flowchart Worksheet The first step is to be sure you understand the problem completely What are the inputs and the outputs and what steps are needed to answer the questions Even when you are specifying a problem of your own you ll find we don t usually think in small detailed sequential steps But that is exactly how a computer operates one step after another in a specified order Therefore it is necessary for you to think the problem solution through step by step You might clarify the problem as shown by the Problem Definition in figure 1 5 After you have this level of narrative problem definition you are ready to develop a flowchart showing the logic steps and sequence of steps you want the computer to execute in order to solve the problem A programming flowchart of this problem is also shown in figure 1 5 You now have a plan of what you w
9. cessing problems A class of similar problems is isolated and a language is developed to process these types of applications Several languages have been designed to process problems of a scientific mathematical nature and others that emphasize file processing The most familiar of these are BASIC and FORTRAN for scientific or mathematical problems and COBOL for file processing Programs written in procedure oriented languages unlike those in symbolic languages may be used with a number of different computer makes and models This feature greatly reduces reprogramming expenses when changing from one computer system to another Other advantages to procedure oriented languages are 1 they ar asier to learn than symbolic languages 2 they require less time to write 3 they provide better documentation and 4 they ar asier to maintain However there are some disadvantages of procedure oriented languages They require more space in memory and they process data ata slower rate than symbolic languages Coding a Program Regardless of the language used there are strict rules the programmer must adhere to with regard to punctuation and statement structure when coding any program Using the programming flowchart introduced earlier we have now added a program coded in BASIC to show the relationship of the flowchart to the actual coded instructions
10. f value form or location of information INPUT OUTPUT SYMBOL is used to represent any function of an I O device Making information available for processing is an Input function recording processed information is an Output function v DECISION SYMBOL is used to depict a point in a program at which a branch to one of two or more alternate paths is possible e TERMINAL INTERRUPT SYMBOL start stop halt delay or interrupt O CONNECTOR SYMBOL represents a junction in a line of flow to another part of the flowchart A common identifier such as an alphabetic character number or mnemonic label is placed within the exit and its associated entry lt It FLOWLINE SYMBOL is used to represent flow direction by lines drawn between symbols Normal direction of flow is left to right and top to bottom If the direction of flow is other than normal arrowheads are required at the point of entry COMPUTE MONTHLY INTEREST Reasi2 Divide I by 12 assign value to R INPUT 6 0 1 Enter these values through the terminal store in locations B Dyk If A is NOT equal to B take NO branch If A is equal to B take YES branch START STOP START STOP flow chart at this point Exit OO This represents the EXIT point and the ENTRY point ina flowchart Initial processing is shown here If the NO branch is taken the processing block is performed
11. g of numbers that represented the instruction code and operand address es In addition to remembering dozens of code numbers for the instructions in the computer s instruction set the programmer also had to keep track of the storage locations of data and instructions This process was very time consuming quite expensive and often resulted in errors Correcting errors or making modifications to these programs was a very tedious process SYMBOLIC LANGUAGES In the early 1950s mnemonic instruction codes and symbolic addresses were developed This improved the program preparation process by substituting letter symbols mnemonic codes for basic machine language instruction codes Each computer has mnemonic code although the symbols vary among the different makes and models of computers The computer still uses machine language in actual processing but it translates the symbolic language into machine language equivalent Symbolic languages have many advantages over machine language coding in that less time is required to write a program detail is reduced and fewer errors are made Errors which are made are easier to find and programs are easier to modify PROCEDURE ORIENTED LANGUAGES The development of mnemonic techniques and macroinstructions led to the development of procedure oriented languages These languages are oriented toward a specific class of pro
12. harts system data and programming The tools of flowcharting are 1 fundamental symbols 2 graphic symbols 3 flowcharting template and 4 flowcharting worksheet The problem definition and flowchart development steps must be done prior to sitting down to code the computer instructions to solve a problem Regardless of the language used there are strict rules you must adhere to with regard to punctuation and statement structure when coding a program Once the program is coded there are several phases that must be done before it can be put into production These are desk checking debugging testing documentation and finally implementation
13. icate with the computer One approach is for the programmer to code the instructions with the help of a translating dictionary prior to giving them to the processor This would be fine so far as the computer is concerned however it would be very awkward for the programmer Another approach is a compromise between the programmer and computer The programmer first writes instructions in a code that is easier to relate to English This code is not the computer s language therefore it does not understand the orders The programmer solves this problem by giving the computer another program one that enables it to translate the instruction code into its own language This translation program for example would be equivalent to an English to French dictionary leaving the translating job to be done by the computer The third and most desirable approach from an individual s standpoint is for the computer to accept and interpret instructions written in everyday English terms Each of these approaches has its place in the evolution of programming languages and is used in computers today The first approach is known as machine language the second as symbolic and the third as procedure oriented MACHINE LANGUAGES With early computers the programmer had to translate instructions into the machine language form that the computers understood This language was a strin
14. jobs that makeup an entire system In the system data flowchart an entire program run or phase is always represented by a single processing symbol together with the input output symbols showing the path of data through a problem solution For example PAY RECORDS PROCESS PAYROLL System Flowchart The second type of flowchart and the one we ll use in this manual is the programming flowchart It is constructed by the programmer to represent the sequence of operations the computer is to perform to solve a specific problem It graphically describes what is to take place in the program It displays specific operations and decisions and their sequence within the pro gram For example PAY RATE ves COMPUTE OVERTIME PAY COMPUTE REGULAR PAY Programming Flowchart Tools of Flowcharting Flowcharting has been defined and two different types of flowcharts discussed We will now take a look at the tools used in flowcharting These tools are the fundamental symbols graphic symbols flowcharting template and the flowcharting worksheet FUNDAMENTAL SYMBOLS To construct a flowchart it is first necessary to know the symbols and their related meanings They are standard for the military as directed by Department of the Navy Automated Data Systems Documentation Standards SECNAVINST 5233 1 Series Symbols are used to represent functions These fundamental functions are
15. lowchart and Coded Program data can reprocessed correctly and that the output is correct The testing process involves processing input test data that will produce known results The test data should include 1 typical data which will test the commonly used program paths 2 unusual but valid data which will test the program paths used to process exceptions and 3 incorrect incomplete or inappropriate data which will test the program s error routines If the pro gram does not pass these tests more testing is required You will have to examine the errors and review the coding to make the coding corrections needed When the program passes these tests it is ready for computer implementation Before computer implementation takes place documentation must be completed Documentation Documentation is a continuous process beginning with the problem definition Documentation involves collecting organizing storing and other wise maintaining a complete record of the programs and other documents associated with the data processing system The Navy has established documentation standards to ensure completeness and uniformity for computer system information between commands and between civilian and Navy organizations SECNAVINST 5233 1 Series establishes minimum documentation requirements Local minimum documentation requirements are usually established by the head of the data processing department divisio
16. m preparation Like a sentence an instruction consists of a subject and a predicate However the subject is usually not specifically mentioned rather it is some implied part of the computer system directed to execute the command that is given For example the chief tells a sailor to dump the trash The sailor will interpret this instruction correctly even though the subject you is omitted Similarly if the computer is told to ADD 1234 the control unit may interpret this to mean that the arithmetic logic unit is to add the contents of address 1234 to the contents of the accumulator In addition to an implied subject every computer instruction has an explicit predicate consisting of at least two parts The first part is referred to as the command or operation it answers the question what It tells the PROBLEM DEFINITION MORTGAGE AMORTIZATION This program is to determine the monthly amount of interest A and amount applied to the principal P of the mortgage giving the balance B at the end of a thirty six month period INPUT The monthly payment is to be entered as variable D the beginning balance of the mortgage is to be entered as variable B and the annual interest rate is to be entered as variable I This input is to be entered into the system via the terminal OUTPUT The end result is to be a listing displaying the amount applied to principal and inte
17. n At most commands this function is delegated to the project manager The key to the minimum amount of documentation required by local commands should be the amount that is required for replacement personnel to understand input processing and output for each program or system for which they will be responsible A documentation package should include 1 A definition of the problem Why was the program written What were the objectives Who requested the program and who approved it These are the types of questions that should be answered 2 A description of the system The system environment hardware software and organization in which the program functions should be described including systems flowcharts General systems specifications outlining the scope of the problem the form and type of input data to be used and the form and type of output required should be clearly defined 3 A description of the program Programming flowcharts program listings program controls test data and test results storage dumps these and other documents that describe the program and give a historical record of problems and or changes should be included 4 Operator instructions Items that should be included are computer switch settings loading and unloading procedures and starting running and termination procedures Implementation After the documentation has been completed a
18. nd be able to m OVERVIEW OF PROGRAMMING Before learnin to establish s programming ef agreement that involved in so g to program in the language BASIC it is helpful ome context for the productive part of the entire fort This context comprises the understanding and there are four fundamental and discrete steps lving a problem on a computer The four steps are 1 State anal 2 Develop the decision table 3 Code the pr yze and define the problem program logic and prepare a program flowchart or ogram prepare the code in machine readable form prepare test data and perform debug and test runs 4 Complete th for implementa Figure 1 1 dep e documentation and prepare operator procedures tion and production icts the evolution of a program Programming ca n be complicated and advance preparation is required befor program The f and flowcharti you can actually start to write or code the irst two steps problem understanding definition ng fall into the advance planning phase of programming It is important at this point to develop ed ete omen n oe er rr PROBLEM CODED DEFINITION PROGRAM FLOWCHART TERMINAL FOR KEYING PROGRAMS ne computer ror ASSEMBLY COMPILATION DEBUGGING AND TESTING Aiii n OUTPUT PROGRAM LISTING Figure 1 1 Evolution of a Program OBJECT PROGRAM
19. nd the user has reviewed and accepted the test output the project request is submitted to upper management usually the ADP department head for production approval Once upper management has approved the program it can be put into production If a program is to replace a program in an existing system it is generally wise to have a period of parallel processing that is the job application is processed both by the old program and by the new program The purpose of this period is to verify processing accuracy and completeness Once the program is in production it maybe necessary to make modifications to the program to satisfy changing requirements This is another important duty of the programmer and it is not unusual to find programmers spending 25 percent of their time on this program maintenance activity In some installations there are programmers who do nothing but maintain production programs SUMMARY The first step in the solution of any problem involves a fundamental but often overlooked concept a thorough understanding of the problem The second step in successful problem solving involves creating a flowchart showing the steps required to solve the problem Flowcharting is a pictorial means of representing a procedural solution to a problem in which different shaped symbols are used to represent operations data flow equipment and so forth There are two types of flowc
20. r keying This process is known as desk checking and should include an examination for program completeness Typical input data should be manually traced through the program processing paths to identify possible errors In effect you will be attempting to play the role of the computer After the program has been desk checked for accuracy the program is ready to be assembled or compiled Assembly and compiler programs prepare your program source program to be executed by the computer and they have error diagnostic features which detect certain types of mistakes in your program These mistakes must be corrected Even when an error free pass of the program through the assembly or compiler program is accomplished this does not mean your program is perfected However it usually means the program is ready for testing Testing Once a program reaches the testing stage generally it has proven it will run and produce output The purpose of testing is to determine that all VLALLUCAIE MONTHLY 10 PRINT ENTER MONTHLY PAYMENT 20 PRINT LOAN AMOUNT INTEREST RATE 30 INPUT D B I 40 LETR 1 12 50 FOR M 1 TO 36 60 LETA B R INTEREST RATE Compute MONTH or LOAN 70 LETP D A 80 LETB B P 90 PRINT M D B P A 100 NEXT M 110 PRINT WITH ONE FINAL PAYMENT OF B 120 END PRINCIPAL COMPUTE LOAN Bac ence Figure 1 6 Programming F
21. rest and the current loan balance each month with one final entry showing the final payment on the mortgage Figure 1 5 Problem Definition and Programming Flowchart computer what operation it is to perform i e read prin input Each machine has a limited number of built in operations that it is capable of executing An operation code is used to communicate the programmer s intent to the computer ie The second specific part of the predicate known as the operand names the object of the operation In general the operand answers the question where Operands may indicate the following 1 The location where data to be processed is found 2 The location where the result of processing is to be stored 3 The location where the next instruction to be executed is found When this type of operand is not specified the instructions are executed in sequence The number of operands and the structure or format of the instructions vary from one computer to another However the operation always comes first in the instruction and is followed by the operand s The programmer must prepare instructions according to the format required by the language and the computer to be used Instruction Set The number of instructions in a computer s instruction set may range from less than 30 to more than 100 These instructions may be classified into categories such as input output I O d
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