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Flowchart Techniques - Distributed Systems Group

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1. Coordinating Module Figure 1 50 A Hierarchy Chart 1 10 Programming Tools These are the programs specially designed for the benefit of pro grammers so that they can formulate the instructions to solve a problem properly and easily One of the important tools is editor This is explained in the following paragraphs 1 10 1 Editors An editor is a piece of software which enables the programmer to enter and edit a program The different kinds of editors are as follows a Screen editor b Line editor c Linkage editor d Text editor Screen editor A screen editor allows the programmer to position the cursor anywhere on the screen and insert or delete text Line Editor A line editor allows lines of text to be entered and edited only Flowchart Techniques 81 by entering commands which refer to a particular line or block of text This type of editor was used in the days before VDU screens were common when the lines typed in were printed out on a piece of paper as well as being stored in the memory An example of a line editor is EDLIN which is supplied with MS DOS This editor is suitable for typing in small amounts of text such as batch files Typical commands include LineNumber Edits theline specified Appends the line Delete line Insert line List text End editing mm o gt Linkage Editor The linkage editor is a utility program whi
2. 1 11 5 Software Life cycle Every software has a life cycle just as a living organism or a new product Commercial programs such as payroll accounts stock control and other software share a common life cycle pattern One method of doing things may work well for a period of time This may last for several years However owing to expansion or changes in the nature of the business the economic environment the need to keep up with new technology or other factors the program may seem to be inadequate for future use At this point investigations are made requirements are analyzed and a new specifications are proposed and a new program is developed The life cycle of the new program thus starts again Stages in Software Life cycle Analysis of the Problem and laying down Specifications The prob lem must be first defined and analyzed and the specifications of input and the output should be prepared Sometimes a systems analyst is asked to prepare a feasibility study and the cost bene fits Once these are accepted the software design starts Design and Development The design stage involves a number of tasks such as designing the output input files database if applicable system controls and test plan Input forms must be designed clerical procedures laid down and all aspects of the design must be documented In the development stage there are two aspects First the program development and next the equip ment acquisition The senior
3. Pseudo Code IF Tea Then Pour a cup of Tea Else Pour a cup of Coffee Example 1 17 In this example the flowchart and its equivalent pseudo code for the process of repetition is shown in Figure 1 35 FLOW CHART PSEUDO CODE MINCE PASTE WHILE paste not Normal Mince paste ENDWHILE PASTE NORMAL Figure 1 35 Process of repetition and its pseudocode using While End While loop Example 1 18 Figure 1 36 illustrates the multichoice selection or the CASE structure In CASE structure selection can be made out of many choices using the word CASE CASE structures are used in eval uating situations that can have a number of different results CASE in this sense refers to a refinement of a basic IF THEN ELSE type of conditional structure IF A is true then Flowchart Techniques 61 do B but a CASE structure functions more like a series of nested IFS IF A then do this if B then do that For example if you have three types of drinks then the flowchart shown in Figure 1 36 gives a method of selecting any one of them This can also be written in pseudocode form using CASE statement An equivalent Pseudocode of the flowchart shown in Figure 1 3 6 is given below Pineapple Pour Juice Pour Juice Pour Juice Into Glass Into Glass Into Glass From From From Lemon Jug Orange Jug Pineapple Jug y _ OFFER DRINK y CASE dri
4. tem and ask for the review or change of the earlier system Flowchart Techniques 105 Test Paper Based on Chapter 1 Time allowed 3 hr Max Marks 100 Answer all questions Ql Q 2 Q 3 Q 4 Q 5 Q 6 Q 7 Q 8 Q 9 Q 10 Answer the following a What are the advantages and limitation of pseudocodes b List the program preparation techniques that are often included under the term Structured Programming What is a Flowchart List the flowcharting rules What are the advantages and limitations of flowcharts Differentiate between the following a Pseudocode and Flowchart b Compiler and Interpreter c Top down and Bottom up design techniques d Testing and Debugging What do you understand by structured programming State the char acteristics of structured programs Write short notes on the following a Data flow diagram DF D b Compiler c Trailer Record d Algorithm What is modular concept in programming Mention a few essential requirements of modular programming What are the two broad types of programming errors How are they detected What do you understand by documenting a program Why is it necessary a What is meant by program maintenance How can proper pro gram design make it easier to maintain programs b What are the different ways of debugging and testing a program
5. 10 soin step 4 X is morethan Y Flowchart Techniques 27 Therefore the Yes route is to be followed Hence the new value of BONUS is the old value of BONUS 100 i e 600 Hence the value of BONUS written in step 5 is 600 b Here the value of X 10 amp Y 20 Therefore in step 4 the diamond decision shows that X is less than Y Therefore the No route is followed The value of BONUS remains 500 only Hence the result is 500 STEP 1 BEGIN y STEP 3 BONUS 500 STEP 4 BONUS BONUS 100 Y STEP 5 STEP 6 Figure 1 14 Bonus calculation Example 1 8 Here are six types of values for the variables A B and C a AS B C 1 b A B C c A 2 B C 7 d A 4 B 8 C 2 e A 6 B 3 C 8 f A 2 B 3 C 6 1 Using each type of data with the flowchart shown in Figure 1 15 state the output in each case 28 Flowcharting Concepts and Algorithms Solution a c What does the procedure do What happens if all the values of A B and C are the same The values of A B and C are accepted as 9 5 and 1 respec tively In step 3 the value of A is compared with B Since 9 is greater than 5 therefore the YES path is followed Once again in step 4 the value of A is compared with C Here 9 is greater than 1 So the YES path is followed In step 5 value of A is printed which is 9 Hence the answer is 9 The values of A B and C are accepted as 7 3 and
6. How is it possible to determine if a connector is used as an entry or an exit point It is very simple if an arrow enters but does not leave a connector it is an exit point and program control is transferred to the identically labeled connector that does have an outlet It may be noted that connectors do not represent any operation and their use in a flowchart is only for the sake of convenience and clarity Example 1 1 Draw a flowchart for adding marks in ten subjects obtained by a student in an examination The output should print the percent age of marks of the student in the examination The flowchart for this problem is given in Figure 1 3 The first symbol is a terminal labeled START It shows that this is the starting point or beginning of our flowchart logic The sec ond symbol is an input output 1 0 symbol that is labeled specif ically to show that this step is to read input data This step will input the roll number name and the marks obtained by the student from an input device into the main storage of the com puter system The third symbol is a processing symbol which is suitably labeled to indicate that at this step the computer will add the marks obtained by the student in various subjects and then store the sum in a memory location which has been given the name TOTAL The fourth symbol is again a processing sym bol The label inside it clearly indicates that the percentage marks obtained by a student is calculated at thi
7. In step 5 2 is compared with 5 Since 2 is less than 5 so the control is 44 Flowcharting Concepts and Algorithms transferred to step 3 and the number 2 is printed This cycle repeats and numbers 3 and 4 are printed When the current value of reaches 5 the control is transferred from step 5 to 6 Thus the numbers printed are 1 2 3 and 4 Exercise 1 2 Q 1 Which numbers will be printed using the flowcharts shown in Figures 1 27 and 1 28 respectively BEGIN I lt 4 o I I 1 Y ee NO D Figure 1 27 Printing of numbers Flowchart Techniques 45 Q2 Write a flowchart to print the following sequence of num bers a 20 19 18 17 1 b 2 4 6 8 32 Q 3 In the flowchart shown in Fig 1 29 the following data is inputted I 0 YES NO I I l y END Figure 1 28 Printing of numbers 46 Flowcharting Concepts and Algorithms BEGIN y INPUT SALES MAN S NAME M INPUT VALUE OF GOODS SOLD WAGE 50 10 OF VALUE WAGE 80 VALUE gt 500 10 OF VALUE PRIINT SALES MAN S NAME VALUE OF GOODS SOLD WAGE Figure 1 29 Flowchart for Q 3 in Exercise 1 2 Flowchart Techniques 47 Input Data Salesman s Name Valueof goods sold a Mohan 1500 b Shyam 2100 c Krishna 510 Calculat
8. Print Commission 1 2 5 Advantages of Pseudocodes Pseudocode has three main advantages 24 Flowcharting Concepts and Algorithms a Converting a pseudocode to a programming language is much more easier as compared to converting a flowchart or a decision table b As compared to a flowchart it is easier to modify the pseu docode of a program logic when program modifications are necessary c Writing of pseudocode involves much less time and effort than drawing an equivalent flowchart Pseudocode is easier to write than an actual programming language because it has only a few rules to follow allowing the programmer to concentrate on the logic of the program 1 2 6 Limitations of Pseudocodes a In case of pseudocode a graphic representation of program logic is not available b There are no standard rules to follow in using pseudocode Different programmers use their own style of writing pseu docode and hence communication problems occur due to lack of standardization c For a beginner it is more difficult to follow the logic or write the pseudocode as compared to flowcharting 1 2 6 Limitations of Pseudocodes a In case of pseudocode a graphic representation of program logic is not available b There are no standard rules to follow in using pseudocode Different programmers use their own style of writing pseu docode and hence communication problems occur due to lack of standardization c For a beginne
9. These may be followed up by interviews with vendors to clarify any misunderstandings or uncertainties in the specifications When the proposals are ready the manufacturer s representative is usually provided with an opportunity for a 102 Flowcharting Concepts and Algorithms presentation to the study group This group studies the manual and decides the selection of equipment and the supplier 1 16 Source Code The source code is the language in which a program is written by the programmer Source code is translated into object code by assemblers and compilers or a line at a time by an interpreter In some cases the source code may be automatically converted into another dialect or language by a conversion program The source code is not executable by the computer directly It must be con verted into machine language first 1 16 1 Command File The command file is a machine language program that can be loaded and executed in the computer For example in Microsoft DOS operating system the Command Com is one such file which is used to boot the computer Command files have a suffix COM These files are designed to work only in specific memory loca tions They contrast with EXE files which can be relocated any wherein memory 1 17 Input Output Report Formats The reports that are generated for the management or for the working of an organization should be different from the data for mat which is entered at the input stage of t
10. and the other action or operation which takes place when the condition is false Figure 1 59 gives the representation of the condition by a rectan gular polygon We have used the concepts of looping and conditional in examples 1 20 and 1 21 as shown in Figure 1 57 and 1 58 See the angular arrows and the rectangular polygon 1 14 Context Analysis Diagram This type of diagram is made in the system analysis phase and it gives a graphic representation of the system as a whole In this Flowchart Techniques 101 Ve ia Input Process Output Caz Conditional Figure 1 59 Looping and conditional in structure chart diagram entire system is shown as a single process This diagram identifies the external entities the inputs and the outputs 1 15 System Manual The system manual is a statement of requirements which defines specifically what is to be accomplished by the proposed computer system It is a fairly detailed document Most of the data needed for it is collected in the feasibility study The document serves both as a summary of the proposed system for internal purposes and as a statement used in inviting equipment proposals from vendors of data processing equipment On the basis of a preliminary screening four or five vendors may be invited to submit proposals Each vendor is provided with a copy of the manual of specifications and the rules for sub mitting proposals
11. any other type of input device that step will be indicated in the flowchart with an input output symbol Similarly all output instructions whether it is output on a printer magnetic tape magnetic disk terminal screen or any output device are indi cated in the flowchart with an input output symbol Processing A processing symbol is used in a flowchart to represent arithme tic and data movement instructions Thus all arithmetic Flowchart Techniques 3 SYMBOL EXAMPLE TERMINAL END INPUT XY INPUT OUTPUT Z X Y PROCESSING ENTRY CONNECTOR YES NO DECISION DIAMOND FLOW LINES CONNECTOR TRANSFER START ACTION HERE STOP ACTION HERE TAKE TWO VALUES FROM AN EXTERNAL SOURCE AND ASSIGN THEM TO X amp Y ON A TERMINAL SCREEN WRITE THE VALUES CONTAINED IN X amp Y ON A TERMINAL SCREEN ADD THE VALUE CONTAINED IN Y TO THE VALUE CONTAINED IN X AND PLACE THE RESULT IN Z AN ENTRY IN THE FLOW CHART IS MADE AT THE CONNECTING POINT MARKED IF CONDITION IS SATISFIED THEN YES PATH IS TO BE FOLLOWED OTHERWISE NO ROUTE IS TO BE TAKEN THE ARROWS INDICATE THE ROUTES FOR SYSTEMATIC SOLUTION OF THE PROBLEM A TRANSFER OF PROBLEM SOLUTION IS MADE AT THE CONNECTOR POINT IN THE FLOW CHART Figure 1 1 Flowchart symbols 4 Flowcharting Concepts and Algorithms processes such as adding subtracting multiplying and dividing are shown by a processing sym
12. by 5 which is 1 x 3 1 The diamond compares the value of B with 20 Since B is less than 20 so the control is transferred back at 2 in this block The new value of B becomes the old value of B multiplied by 3 3x3 9 This new value of B i e 9 is again compared in the decision diamond Since 9 is less than 20 the control goes to con necter 2 B is again multiplied and the current value of B is 3 x 9 27 As 27 is not less than 20 so the NO path is followed The value of C current value of B 3 27 3 30 The value 30 of C is now transferred to step 6 i e PRINT C Hence the value 30 is printed Flowchart Techniques 31 STEP 1 A A 3 STEP 2 Yes 2 No STEP 3 csa bO STEP 4 B B 3 STEP 5 Yes 2 STEP 6 No C B 3 gt STEP 7 Figure 1 16 Flowchart for example 1 9 d Here A 10 and B5 In step 3 the value of A is not less than 10 so the NO path is followed 32 Flowcharting Concepts and Algorithms In step 4 the value of B is 5 which is less than 20 Hence connector 2 takes the control to right hand lower side flowchart The current value of B becomes the old value of B multiplied by 3 which is now 15 This value of B i e 15 is the current value of B In the decision diamond this value of B is compared with 20 Since 15 is less than 20 so the YES path is followed The control is transferred back via connector 2
13. from the memory of the computer In step 6 a check is made on the value of If the current value of is less than 5 the cycle is repeated from steps 3 to 5 If the value of is equal to or more than 5 the process of reading and printing NAME stops Using this type of flowchart we can read and print the NAME five times 42 Flowcharting Concepts and Algorithms Example 1 11 Which numbers will be printed by the flowcharts shown in Fig ures 1 25 and 1 26 respectively BEGIN STEP 1 I 0 STEP 2 _ gt ___ VW I I 1 STEP 3 y PRINT I STEP 4 STEP 5 STEP 6 Figure 1 25 Flowchart for printing numbers Solution a In Figure 1 25 the value of is initialised to zero in step 2 In step 3 the value is incremented by 1 i e itis 1 In step 4 Flowchart Techniques 43 STEP 1 STEP 2 STEP 3 STEP 4 STEP 5 STEP 6 Figure 1 26 Flowchart for printing numbers is printed In step 5 the current value of is compared with 5 Since the current value of is 1 and 1 is not greater than or equal to 5 the control is transferred to step 3 Steps 3 and 4 are repeated again till the current value of is 5 Thus the values of that are printed would be 1 2 3 4 5 In Figure 1 26 the value of is initialised to 1 in step 2 The number 1 is printed in step 3 In step 4 the value of is increased by 1 So the current value of is 2
14. if they can understand the results and analyse them Hence the output format should be attractive easy to read and self explanatory 1 4 4 Step 4 Program Development You should now draw a flowchart for the procedure that you have developed in steps 1 to 3 above Standard symbols should be used for drawing a flowchart If a problem is complex you should divide it into different parts Then draw a flowchart for each part separately and join them together using connectors A flowchart for the problem in Example 1 12 and stated in step 1 can be drawn as shown in Figure 1 32 When a flowchart is drawn correctly you can convert it intoa programme using any of the high level languages like BASIC COBOL FORTRAN or PASCAL 1 4 5 Step 5 Testing the Program You should give a dry run to a program that translates the flow chart of step 4 This means giving some known values to the variables and checking the result Test values are so selected that each arm of the flowchart is tested and consequently the program is confirmed to be free from logic errors 1 4 6 Step 6 Validating the Program It is quite likely that the user of your program may enter values which are not expected by the program Such values should be rejected by the procedure drawn by you This is known as valida tion of data program For example in the problem in Example 1 12 and stated in step 1 above we may give the limit to the value of M and M should be a numerica
15. in the development the individual operation will be refined into a number of more elementary steps If we are not sure how to proceed with step 1 we can still work on step 2 c By dividing the problem into a number of subproblems we have made it easier to share problem development For example one person may solve part 2 of the problem and the other person may solve part one of the problem d Since debugging time grows so quickly it will be to our advantage to debug a large program as a number of smaller units rather than one big chunk The top down development process specifies a solution in terms of a group of smaller individual subtasks These subtasks thus become the ideal unit of program testing and debugging By testing the program in small pieces we greatly sim plify the debugging process In addition we will have the satisfaction of knowing that everything we have coded so far is correct When we add a new piece of code say p to the 72 Flowcharting Concepts and Algorithms overall program P and an error condition occurs we can definitely state that the error must either be in p itself or in the interface between p or P because P has been previously checked and certified e Another advantage of the top down development process is that it becomes an ideal structure for managing the imple mentation of a computer program using teams of program mers A senior programmer can be responsible for the design o
16. of amount 25 000 down payment payment 1 payment 2 END IF print down payment Q 10 Salesman s commission is calculated using the following Pseudocode Use this for writing a flowchart Input sales IF sales lt 500 THEN Commission 2 of sales ELSE Commission 5 of sales END IF Print Commission Q 11 Convert the flowchart shown in Figure 1 46 into a pseudo code for finding the largest of three numbers START INPUT N1 N2 N3 y PRINT N2 PRINT N3 PRINT N1 Figure 1 46 Flowchart for Q No 11 70 Flowcharting Concepts and Algorithms Q 12 The pseudo code for the year and bonus is given below Draw a flowchart corresponding to this pseudo code INPUT employee number pay position code amp years IF position code 1 THEN set bonus to 1 week s pay ELSE IF position code 2 THEN IF 2 weeks pay gt 700 THEN set bonus to 700 ELSE set bonus to 2 week s pay END IF ELSE set Bonus to 1 5 week s pay END IF IF year greater than 10 THEN Add 100 to bonus ELSE IF years less than 2 THEN cut bonus to half ELSE bonus stays the same END IF END IF Print enployee number amp bonus 1 7 Programming Methods 1 7 1 Top down Design Top down design is the technique of breaking down a problem into the major tasks to be performed Each of these tasks is then further broken down into separate subtasks and so on until each subtask is sufficiently simple to be written as a sel
17. of the loop in the DO WHILE loop structure and at the bottom of the loop in the REPEAT UNTIL structure The ENDDO marks the end of a DO WHILE structure and UNTIL followed by some condi tion marks the end of the REPEAT UNTIL structure Example 1 4 The following pseudocode describes the policy of a company to award the bonus to an employee Input Employee number pay position code amp years IF position code 1 THEN set bonus to 1 week s pay ELSE IF position code 2 THEN IF 2 weeks pay gt 700 THEN set bonus to 700 ELSE set bonus to 2 week s pay END IF ELSE set Bonus to 1 5 week s pay ENDIF END IF IF year greater then 10 THEN Add 100 to bonus ELSE IF years less than 2 THEN cut bonus to half Flowchart Techniques 23 ELSE bonus stays the same END IF Print employee number amp bonus Example 1 5 This example illustrates the policy of a bank or a financial insti tution for giving a loan to an individual Input mortgage amount IF amount lt 25 000 THEN down payment 3 of amount ELSE payment1 3 of 25 000 payment2 5 of amount 25 000 down payment payment1 payment2 END IF print down payment Example 1 6 The following program in pseudocode form illustrates the policy of a company to give the commission to a sales person Input sales IF sales lt 500 THEN Commission 2 of sales ELSE IF sales lt 5000 THEN Commission 5 of sales ELSE Commission 10 of sales END IF
18. once making sure that each decision is tested for all outcomes 1 10 9 Debugging Aids Once the presence of logic errors has been detected with the help of test runs there are various ways of finding where the error or errors lie These include the following a A dry run through the program building up a trace table while manually following the program steps b The inclusion of extra write statements to examine the contents of variables at various points in the program c The printouts of file contents before and after processing d An On line debugger which allows a programmer to step through the program line by line and examine the values of variables at any point in the program 86 Flowcharting Concepts and Algorithms 1 10 10 Assembler A program which translates an assembly language program into a machine language program is called an assembler An assem bler which runs on a computer for which it produces object codes machine codes is called a self assembler or resident assembler A less powerful and cheaper computer may not have enough soft ware and hardware facilities for program development and con venient assembly In such a situation a faster and powerful computer can be used for program development The programs so developed are to be run on smaller computers For such program development a cross assembler is required A cross assembler is an assembler that runs on a computer other than that for
19. program The situation is analogous to testing children on multiplica tion tables once a child has answered a certain number of multi plication table tests correctly at some point or other the teacher assumes that all other tests will be answered correctly and testing ceases 84 Flowcharting Concepts and Algorithms 1 10 5 Designing a Test Plan Good testing requires the following a A thorough knowledge and understanding of what the pro gram is supposed to do b Plan out in advance what ought to be tested c To work out expected results for each of the test cases d Writing out the test plan Since we cannot test everything each test must be carefully planned to provide more information about the program A major benefit of preparing a comprehensive test plan with expected results is that it forces the programmer to think carefully about the program and often errors are spotted even before running the test 1 10 6 Methods of Testing The objectives of testing can be stated in two basic questions a Does the logic work properly This means answering the following i Does the program work as intended ii Can it be made to crash b Is the necessary logic present This means answering the following i Are there any functions missing ii Does the program or module do everything specified There are two different ways of testing These are a Functional testing b Logical or structural testin
20. used to link the portions of the flowchart on different pages 1 1 4 Advantages of Flowcharts Conveys Better Meaning Since a flowchart is a pictorial representation of a program it is easier for a programmer to understand and explain the logic of the program to some other programmer Analyses the Problem Effectively A macro flowchart that charts the main line of logic of a software system becomes a system model that can be broken down into detailed parts for study and further analysis of the system Effective Joining of a Part of a System A group of programmers are normally associated with the design of large software systems Each programmer is responsible for designing only a part of the entire system So initially if each programmer draws a flowchart for his part of design the flow charts of all the programmers can be placed together to visualize the overall system design Any problem in linking the various parts of the system can be easily detected at this stage and the design can be accordingly modified Flowcharts can thus be used as working models in the design of new programs and software systems Efficient Coding Once a flowchart is ready programmers find it very easy to write the concerned program because the flowchart acts as a roadmap for them It guides them in proceeding from the starting point of the program to the final point ensuring that no steps are omitted The ultimate result is an error free program deve
21. 0 then calculate Root X1 B B 4AC 2A Root X2 B B 4AC 2A Flowchart Techniques 55 1 5 1 Characteristics of the Instructions in an Algorithm Write values of Root X1 Root X2 and stop The sequence of instructions must possess the following characteristics for qualifying as an algorithm 1 Each and every instruction should be precise and unambig UOUS 2 Each instruction should be such that it can be performed in a finite time 3 One or more instructions should not be repeated indefi nitely This ensures that the algorithm will ultimately ter minate 4 After performing the instructions that is after the algo rithm terminates the desired results must be obtained Example 1 14 Solution Let us consider another case where there are 50 students in a class who have appeared in their final examination Their mark sheets have been given We are required to write an algorithm to calculate and print the total number of students who have passed in first division Step 1 Initialize TOTAL FIRST DIVISION and TOTAL MARK SHEETS CHECKED to zero Step 2 Take the marksheet of the first student Step 3 Check the division column of the marksheet to see if it is FIRST DIVISION if no goto step 5 Step 4 Add 1 to TOTAL FIRST DIVISION 56 Flowcharting Concepts and Algorithms Step 5 Add 1 to TOTAL MARKSHEETS CHECKED Step 6 Is TOTAL MARKSHEETS CHECKED 50 if no goto step 2 Ste
22. 0 INPUT ENTRIES OK Y OR N OK 460 WHILE OK lt gt Y AND OKS lt gt N 470 INPUT PLEASE ENTER A Y OR AN N OKS 480 WEND 490 WEND 500 RETURN c d e A rule of thumb is that the modules should not be more than one half page long If they are longer than this they should preferably be split into two or more submodules Two way decision statements are based on IF THEN IF THEN ELSE and nested IF statements Loops are not custom designed with the use of the GO TO statement but are based on the consistent use of WHILE WEND and FOR NEXT In WHILE WEND the loop is based on the truth of a condition and in FOR NEXT on a counting process and the number of repetitions that can easily be predicted See Figure 1 48 1 8 3 Other Characteristics of GOOD Programs Readability The ease with which some one can read a program is based on the Flowchart Techniques 77 Driver module X PRINT Calculate Calculations INPUT Title monthly for detail PRINT Data Column heads payment Totals G TO GOTO lines Figure 1 48 GOTO statements are removed manner in which it has been typed This includes printing gaps between the modules Documentation The documentation is greatly improved if the variable choice is descriptive This serves as a mnemonic device to aid in remem bering the meaning of the variables
23. 1 1 CHAPTER 1 Flowchart Techniques Programming Aids Programmers use different kinds of tools or aids which help them in developing programs faster and better Such aids are studied in the following paragraphs Important aids available to a pro grammer are flowcharting and decision tables which help him in constructing programs very fast and very easily Flowcharts A flowchart is a graphical representation of the sequence of oper ations in an information system or program Program flowcharts show the sequence of instructions in a single program or subroutine Flowchart uses boxes of different shapes to denote different types of instructions The actual instructions are written within these boxes using clear and concise statements These boxes are connected by solid lines having arrow marks to indicate the flow of operation that is the exact sequence in which the instructions are to be executed Since a flowchart shows the flow of operations in pictorial form any error in the logic of the procedure can be detected easily Once the flowchart is ready the programmer can forget about the logic and can concentrate only on coding the operations in each box of the flowchart in terms of the statements of the programming language This will normally ensure an error free program A flowchart is basically the plan to be followed when the pro gram is written It acts like a road map for a programmer and 2 Flowcharting Concepts and Algorit
24. 2 and 1 6 2 There is no doubt that structured programming has been successful but it does not solve all our problems Poorly con structed system designs can still negate the benefits provided by structured programming It was not surprising then that similar principles were applied to the tasks of analysis and design and a full range of structured methods came into being 1 8 1 Why Structured Programming In computer programming the spaghetti code is the method of coding that confuses the program flow because of the excessive use of GOTO or jump statements Hence one of the major improvements has been the shift from spaghetti code to TOP Down modular design and structured programming methods The reason for the evolution to structured programming is the need for well organized programs that are ultimately easier to a Design b Read and understand c Modify d Test and Debug e Combine with other programs Writing programs that are clear for any programmer to read and understand is a very important consideration particularly if there is a change in programming personnel Flowchart Techniques 75 1 8 2 Characteristics of Structured Programs In general terms structured programming is the development of computer programs that are well organized Here is a list of characteristics of structured programs a The programs are based on top down modular design In other words the problem at hand is analysed or broken d
25. 9 respec tively In step 3 the value of A is compared with B Since 7 is greater than 3 therefore the YES path is followed In step 4 the value of A is compared with C Since 7 is less than 9 therefore the path corresponding to NO is followed Hence the value of C which is 9 will be printed The values of A B and C are accepted as 2 9 and 7 respec tively As understood from steps a and b above we find that in step 5 the value of B will be printed as 9 d The values of A B and C are accepted as 4 8 and 2 respec tively In step 5 the value of B will be printed as 8 e The values of A B and C are accepted as 6 3 and 8 respec tively The value of C which is 8 will be printed in step 5 f The values of A B and C are accepted as 2 3 and 6 respec tively The value of C which is 6 is printed in step 5 It is evident from the flowchart that the values of A B and C are compared with each other and the one that contains the highest numeral value is printed If A has the highest value then A is printed otherwise if B has the highest value then B is printed or finally the value of C is printed if it has the highest value If A B and C have equal values then the value of C which is the same as that of B or A is printed Flowchart Techniques 29 BEGIN STEP 1 STEP 2 NO YES STEP 3 NO YES o Er STEP 4 Y y y y PRINT C VA va PRINT B J PRINT C vA PRINT A ae STEP 5 y y y y END C END DC END
26. C will not be the sum of A and B but it will be the difference of A and B which is quite different Such errors can only be detected with the help of test data that will give the input values of A and B and the resultant value that should come out of the program as a result of the operation performed on A and B If the result given by the computer and the result calcu lated manually with the help of a calculator are the same then you can say that there is no logical error Otherwise a logic error may be present in the program Runtime error Runtime errors occur when a program is run on the computer and the results are not achieved due to some misinterpretation of a particular instruction This could be some thing like dividing a number by zero which results in a very large value of quotient It may also be any other instruction which a computer is not able to understand To overcome this problem there is a built in error detector in the language interpreter or compiler which will give the message and that will reflect the reason for the run time error 1 10 4 Program Testing It is the job of the programer to test as far as possible that all parts of the program work correctly It should be realised that complete testing is not possible except in the case of the most trivial program one can never be completely certain that all errors have been removed but sufficient tests can be performed to give a reasonable measure of confidence in the
27. Efficiency The speed of execution is something to consider but it is not a primary concern when using a particular programming language In terms of the manipulation of numbers integers are the fastest followed by single precision with double precision being the slowest 1 8 4 Importance of Structured Programming Structured programming is important for the following reasons a It is much easier for students to debug structured programs and for instructors to grade them 78 Flowcharting Concepts and Algorithms b Students who learn top down modular design retain what they have learned over a much longer period of time c Students who go on from structured BASIC to PASCAL and or structured COBOL are better prepared for these lan guages 1 9 Modularity One way to improve the structure of a program is to break down the original problem to be solved into independent tasks called modules in pseudocode and subroutines in BASIC and then execute these modules in a predefined sequence The resulting design consists of a network of modules Breaking down a problem into smaller pieces modules allows you to focus more easily on a particular piece of the prob lem without worrying about the overall problem The tasks become easier to solve and are more manageable since each performs a very specific function Typically you can code each module independently of the others and test or debug each mod ule separately Once all modu
28. GIN SUM 0 m NO SUM SUM a M M M 2 Figure 1 44 Flowchart for Q No 5 Q 7 The following steps are written to calculate the standard deviation for any given numbers Use this algorithm to cal culate the standard deviation for the numbers 8 10 12 16 19 1 2 3 4 De 6 Find the sum of the list of numbers Divide the sum by the total number of numbers to obtain the mean Subtract the mean from each number in the list and square this result Calculate the sum of the squares found in step 3 Divide the sum of step 4 by the total number of num bers in the original list Find the square root of the result found in step 5 This number is known as the standard deviation of the original list 68 Flowcharting Concepts and Algorithms BEGIN INPUT N AA SUM 0 M 1 NO SUM SUM ae M M M END Figure 1 45 Flowchart for Q No 5 Q8 Write an algorithm to compute a sales person s commission based on the following table Amount Sales Commission of sales Under Rs 500 2 Rs 500 or more but under Rs 5000 5 Rs 5000 and above 10 Q9 Draw the flowchart for the following pseudocode BEGIN Input mortgage amount IF amount lt 25 000 Flowchart Techniques 69 THEN down payment 3 of amount ELSE payment 1 3 of 25 000 payment 2 5
29. M anual b Operating Instruction c Data Preparation Instruction ESTE Clerical Procedure Manual This manual details the activities that the clerical staff will undertake in preparing data for input to the system For exam Flowchart Techniques 93 ple batching documents and calculating hash totals It will also describe what action is to be taken when errors occur for example when a validation program reports errors Operating Instructions This document gives the details to the computer operator of how to run the program It may include a Details of the procedure for starting the program b Details of disks and tapes required c Special stationery to be used d The number of copies of each report and who is to receive the output e Backup procedures to be followed f Recovery procedures in the event of hardware failure Data Preparation Instructions This will contain instructions on data entry showing if necessary how each field should be entered For example a date field may be entered in various formats and the correct one needs to be specified In a small system written perhaps for a single user working on a micro computer these three manuals may be combined into one User Manual 1 12 Data Flow Diagrams DFD Data flow diagrams are used to emphasize the logical flow of data through a system The basic symbol is a circle or bubble and is called a transform since it identif
30. The new value of B is calculated which will be 15 x 3 i e 45 This current value of B is again compared with 20 As it is not less than 20 sothe NO path is followed The value of C current value of B 3 45 3 48 Control is transferred to step 6 via connector 3 and the value of C is printed Thus the value of C 48 1 3 2 Loop Many jobs that are required to be done with the help of a com puter are repetitive in nature For example calculation of salary of different workers in a factory is given by the No of hours worked x wage rate This calculation will be performed by an accountant for each worker every month Such types of repetitive calculations can easily be done using a program that has a loop built into the solution of the problem What is a Loop A loop is defined as a block of processing steps repeated a certain number of times An endless loop repeats infinitely and is always the result of an error Figure 1 17 illustrates a flowchart showing the concept of looping It shows a flowchart for printing values 1 2 3 20 In step 5 of Figure 1 17 the current value of A is compared with 21 If the current value of A is less than 21 steps 3 and 4 are repeated As soon as the current value of A is not less than 21 the path corresponding to NO is followed and the repetition process stops Flowchart Techniques 33 Terms Used in Looping Initialisation STEP 1 STEP 2 STEP 3 Figu
31. Y in step 5 and print the name and pay in step 6 In step 7 the value of COUNT is increased by 1 and the cur rent value of COUNT is compared with 100 in step 1 If it is more than 100 the process is halted Exercise 1 1 Q 1 How many records will be read by the flowcharts shown in Figures 1 19 and 1 20 Q 2 A certain file contains 15 records Which of the flowcharts shown in Figures 1 21 and 1 22 read 15 and only 15 records Q 3 The formula to compute simple interest on a loan of rupees P at an interest rate R for T years is given as _ PRT 100 Draw a flowchart to input the values of P R and T and to calculate the value of interest Also print the values of P R T andl 36 Flowcharting Concepts and Algorithms Q 4 The flowchart shown in Figure 1 23 is drawn to print the sum of integers 1 to 100 What changes would you make in this flowchart if the SUM for the first 100 odd integers is required Redraw the flowchart BEGIN I I 1 READ K YES NO Figure 1 19 Reading of records Flowchart Techniques 37 BEGIN Il I I 1 YES Ee END Figure 1 20 Reading of records Q5 Consider an equation Y X 2X 43 Draw a flowchart which gives a method for calculating the values of Y for different values of X varying from 4 to 4 in steps of 1 and prints each value of X and the corresp
32. ack of consistency between modules and considerable re programming may have to be done Flowchart Techniques 73 1 7 3 Modular Design and Programming In industry and commerce the problems that are to be solved with the help of computers need thousands or even more number of lines of code The importance of splitting up the problem intoa series of self contained modules then becomes obvious A module should not exceed about 100 or so lines and should preferably be short enough to fit on a single page Advantages of modular design a Some modules will be standard procedures used again and again in different programs or parts of the same program b Since module is small it is simpler to understand it as a unit of code It is therefore easier to test and debug especially if its purpose is clearly defined and documented c Program maintenance becomes easier because the affected modules can be quickly identified and changed d In avery large project several programmers may be work ing on a single program Using a modular approach each programmer can be given a specific set of modules to work on This enables the whole program to be finished sooner e More experienced programmers can be given the more com plex modules to write and the junior programmers can work on the simpler modules f Modules can be tested independently thereby shortening the time taken to get the whole program working g Ifa programmer leaves p
33. ailed programming Applica tion generators are one or more levels higher than the pro gramming language whose source code they generate but still require the user to input basic mathematical expressions in order to state complex processing on their business data For example a complicated pricing routine will require that the pricing algorithms be stated just as they would bein any programming language 1 10 3 Types of Program Errors Once a program has been typed in different types of errors may show up These include a Syntax semantic errors b Logicerrors c Runtimeerrors Syntax semantic errors Syntax is a set of rules governing the structure of and relation ship between symbols words and phrases in a language state ment A syntax error occurs when a program cannot understand the command that has been entered Logic errors Logic refers to a sequence of operations performed by a software or hardware Software logic or program logic is the sequence of instructions in a program Logic errors are the errors that have been entered in the instructions created because of the mistake made by a programmer Suppose you wanted to do the sum of A and B and put the result in the variable C This is accomplished by typing C A B Flowchart Techniques 83 But while typing the programmer has typed the following expression Co A 1B Such a program will run properly but will give erratic result because the value of
34. ains unchanged There is a constant need for mainte nance and enhancements Maintenance is required because pro grams inevitably have errors that must be corrected when they appear As users work with the new software system they will learn more about it and will develop ideas for change and enhancements The system continues to evolve throughout its life cycle 1 11 6 Documentation and its Importance Documentation provide a general outline as well a few specific details of the overall program structure The documentation of a program is a continuous process After successfully completing the program we must ensure that documentation is complete and is in a finished usable form This includes both technical documentation for the programmers who may be working with and modifying the completed program and user leve documenta tion for the users of the program A good user documentation is essential if a program is to bea useful tool Good technical documentation is essential for main taining a program We may decide at a future date to add fea tures tothe program or we may have to find and correct errors in the program both of which can be virtually impossible if the technical documentation is inadequate 1 11 7 Aim of Program or System Documentation The aims of documentation are 92 Flowcharting Concepts and Algorithms a To help in the design of the system by working to a set of standards and having available a clear descr
35. am Choose some test data so that each part of the program is checked for correctness 6 Finally use the data validation program to guard against processing of wrong data The above six steps are further explained in the following para graphs Step 1 Understanding the Problem Read each statement in the problem carefully so that you can answer the first question What is expected by solving the prob lem Do not start drawing a flowchart straight away Instead read each statement of the problem slowly and carefully understanding the keywords Take a pencil and paper and try to solve the problem manually for some test data Let us under stand this point by solving the problem given in Example 1 12 Example 1 12 Solution Write a flowchart to accept a value M and find the sum of first M even integers The solution of this problem requires you to draw a flowchart so that if you input 6 as the value of M the flowchart should get you the sum of first 6 even integers In the first step you should be able to answer the following two questions What are the first 6 even integers These are 2 4 6 8 10 and 12 What is their sum Flowchart Techniques 51 The sum is 42 Hence the flowchart is to be so framed that the sum of first 6 even integers comes out to be 42 1 4 2 Step 2 Construction of the List of Variables In this step you should think in advance the number of variables and the names of the variables b
36. art way through a project it is eas ier for someone else to take over a set of self contained mod ules h A large project becomes easier to monitor and control 1 8 Structured Programming In the 1960s in the USA a number of surveys confirmed what most data processing managers had believed for a long time that there is a substantial variation in programmer abilities and that too much time is spent on debugging programs and on maintenance activities The surveys generated much contro versy but the effect they had was dramatic Suddenly everyone became concerned with the programmer s productivity and the 74 Flowcharting Concepts and Algorithms way in which he actually programmed In 1965 Professor Dijk stra of Eindhoven University in Holland presented a paper at the IFIP Congress in New York suggesting that the GOTO statement should be eliminated from programming languages altogether since a program s quality was inversely proportional to the num ber of GOTO statements in it In the following year Bohm and J acopini showed that any program with single entry and exit points could be expressed in terms of three basic constructs a Sequence or carrying out a process b Iteration or looping c Selection or decision taking This was the beginning of structured programming This dramatically improved the quality of programming and of pro grammer productivity The above three constructs have been explained in sections 1
37. bol The logical process of moving data from one location of the main memory to another is also denoted by this symbol When more than one arithmetic and data movement instructions are to be executed consecutively they are normally placed in the same processing box and they are assumed to be executed in the order of their appearance Flow lines Flowlines with arrowheads are used to indicate the flow of oper ation that is the exact sequence in which the instructions are to be executed The normal flow of flowchart is from top to bottom and left to right Arrowheads are required only when the normal top to bottom flow is not to be followed However as a good prac tice and in order to avoid confusion flow lines are usually drawn with an arrowhead at the point of entry to a symbol Good practice also dictates that flow lines should not cross each other and that such intersections should be avoided whenever possible Decision The decision symbol is used in a flowchart to indicate a point at which a decision has to be made and a branch to one of two or more alternative points is possible Figure 1 2 shows three differ ent ways in which a decision symbol can be used It may be noted from these examples that the criterion for making the decision should be indicated clearly within the decision box Moreover the condition upon which each of the possible exit paths will be executed should be identified and all the possible paths should be accoun
38. ch adapts a program that has just been assembled or compiled into a particular com puter environment It formally links cross references between separate program modules and it links the program to various libraries containing prewritten subroutines The output of a linkage editor is a load module a program ready to run in the computer Text Editor A text editor is a software program that creates and manages text files Text editors are used to create and edit source lan guage programs data and text files Unlike word processors text editors do not have elaborate formatting and printing features For example there is usually no automatic word wrap or under line bold face and italics printing in text editors 1 10 2 Other Program Development Aids Some of the other aids for a programmer may include a An on line help facility giving information about any com mand standard function or procedure b Utility programs enabling the user to design input screens and have the code automatically generated 82 Flowcharting Concepts and Algorithms c Separate compilation of modules allowing the programmer to build up a precompiled tested code d An integrated development environment combining a text editor and a compiler with pull down menus windows help facility and debugger e Application generators These are the software programs that generate application programs from a description of the problem rather than from det
39. d benefits will be compared with the estimates produced at the system inception This particular activity is often known as Post Audit The new system will also need to be reviewed and maintained periodically for the following reasons a To deal with unforeseen problems arising in operation For example programs may need to be modified to deal with unforeseen circumstances b To confirm that the planned objectives are being met and to take action if they are not c Toensure that the system is able to cope with the changing requirements of business The results of a systems review would be used in future sys tems analysis assignments 1 20 1 Management Decision Orders In the event of adverse remarks given by the post audit team in the functioning of the new computer system it may be necessary for the management to take some bold decision or issue orders for the change review of the system For example if the system is not able to cope with the load of the work for which it was originally designed then it may not be worthwhile to continue with the automatic new system Let us take the case of the system designed for the school fee collection The system may be required to meet the immediate collection of the fee But if the system does not meet this need as the working of the software is not reliable or there is some other inherent defect in the system created then it will be necessary for the management to look into the new sys
40. dinary natural language e g English French German etc Instead of using symbols to describe the logic steps of a program as in flowcharting pseudocode uses a structure that resembles computer instructions Because it emphasises the design of the program pseudocode is also called Program Design Language PDL Pseudocode is made up of the following basic logic structures that have been proved to be sufficient for writing any computer program 1 Sequence 2 Selection IF THEN ELSE or IF THEN 1 Iteration DO WHILE or REPEAT UNTIL 1 2 1 Sequence Sequence logic is used for performing instructions one after another in sequence Thus for sequence logic pseudocode instructions are written in the order or sequence in which they are to be performed The logic flow of pseudocode is from the top to the bottom Figure 1 8 shows an example of sequence logic structure 1 2 2 Selection Selection logic also Known as decision logic is used for making decisions It is used for selecting the proper path out of the two or more alternative paths in the program logic Selection logic is depicted as either an IF THEN ELSE or IF THEN structure The flowcharts shown in Figures 1 9 and 1 10 illustrate the logic of these structures Their corresponding pseudocode is also given in these figures Flowchart Techniques 17 ThelF THEN ELSE construct says that if the condition is true then do process 1 else if
41. e 64 Flowcharting Concepts and Algorithms BEGIN y Ea r y READ RECORD y I I 1 Figure 1 40 Flowchart for Q N 1 flowcharts shown in Figures 1 39 and 1 40 will read 5 and only 5 data records Q 2 How many records will be read by each of the following flowcharts see Figure 1 41 and 1 42 Q 3 Consider the flowchart shown in Fig 1 41 Find out the output if the input values of X Y and Z are as follows a X 7 Y 9 Z 11 b X 11 Y 9 Z 7 0 X Y 11 Z 7 Q 4 Draw a flowchart that interprets the following statements a lf SALES is 10 000 or more then BONUS 3 of SALES b If SALES is 10 000 or more then BONUS 3 of SALES ELSE BONUS 2 of SALES Flowchart Techniques 65 BEGIN Y Nad E END Figure 1 41 Flowcharts for Q N 2 BEGIN ESSA GE N 00 E IS YES N gt 7 NO N N 1 Vv READ RECORD END Figure 1 42 Flowchart for Q N 2 66 Flowcharting Concepts and Algorithms BEGIN INPUT X Y Z Figure 1 43 Flowchart for Q N 3 Q 5 What is the value of SUM for the flowchart shown in Fig ures 1 44 and 1 45 Q 6 What is an algorithm Write algorithms for each of the fol lowing a Formatting a disk in your computer b Finding a book in the library Flowchart Techniques 67 BE
42. e 1 2 highlights the differences between data flow diagram and structure chart Table 1 2 Difference between data flow diagram and structure chart SI No Data Flow Diagram Structure Chart 1 Ina data flow diagram only the In a structure chart the process is shown but the sequencein which process is sequence is not important to be done is also important 2 In this case the hierarchy or In this case hierarchy of the the ladder in which the process process is important is to be executed is not impor tant 3 A data flow diagram is nor A structure chart is nor mally made at the system anal mally made at the system ysis phase design phase 1 13 1 Elements of Structure Chart Structure charts have three basic elements These are Module It is a rectangular shape with the process name written in it Figure 1 54 shows a module The box represents a module and the alphabets such as A B C written inside the box are the names of the processes performed Connectors Connectors connect any two modules with the arrows drawn in the downward direction Figure 1 55 shows the arrow which is a connector Flowchart Techniques 97 Process Module ie Process Process Figure 1 54 Module Process Connector gt lt Connecter Process Process Figure 1 55 Connector Couple The carriers o
43. e the value of wage in each case and give the result of the print statement 1 3 4 Counting for Controlling a Loop Sometimes it is essential to repeat a process for a specific num ber of times only In such a case there are two standard tech niques used These technique are as follows Technique 1 In this technique we use the following six steps ne Initialise a counter to 0 i e COUNT O Input value of N where N stands for the number of times a loop is to be repeated 2 Increase the counter by 1 r COUNT COUNT 1 3 Test the value of counter and compare the current value with N If the current value of the COUNT is greater than N then branch off to step 6 otherwise continue 4 Carryout the sets of instructions procedure 5 Go back to step 2 6 End the loop and continue further programming These six steps are shown in Fig 1 30 Technique 2 1 In this method the counter is first initialised to zero and the value of N is inputted 2 Carry out the sets of instructions of the program 3 Increase the counter by 1 4 Test the counter If COUNT lt N then Goto step 2 5 ELSE END The above mentioned six steps are represented pictorially by the flowchart shown in Figure 1 31 48 Flowcharting Concepts and Algorithms STEP 1 COUNT 0 COUNT COUNT 1 YES STEP 3 NO SET OF STEP 4 INSTRUCTIONS STEP 5 STEP 6 Figure 1 30 Flowchart for contro
44. efore drawing a flowchart The names chosen for variables should be an aid to memory For example in the case of the problem stated in step 1 above the variables may be SUM and COUNT as given below 1 Generate even integers 2 4 6 I 2 Total the sum of even integers 2 446 SUM 3 Count the number of even integers i e COUNT 1 2 3 COUNT Thus it is clear that we need to use the above three variables and one more variable M whose value will be inputted from the keyboard Hence the four variables are M Which is to be inputted from the keyboard Which is to generate even integers COUNT A counter to keep a track of the number of even inte gers that have been summed SUM An accumulator that contains the current total of the even integers 1 4 3 Step 3 Output Design Sometimes the output format is specified in the problem but most of the times it is not so If the output format is not specified we must keep in mind that the output report should be easily understandable by a reader The headings should not cause any ambiguity in the mind of the reader In the problem of Example 1 12 and stated in step 1 above the output format could be as follows No of integers Total value 6 42 You should keep one point in mind The programs and prob lem solutions are for other people teachers supervisors contrac 52 Flowcharting Concepts and Algorithms tors etc They will give you credit only
45. eral times depending on some condition It uses two structures called the DO WHILE and the REPEAT UNTIL They are illustrated by flowcharts in Figure 1 11 and Figure 1 12 respectively Their corresponding pseudocodes are also given in these figures Both DO WHILE and REPEAT UNTIL are used for looping 20 Flowcharting Concepts and Algorithms 1 2 4 Differences between Do While and Repeat Until loops The differences between the two loops are that FLOWCHART CONDITION v PSEUDOCODE e e DO WHILE CONDITION PROCESS 1 PROCESS n ENDDO Figure 1 11 Pseudo code for Do While structure Flowchart Techniques 21 FLOWCHART o PROCESS 1 PROCESS n NO PSEUDOCODE REPEAT PROCESS 1 PROCESS 2 UNTIL CONDITION Figure 1 12 Pseudo code for Repeat Until structure DO WHILE the looping will continue as long as the condition is true The looping stops when the condition is not true On the other hand in case of REPEAT UNTIL the looping continues 22 Flowcharting Concepts and Algorithms until the condition becomes true That is the execution of the statements within the loop is repeated as long as the condition is not true In both the DO WHILE and REPEAT UNTIL the loop must contain a statement that will change the condition that controls the loop Also the condition is tested at the top
46. f a high level task and the decomposition into subtasks Each of those subtasks can then be farmed out to a more junior programmer who work under the direction of the senior staff Since almost all software projects are done by teams of two or more programmers this top down charac teristic is very important In summary top down programming is a program design technique that analyses a high level problem in terms of more elementary subtasks Through the technique of stepwise refine ment we then expand and define each of these separate subtasks until the problem is solved Each subtask is tested and verified before it is expanded further The advantages of this technique are a Increased intellectual manageability and comprehension b Abstraction of unnecessary lower level detail c Delayed decisions on algorithms and data structures until they are actually needed d Reduced debugging time 1 7 2 Bottom up Design and Implementation When faced with a large and complex problem it may be difficult to see how the whole thing can be done It may be easier to attack parts of the problem individually taking the easier aspects first and thereby gaining the insight and experience to tackle the more difficult tasks and finally to try and bolt them all together to form the complete solution This is called a bottom up approach It suffers from the disadvantage that the parts of the program may not fit together very easily There may bea l
47. f contained module or procedure The program then consists of a series of simple modules Flowchart Techniques 71 In top down design we initially describe the problem we are working on at the highest most general level The description of the problem at this level will usually be concerned with what must be done not how it must be done The description will be in terms of complex higher level operations We must take all of the operations at this level and individually break them down into simpler steps that begin to describe how to accomplish the tasks If these simple steps can be represented as acceptable algorithmic step we need not refine them any further If not we refine each of these second level operations individually into still simpler steps This stepwise refinement continues until each of the original top level operations has been described in terms of acceptable shortest primitive statements Advantages of Top down approach a It allows a programmer to remain on top of a problem and view the developing solution in context The solution always proceeds from the highest levels down With other tech niques we may find ourselves bogged down with very low level decisions at a very early stage It will be difficult to make these decisions if it is not clear how they may affect the remainder of the problem b It is avery good way to delay decisions on problems whose solution may not be readily apparent At each stage
48. f data are called couples These indicate the data flow between the modules Figure 1 56 shows a couple Couple can be of two different types a Data couple b Control couple 98 Flowcharting Concepts and Algorithms Data Couple and Control Couple Data couple carries data between two modules and it can have upward or downward direction But control couple only carries information about data couple and does not carry any data Con trol couple is always directed upwards because it shows the mod ule which is to be evoked Figure 1 56 show the two different types of couple The arrows with a blank circle at the tail is called data couple The arrow with a completely filled circle at the tail end is called a control couple A Process Data Control Couple Data X Couple Couple B C Process Process Figure 1 56 Couple data and control How to Draw Structure Chart In order to draw a structure chart you will need to identify the inputs process and the outputs You should draw different mod ules for different processes in a system This will be more dear with the help of the example given below Example 1 20 Draw the structure chart for calculating the amount of scholar ship a cut in the tuition fee to be awarded to a student The conditions are as follows a If marks are gt 90 give 15 cut in the fee b If marks are gt 85 and lt 90 the
49. fication in the original program High Cost of Software Major problem with software maintenance is that the program writing is labour intensive in nature Human beings who write programs are likely to make errors For example the programmer who was originally assigned the task of solving and coding the program may not be available to modify this program at a later date Therefore the new person who is given the job of modifica tion will have to study and understand the logic of the original program and then only he can modify the program This process may involve more time money and there are more chances of making errors In such cases it may be easier and economical to rewrite a new program rather than amending the old one Errors Caused due to Modification in the Original Program Alteration in the original program no matter how slight must be manually introduced There is no easy way of making sure that the modifications made will not cause any errors elsewhere in any of the subprograms or the main program Using the old codes Flowchart Techniques 89 depend mostly on the programmer s ability to judge what the code can and cannot do Hence the program is to be thoroughly tested after modification before implementation 1 11 3 Impact of Software Errors The quality of a software system depends on its design develop ment testing and implementation An important aspect of soft ware quality is its reliability A program is
50. g 1 10 7 Functional Testing Functional testing is carried out independently of the code used in the program It involves looking at the program specification and creating a set of test data that covers all the inputs and out puts and program functions This type of testing is also known as black box testing For example to test the program that calculates check digits we could draw up the following test plan Flowchart Techniques 85 Table 1 1 Test Plan for Check Digits Serial Test for numer Purpose Expected Actual Number ical data result result 1 Enter 1234 Test validity of data 1234 Digits 3 2 Enter 8 digits Test extreme case are printed 3 as itis 3 Enter 123W Testing invalid data Data not Error accepted From Table 1 1 we will be able to make out whether the software is testing the data correctly or not If it is not testing properly then we may have to correct the program 1 10 8 Logical Structural Testing Logical testing white box testing is dependent on the code logic and derives from the program structure rather than its function In other words we study the program code and try to test each possible path in the program at least once The problem with logical testing is that it will not detect the missing functions One method of devising a test plan is to start with a set of functional test cases and then add additional tests to exercise each statement in the program at least
51. g and is increased by 1 every time the operation WRITE OUTPUT DATA is performed But we have seen that the opera tion WRITE OUTPUT DATA is performed only for the students who have passed Hence the variable COUNT will be increased by 1 only in the case of those students who have passed Thus the value of COUNT will always be equal to the number of stu dents whose data has already been processed and who have been identified as passed Finally when the trailer record is detected the operation WRITE COUNT will print out the final value of COUNT that will be equal to the total number of students who have passed the examination 1 1 3 Flowcharting Rules a First formulate the main line of logic then incorporate the details b Maintain a consistent level of detail for a given flowchart c Do not give every detail on the flowchart A reader who is interested in greater details can refer to the program itself d Words in the flowchart symbols should be common state ments and easy to understand e Beconsistent in using names and variables in the flowchart f Go from left to right and top to bottom in constructing the flowchart Flowchart Techniques 13 g Keep the flowchart as simple as possible The crossing of flow lines should be avoided as far as possible h If a new flowcharting page is needed it is recommended that the flowchart be broken at an input or output point Moreover properly labeled connectors should be
52. gen erally written one per line Indentation is used in the IF state ment to outline which actions are to be taken if a condition is true and which are to be taken if the condition is not true Differences between PseudoCode and Flowchart Pseudocode differs from the flowchart in the following ways 58 Flowcharting Concepts and Algorithms a Pseudocode is self explanatory and does not require a sepa rate documentation This is so because it is written in plain English language b Pseudocode has a structure similar to that of a programme written in BASIC or PASCAL language But flowcharts have a tendency to extend flow lines in all directions and thus their paths of instructions do not parallel the final BASIC code The following are some examples of flowcharts and their equiva lent pseudocode Example 1 15 Working with Masala Dosa Mincer BEGIN t TURN MINCER ON MINCE DOSA MASALA TURN MINCER OFF C Figure 1 33 Flowchart for Example 1 15 Flowchart Techniques 59 Pseudo code BEGIN Turn Mincer on Mince dosa masala Turn Mincer off END This is a case of simple sequence The flowchart is given in Figure 1 33 Example 1 16 In this example a flowchart for Drink selection is shown in Figure 1 34 Pour A Cup Pour A Cup Of Coffee Figure 1 34 Process of selection for example 1 16 60 Flowcharting Concepts and Algorithms
53. gt C END STEP 6 Figure 1 15 Calculation of output for different values of A B and C Example 1 9 The flowchart in Figure 1 16 uses connector symbols labelled as 1 2 and 3 Find the output if the input is a A 10 B 15 b A 20 B 20 A BA d A 10 B 30 Flowcharting Concepts and Algorithms Solution In step 2 of Figure 1 16 the values of A and B are taken to be 10 and 15 respectively In step 3 the value of A is not less than 10 sothe path corresponding to NO is followed In step 4 the value of B is not less than 20 hence a path corresponding to NO is followed In step 5 the value of A B is assigned to C i e C becomes 10 15 or equal to 25 Finally in step 6 the value of C which is 25 is printed In step 2 the values of A and B are taken as 20 and 20 respectively Steps 3 to5 aresimilar to that followed in part a above The value of C is now equal to A B which is 40 Hence 40 is printed In step 2 the values of A and B are taken as 4 and 1 respectively In step 3 the value of A is less than 10 Hence the YES path is followed This is connected to the adjacent figure via the connector 1 Hence the value of A is now the old value of A 3 i e 7 Further the decision diamond puts the question Is A less than 10 The answer is YES Hence the control is trans ferred to the lower figure via connector 2 The new value of B becomes the old value of B multiplied
54. he 50 students In this situation where the same logical steps can be repeated the flow line sym bols are used in a flowchart to indicate the repetitive nature of the logic in the form of a loop Figure 1 4 shows a flowchart which uses a decision step to terminate the algorithm In this flowchart another variable COUNT has been introduced which is initialized to zero outside the process loop and is incremented by 1 after processing the data for each student Thus the value of COUNT will always be equal to the number of students whose data has already been pro cessed At the decision step the value of COUNT is compared with 50 which is the total number of students who have appeared for the examination The steps within the process loop are repeated until the value of COUNT becomes equal to 50 As soon as the value of COUNT becomes equal to 50 the instruction at the decision step causes the control to flow out of the loop and the processing stops because a terminal symbol labeled STOP is encountered Designing a General Flowchart The flowchart shown in Figure 1 4 is not a general flowchart for the Example 1 2 for calculating the percentage of marks of any number of students appearing in the examination A good pro gram should be general in nature For example in this case we should write a program that need not be modified every time even if the total number of students changes To overcome these drawbacks another method can be adopted
55. he processing cycle Thus the system analysis shows the relationship between the individual items on each output and the items available as inputs to the system The output reports and input documents should be docu mented in terms of data contents and approximate layout It is possible to work back from the output contents through the system to the inputs required This is done by determining which output data items are derived by calculation or by logical deduc tion All other items can then be broken down into those which require fresh input every time as part of input transaction documents and those which can be stored on file because they are historical or relatively static Flowchart Techniques 103 1 18 Data item Dictionaries Data item dictionary is used to define data including identifiers location and format for storage characteristics It holds the name type range of values source and authorization for access of each data element in the organization s files and databases It also indicates which application program what data so that whenever a change in a data structure is contemplated a list of the affected programs can be generated The data dictionary may be a stand alone information system used for management and documentation purposes or it may be an integral part of data base management system where it is used to actually control its operation Data integrity and accuracy is better insured in the
56. hms guides him in proceeding from the starting point to the final point while writing a computer program For a beginner it is strongly recommended that a flowchart be drawn first in order to reduce the number of errors and omis sions in the program Moreover it is a good practice to have a flowchart along with a computer program as it is very helpful during the testing of the program and also in incorporating any modifications in the program 1 1 2 Flowchart Symbols Only a few symbols are needed to indicate the necessary opera tions in a flowchart These symbols have been standardized by the American National Standards Institute ANSI These symbols are shown in Figure 3 1 and their functions are dis cussed below Terminal The terminal symbol as the name implies is used to indicate the starting BEGIN stopping END and pause HALT in the pro gram logic flow It is the first symbol and the last symbol in the program logic In addition if the program logic calls for a pause in the program that also is indicated with a terminal symbol A pause is normally used in the program logic under some error conditions or in case the forms had to be changed in the comput er s line printer during the processing of that program Input Output The input output symbol is used to denote any function of an input output device in the program If there is a program instruction to input data from a disk tape card reader terminal or
57. iagram of the solution of a problem As explained earlier flowcharts use a standard set of Flowchart Techniques 95 Dataflow 4 Data lenient Dataflow 3 Dataflow 1 SOURCE DESTINATION Dataflow 2 DATA STORE Figure 1 53 Data Flow Diagram for customer enquiry system symbols and the actual operation to be performed is written inside the symbol The arrow coming out of the symbol indicates which operations is to be performed next There are special types of flowcharts called structure charts that restrict the types of allowable operations and inter connec tions in order to produce well organized and readable diagrams Structure charts are thus pictorial representation of the design of a system The flowcharting technique is useful primarily for macro level or system flowcharts level where we are concerned with the most general level of operations needed to solve a large problem Each element of a system flowchart would typically represent a fairly large and complex manual clerical or computer procedure 96 Flowcharting Concepts and Algorithms for which an algorithm must be developed and implemented These individual procedures could be developed and represented using an algorithmic language However in a structured chart there is a sequence of process shown along with the hierarchy of the process These structure charts are used at the system design phase Tabl
58. ies a function that transforms data Figure 1 51 illustrates a data flow diagram for a small organization Data flow diagrams can be made at different levels Symbols are also used to denote logical conditions such as AND or an exclusive OR Figure 1 52 shows the logical AND and the exclu sive OR symbols used in a data flow diagram concerned with val idating input Both the transaction input and the master file input are required for the transform VALIDATE INPUT One of the inputs by itself is insufficient As a result of VALIDATE INPUT either a rejected transaction or a valid transaction will be produced However both cannot be produced since the output 94 Flowcharting Concepts and Algorithms CUSTOMERS CUSTOMERS Customer information Reports SALESFORCE MANAGEMENT FINANCE Figure 1 51 Data flow diagram for a small business organization Master file Rejected input transaction VALIDATE INPUT OR D Transaction input Accepted transaction Figure 1 52 Data flow diagram for validating input data form the transform is an exdusive OR The data flow diagrams shows the inputs and outputs clearly A data flow diagram for customer enquiry system is shown in Figure 1 53 This data flow diagram has the basic elements namely SOURCE DATA STORE and DESTINATION 1 13 Structure Charts A flowchart is a blueprint or a logical d
59. ime it may not beso easy For example you have to define the word READY precisely so that he knows exactly what he has to do by 7AM to get READY Similarly in step 2 you may have to clearly specify the bus route number the bus stop to board the bus the place to get down from the bus etc You may also like to tell that a bus is not to be boarded if it is overcrowded The word overcrowded needs to be exactly defined Finally steo 3 needs further elaboration about the room number and floor number where the computer laboratory is located and how to reach there You can explain all this to a person who does not know any thing about the computer laboratory provided you know it cor rectly In the same way you can solve a problem on a computer if you know exactly what it is and how to solve it manually We shall solve a few problems using flowchart 26 Flowcharting Concepts and Algorithms GET READY BY 7AM STEP 1 TAKE A BUS FOR SCHOOL STEP 2 REACH COMPUTER STEP 3 LAB BY 8 AM Figure 1 13 Step by step solution to reach school computer laboratory LAB Example 1 7 Solution Consider the flowchart shown in Figure 1 14 Give the value of BONUS under the following conditions a X 20 Y 10 b X 10 Y 20 a ThevalueofX and Y are 20 and 10 respectively These val ues are inputted in step 2 The value of BONUS is taken as 500 in step 1 Since the values of X 20 and Y
60. iption of the work done so far The documentation needs to be kept up to date throughout the project b Good documentation ensures that everyone involved in the system system designers programmers and users fully understand how their aspect of the system will work For example what data will be inputted and how and what information will be available from the system This allows any misunderstandings or disagreements to surface before they become deeply entrenched in the system c To ensure that the system can be maintained after comple tion even though the programmers involved in the original design or programming of the system may not be available It is essential that proper documentation is kept to enable a newcomer to make necessary corrections alterations or enhancements 1 11 8 Contents of a Document of a System The following are the parts of a document of the system a An accurate and up to date system specification b System flowchart s or data flow diagrams showing the inputs to the system files required processes to be carried out and output from the system c A description of the purpose of each program within the system Organization contents and layout of each file used Layout and contents of all output prints and displays Current version of each program listing Test data and expected results In addition the following items of documentation will need to be prepared a Clerical Procedure
61. l value Such types of checks can be included in our validation program 1 5 Algorithm The sequence of instructions for solving a particular problem is known as algorithm Constructing an algorithm to solve a given problem requires a high degree of ingenuity But once an Flowchart Techniques 53 algorithm is laid out it can be used by a person who does not even know its purpose BEGIN INPUT M I 0 SUM 0 o COUNT 0 gt SUM SUM I YES PRINT SUM COUNT Figure 1 32 Flowchart to Example 1 13 54 Flowcharting Concepts and Algorithms We shall write an algorithm to solve a quadratic equation and compute its real roots Example 1 13 Solution Compute real roots of a quadratic equation Ax Bx C 0 Step 1 Read the values of the coefficients of X X and constant quantity i e the value of A B and C and store them in the memory Step 2 If A O and B O then print No root exists and stop Else con tinue Step 3 IfA O and B is not equal to 0 then root X1 C B Write the value of root and also write Linear Equation and stop Else continue Step 4 Compute B 4AC and set D B 4AC Step 5 If D 0 then compute Root X1 Root X2 B 2A write values of Root X1 Root X2 and stop Else continue Step 6 If D lt 0 then write Roots are not real and stop Else continue Step 7 If D gt
62. latter case The data item dictionary will contain the following type of information a What tables and columns are included in the present struc ture b The names of the current tables and columns c The characteristics of each item of data such as its length and data type Any restrictions on the value of certain columns The meaning of any data fields that are not evident The relationships between items of data Se See 1 19 Testing Results In order to completely test the program logic the test data must test each logical function of the program The test data selected for testing a program should include a Normal data which will test the generally used program paths b Unusual but valid data which will test the program paths used to handle exceptions Such data might be encountered occasionally in running the program c Inappropriate data which will test the error handling capa bilities of the program 104 Flowcharting Concepts and Algorithms If a program runs successfully with the test data and pro duces correct results it is normally released for use However even at this stage errors may remain There are certain errors in complex systems that remain hidden for months and years together 1 20 Review Reports and Management Decisions Orders Once the computer run system has become operational it will need to be examined to see if it has met its objectives For exam ple the costs an
63. les are working properly you can link them together by writing the coordinating code generally called the root segment or the main code The coordinating code activates the various modules in a predetermined sequence Con sider Figure 1 49 which illustrates these principles Note that the resulting program consists of five modules the coordinating module and the four modules A B C and D It is of course conceivable that a particular module itself might be broken down into other modules By breaking down a problem into independent modules a programmer in charge of a very complex problem can easily assign various members of a team the responsibility for develop ing one or more modules Such modules can be run and tested independently of one another Making one change in one module is a very local intervention that does not require an understand ing of all other modules In contrast making one change in a nonmodular program held together by myriads of GOTO statements not only requires an understanding of the whole pro gram but can also produce masses of error messages and a lot of unwanted output Another advantage of a modularized design is that you will find yourself using the GOTO statement less frequently This in Flowchart Techniques 79 Coordinating Module A Coordinating code Problem a Carry out A gt Carry out B C Carry out C N Intial proble
64. lling a loop Technique 1 Sometimes it may be necessary to repeatedly use any of the above two techniques in order to solve a specific problem This is called nested loop It means that we have the first loop and within this loop there is another loop Solving a problem using the nested loop technique is very helpful for a multidimensional array Flowchart Techniques 49 BEGIN COUNT 0 STEP 1 SET OF Coe INSTRUCTIONS COUNT lt COUNT 1 STEP 3 STEPS 4 amp 5 STEP 6 Figure 1 31 Flowchart for controlling a loop Technique 2 1 4 Procedure for Problem Solving Though every problem is an entity in itself there are a few basic steps that should be understood and followed for effectively solv ing a problem using computer techniques On following these steps your problem solving capacity will improve There are basically six steps in solving a problem These are 50 Flowcharting Concepts and Algorithms 1 4 1 1 First spend sometime in understanding the problem thor oughly In this you are not required to use a computer Instead try to answer and solve the problem manually 2 Now construct a list of variables that are needed to solve the problem 3 Once you have completed step 2 you have to decide the layout for the output format 4 Next select the programming technique which is best suited to solve the problem and carryout the coding 5 Test your progr
65. loped at a faster rate 14 Flowcharting Concepts and Algorithms Systematic Debugging Even after taking full care in program design some errors may remain in the program because the designer might have never thought about a particular case These errors are detected only when we start executing the program on a computer Such type of program errors are called bugs and the process of removing these errors is Known as debugging A flowchart is very helpful in detecting locating and removing mistakes bugs in a program in a systematic manner Systematic Testing Testing is the process of confirming whether a program will suc cessfully do all the jobs for which it has been designed under the specified constraints For testing a program different sets of data are fed as input to that program to test the different paths in the program logic 1 1 5 Limitations of Flowcharts Takes More Time to Draw Flowcharts are very time consuming and laborious to draw with proper symbols and spacing especially for large complex pro grams Difficult to Make Changes Owing to the symbol string nature of flowcharting any changes or modifications in the program logic will usually require a com pletely new flowchart Redrawing a flowchart is tedious and many companies either do not change them or produce the flowchart by using a computer program to draw it Non standardization There are no standards determining the amount of detail that sh
66. m D Carry out D task Decomposition into unrelated subtasks A B C and D Module B Independent modules are activated Module D by the coordinating module ya Each module returns control E Module A to the coordinating module i Module C Figure 1 49 Program Decomposition itself is very important since the undisciplined use of the GOTO statement can often give rise to the spaghetti code syndrome which makes it very difficult for the program reader to remember where in the program he she is coming from and where he she is going In a modular environment each module can be respecified as a sequence of smaller modules describing what is to be done at increasing levels of detail The technique of expanding a program plan into several levels of detailed subplans and presenting the program structure as a hierarchy of tasks is sometimes referred to as top down design A hierarchy chart sometimes called a structured diagram is a useful tool for illustrating module rela tionships and hierarchies Figure 1 50 shows a hierarchy chart for the problem shown in Figure 1 49 In summary modularization helps the programmer write better structured programs that are generally more compact and thus easier to work with and more readable A subroutine can also reduce the code required for writing tasks that are to be per formed repeatedly at different places in a program 80 Flowcharting Concepts and Algorithms
67. n give 12 cut in the fee Flowchart Techniques 99 c For all other cases no cut in the fee Solution The structure chart is shown in Figure 1 57 Scholar Ship of Student Valide 7 Flag Print Name of Validate Fee Get Validated Compute Student get Marks Scholarship Scholarship aude v a ye aS Fee Get Fee Get Validated Get Marks Get Validated Compute Compute Fee Marks 15 of Fee 12 of Fee Figure 1 57 Structure chart for example 1 20 Example 1 21 Draw a structure chart for searching a record as roll no and then print the record Solution The structure chart for example 1 21 is shown in Figure 1 58 The diagram is self explanatory Looping in a Structure Chart Looping means the repetitions of a set of statements in a 100 Flowcharting Concepts and Algorithms program In a structure chart looping is shown by an angle with the arrow mark See Figure 1 59 Search the Record Valide Flag RollNo Get Valid Find Print the Student RollNo Record Record Validated Get Student RollNo RollNo Figure 1 58 Structure chart for example 1 21 Conditional in Structure Chart Conditional is a term which describes one action or operation which takes place only when the condition is true
68. nk Lemon Pour juice into glass from Lemon jug Orange Pour juice into glass from Orange jug Pineapple Figure 1 36 Flowchart for case or multichoice selection Pour juice into glass from Pineapple jug END CASE 62 Flowcharting Concepts and Algorithms REPEAT UNTIL LOOP Structure Example 1 19 In this example REPEAT UNTIL loop structure is used This loop structure is an alternate to While End While Loop Suppose you want to insert a nail in the wall by hitting its head with a hammer Then the flowchart representation and its equivalent pseudo code will be as follows Pseudo code for Figure 1 37 REPEAT Hit head of nail UNTIL nail fully in Hit Nail With Hammer Nail Completely In Figure 1 37 Flowchart for repeat until loop of inserting a nail in the wall An equivalent of the above flowchart using WHILE END WHILE structure will be as follows WHILE Nail is not fully in Hit nail head with hammer END WHILE Flowchart for this pseudocode is shown in Figure 1 38 Flowchart Techniques 63 a Y Hit Nail With Hammer A Nail Completely No In 2 Yes Figure 1 38 Flowchart for While End While loop of inserting a nail in the wall Exercise 1 3 BEGIN Yy 1 0 READ RECORD Figure 1 39 Flowchart for Q N 1 Q 1 A certain file contains 5 data records Which of th
69. onding value of Y 38 Flowcharting Concepts and Algorithms BEGIN os READ RECORD I I y Figure 1 21 Counting of records Flowchart Techniques 39 READ RECORD END Figure 1 22 Counting of records 1 3 3 Counting Counting is an essential technique used in the problem solving process It is mainly for repeating a procedure for a certain num ber of times or to count the occurrences of specific events or to generate a sequence of numbers for computational use Since a 40 Flowcharting Concepts and Algorithms BEGIN A 1 S UM 0 SUM SUM A A A 1 YE S IS A lt 10l N S O PRINT SUM Figure 1 23 Calculating sum of integers 1 to 100 computer cannot count by itself the user has to send the neces sary instruction to do so The counting process is illustrated in the flowchart shown in Figure 1 24 Herel is a counter which is initialised to a value zero in step 2 In step 3 a NAME is read and stored in the memory of the Flowchart Techniques 41 BEGIN STEP 1 y I 0 STEP 2 a READ NAME Fi STEP 3 I 1 STEP 4 y PRINT NAME STEPS STEP 6 STEP 7 Figure 1 24 Counting process computer The value of the counter is incremented by 1 in step 4 In step 5 the NAME is printed
70. ould be included in a flowchart 1 1 6 Levels of Flowcharts A flowchart that outlines the main segments of a program and shows lesser detail is a macro flowchart On the other hand a Flowchart Techniques 15 PART OF A MACRO FLOW CHART STN A MICRO O FLOW CHART I TOTAL 0 y ADD MARKS OF TOTAL TOTAL MARKS I ALL SUBJECTS GIVING TOTAL N Figure 1 7 Details of the processing block of Figure 1 3 for adding marks in 10 subjects flowchart with more detail is a micro flowchart For example let us consider the examination problem that we have already dis cussed in Examples 1 3 and 1 4 In all the flowcharts of the examination problem there is a processing box having the instruction ADD MARKS OF ALL SUBJECTS GIVING TOTAL In order to display how the values of TOTAL is calcu lated a detailed flowchart can be drawn as shown in Figure 1 7 In a similar manner the input output 1 0 boxes for the READ and WRITE operations can also be converted to a detailed flow chart 16 Flowcharting Concepts and Algorithms 1 2 Pseudocode or Metacode or PDL Pseudocode is another program analysis tool that is used for planning program logic Pseudo means imitation or false and Code refers to the instructions written in a programming lan guage Pseudocode therefore is an imitation of actual computer instructions These pseudo instructions are phrases written in or
71. owchart should give the result of the students scoring the percentage marks equal to or more than 30 ROLL NO 9999999 y ADD MARKS OF ALL SUBJECTS GIVING TOTAL y PERCENTAGE C STOP D TOTAL 10 IS PERCENTAGE gt 30 WRITE OUTPUT DATA y ADD 1 TO COUNT y Figure 1 6 Flowchart for example 1 3 12 Flowcharting Concepts and Algorithms The flowchart in Figure 1 6 is a solution to this problem There are two decision symbols in this flowchart The first deci sion symbol checks for a trailer record by comparing ROLLNO against the value 9999999 to determine if processing is complete The second decision symbol is used to check whether the student has passed or failed by comparing the percentage marks obtained by him against 30 If the student s PERCENTAGE is equal to or more than 30 then he has passed otherwise he has failed Note from the flowchart that the operation WRITE OUTPUT DATA is performed only if the student has passed If he has failed we directly perform the operation READ INPUT DATA without per forming the WRITE operation This ensures that the output list provided by the computer will contain the details of only those students who have passed in the examination Another point to be noted in this flowchart is the use of vari able COUNT This variable has been initialized to zero in the beginnin
72. own into major components each of which is again broken down if necessary Therefore the process involves working from the most general down to the most specific The design of the modules is reflected in hierarchy charts such as the one shown in Figure 1 47 Driver module INPUT Gross Net OUTPUT pay pay FET FICA NJIT Driver module PRINT Calculate Calculations INPUT Title monthly for detail PRINT Data Column heads payment lines Totals PRINT Detail lines Figure 1 47 Top Down modular Design 76 Flowcharting Concepts and Algorithms b 340 REM PROMPTS WILL SHOW ON THE SCREEN DATA WILL BE ENTERED 350 Each module has one entry point and one exit point The GOTO statement is never used to jump from one module in the program to another Pure structured programs do not use GOTO The following program in BASIC is an example of structured programming k k k k kkk INPUT DATA k k k k k kk kkk AT KEYBOARD 360 CLS CLEAR SCREEN 370 OKS N 380 WHILE OKS N 390 INPUT ENTER THE EMPLOYEE NAME EMPNAMES 400 INPUT ENTER THE HOURS WORKED HOURS 410 INPUT ENTER THE RATE PER HOUR RATE 420 INPUT ENTER THE NUMBER OF EXEMPTIONS EXMP 430 INPUT ENTER THE SALARY TO DATE SALDATE 440 PRINT PRINT 45
73. p 7 Print TOTAL FIRST DIVISION Step 8 Stop 1 6 Programming If we compare structured programming to building a house then structured programming is to build the house after the plan for the house is drawn We would like to build a house using stan dard bricks window frames doors etc so that the house so con structed iS appealing and comfortable Thus structured programming also contains three standard control structure These are Simple Sequence Simple Selection Simple Repetition The above three structures are simple to use as they can be recognised easily They have one entry and one exit point and they are free from any programming language used for coding a solution of a problem This is discussed in detail in section 1 8 1 6 1 Modular Top Down Program Design You must have realised that an effective approach to follow in the programming analysis stage of program development is to break down a large problem into a series of smaller and more under standable tasks Thus the programmer may first develop a main control program that is used to outline the major segments or modules that are in turn needed to solve a problem The main control program specifies the order in which each subordi nate module in the program will be processed The programming Flowchart Techniques 57 analysis stage continues until every module has been reduced to the point that the programmer is confident that he or she ha
74. preter is not saved If an instruction is used next time it must be interpreted once again and translated into machine code For example during the repetitive processing of the steps in a loop each instruction in the loop must be reinterpreted every time the loop is executed 1 10 13 Data Description Language Data description language DDL is a language used to define data and their relationships to other data It is used to create files databases and data dictionaries Hierarchical and network database management packages are used in large computers such as mainframes or mini comput ers In these systems large database packages are controlled by the database administrator whose job is to identify the logical relationships that exist in an organization s records A special data description language is used to retrieve the stored informa tion Programming skills are needed by those who work with these software products and DDL helps them to do the job more efficiently 1 11 What is Program Maintenance User requirements from a specific program do not remain static They change frequently in response to such factors as new laws new ideas new products or new computer facilities Program maintenance covers a wide range of activities including correct ing coding and design errors updating documentation and test data and upgrading user s support In other words maintenance may be viewed as enhancement i e adding modifying or de
75. programmer will rewrite program specifications to describe what each program in the system will do and how it will do it The equipment will be acquired and the program will be tested on the computer system Testing and Debugging The program so developed will be tested for conforming the specification laid down and the results achieved At the same time if there are any bugs in the system these will be removed and programs are re tested Implementation This is the stage when the new software becomes operational It is a critical phase of the project requiring careful timing coordination and training of all the user departments Maintenance All software need to be maintained It means per formance monitored modifications made if required errors cor rected documents kept up to date If the system needs Flowchart Techniques 91 major modification then the life cycle starts again It means the changes are done and the software development is once again carried out Training the User Since one purpose of the new software system is to change exis ting procedures training is crucial All individuals have to understand what is required by the new software system After the problems of installation have been resolved and the organi zation has adjusted to the changes created by the new software system the operational stage begins That is the system now operates on a routine basis However this routine does not mean that it rem
76. r it is more difficult to follow the logic or write the pseudocode as compared to flowcharting 1 3 Programming Techniques You can solve different types of business or scientific problems on a computer All you have to do is to analyse the problem write a step by step solution and translate it into a language under standable by a computer Flowchart Techniques 25 1 3 1 Problem Definition Let us take an example of a problem faced in day to day life Suppose you want to reach your school computer laboratory at 8 AM You would lay out a plan to get ready by 7 AM then takea bus rikshaw and reach at the gate of your school Then climb up the stairs to arrive in the laboratory For all these movements you will note the time taken for each part If due to some reason you are unable to get ready by 7 AM and you already know that it takes one hour to reach from house to school laboratory by bus rikshaw then you will take a faster means of transportation You may take an autorikshaw or a taxi Thus a very simple problem of reaching the computer laboratory of your school by 8 AM will need several steps for solution Each step is to be accu rately defined marked so that no guess work is necessary You can thus represent the solution of this problem in three steps shown in Figure 1 11 In Figure 1 13 steps 1 2 and 3 appear to be very simple In actual practice when you have to give instructions to a student whois going for the first t
77. re 1 17 Concept of looping It is the preparation required before entering a loop In Figure 1 17 step 2 initialises the value of A as 1 Incrementation t is the numerical value added to the variable each time one goes round the loop Step 4 in Figure 1 17 shows the increment of A by 1 34 Flowcharting Concepts and Algorithms BEGIN STEP 1 COUNT 1 STEP 2 STEP 3 INPUT NAME WAGE STEP 4 HOURS PAY WAGE x HOURS STEP 5 y PRINT NAME PAY 7 STEP 6 y COUNT COUNT 1 STEP 7 Figure 1 18 Flowchart for calculating the salary of 100 workers Flowchart Techniques 35 The Loop Variable t is an active variable in a loop In Figure 1 17 A is an active variable Loop Exit Test There must be some method of leaving the loop after it has revolved the requisite number of times In Figure 1 17 step 5 is the decision diamond where the value of A is com pared with 21 As soon as the condition is satisfied control comes out of the loop and the process stops Example 1 10 Solution Draw a flowchart for calculating the salary of 100 workers in a factory Figure 1 18 represents the flowchart In Figure 1 18 step 2 is for initialisation of the value of COUNT where COUNT is an active variable Step 7 is the incrementation Step 3 is for the EXIT test Steps 4 to 6 are the repetitive steps in the loop to input the NAME WAGE and HOURS and then calculate the value of PA
78. reliable if when used in a reasonable manner it does not produce failures that are dangerous or costly Software errors can cause failure of the sys tem or produce inaccurate results Programmers should therefore strive to design error free programmes The software errors are mainly due to design errors or specifications Hence these are also to be rechecked before studying the impact caused by the errors 1 11 4 The Problem of Software Modification The basic problems of modifying software can be attributed to time schedule and the user need satisfaction These are as fol lows Time schedule Modification of a program may not be feasible within the time schedule because of several reasons The reasons may be non availability of the right kind of manpower improper documenta tion of the old program or testing data For such cases the earlier version of the software will have to be used till all the errors are removed in the newer version after it has been tested thoroughly User need Satisfaction People who are using the program are the final evaluators of the modification Hence it should be found out whether these users are now Satisfied with the new version of the software or not Further how useful is the new software for them How enthu siastic are they about the friendliness and ease of working with the new software Answers to all these questions are to be evaluated and implemented 90 Flowcharting Concepts and Algorithms
79. s a solution method that will solve the task When this modular top down program design practice is used an instruction in the main control program branches con trol to a subordinate program routine Subroutine or module When the specific processing operation performed by the module is completed another branch instruction may transfer program control to another module or return it to the main control pro gram Thus the modules or subroutines are really programs within a program Each module typically has only one entry point and only one exit point Some of the advantages of using this construction option are a Complex programs may be divided into simpler and more manageable elements b Simultaneous coding of modules by several programmers is possible c A library of modules may be created and these modules may be used in other programs as needed d Thelocation of program errors may be more easily traced to a particular module and thus debugging and maintenance may be simplified e Effective usecan be made of tested subroutines prepared by software suppliers and furnished to their customers 1 6 2 Pseudo Code Revisited Pseudo code is an abbreviated form of expression that makes use of both the English language and certain programming language control words such as IF THEN ELSE amp END IF The user describes in plain English language the sequence of steps necessary to solve a particular problem Sentences are
80. s stage by dividing TOTAL by 10 and the result is stored in a memory loca tion which has been given the name PERCENTAGE The fifth symbol is an input output I O symbol and is labeled WRITE OUTPUT DATA Flowchart Techniques 7 START ADD MARKS OF ALL SUBJECTS GIVING TOTAL TOTAL 10 PERCENTAGE C STOP Figure 1 3 Flowchart for calculating percentage of marks Example 1 2 Draw a flowchart for calculating the average percentage marks of 50 students Each student appeared in ten subjects The flow chart should show the counting of the number of student who have appeared in the examination and the calculation should stop when the number of counts reaches the number 50 Since all the students have appeared in the same examina tion so the process of calculation and printing the percentage marks obtained by each student will basically remain the same The process of reading the input data adding the marks of all 8 Flowcharting Concepts and Algorithms C START COUNT 0 READ INPUT DATA l ADD MARKS OF ALL SUBJECTS GIVING TOTAL l PERCENTAGE TOTAL 10 l WRITE OUTPUT DATA i ADD 1 TO COUNT No Figure 1 4 Flowchart for example 1 2 Flowchart Techniques 9 subjects calculating the percentage and then writing the output data is to be repeated for all t
81. ted for During execution the appropriate path is fol lowed depending upon the result of the decision Connector If a flowchart becomes very long the flow lines start crisscrossing at many places that causes confusion and reduces the clarity of the flowchart Moreover there are instances when a flowchart becomes too long to fit in a single page and the use of flow lines becomes impossible Thus whenever a flowchart becomes too complex that the number and direction of flow lines is confusing or it spreads over more than one page it is useful to utilize the Flowchart Techniques No Yes a Two way branch COMPARE A amp B A B b Three way branch 0 TIE 2 3 4 5 Other q at _ c Multiple way branch Figure 1 2 Different decision symbols with different ways of branching 6 Flowcharting Concepts and Algorithms connector symbol as a substitute for flow lines This symbol rep resents an entry from or an exit to another part of the flowchart A connector symbol is represented by a circle and a letter or digit is placed within the circle to indicate the link A pair of identically labeled connector symbols are commonly used to indi cate a continued flow when the use of a line is confusing So two connectors with identical labels serve the same function as along flow line That is they show an exit to some other chart section or they indicate an entry from another part of the chart
82. the condition is not true do pro cess 2 Thus in this case either process 1 or process 2 will be executed depending on whether the specified condition is true or false However if we do not want to choose between two pro cesses and we simply want to decide if a process is to be per formed or not then the IF THEN structure is used FLOWCHART PROCESS 1 y PROCESS 2 v PSEUDOCODE e e e Process 1 Process 2 e e Figure 1 8 Pseudocode for sequence structure 18 Flowcharting Concepts and Algorithms The IF THEN structure says that if the condition is true then do process 1 and if it is not true then skip over process 1 In both the structures process 1 and process 2 can actually be one or more processes They are not limited to a single process END IF is used to indicate the end of the decision structures FLOWCHART ROLL NO 9999999 YES y PROCESS 2 PROCESS 1 as M PSEUDOCODE If Condition THEN process 1 ELSE process 2 END IF e Figure 1 9 Pseudocode for If Then Else structure Flowchart Techniques 19 FLOWCHART NO YES PROCESS 1 ls PSEUDOCODE e e e IF CONDITION THEN PROCESSI END IF e Figure 1 10 Pseudocode for If Then selection structure 1 2 3 Iteration Logic Iteration logic is used when one or more instructions may be executed sev
83. to control the loop In this method the end of input data is marked by a trailer record that is the last data record in the input is followed by a record whose main purpose is to indicate that the end of the input data has been reached Suppose the first 7 characters of the input record of a student represents his roll number ROLLNO Since 0000000 is never used as a roll num ber a value of 0000000 as the first 7 characters can be used to represent the traile record As each input record is processed the ROLLNO can be compared with 0000000 to determine if pro cessing is complete The logic of this process is illustrated in the flowchart given in Figure 1 5 10 Flowcharting Concepts and Algorithms ADD MARKS OF STOP ALL SUBJECTS GIVING TOTAL PERCENTAGE TOTAL 10 Figure 1 5 General flowchart for example 1 2 What is Trailer Record The concept of a trailer record centers around the notion of selecting a field a particular item of data in the input record which will be used to indicate the end of data and then selecting a trailer value also Known as sentind value which will never occur as normal data value for that field The roll number 0000000 is a trailer record for Example 1 2 Flowchart Techniques 11 Example 1 3 Extend the flowchart represented in Figure 1 5 to count the number of students who have scored percentage marks more than 30 The fl
84. vel oping the code to support changes in the specifications 1 11 1 Why Program Maintenance Although software does not wear out like a piece of hardware it ages and needs to be updated for the following reasons a Errors are found that were not detected when the system was tested initially Even though the system was thoroughly tested errors or bugs often appear after the system has been in use for some time 88 Flowcharting Concepts and Algorithms b A new function may have to be added to the system For example the school management had initially asked for the preparation of monthly report of those students who had not paid their feein time But at a later date the auditors or the principal of the school needs a report of those students who are defaulters in paying their fee for more than three months so that their names can be struck from the school In such a case the report format will need a change c Alteration in the original program may cause errors else where in the program and detected later This will require modifications in the program d The final reason for program maintenance is that the requirements of the user change with time For example programs that produce income tax returns have to be modi fied almost every year because of changing tax laws 1 11 2 Problem Areas in Program Maintenance Two problem areas in program maintenance are a high cost of software and b errors caused due to modi
85. which it produces machine codes 1 10 11 Compiler A program which translates a high level language program into a machine language program is called a compiler A compiler is more intelligent than an assembler It checks all kinds of limits ranges errors etc But its program execution time is more and occupies a larger part of the memory It has low speed and low efficiency of memory utilization If a compiler runs on a computer for which it produces the object code then it is known as a sdf or resident compiler If a compiler runs on a computer other than that for which it produces object code then it is called a cross compiler 1 10 12 Interpreter An interpreter is a program which translates one statement of a high level language program into machine codes and executes it In this way it proceeds further till all the statements of the pro gram are translated and executed On the other hand a compiler goes through the entire high level language program once or twice and then translates the entire program into machine codes A compiler is nearly 5 to 25 times faster than an interpreter An interpreter is a smaller program as compared to the compiler It occupies less memory space It can be used in a smaller system which has limited memory space The object program produced by the compiler is permanently saved for future reference On the Flowchart Techniques 87 other hand the object code of the statement produced by an inter

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