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SQA Higher Computing Unit 2 Software Development

1. 157 A A TA A O Ari OS nr pip ck 159 6 16 The Select Case Statement 164 61 ASUMMARY bo eee a A A WE lee aiia 170 6 18 Endoftopictest 170 Prerequisite knowledge Before studying this topic you should be able to describe and use the following constructs in pseudo code and a suitable high level language input and output numeric and string variables assignment statements arithmetical operations logical operators AND OR NOT conditional loops using fixed and complex conditions IF statement nested loops Learning Objectives understand the need for programming variables understand and be able to use real integer string and boolean variables understand string operations such as concatenation and substrings be aware of local and global variables understand what is meant by the scope of variables understand the nature and use of sub procedures understand the use of selection in programming an in particular the CASE construct HERIOT WATT UNIVERSITY 2006 107 Revision e Q1 Which one of the following program constructs does NOT represents the process of selection a The IF THEN statement b The FOR NEXT loop c The CASE statement d The DO WHILE loop Q2 One of the following program statements produces the value 13 for the variable Answer Which one Answer 5 8 3 2 Answer 5 8 3
2. 2 12 Alternative models 11 12 13 14 15 15 16 17 18 19 19 20 20 21 21 22 23 23 24 25 26 28 29 29 30 30 31 32 33 34 35 10 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS 2121 SSADM ui a ee 35 2 12 2 Prototyping ss 2 ER E e o 36 2 12 3 Rapid Application Development RAD 37 2 12 4 Commercial Off The Shelf COTS 38 2 12 5 Spiral model 38 2 12 6 Open Source 38 2 13 SUMMALY a oS a eee ea dt 39 2 14 End of topic test a s ee ea ek A gE Pa AA Me a wal 39 Prerequisite knowledge Before studying this topic you should be able to e describe the following stages of the software development process analysis design implementation testing documentation evaluation maintenance e describe and be able to use test data normal extreme and exceptional e describe the features of a user guide and a technical guide e evaluate software in terms of fitness for purpose user interface and readability Learning Objectives e understand the iterative nature of the software development process e understand each stage of software development e identify various models of the software development process e understand the purpose of the software specification and its status as a legal contract e understand and be able to describe corrective adaptive and preventative maintena
3. 2 11 Weaknesses of the Waterfall Model 2 12 Alternative models 2 13 Summary 2 14 End of topic test 3 1 Introduction Design notation data flow and evaluation 3 2 Tools and Techniques 8 il ANA hat dns ADA A 3 3 Design methodologies 6 fe ne out a Sle ah eae se tre Da 3 4 Test Data 3 5 Structured Listing 242 44 6 ve Le ses ele des Sieve aloe 3 6 Error Reporting 3 7 Module libraries 3 8 CASEtools 3 9 Software characteristics 3 10 Summary 3 11 End of topic test I O O1 BP D D 11 12 13 21 21 24 26 30 32 33 34 35 39 39 41 43 44 44 53 57 57 61 62 62 64 65 CONTENTS 4 Personnel 67 AL CANTO AUCHON t irc a o A les a y a 68 4 2 Personnel xs t al e a us Boe epee BRE aot il 68 AB AMOS MONE Le at AA e AE rie eue ER te peda 68 4 4 The Project Manager 4 242 428 Hans Gwe el Re air Re 69 45 Th Systems Analyst o cimas ds pt han he ta ee da 70 4 6 The Programming Team 2 2 aaa ee eA 408 e an 74 4 7 Independent Testing Group 75 48 Summary A rares A ar ons 77 49 Endoftopictest 77 5 Languages and Environments 79 Bid Intoduetiont ssa aoe se ee eur aus mean ul a porn nu 81 5 2 Programming Languages 82 5 3 Classification of High Level Languages 82 5 4 Imperative la
4. HERIOT WATT UNIVERSITY 2006 6 7 DECLARING VARIABLES 127 Options Editor Editor Format General Docking Enviranment Advanced Code Settings NM Auto Syntax Check V Auto Indent Tab Width 4 M Auto List Members z M Auto Quick Info M Auto Data Tips Window Settings V Drag and Drop Text Editing M Default to Full Module View IM Procedure Separator Figure 6 4 The program of Code 6 2 can now be re written as Option Explicit Private Sub Form_load Dim FirstNumber As integer Dim SecondNumber As integer Dim Total As integer Dim MyText As string FirstNumber 5 SecondNumber 10 Total FirstNumber SecondNumber MyText Sample Program End Sub Code 6 3 HERIOT WATT UNIVERSITY 2006 128 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 6 8 Declaring constants A constant is a quantity that is allocated by the user usually at the start of a program with variables although they can be defined anywhere in the program A constant retains the same value throughout program execution and cannot be altered Constants are declared using the const statement to create string or numeric values Examples of constant declarations are Const cPi As single 3 141592 Const cAvogadro 6 023E23 Const cName This is my name Like variables if a constant is not defined then it will be assigned the variant type Some programmers like to express constants all in capital letters to differentiate them
5. Form Monday is a weekday thursday is a weekday Saturday is the weekend anuan is not a day sunday is the weekend april is not a day Exit Program Figure 6 19 It is really important that you study this example carefully You will probably use the case statement a lot This program uses the case statement to check whether the letter typed in by the user matches s Saturday and Sunday m Monday t Tuesday and Thursday w Wednesday or f Friday If the match is with s it can only be a weekend All other matches must be week days Note Here you are comparing with the single character and not the entire string called Day so single quotes are required to show that you are using a character In order to test the first character of the string Day the Visual Basic in built function Left is used HERIOT WATT UNIVERSITY 2006 169 170 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 For example Left Monday 1 would produce the character M Musical Notes Sentence completion case statement On the Web is a interactivity You should now complete this task Learning Objective 40 min Be able to use the switch statement a b c d e f and g are valid musical notes Write a program that allows the user to input a character and uses a CASE statement to test and display if the character is a valid musical note 6 17 Summary The following summary points are related to the learning objectives i
6. HERIOT WATT UNIVERSITY 2006 ANSWERS TOPIC 2 Answers from page 25 Q21 c It can make running a program a less irritable experience Q22 b The requirements Q23 c Assembler Q24 d All of these Q25 a To allow for faster processing Answers from page 29 Q26 b Testing is done within the organisation Q27 c No computers are involved Q28 a The program is tested by the clients Q29 b You cannot account for all possible errors Q30 a The input of silly data HERIOT WATT UNIVERSITY 2006 271 272 ANSWERS TOPIC 3 3 Design notation data flow and evaluation Revision page 43 Q1 c It is very useful in complex program designs Q2 d They can reduce the overall development time of a program Q3 b English and high level language code Q4 c Maintenance Q5 a An input error Answers from page 52 Q6 Q7 Q8 Q9 Q10 d All of the above b It is breaking complex problems down into smaller units d All of the above a Thinks more about the solution to the problem c Makes the process more complex to novices Answers from page 56 Q11 Q12 Q13 Q14 Q15 To determine that the system meets the specification Output statements at key points in the code a b b Testing can never show that a program is correct c Design input routines that will not crash when presented with unexpected data a They could remain hidden until the program
7. Since some of the programs can be quite complex they are dealt with in meaningful chunks and more of this will be dealt with later Example 1 Calculating the average temperature Problem Write a program to access each of the temperatures of a room over 14 days which are to be held in an array Calculate the average temperature during the period No display of the results is required Solution First try A typical solution to this problem is shown in Code 7 10 Option Explicit Private Sub Commandi_Click program CalculateAverageTemp program to calculate average temperature 20th February 2004 Program by Fred Fink Dim Store 14 As Single Dim total As Single average As Single Temp As Single Dim day As Integer HERIOT WATT UNIVERSITY 2006 210 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 total 0 0 initialise total program now puts the values into the Store array For day 0 To 13 Temp InputBox Enter temperature of day PicValues Print day Store day Temp total total Store day PicArray Print Store day Next day average total 14 PicResult Print Format average standard End Sub This file Average Temp txt can be downloaded from the course web site Code 7 10 Second refinement The program in Code 7 10 does not yet deal with inputting values into the temperature array One solution to this could be to hardcode the temperature array values into the program although this does not
8. Arithmetic operators are evaluated in the following order of precedence Arithmetic operator precedence Parentheses Exponentiation Negation Multiplication and division Integer division Modulus arithmetic Mod NII BR WO ND Addition and subtraction HERIOT WATT UNIVERSITY 2006 139 140 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Example 1 Operator precedence 4 5 2 Problem What is the result of 4 5 2 Solution The multiplication is calculated first then the addition since multiplication has a higher precedence than addition e g 4 5 2 4 10 14 and so 4 5 2is equal to 14 Example 2 Operator precedence 4 5 2 Problem What is the result of 4 5 2 Solution The expression in the brackets is calculated first then the multiplication the brackets have altered the order of precedence e g 4 5 2 9 x 2 18 and so 4 5 2 is equal to 18 Example 3 Operator precedence 3 7 5 42 4 Problem What is the result of 3 7 5 12 4 Solution The expression in brackets is evaluated first then exponentiation followed by multiplication then addition i e 7 5 72 4 272 4 4 4 16 1 mw Ww ww and so 3 7 5 2 4 is equal to 19 Matching operations and results On the Web is a interactivity You should now complete this task HERIOT WATT UNIVERSITY
9. integer division 1617 2 mod modulus operator 25 mod 7 4 A raise to the power 1013 1000 It is important to remember that integer division gives you a whole number answer only any remainder is discarded For example HERIOT WATT UNIVERSITY 2006 6 10 OPERATORS 5 2 gives 2 as the answer 16 5 gives 3 as the answer The modulus operator is used for division to obtain the remainder The expression x mod y produces the remainder when x is divided by y The mod operator can be applied to integers and also with real For example 5 mod 2 gives 1 8 mod 3 gives 2 9 mod 3 gives O zero 7 1 mod 3 1 gives 1 numbers rounded down 10 8 mod 3 6 gives 3 numbers rounded up Make sure you understand why 6 10 1 Operator precedence When several operations occur in an expression each part is evaluated and resolved in a predetermined order called operator precedence Parentheses can be used to override the order of precedence and force some parts of an expression to be evaluated before other parts Operations within parentheses are always performed before those outside Within parentheses however normal operator precedence is maintained When multiplication and division occur together in an expression each operation is evaluated as it occurs from left to right Likewise when addition and subtraction occur together in an expression each operation is evaluated in order of appearance from left to right
10. 195 196 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Guess my age 60 13 too high 16 is too low 45 is too high 18 is too low 31 is too high 23 is too highl 22 is too high Ok so its 21 but it took you 8 tries Figure 7 10 Example 2 Use of two do until loops to output a number series like Fibonacci numbers and to validate the input Problem Write a program to output numbers belonging to the Fibonacci series up to a specified maximum Solution Fibonacci was a famous Italian mathematician who identified the following series of numbers a ty e Sy wy Bs sra Successive terms of the series are calculated by adding the previous two numbers The following algorithm will produce the series given the first two values as input Do input number of terms to output loop until input is within range input two starting values do compute numbers display numbers loop until number of terms have been output o J oanP WYN FE HERIOT WATT UNIVERSITY 2006 7 4 DOLOOPS 197 Option Explicit Private Sub Command1_Click program Fibonacci 217th February 2004 gt Program by Fred Fink This program will prompt the user to input the maximum value of terms to be displayed Two starting values are also input Dim NoOfTerms As Integer First As Integer Second As Integer Dim Third As Integer Count As Integer PicDisplay Cls PicDisplay2 Cls Do NoOfTerms InputBox How many terms to display Validation check Loo
11. Dim numberOk As boolean do Print Input a number numberOk number gt 0 if not number0k then print The number must be greater than 0 end if loop until number0k End sub Answer function getValidNumber As integer Dim numberOk As boolean Dim number As Integer do print Input a number numberOk number gt 0 if not numberOk then print The number must be greater than 0 end if loop until numberOk getValidNumber number end function Write a program to add two validated numbers together First use the sum function and the getValidNumber procedure Then write another program using the sum and getValidNumber functions Answer Using the procedures program sumi Dim first As integer second As integer Sub getValidNumber ByRef number As integer Dim numberOk As boolean do print Input a number number0k number gt 0 if not numberOk then print Make it positive end if loop until numberOk end sub function sum a as integer b as integer as integer sum a b HERIOT WATT UNIVERSITY 2006 8 4 FUNCTIONS end function Main program getValidNumber first getValidNumber second print The total is sum first second Using the functions program sum2 Dim first as integer second as integer function getValidNumber as integer Dim number0k as boolean Dim number as integer do print Input a number numberOk number gt 0 if not numberOk then print Make
12. Hint 1 shows several years and indicates whether they are leap years or not This data could be used to test your program Table 8 2 Table 8 2 Calculation of leap years Year Is a Leap Year 1900 No 1996 Yes 2000 Yes 2001 No HERIOT WATT UNIVERSITY 2006 270 ANSWERS TOPIC 2 Answers to questions and activities 2 Features of Software Development Process Revision page 11 Q1 Q2 Q3 Q4 Q5 c Design implementation documentation evaluation b Certain stages of the process are re visited to make sure all is well d All of these a Plenty of colour b It is part of the design stage of the software development process Answers from page 14 Q6 Q7 Q8 Q9 Q10 c The evolution of software systems were disorganised d Analysis design testing evaluation a The model will be more realistic d All of the above b To enable personnel to discuss progress Answers from page 16 Q11 Q12 Q13 Q14 Q15 Top down design requirements specification a c d All of the above b Robust a A description of how the program should operate Answers from page 20 Q16 Q17 Q18 Q19 Q20 Testing finds faults and debugging removes them lt makes the program run more reliably c c b The final program meets the original specification d All of these a Structured program listing installation guide user guide technical guide
13. Private Sub BlankLines ByVal Number as Integer Dim count As Integer For count 1 To Number Print Next Count End Sub Code 8 1 By calling BlankLines 5 in the main program the formal parameter Number in the procedure declaration block is passed the actual parameter value 5 The procedure code is executed and then terminates Note that the formal parameter is preceded by the Visual Basic keyword ByVal to indicate a value parameter This is optional but if left out then Visual Basic will default to ByRef which indicates a call by reference see later The following worked example will help you understand passing by value Example 1 Use of procedures with value parameters Problem Write a program that outputs the square and square root of a number that is input by the user This number will be passed to each of the procedures Solution The following algorithm uses two procedures with va ue parameters Set up variables Validate user input call sub procedure square procedure 1 call sub procedure sqrRoot procedure 2 display results end program OoFr WN H HERIOT WATT UNIVERSITY 2006 230 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS The full Visual Basic program is shown in Code 8 2 Option Explicit Private Sub Command1_Click Main Program gt Program by Fred Fink 25th February 2004 This program exemplifies the use of value parameters Dim ActualValue As Integer Do ActualValue InputBox Input a
14. Q20 Using the same array set array 0 7 What are the array contents now a array 0 O O 0 b array 3 7 0 0 c array 8 0 7 0 d array 7 3 0 0 e array 0 3 7 0 f array 7 0 3 0 g array 0 7 3 0 h array 0 7 0 3 i array 0 0 7 3 HERIOT WATT UNIVERSITY 2006 7 5 ARRAYS 207 j none of the above Q21 Set up a 4 element array with a subscript range of 0 3 with the following values array 3 6 2 8 What is the value of array 2 Q O 0 9 ZX a D Ww e none of the above Q22 In the same array as the previous question what is the value of the element with index 0 a0 0 9 YS Power ar wa D OO Ww e none of the above Q23 Set up an 8 element array with a subscript range of 0 7 e g array 8 23 5 19 3 0 7 52 Now set array 1 12 What are the array contents now a array 8 23 5 19 3 0 7 52 b array 12 23 5 19 3 0 7 52 c array 8 12 5 19 3 0 7 52 d array 8 23 12 19 3 0 7 52 e array 8 23 5 12 3 0 7 52 f array 8 23 5 19 12 0 7 52 g array 8 23 5 19 3 12 7 52 h array 8 23 5 19 3 0 12 52 i array 8 23 5 19 3 0 7 12 none of the above Q24 Again starting with an 8 element array with a subscript range of 0 7 e g array 8 23 5 19 3 0 7 52 Set array 3 9 element with index 6 11 and array 6 4 What ar
15. Super Class Sub Class Sub Class Sub Class Objects Kitty Puss This property of object oriented programming forces a more thorough data analysis reduces development time and ensures more accurate coding Java One of the first object oriented computer languages was called Smalltalk C and Java are the most popular object oriented languages today In fact Java is an example of a language that is platform independent The Java compiler produces a sort of machine code called bytecode This can t run directly on any machine Rather it runs the Java virtual environment This is a piece of software that is specially designed for the architecture of the computer in question This is freely available on the internet and enables the computer to run Java programs A Java enabled computer whatever the architecture can run bytecode i e if Java is written on a Sun workstation the program will run on PCs and Apple Macs HERIOT WATT UNIVERSITY 2006 97 98 Ea Es ES TOPIC 5 LANGUAGES AND ENVIRONMENTS Object orientation On the Web is a interactivity You should now complete this task Derived classes On the Web is a interactivity You should now complete this task Inheritance On the Web is a interactivity You should now complete this task 5 9 Functional languages Functional programming emphasizes the evaluation of expressions rather than execution of commands The expressions in such languages are formed by using
16. Team Count Next Count Print End Sub HERIOT WATT UNIVERSITY 2006 85 86 TOPIC 5 LANGUAGES AND ENVIRONMENTS Notice that 1 the program is expressing at each step precisely how each statement is executed 2 the program has beginning and end points which is an indicative feature of imperative coding The program output is Form Leith Leamers Bonaly Boys Royston Rovers Calder Colts Juniper Juniors Wardie Wanderers Structures in procedural languages On the Web is a interactivity You should now complete this task 5 4 1 Review Questions Q6 One of the main reasons for the many programming languages existing is Older languages can no longer function in the present day computer systems Languages have to be adapted so new versions are released There are many different types of operating system People devise new languages because they do not like existing ones a b c d Q7 Which one of the following lists only contains general purpose programming languages Pascal C Basic Comal Algol Fortran Prolog Comal Basic Algol Pascal Comal a b c d Fortran Basic Comal Algol HERIOT WATT UNIVERSITY 2006 5 5 DECLARATIVE LANGUAGES 87 Q8 In computer programming there are three basic constructs Which one of the following is NOT a programming construct a Sequence b Selection c Iteration d Moderation Q9 Which one of the following languages could b
17. gt the variables used in the program main parts of the program INPUT PHASE read in data from keyboard file mouse etc CALCULATION process the data to give us the results we want HERIOT WATT UNIVERSITY 2006 6 4 PROGRAM STRUCTURE OUTPUT send results to a window printer file disk etc End sub Sub procedures Procedure and function definitions End Sub Code 6 1 The program area contains the following A general area this area is public and variables declared here will be seen by all parts of the program More on this will be discussed later under the term scope A sub procedure cmd_click this contains the main program code that will be initiated in the event of a mouse click for example Within this code there are further declarations local to the sub procedure The declarations are Constants any fixed values which will stay constant throughout the program are declared here Variables variables other than global variables that are going to be used in the program are declared here Sub procedures any subprocedures required by the program are declared after the main sub procedure These are described more fully later on Functions any functions the program will use are also declared here These are described more fully later on The input may be from a variety of devices not just the keyboard A disk is an input device when the computer reads data including programs from it The pro
18. sum first second end function Using the functions program sum2 dim first as integer second as integer function getValidNumber as integer dim number0k as boolean dim number as integer do number Inputbox Input a number numberOK number gt 0 if not numberOK then Print Make it positive end if loop until number0K getValidNumber number end function function sum a as integer b as integer as integer sum a b end function main program first getValidNumber second getValidNumber Print The total is sum first second Answers from page 247 Q11 a A function does not need to be declared Q12 c Square Q13 b y ABS 5 HERIOT WATT UNIVERSITY 2006 283 284 ANSWERS TOPIC 8 Q14 d A procedure or function can call itself Q15 d 12 HERIOT WATT UNIVERSITY 2006
19. test FALSE condition rest of program Figure 7 6 The do while loop is an example of a top tested while true structure The variant do loop while is an example of a bottom tested while true structure Do statements Loop while test condition The top tested loop can iterate between 0 and N times whereas the bottom tested loop may iterate between 1 and N This means that using the bottom tested loop the iteration must occur at least once so the condition can be tested immediately Care should be taken when writing programs using loops as an incorrect condition or mistakes in the body of the loop can cause the program to get stuck in an infinite loop when executing even when compilation produced no errors Should this occur in Visual Basic simply click on program Run and choose End In more extreme cases pressing ctrl alt delete will allow you to abort Visual Basic 7 4 2 Examples of Do While Loop Example 1 Calculating a sum of positive integers Problem A program is written to accept positive numbers from the keyboard calculate and display a sum of all the numbers entered lt uses a do while loop which tests whether each number entered is greater than or equal to zero If the user enters a negative number then the loop will terminate and the total will be displayed on the screen HERIOT WATT UNIVERSITY 2006 187 188 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Solution The algorithm is shown below set
20. Example 1 Problem What is the output of the following code Dim Numberi As Integer Number2 As Integer Number 1 10 Number2 5 if Numberi gt Number2 then Print Numberi is biggest else Print Number2 is biggest End if Solution This piece of code first declares two integer variables Number1 and Number2 Number1 is assigned a value of 10 and Number2 is assigned a value of 5 The condition for the if statement is is Number1 greater than Number2 If this is true then the statement Number1 is biggest is displayed If the condition is false then the statement Number is biggest is displayed on the screen In this case the condition is true since Number1 has a value of 10 which is greater than the value of 5 that has been assigned to Number2 and so the output from this code is Number1 is biggest Example 2 Problem What is the output of the following code Dim Valuei As Integer Value2 As integer Valuel 10 Value2 0 if Valuel lt gt 0 and Value2 lt gt 0 then Print One else Print Two End if Solution This condition for the if statement uses a logical and It is testing if Value is not equal to zero and if Value2 is not equal to zero In this case Value1 is equal to zero true but Value is not false Therefore the whole expression is false and the text Two would be printed on the screen Which is bigger Write a program which prompts a user to type in two numbers first one then the other
21. Next Counter End Sub Code 7 2 Note that in this case the output has been formatted using the SPC function This allocates a number of spaces between output items depending on the value expressed within the function The program also uses the CHR function to convert a numerical value to its corresponding character For example Chr 65 returns the character A Part of the program output is shown in Figure 7 3 HERIOT WATT UNIVERSITY 2006 7 2 ITERATION w For Next Integer Character 90 89 88 87 66 85 84 83 82 81 80 79 78 77 ZZODODAIACIEX lt N Prt ee Execute For Loop Neccececcscecesesmccscecssessscessmscesessecessesssemsses Figure 7 3 7 2 2 Nested For loops For Next loops can be nested to allow the programming of loops within loops Example 1 Use of nested loops Consider the Visual Basic program in Code 7 3 See if you can visualise what the output will be before looking at the results screen Option Explicit Private Sub Commandi_Click 16th February 2004 Program by Fred Fink This program will illustrate nested loops Dim Outer As Integer Inner As Integer For Outer 1 To 15 For Inner Outer To 15 PicDisplay Print Inner Next Inner HERIOT WATT UNIVERSITY 2006 179 180 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 PicDisplay Print Next Outer End Sub This file NestedlF2 ixt can be downloaded from the course web site Code 7 3 In this program the
22. Print size is in range Else Print size is out of range try again size InputBox What size is required End If Loop Print Out of loop End Sub This file RangeCheck txt can be downloaded from the course web site Code 7 7 Sample program output is seen in Figure 7 8 HERIOT WATT UNIVERSITY 2006 191 192 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Do while 15 is in range Out of loop 5 is out of range try again 25 is out of range try again O is out of range try again 10 is in range Out of loop 20 is in range Out of loop giteeesenmerenccesenessssemessaseressenssrmenssenssonars Run program Necsececeascecescscecsssesmescsssesssecserascsssscececes Figure 7 8 Q11 What is wrong with the following n 0 assume n is an integer do while n lt 100 value n n loop Q12 What is wrong with the following i 1 assume i is an integer do while i lt 10 Print i 1 i3 1 Q13 Write a while loop that calculates the sum of all numbers between O and 20 inclusive Hint use two integer variables one for a loop counter and one for keeping a running total of the numbers 7 4 3 Do Until Loop The while do loop performs the conditional test first and then executes the loop so the statements within a loop may never be executed The do until loop performs the statements first and then tests the condition This means that the body of the loop is always executed at least once Th
23. eg Apple Macintosh 5 3 Classification of High Level Languages At the time of writing it has been estimated that around 2 400 programming languages have been catalogued over the years For further information and a chance to download a time line of language development HERIOT WATT UNIVERSITY 2006 5 3 CLASSIFICATION OF HIGH LEVEL LANGUAGES as a poster consult the following links http people ku edu nkinners LangList Extras langlist htm http www levenez com lang history html 08 Classification of programming languages is fraught with problems since as you will see many languages can fall into more than one category Historically programming languages were classified according to whether they were a general purpose language that could be applied to a broad range of situations or a special purpose language that were designed for specific tasks Table 5 1 summarises the main high level languages and variants Table 5 1 Historical classification of programming languages Area Language s Purpose General ALGOL ALGOL 60 Coding of general algorithms ALGOL 60 purpose ALGOL 68 was the first defined language i e code AL GOrthimic produced identical results on any Language mainframe computer world wide Also introduced procedural programming and parameter passing Derivations are Pascal C C and COMAL Scientific FORTRAN FORmula Developed in the 1950 s for use in TRANslation
24. members of the public Bottom up design A method of program refinement that starts with individual modules and builds them up into a complete program Boundary testing Running a program with test data that represents the extreme upper and lower values Within this range the program should operate normally Bugs A bug is a program error Bytecode This is produced by JavaScript and is a form of machine code that runs under the Java virtual environment The latter is freeware and enables any computer to run Java programs Client The person or group that initiates the development process by specifying a problem Compiler A program that translates a complete high level language program into an independent machine code program Concatenation Joining of Visual Basic string variables to make longer strings using the amp operator Corrective maintenance Correction of previously undetected errors during development that is now apparent after installation of the software on the client site HERIOT WATT UNIVERSITY 2006 GLOSSARY 261 COTS Commercial Off The Shelf software An alternative software development system that allows programmers to purchase ready made software Can be an expensive option Data Unstructured information A collection of numeric or alphanumeric characters which can be processed by a computer Raw data is meaningless to people Database An organised and structured collection of related data Data modelli
25. the variable and change its value The scope of a variable is determined not only by the type of declaration but also the declaration s location For instance the Dim keyword assumes different meanings in different parts of a form s code In Visual Basic variables can be declared as shown in Figure 6 8 Declarations section PE Piojecli Ford Code Command Click Option Explicit Public variableGLOBALL Public variable visible throughout program Private varimbleLOCAL 1 Global variable visible to entire form Din variableGLOBAL1 Global variable visible throughout program Private Sub Commandi Click Dir variableLOCBL Local variable only visible within sub procedure End Sub Private sub procedure Figure 6 8 1 If a variable is declared in the general declarations section with the Dim statement then it is Public or Global to the entire program 2 If itis declared as Public in the general declarations section then it is Global to the entire program 3 If it is declared Private in the general declarations section then it is Global to the entire form and modules 4 If declared within the sub procedure then the variable becomes Local to that sub procedure and will not be recognised elsewhere Consider the following program in Code 6 7 Option Explicit gt Program to demonstrate global and local variables Public TestVariable As Integer Dim TestString As String Private Sub ExecuteMain_Click Tes
26. 1 Review questions 2 8 2 The Analysis SILAGE na ia ii Se a cS 2 3 3 The Design Stage 2 3 4 Review questions 2 3 5 The Impleme ntatiO Stage Tea eae ar a Hope eae Hdd 2 3 6 The Testing Stage 2 3 7 The Documentation Stage 2 3 8 The Evaluation Stage 2 3 9 The Maintenance stage 2 3 10 Review questions 2 4 Analysis in closer detail 2 5 Design in closer detail 2 5 1 The human computer interface 2 5 2 Data structur CR UE mener EA O at ne M TO GE a yal at aie A aa 2 5 3 The Main program 2 6 Implementation in cl ser detal s 55 25 5 si a NU pig ed 2 6 1 Review questions 2 7 Testing in closer detail 2 7 1 Alpha testing 2 7 2 Beta testing 2 7 3 Review questions 2 8 Documentation in closer detail 2 8 1 User guide 2 8 2 Technical gui A bam BA wes ENS A ahaa oat ph oe sarees ahi a 2 9 Evaluation in more detail 2 10 Maintenance in closer detail 2 11 Weaknesses of the Waterfall Model
27. 2006 6 11 PROGRAMMING CONSTRUCTS si 6 11 Programming constructs Structured programming is based on three constructs e sequence e selection e repetition 6 11 1 Sequence This is the computer s basic mode of operation This is how it s designed to work A computer is designed to carry out an instruction and move automatically onto the next instruction A program is working in sequence when it e begins at the beginning e carries out each statement or instruction once and only once e stops when it s reached the end In other words it misses nothing out which happens under selection and it does nothing more than once which happens under repetition Sequence is the default mode of operation for a program a program works in sequence unless it is explicitly told to do otherwise by means of one of the other programming constructs Left to itself it will always carry out a statement and proceed automatically to the next Example of simple sequence The program examples you have seen so far follow simple sequences Try the following activity Problem A program is written to ask the user to enter a number at the keyboard The program then doubles it and displays the result on the screen Code the following algorithm in Visual Basic and run the program request a number from the user get the number typed in by the user double the value of the number display the new value on the screen e NN Sequential control
28. 5 1 Introduction This topic will introduce you to the various types of programming languages that would be available at the implementation phase of the software development process As you will see the choices are numerous and expertise is required in matching the system specification with the most appropriate programming language available How programming languages translate source code into object code is further explained emphasising the advantages and disadvantages of the methods used HERIOT WATT UNIVERSITY 2006 82 TOPIC 5 LANGUAGES AND ENVIRONMENTS 5 2 Programming Languages In this topic and others all language features are exemplified using Visual Basic During the implementation phase of the software development process the program specification will now be coded using a suitable high level programming language High level languages help software developers to identify more with the problem rather than the hardware on which the final program will run i e they are problem oriented Program statements and expressions in such languages generally incorporate English words which mean that they are easier to understand and use than assembly code There are many programming languages that could be used for the implementation phase of software development such as C and C Pascal and Java Older languages still much used include Cobol and Fortran Cobol is used mostly on main frames for batch processing organisations still use it
29. And Not Found If List Pointer SearchKey Then Found True PicResult Print Search item SearchKey found at position HERIOT WATT UNIVERSITY 2006 252 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS Pointer Else Pointer Pointer 1 End If Loop If Not Found Then PicResult Print Search item SearchKey is not in list End If End Sub Private Sub Command2_Click End End Sub This file Linear txt can be downloaded from the course web site Code 8 7 Linear Search 2 61 30 82 90 38 79 26 13 39 95 35 35 48 68 49 23 Seareh item 68 found at position 14 End Program Figure 8 8 The linear search is not a very efficient strategy since each array element has to be compared with search key until a match is found For example it can be shown that for an array holding 1000 items an average of 500 comparisons will be made If the data items are ordered however then the search time can be improved but in this instance a binary search is significantly faster Despite the large number of comparisons required to find an entry it is probably the fastest technique for small arrays It is also the most simplistic in terms of coding It may also be the only method to search larger unordered tables of data HERIOT WATT UNIVERSITY 2006 8 6 STANDARD ALGORITHMS 253 Searching a list of names Write a program that will search a list of names for a given name You should consider the following tests
30. Because the output is First and Second the value of Count is halved otherwise the output would be twice that required i e Do Until Count NoOfTerms 2 2 Also the value of NoOfTerms is decreased by 2 to take into account the first two values which are output first and are not part of the loop Sample program output is shown in Figure 7 11 Fibonacci Fibonacci numbers 11235813 21 34 55 89 144 233 377 610 987 No of terms 16 f Run Program Recccwsccsccenesccsscomececcsccssccsssmeensosees 0 Figure 7 11 7 4 4 Review Questions Q14 Which one of the following statements is true regarding the do while loop The conditional statement is always satisfied The block of code is entered first before the condition is tested The loop need not be entered if the condition fails at the start a b c d The loop terminates when the condition becomes true HERIOT WATT UNIVERSITY 2006 7 4 DOLOOPS 199 Q15 Looping structures have several features in common Which one of the following is NOT one of these features Selection Increment Initialisation Condition a b c d Q16 What is the output of the following program fragment that uses a do while loop i 0 Do i iti Print i Loop While i lt 5 a 01234 b 12345 c 012345 d 123456 Q17 In the previous example the do while loop is replaced by a do until loop as follows i it i Print 1 Loop Until i lt 5 Q18 What
31. End End Sub Code 6 8 In this program input is via an InputBox and output by means of the PictureBox function Although a PictureBox is meant for graphics it can deal with text as well and this somewhat tidier than displaying text on a form The PictureBox property is set to the name PicDisplay in the properties window Program output is seen in Figure 6 10 Form like Ss rogram End Figure 6 10 Several examples are given here that use comparison operators and if constructs within a program to solve a problem Try writing the programs for yourself and experiment with making changes to the code to ensure you understand what is happening Example 1 Calculating the area and circumference of a circle Problem Write a program that calculates the area and circumference of a circle The calculations should only be performed if the radius is positive i e a valid radius Solution In the previous topic an example was given for calculating the circumference of a circle using a constant for the value of pi This example could be modified to use an HERIOT WATT UNIVERSITY 2006 6 13 THE IF THEN ELSE STATEMENT 145 if statement to validate the radius i e if radius gt O then do calculations display results Example 2 Write a program to input numbers from the keyboard and to print them out The program terminates when 1 is entered A suitable message should be output input number if number gt 0 output
32. ICL were to install in throughout Britain lt began in 1996 and was stopped in 1999 having been as the official report said blighted from the outset 8 French national library received a new system two years late and 40 over budget which worked so badly that librarians walked out 9 ATMs in Germany during the changeover from Marks to Euros in 2002 a programming error in the banking system allowed people to withdraw any amount cash by typing in an arbitrary PIN code 10 London Millennium Bridge in 2000 the newly built Millennium Bridge wobbled when pedestrians attempted to walk over it In the computer simulation the programmers had used the wrong estimates for pedestrian forces Of course all these systems were planned but with better planning these mishaps might have been prevented Without planning probably all large projects would go wrong The most basic notion of well planned programs is producing software which does what the user wants This is easy to say but more than a little difficult to do If you are taking this course at the same time as learning a programming language then we are sure you know this is so from your own experience 1 5 Information sources on computing disasters The World Wide Web and Internet links go out of date rather quickly You might want to try accessing the following sites which are current at the beginning of 2004 1 Ariane 501 e A Bug and a Crash by James Gleick http www aroun
33. Identifying the characteristics of good software design On the Web is a interactivity You should now complete this task 2 3 4 Review questions Q11 Which one of the following processes describes breaking a complex system down into more manageable components Top down design using pseudo code OT refined design prototyping Q12 In the software development process a legal contract is represented by which one of the following d functional specification problem specification requirements specification systems specification 208 1 HERIOT WATT UNIVERSITY 2006 2 3 THE WATERFALL METHOD 17 Q13 The outcome of the analysis stage of software development is to ascertain which one of the following a the main costs of the project b time taken to complete the project c hardware required to run the system d All of the above Q14 The completed software system should be able to cope with many errors while running This means that the software is choose one a Portable b Robust c Reliable d Stable Q15 Which one of the terms below is included in the functional specification A description of how the program should operate the hardware used to run the software the nature of the problem to be solved a b c d an outline of the problem solution 2 3 5 The Implementation stage At this stage the programming team will make use of test data This data is designed to check that th
34. Important differences will be flagged where appropriate Visual Basic 6 Visual Basic is an events driven programming language that works within the graphical environment of Windows Visual Basic code is associated with objects and each object has a set of events associated with it Events are actions which Visual Basic detects and respond to For example a user clicking on a command button on a form will generate a click event for that button pressing a key on the keyboard could initiate a load event for a programming module When an event is generated Visual Basic will run any code that you have entered for that event Since there may be many objects associated with a single program it means that each object must be coded separately Objects are coded in Visual Basic using sub procedures that may be executed individually or be linked together in one way or another Visual Basic Environment When Visual Basic is launched using the Standard EXE option a number of separate windows appear as seen in Figure 6 1 HERIOT WATT UNIVERSITY 2006 6 2 THE PROGRAMMING ENVIRONMENT s Projecti Microsoft fisual Basic design Ale Edt View Project Format Debug Run Query Diagram Took Addins Window Help EY Properties ses E Project DIX amp ejes Form1 Form P aa o Geral Alphabetic Categorized iee A EA Fi Formi i PAR NS POE Seance T O a F e 1 7 nu tie z s False Ms EE E E De hee Ed EB su aaa i oh Ge te 2 Szabl
35. It will therefore always have a value of 0 which is less than 100 and hence this will produce an infinite loop which will never terminate The program will therefore never end The code could be altered to include an increment i e n 0 do while n lt 100 value n n n nt i loop Q12 There is no loop to end the do while Add loop at the end of the code i 1 do while i lt 10 print 1 isi 1 loop Q13 A typical solution to the problem is shown here HERIOT WATT UNIVERSITY 2006 280 dim i as integer sum as integer sum 0 i 0 do while i lt 20 sum sum i i it i loop ANSWERS TOPIC 7 You should obtain a value of 210 for the sum of all numbers between 0 and 20 inclusive Answers from page 198 Q14 Q15 Q16 Q17 Q18 The loop need not be entered if the condition fails at the start c a Selection b 12345 b 1 d Any one of the above Indexing arrays page 206 Q19 Q20 Q21 Q22 Q23 Q24 Q25 Q26 Q27 c array 0 3 0 0 SA x d array 7 3 0 0 c 2 a 3 c array 8 12 5 19 3 0 7 52 Z i wa c array 8 23 5 9 3 4 7 52 array 0 9 3 0 array 0 7 0 O 6 0 0 3 2 0 The program fragment which will help you to do this is for i 0 to 9 myarray i i Answers from page 208 Q28 Q29 Q30 d All of the above options b A for loop d 046257 HERIOT WATT UNIVERSITY 2006 ANSWERS TOPIC 7 2
36. Num2 Solution The comparison can be made using the relational operator gt e g Numi gt Num2 This comparison could be reversed to check if Num2 is less than Num1 e g Num2 lt Numi Example 2 Using a relational operator in an if statement Problem Construct an if statement that will display a message to the screen if two variables Vali and Val2 are equal HERIOT WATT UNIVERSITY 2006 6 13 THE IF THEN ELSE STATEMENT Solution A typical solution is shown here Dim Vali As Integer Val2 As integer if Vali Val2 then Print Vali and Val2 are equal end if Sentence completion relational operators On the Web is a interactivity You should now complete this task 6 13 3 Logical Operators Logical operators test conditions as either being true or false In computer programming they are referred to as Boolean operators named after George Boole a mathematician and logician 6 13 4 Logical AND Logical and means that an expression is true only if both the part before the and and the part after the and are true Both must evaluate to true So if number lt 0 and number gt 10 then the expression will always evaluate to false Why Because a number cannot be less than zero and greater than 10 at the same time and both must be true for the and statement to produce a true result Use of the logical and operator can be seen in the expression below if Vone 6 and Vt
37. PROCEDURES AND STANDARD ALGORITHMS Finally three common algorithms for Higher Grade Software Development Process are discussed with exemplar code for each supplied 8 2 Modularity You will recall from Topics 3 that an important aspect of the design phase was the idea of refining a complex program by progressively breaking it down into smaller easier to solve units top down design with step wise refinement Each of these units called modules or program blocks can be independently coded in a high level language and then amalgamated to form the complete program The use of structure charts emphasise this modular design and also the relationship between all the modules in the software system Modularity was the basis of structured programming a concept which evolved in the 60s and 70s when procedural or imperative languages came to the fore Today it is still an important aspect of modern programming techniques and even lends itself to current object oriented programming In comparison to commercial software the programs that you will be writing in Visual Basic will be relatively short and you might not see the need to use modular techniques The Windows operating system for example contains well over 30 million lines of code Just think of trying to program this in one large block of code This would be an impossible task without the system being decomposed into many smaller discrete units that can be easily modified and more readily deb
38. RA BG BE a tee 112 OVOIVISWO Li e a A dd de Lt Y NES 1 2 1 Software engineering 1 2 2 Software development 1 3 Real life programs and classroom programming 1 4 Computing disasters 1 5 Information sources on computing disasters 1 6 Well planned programs dy SUMMA ne A te NN ee EDR RENNES ZE 1 38 End Of Topic Test i ii a a a ee SRE bee ee Pek DOAN OA KR WBN D PY Prerequisite knowledge There are no prerequisites for this introductory topic Learning Objectives e understand what is meant by software engineering e understand what is meant by software development e recognise the professional issues that are involved in the development of a computer system e understand the need for software development e understand what is meant by well planned programs 2 TOPIC 1 INTRODUCTION TO SOFTWARE DEVELOPMENT PROCESS 1 1 Introduction In this topic you will be introduced to the Software Development Process and the reasons why such approaches to the topic exist The subject has its roots in software engineering and this is discussed from a historical perspective where the magnitude of the processes involved are made clear This leads on to the need for well planned programs together with the associated problems and preferred solutions 1 2 Overview Computer s
39. Table 5 2 Table 5 2 Classification based on structure Programming Structure Purpose Language Pascal imperative general purpose language widely used Visual BASIC imperative windows interface applications multimedia PROLOG declarative artificial intelligence Visual C event driven used as front end to develop user interface COBOL imperative business use Java object oriented platform independent an object oriented language VBscript scripting creating and editing macros FORTRAN 90 object oriented scientific and software engineering Lisp functional artificial intelligence uses many other languages are derived from it JavaScript scripting writing and enhancing web pages BASIC imperative easy to learn originally developed to teach non specialists the art of programming FORTRAN imperative scientific programming language The above list is not in any way rigorous There are many instances of particular languages fitting into more than one category For example although Visual basic is listed as an imperative language it can also be classed as an event driven language and also an object oriented language HERIOT WATT UNIVERSITY 2006 5 4 IMPERATIVE LANGUAGES 5 4 Imperative languages Imperative languages are also known as procedural languages because they employ structures which include procedures and functions Programs generated in procedural languages involve
40. The program responds by printing the bigger of the two Use the code fragments in the examples above to help you and make sure that the program has user friendly prompts for the input and output HERIOT WATT UNIVERSITY 2006 6 13 THE IF THEN ELSE STATEMENT 149 Even or odd Write a program to test if a user entered number is even or odd In this program you will have to use the modulus operator mod to calculate the oo remainder when the value stored in the variable number is divided by 2 An even number has no remainder if divided by 2 Calculating wages Write a program to calculate the commission based wages of a computer salesman His basic wage is 50 per week and he is expected to sell at least 10 computers If he sells 20 min more than 10 computers he receives an extra 5 50 per computer he sells after the 10th computer The basic algorithm could be drawn as shown in Figure 6 12 input computers sold calc commission calc pay output pay Figure 6 12 Outwith range When does the following statement evaluate to be TRUE 194 number lt 0 or number gt 9 6 13 1 Comparison Operators There are two kinds of operators that allow comparison within Visual Basic 1 Relational 2 Logical HERIOT WATT UNIVERSITY 2006 150 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 6 13 2 Relational operators Relational operators are used for testing of conditions They are used to construct the
41. This collection is known as a module library Program libraries or software libraries are made available for common use It may contain compilers utility programs or code fragments to perform specific operations Modules in the library can often be used over and over in new projects This saves time spent designing and coding If a module can be used without alteration there is the added advantage that it has been thoroughly tested and is reliable Use of unaltered modules reduces the time spent on the detection and correction of errors in the project as a whole Sometimes adjustments might be needed to a library module After the necessary work HERIOT WATT UNIVERSITY 2006 62 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION the module will require to undergo error and other testing Characteristics of module libraries On the Web is a interactivity You should now complete this task 3 8 CASE tools Programmers also use Computer Assisted Software Engineering CASE tools to automate much of the coding process These tools enable a programmer to concentrate on writing the unique parts of the program CASE tools generate whole sections of code automatically rather than line by line This produces more reliable and consistent programs and increases programmers productivity by eliminating some routine steps When one is designing or re designing a software system it s important to be consistent and not to break any
42. Top Figure 8 4 Recursion 1 2 3 4 5 6 7 8 9 1 End Program Figure 8 5 HERIOT WATT UNIVERSITY 2006 244 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS Exercise How could you amend the program to print the values out in reverse order Answer Interchange the If and Print statements Example 2 Recursion cannot be covered without a look at the factorial function A factorial is a number multiplied by every other integer below itself down to 1 For example the factorial of the number 5 is Factorial 5 5 4 3 2 1 This give factorial 5 the value 120 From this example it can be seen that factorial 5 5 factorial 4 Similarly factorial 4 4 x factorial 3 and so on down to 1 A general rule for calculating factorial numbers is factorial n n factorial n 1 The above rule terminates when n 1 as the factorial of 1 is 1 The following example in Code 8 6 calculates the Factorial of a number using recursion Option Explicit Private Sub Command1_Click Dim Result As Double Number As Double For Number 1 To 7 Result factorial Number Print Factorial Number Result Next Number End Sub Private Function factorial ByVal Num As Double As Double If Num 1 Then Sfactorial of 1 is 1 factorial 1 Else factorial Num factorial Num 1 recursive call End If End Function Private Sub Command2_Click End End Sub This file Factorial txt can be do
43. UNIVERSITY 2006 100 TOPIC 5 LANGUAGES AND ENVIRONMENTS 5 10 1 Compiler A compiler which is a complex program in itself translates source code into object code that is then loaded into main memory and executed machine code program source program Compiler errors Translating source code into object code is a complicated task that it is unreasonable to expect it to occur in a single coherent step Compilation is thus broken down into several logical phases as seen in the following diagram Compiler Front End Back End Structural analysis Generation of meaning of source code target machine code At the highest level a compiler consists of a front end and a back end The front end carries out an analysis of the structure syntax and meaning semantics of the source code while the back end generates the object code Looking at the operations of the front end in a little more detail it can be seen as being composed of the following three stages 1 lexical analysis 2 syntax analysis 3 semantic analysis HERIOT WATT UNIVERSITY 2006 5 10 TRANSLATION METHODS 101 A closer look at the operations of the back end reveals 1 intermediate code generation 2 code optimisation 3 machine code generation The sequencing of these phases is shown in the following figure Source Code Lexical Analysis Symbol Table Syntax Error Management Analysis Handling Intermediate Code G
44. WATT UNIVERSITY 2006 109 110 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Table 6 1 shows the common files types in a Visual Basic Project Table 6 1 File Type Description FRM Form BAS Module OCX ActiveX control CLS Class module VBP Visual Basic project When starting to write Visual basic programs the two most common file types are Form and Project 6 3 Building applications Constructing a program in Visual Basic involves two processes 1 creating the visual design of the program 2 entering and implementing programming code In the first process the properties of the form are established followed by the creation of controls inside the form The properties of each control are then established E Properties C Sele Commandi1 CommandButton Alphabetic categorized Commandi 1 3D O H8000000F False Commandi CausesValidation True Defaut False DisabledPicture None None None 0 Manual Caption Returns sets the text displayed in an object s title bar or below an object s Pressing function key F4 on an active button will open the Properties box as seen above HERIOT WATT UNIVERSITY 2006 6 3 BUILDING APPLICATIONS Figure 6 2 shows five objects 3 control buttons a message box and a form each with event coding Form Visual Basic is FUN Figure 6 2 In the second process programming code is written for each event and attached to eac
45. a prototyping loop of design construction of prototype implementation use of prototype and analysis of feedback from the prototype Note that implementation has here a different meaning from its meaning in structured design Results of the analysis suggestions for changes in design or alterations to requirements are then fed back into the design stage and the loop runs again When the prototype seems satisfactory the process moves on to full implementation Disadvantages of RAD A disadvantage of RAD is that the resulting software can be patchy representing a series of ad hoc responses on the programmer s part than a methodical attempt to provide a robust system Problems with such software which might arise at the testing or maintenance stages can be difficult to debug 2 12 4 Commercial Off The Shelf COTS When structured design was invented there was not by today s standards a lot of software available Software houses create software packages for use by individuals and organisations Rather than have programmers develop a new system from scratch many organisations first look to see if a packaged software solution already exists for sale or for hire This approach is sometimes called the COTS approach COTS packages can be very expensive Commercial software is generic and requires to be configured to the client s requirements The client s existing software may need to be adjusted to suit the new package Furthermore th
46. a sequence of operations and are often described as linear programs A procedural imperative programming language tells the computer how to do something written as an ordered sequence of steps that describe exactly what it must do at each step These instructions which form the basis of an algorithm are followed in written order by the computer Three basic constructs are used to define the order of the steps 1 sequence the logical ordering of steps 2 selection a step or sequence of steps are performed if a condition or set of conditions is true 3 iteration a step or sequence of steps are carried out repeatedly Both iteration and selection are control constructs because they can alter the flow of control of program execution You will see more of this in later topics Examples of imperative languages are Algol Fortran Pascal Basic C and COBOL Example of a program to read data into an array and output results Problem In Visual Basic we might tell the computer how to input data into an array and then print out the results Solution Program to fill an array with team names and print them out Private Sub Command1_Click Dim Team 5 As String Dim Count As Integer Assign array values Team 0 Leith Learners Team 1 Bonaly Boys Team 2 Royston Rovers Team 3 Calder Colts Team 4 Juniper Juniors Team 5 Wardie Wanderers For Count 0 To 5 Print Teams Tab 8 Count 1 Tab 14
47. a value and gt a condition Dim iTemp As Integer Dim weather As String iTemp InputBox Please input today s temperature HERIOT WATT UNIVERSITY 2006 6 13 THE IF THEN ELSE STATEMENT 155 weather InputBox Please input Sunny or Rainy If iTemp gt 15 Or weather Sunny Then PicDisplay Print iTemp deg and weather Wash the car Else PicDisplay Print iTemp deg and weather No way End If End Sub Private Sub Command2_Click End End Sub This file WashCar txt can be downloaded from the course web site Code 6 11 The program output is shown in Figure 6 15 Form 18 deg and Sunny Wash the car 14 deg and Sunny Wash the car 22 deg and Rainy Wash the car 14 deg and Rainy No way End Program Figure 6 14 6 13 6 Logical XOR Exclusive OR If either the expression before the or or after the or is true then the whole expression is true in this case however if both the expressions are true the or expression will evaluate to false So or means either one or the other but not both Hence the term exclusive HERIOT WATT UNIVERSITY 2006 156 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Use of the logical XOR operator is shown below if Vone 6 xor Vtwo 6 then statement 1 else statement 2 end if This code means that when either Vone or Vtwo is equal to 6 then statement 1 is executed If both of the conditions are true or if both of th
48. any character text Note that 1 Although the range of floating point numbers is huge they are not all that accurate often not much more than 8 16 digits depends on the machine and compiler The rest of the number you may see on the screen is an approximation For accuracy you need to use integers 2 The data type variant is the default mode in Visual Basic and will be discussed later in the topic Identifying data types On the Web is a interactivity You should now complete this task 6 6 Visual Basic Nomenclature An important aspect of any language is the rules for naming the objects such as constants variables subprocedures and functions There are five rules in Visual Basic which prescribe valid variable names All Visual Basic variable names 1 must always begin with a letter 2 must contain no spaces 3 must only consist of letters or digits with no embedded periods or other punctuation HERIOT WATT UNIVERSITY 2006 6 6 VISUAL BASIC NOMENCLATURE 123 marks except the underscore character 4 can be no longer than 255 characters 5 cannot use Visual Basic reserved words see Table 6 5 The variable names shown in Table 6 3 are valid Table 6 3 temp1 velocity unit1 pay_period fred day_month_year The variable names shown in Table 6 4 are not valid Why Table 6 4 40th_birthday discount _rate constant bad variable string In addit
49. can be done to make the output of the program fragment in 3 the same as the program fragment in 2 Change last statement to Loop Until NOT i lt 5 Change last statement to Loop Until i gt 5 Use a for loop with counter variable i a b c d Any one of the above HERIOT WATT UNIVERSITY 2006 200 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 7 5 Arrays In the exercises so far you have looked at simple data types such as single real and integer The next thing we want to look at is how related data items can be stored together using arrays In this topic we will investigate 1 the requirement for arrays 2 array declaration Much of this material may be familiar to you already However itis necessary gain more practice in the use of arrays in order to better prepare you for a later topic on standard algorithms which makes extensive use of this type of data structure A data structure is a way of storing data in a computer in an organised way One of the simplest data structures used in computer programming is called an array and is an example of a static data structure because it is of a fixed size within memory as defined within the structure of the program An array is a list of data items such that each item is uniquely identified by its position in the list Also an array is given a name which is usually related to the group of data it holds Some examples might be Data Items Array Name Sun
50. computer journalists and authors and also makers of related computing products such as printers This is of benefit to both parties the software house gets its product tested by people who are good at noticing faults and the writers get to know about products in advance which further benefits both parties when the final production software is released the software house getting publicity and the writers receive credit for being up to date People involved in beta testing will send back error reports to the development team An error report is about a malfunction of the program and should contain details of the circumstances which lead to in the malfunction These error reports are used by the development team to find and correct the problem 2 7 3 Review questions Q26 Which one of the following statements is true relating to alpha testing a Testing is done by the users b Testing is done within the organisation c Testing is done by specialist companies d Testing is done by the client Q27 The statements refer to a dry run testing of software Which one is involved in the process a No software is involved b No users are involved c No computers are involved d No programmers are involved Q28 Beta testing differs from alpha testing in one of the statements below Which one The program is tested by the clients The testing is more rigorous than alpha The testing is for market research a b c d The program is tes
51. development process the order of appearance of the documents will be Structured program listing installation guide user guide technical guide Installation guide structured program listing technical guide user guide User guide structured program listing installation guide a b c d Technical guide structured program listing technical guide user guide 2 4 Analysis in closer detail Analysis sometimes called systems analysis is the job of a specialist person the systems analyst The work that takes place in this stage of the development process varies from case to case Where only a rough outline of a problem exists the analyst will have to perform a full systems analysis A requirements specification is the starting point and the analyst must proceed from there The aim is to produce a clear specification that the rest of the development team will use in the subsequent stages Full systems analysis has three phases 1 collection of information 2 analysis of information collected 3 production of a problem specification or user requirements specification These ideas are explored further later on under the role of the systems analyst 2 5 Design in closer detail The product of the analysis stage is the completed specification During the design stage the specification of the problem is used as the basis for a planned solution The work on the design is carried out by a designer this might be same
52. education authorities colleges teachers and students who contributed to the SCHOLAR programme and who evaluated these materials Grateful acknowledgement is made for permission to use the following material in the SCHOLAR programme The Scottish Qualifications Authority for permission to use Past Papers assessments The Scottish Executive for financial support All brand names product names logos and related devices are used for identification purposes only and are trademarks registered trademarks or service marks of their respective holders Contents 1 1 Introduction 1 2 Overview Introduction to Software Development Process 1 3 Real life programs and classroom programming 1 4 Computing disasters oca a fee a eS ewe 1 5 Information sources on computing disasters 1 6 Well planned programs 0 4 4 44046 genre foes wa ht 1 7 Summary 1 8 End Of Topic Testa ds o as a a Shee sia ci dido o a 2 1 Introduction 2 2 Preamble Features of Software Development Process 2 3 The Waterfall Method 2 4 Analysis in closer detail 2 5 Design in closer detail A E AAA E 2 6 Implementation in closer detail 2 7 Testing in closer detalli ERA A 2 8 Documentation in closer detail 2 9 Evaluation in more detail 2 10 Maintenance in closer detail
53. expression which is used in the if statement The relational operators check whether two quantities are the same or whether there is a difference between them Because of the inexact way floating point numbers are stored in computers you should not use the equality operator between two real numbers Even if two real numbers are printed to the screen as the same two numbers this is no guarantee that they are the same internally The only way to test equality between real numbers A and B is to use the following expression If ABS A B lt small difference Then The function ABS returns the absolute value of any number ABS 5 3 gives 5 ABS 43 gives 43 Depending upon how accurate real numbers are held on the computer small difference is usually of the order 0 0000001 The relational operators are summarised in Table 6 9 These operations can be performed between most types of object but they will be used most often to compare two integer values or two characters Table 6 9 Relational Operators Symbol Example Meaning gt a b a equal to b lt a lt b a less than b lt a lt b a less than or equal to b gt a gt b a greater than b gt a gt b a greater than or equal to b lt gt a lt gt b a not equal to b Example 1 Using a Relational Operator Problem How can a comparison be made between two variables Numi and Num to find out if Num1 is greater than or equal to
54. following week Prototyping at least in respect of designing the HCI is still welcomed by the clients and programmers 2 12 3 Rapid Application Development RAD RAD requires languages like Delphi or Visual Basic These are event driven languages which allow easy construction of interactive forms Another term for this sort of approach which stresses the partnership of clients and developers in the production of the final software is Joint Application Development The term RAD has not been current for very long but has already evolved and its meaning altered Originally RAD was applied to small but highly interactive programs that could be completed in a day or two The programmer would simply study the specification plan the windows needed and how they would link together and create HERIOT WATT UNIVERSITY 2006 37 38 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS the program This could be used as a prototype the client could look at it even take it away and test it amendments could be made easily Many programmers wanted to extend this approach to deal with large programs Programmers use it for larger projects and involve their clients all the way through The process is iterative and makes use of feedback from clients The advantages are that projects tend to be finished quickly clients feel involved and time isn t wasted creating things that the clients don t want The process has been formalised and centres on
55. footers d Changing audio CDs 5 8 Object oriented languages Object oriented programming was borne out of the need to overcome the problems of conventional programming projects that could involve many thousands of lines of code the latest Window OS for example contains many millions of lines of code Needless to say managing projects of this magnitude are extremely error prone changing the program specification or tinkering with a few lines of code can mean a complete re write of program modules probably involving several month s work Object oriented programming OOP requires a new way of thinking that might seem strange to you at first sight Object oriented programming is a programming language model organized around objects rather than actions and data rather than logic Object oriented programming takes the view that what we really care about are the objects we want to manipulate rather than the logic required to manipulate them The primary concept in object oriented programming languages is a class A class is a user defined type that represents an object or a concept a file a hardware device a database record a document an airplane a chair a computer etc in fact anything in the real world An object is an instance of a class just like a variable in procedural programming languages is an instance of a type An object is an entity in itself that can interact with other objects The first step in object oriented programming i
56. for new programs because all their old programs are written in it Fortran is still used for applications where the emphasis is on numerical processing such as processing meteorological data Programming languages however don t remain unchanged They develop due to a variety of reasons people perceive shortcomings in a language and try to correct them the world moves on and people try to adapt a language to cope with new demands and expectations Some changes are formalised with new versions of a language being agreed and released from time to time The choice of language may be based on e the experience and expertise of the development team e the range of languages and development platforms available to the organisation e which language has the facilities most appropriate to solving the required problem e the choice of a particular language substantially reducing the overall development time e a suitable compiler interpreter available for the client hardware If the task requires text processing for example a language which supports data of type string is necessary In other circumstances a language which supports arithmetic logical operators sound or graphics may be necessary Another factor is portability A program is portable to the extent that it can be used on different computer hardware If the programs are in the form of machine code a program compiled into machine code on a PC will not be executable on a different machine
57. for the design of the computer systems Systems developer Another name for a systems analyst Systems specification An indication of the hardware and software required to run the developed program effectively lt will be the basis of subsequent stages which prepare a working program Technical guide Documentation intended for people using a system containing information on how to install software and details system requirements such as processor memory and backing storage Test data Data that is used to test whether software works properly and that it is reliable and robust Testing Running a program with test data to ensure a program is reliable and robust Test log A record of how a program responds to various inputs Test plan A strategy that involves testing software under verifying conditions and inputs Top down design A design approach of sectioning a large and complex system into smaller and more easily manageable components HERIOT WATT UNIVERSITY 2006 267 268 GLOSSARY Trace facility A method used to debug a program by tracing the change in values of the variables as the program is run Traditional model An alternative name for the waterfall model that details the seven stages of program development Unusual user activity Running a program with exceptional data User guide A document intended for people using a system containing information on how to use the software Value parameter Here a cop
58. from 2 to 1 Move a disc from 2 to 3 Move a disc from 1 to 3 End Program Move a disc from 1 to 2 Move a disc from 3 to 2 Move a disc from 3 to 1 Move a disc from 2 to 1 Move a disc from 3 to 2 Move a disc from 1 to 3 Move a disc from 1 to2 Move a disc from 3 to 2 Figure 8 6 Towers of Hanoi ES There is a interactivity of the Towers of Hanoi online at this point 8 5 1 Review Questions Q11 Which one of the following statements regarding a function is false A function does not need to be declared A function does not have parameters A function returns a single value d A function can not call itself Q12 Below are four functions Which one does not belong in Visual Basic Inputbox Val Square Rnd 205 a HERIOT WATT UNIVERSITY 2006 248 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS Q13 Look at the Visual Basic statements below that use built in functions Which one represents a valid function call a SQR x x b y ABS 5 c 65 CHR A d z SQR z Q14 Procedures and functions can be recursive This means that choose one a Procedures and functions can be nested b They are called twice within a program c The process can go on for ever d A procedure or function can call itself Q15 What would be the value of x in the following expression x 0 5 factorial 4 a 2 b 5 c 10 d 12 8 6 Standard Algorithms An algorithm is a finite sequence of steps which when fo
59. full Visual Basic code for this program is shown in Code 6 5 Private Sub cmdRun_Click 10th February 2004 Program by Fred Fink Dim number As Integer Dim result As Boolean E This is a program that will prompt the user for a number It will then check whether the number is less than or equal to zero or greater than 0 A boolean variable will hold the result A message saying true or false will be printed on the screen to say whether it is greater than zero Start of main program number InputBox Please enter a number result number gt 0 Print number greater than or equal to zero result End Sub Code 6 5 In this program the InputBox function is used to input the data as before The output is shown in Figure 6 7 HERIOT WATT UNIVERSITY 2006 6 8 DECLARING CONSTANTS 131 Form 6 greater Ihan or equal ta zero True 1 greater Ihan or equal ta zero True 0 greater Ihan or equal ta zero True 1 greater Ihan or equal ta zero False 6 greater Ihan or equal ta zero False Erronea cero Execute Figure 6 7 Boolean values are easy to use and when used they can often make a program more readable They are often tested to control the flow of execution of a program When defining a list of variables with the same type specifier the variables can all be defined on the same line as the type specifier or separate type specifiers can be used for each variable F
60. give a lot of flexibility for the user as the values must be changed in the program and the program recompiled for every new set of values used Another would be to allow the user to enter them which is the method we will use here There are other input methods which could be used such as reading a file or downloading the information from a remote monitor but we will stick to the straightforward method at the moment for day 0 to 13 InputBox Enter temperature of day day next day Inserting this section of code into code 10 plus the output statements produces the following Code 7 11 Option Explicit Private Sub Command1_Click program CalculateAverageTemp program to calculate average temperature 20th February 2004 Program by Fred Fink Dim Store 13 As Single Dim total As Single average As Single Temp As Single Dim day As Integer HERIOT WATT UNIVERSITY 2006 7 5 ARRAYS 211 total 0 0 initialise total program now puts the values into the Store array For day 0 To 13 Temp InputBox Enter temperature of day PicValues Print day Store day Temp total total Store day PicArray Print Store day Next day average total 14 PicResult Print Format average standard End Sub Code 7 11 As the temperature values are entered they are stored in the array Store When the loop terminates the value of average is displayed The program output is shown in Figure 7 15 HERIOT WATT UN
61. hard disk aa P hard disk 2 3 6 The Testing Stage Testing has several purposes It should check that e the software meets the specification i e is correct e it is robust e itis reliable Testing follows a test plan or strategy involving carefully selected test data with a view to ensuring that a reliable product has been constructed Important aspects would be e what part of the program is being tested e what is the expected output using suitable test data Testing can never show that a program is correct Even with extensive or exhaustive testing it is almost certain that undetected errors exist Testing can only demonstrate the presence of errors it cannot demonstrate their absence A program can be regarded as succeeding if it passes a test the test can be regarded as succeeding if it makes the program fail Commercial software is not exhaustively tested at the testing stage Software can be complicated and the available time is limited There must be a balance between creating a product for the market and exhaustive testing If errors become apparent after release the company will fix them and release with an updated version HERIOT WATT UNIVERSITY 2006 2 3 THE WATERFALL METHOD 2 3 7 The Documentation Stage Users will need to be able to read and learn about the new system The documentation should include a user guide for people who will be using the system and a technical guide for those who will b
62. in accordance with the conventions of the implementation language The code should be properly indented this helps people follow the structure of the code Meaningful names should be used for modules constants and variables The use of internal commentary will help to explain the logic of the code to others and also serve as a documentation aid for the programmer A structured listing can be produced at any time during implementation lt can serve as a tool for checking program logic and also form part of the final software documentation Figure 3 6 shows a structured listing of a program coded in the language Visual Basic A Projecti Form Code commandi AA OCR ul Option Explicit i 3 PY Private Sub Command Click start of program block program nested IF 15th February 2004 Program by Fred Fink This program vill prompt the user to enter a number between 1 and 99 The program will test the number to see if it is less than 10 and print the message that it is a single digit number IZ 18 19 gt 9 at will output double integer number othervise out of range Dim testNumber As Integer declare variable cestNumer InputBox Please input a number betueen 1 and 99 ask for number If testiumber gt 0 And testiuxber lt 99 Then 12 testNumber lt 10 Then Picbisplay Print testNumber as a single digit number Else PicDisplay Print testNwmber is a double digit numbe
63. in sequence If the 2nd and 4th elements are now assigned the values 8 and 9 respectively the array List will now contain Q5 All array elements have to be set with similar values The process to accomplish this is called Sequence Selection Iteration None of the above 7 1 Introduction An important aspect of this topic is the 1 dimensional array Declaring and initialising arrays are introduced together with how data is manipulated within arrays using various looping structures Each sub topic has working solutions to the example programs thus providing a suitable environment for building confidence in writing programs before the final topic dealing with standard algorithms is covered HERIOT WATT UNIVERSITY 2006 173 174 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 7 2 Iteration The aim of this topic is to introduce you to iterative structures or loops Iteration simply means repetition which in the context of programming is the execution of blocks of code many times over Iteration is a fundamental part of almost every program and is one of the most useful features of programming You do not want a computer to produce one payslip but many payslips to add up just two numbers but thousands of numbers to put in order just two items but thousands of items There are three different looping constructs you can use in Visual Basic 1 For Next loop 2 Do While loop 3 Do Until loop Most loops have the followin
64. in the third module in the main part of the program A line of pseudo code 3 1 10 would indicate the tenth line in this module Here is an example of a routine that you will meet in your programming exercises Counting occurrences 1 set counter to zero 2 prompt user to input search value 3 set pointer to start of list 4 do 4 1 compare search value to item at current list position 4 1 1 if search value current item then 4 1 2 increment counter by 1 4 1 3 set pointer to next position in the list 4 2 loop until end of list 5 output number of occurrences counter Characteristics of pseudo code On the Web is a interactivity You should now complete this task 3 3 5 Review questions Q6 Which one of the following notations is commonly used to describe software logic a Structure charts b Stubs c Pseudo code d All of the above Q7 What statement refers to the term top down design a Itis a software testing approach b Itis breaking complex problems down into smaller units c Itis the detailed design of software logic d Itis the use of pseudo code Q8 The main idea behind structure charts is choose one HERIOT WATT UNIVERSITY 2006 3 4 TEST DATA 53 a To allow descriptive expressions of purpose b To show the main elements of a solution c To show the various elements fit together d All of the above Q9 In the context of pseudo code which statement concerning the user is true a Thi
65. is run under all conditions Answers from page 60 Q16 Q17 Q18 Q19 Q20 An error generated by the source translator Do all program loops terminate b a d All of the above c Logic error b De bugging HERIOT WATT UNIVERSITY 2006 ANSWERS TOPIC 3 Answers from page 63 Q21 c The program can cope with mistakes that the user might make Q22 d All of the above Q23 b A printer jam Q24 b Produce output come what may Q25 c Java HERIOT WATT UNIVERSITY 2006 273 274 ANSWERS TOPIC 4 4 Personnel Answers from page 73 Q1 Q2 Q3 Q4 Q5 c The group who will purchase the software d Benefit the organisation in some way d The systems analyst is responsible for the entire project a Allow the systems analyst to produce a clear specification of the problem b The project manager Answers from page 76 Q6 Q7 Q8 Q9 d All of the above a They report directly to the project manager at all stages of programming b Programmers will tend to test only within the functionality of their own code c The systems analyst Q10 c Testing is done by external groups on a variety of computer platforms HERIOT WATT UNIVERSITY 2006 ANSWERS TOPIC 5 275 5 Languages and Environments Revision page 81 Q1 dj All of the above Q2 a A compiler produces object code whereas an interpreter is much faster Q3 d Syntax error Q4 c Pro
66. less than Y 7 6 Summary The following summary points are related to the learning objectives in the topic introduction e understand and be able to use the for next structure e understand and be able to use the do while structure and variant e understand and be able to use the do until structure and variant e howto declare 1 D arrays e initialise a 1 D array e manipulate data held in 1 D arrays 7 7 End of topic test An online assessment is provided to help you review this topic HERIOT WATT UNIVERSITY 2006 Topic 8 Procedures and Standard Algorithms Contents 821 Untroduetion s25 55 a E E BE A 8 8 2 Modularity 04 4 64 coc a MN AN dd de dd ee A ad 8 3 Procedures and Functions 3 331 Procedure Siy ami aceno a dd a 8 3 2 General Procedures 8 3 3 Parameter passing 8 3 4 Call by Value 8 3 5 Call by Reference 8 3 6 Review Questions 8 41 FUNCUONS 3 2 2 a a a is a en et din se 8 5 Recursion 8 5 1 Review Questions 8 6 Standard Algorithms 8 61 Linear Search a Li ana EE LR EE A a 8 6 2 Counting Occurrences 8 6 3 Finding Maximum and Minimum 87 SUMM
67. must perform operations on the data supplied to it The data should be structured data The choice of data structure will affect the entire program A sorted array for example can be searched quickly but it is more difficult to maintain or to add data items The array must be sorted in the first place Any additions or deletions must leave the array in order and tightly packed An unsorted array allows additional items to be easily added but searching can be slow When the amount of data is likely to be very large the designer must consider the physical capacity of the hardware For example a million records of a thousand bytes each will require about a gigabyte If the clients want these records ordered in different ways in different parts of the program even a modern PC may have insufficient memory Many large systems involve a database In many cases the data are held in different tables which are linked together These links are called relations and such a database is known as a relational database The fields that are to be in the tables and the relations between tables need to be defined at the design stage Object oriented design attempts to treat data and objects together An object brings together items of data and the operations that can be carried out on it For example a data item might be a customer s record and the operations might include creating displaying editing and deleting 2 5 3 The Main program This is the en
68. one by one into the array Days Sunday Monday Tuesday Wednesday Thursday Friday Saturday In this case when Index takes the value 0 the first data item Sunday will be read in to the array element Days 1 Index then takes the value 1 and the process repeats itself until all the data has been entered 7 5 3 Examples of using arrays Example 1 Using an integer variable to access an array Problem How can the array temperature be initialised to zero using a for loop Solution A typical solution to this problem is shown here for count 0 to 4 temperature count 0 next count The first time round the loop the variable count has the value O and so the element with index number 0 of the array temperature is set to 0 The next time round the loop count has been incremented by 1 and has the value 1 and so element index number 1 of the array will be set to 0 and so on This one simple loop replaces 5 lines of code i e temperature 0 temperature 1 temperature 2 temperature 3 temperature 4 Il Example 2 Writing out the contents of an array Problem How can the contents of an array be displayed using a for loop Solution If you assume you have an array called Store which has 6 elements then you could use the following code to display the contents of each element for count 0 to 5 Print element count Store count next count For example if the array Store held the
69. perform a simple calculation or consult a calendar for inputting dates This is achieved by embedding ActiveX controls or Java applets into the script HERIOT WATT UNIVERSITY 2006 5 7 SCRIPTING LANGUAGES 910 11 12 13 14 15 16 17 18 19 20 21 22 Pop up Calander 23 24 25 26 27 28 29 Cancel c Validating the content of fields When filling in forms each field especially required fields denoted by an asterisk are validated for correct input If the field is left blank or incorrect information entered then a user message will be generated and you may not continue Please provide the following details This is necessary in case we need to contact you regarding delivery of your order Title Select v FirstName Last Name Email Address Phone Number If you would like your order delivered to someone other than yourself please enter their contact details below Title FirstName LastName sd 5 7 2 The need for scripting languages Nowadays scripting languages are becoming more popular due to the emergence of web based applications The market for producing dynamic web content is now expanding extremely rapidly such that new scripting languages have been developed to allow users with little or no programming expertise to develop interactive web pages with minimum effort HERIOT WATT UNIVERSITY 2006 93 94 TOPIC 5 LANGUAGES AND ENVIRONMENTS Also the increases in computer p
70. person as did the analysis or it may be a member of the programming team Most analysts can program and many programmers can carry out analysis People who can do both are described as analyst programmers The three major elements of the design are the e interface e data structure e main program HERIOT WATT UNIVERSITY 2006 21 22 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS 2 5 1 The human computer interface The human computer interface is all that a user sees of a program The HCI can be called the Human Computer Interaction Man Machine Interface user interface or user environment Design of the HCL is an important aspect of this stage A programs viability often relies on the quality of the HCI A good interface makes things easier for the user A bad interface can introduce mistakes and cause irritation and impatience Information 1 206 89 e Petrol 87p litre lans Birthday 21 6 78 64 Car Registration UTN769H Computer Speed 500Mhz Phone No 558 458552 Name of Dog Sandy 11 00pm S x M ZTZT SSS TETO eu Y ES A Modern HCls are often designed as Graphical User Interfaces GUIs which provide a WIMP environment WIMP stands for Windows Icons Menus Pointers although some textbooks refer to Windows Icons Mouse Pulldown menus A GUI provides a set of Windows which contain Icons and Menus The user controls the program by means of a Pointer which reflects movem
71. planned They prepare specifications work diagrams and structure charts for computer programmers to follow and then work with them to debug or eliminate errors from the system Analysts who do more in depth testing of products may be referred to as software quality assurance analysts In HERIOT WATT UNIVERSITY 2006 74 TOPIC 4 PERSONNEL addition to running tests these individuals diagnose problems recommend solutions and determine if program requirements have been met Once the analyst has arrived at a clear idea of the problem this is expressed in a document called a specification It may be called the problem specification requirements specification or user requirements specification The specification includes a full description of the problem All the inputs processes and outputs are described No system works on its own independently of the outside world certain assumptions have to be made about the boundaries between a system and its environment and these must be indicated described and included In some cases the specification represents an agreement between the clients and the development team The process of reaching agreement will be iterative the analyst will present a draft specification to the clients who will suggest amendments and so on until a specification is agreed The specification is used throughout the rest of the development process Material produced is based on it and compared with it
72. point then the array is not a palindrome this is what a boolean flag is for You set it to a state here it is either true or false and you use this value to see whether a certain condition still holds true so what might set isPalindrome to false It is the code inside the while do loop which compares the first and last items e if they are not the same the boolean flag is set to false Otherwise nothing happens then the second and second from last are compared and so on In terms of loop tests this is probably about as complicated as it gets If you do not understand it this time around just be patient you will probably find that you need to code something like this yourself in the future and you can come back to this example By actually doing it the difficulties seem much less than by reading it as you are doing now When you do code it successfully you will results like those shown in Figure 7 18 HERIOT WATT UNIVERSITY 2006 7 5 ARRAYS 219 w Palindromes eve is a palindiome 123454321 is a palindiome EVIL RATS ON NO STARA LIVE is a palindrome 123456 is not a palindiome mas not a ton sam is a palindrome MADAM IM ADAM is not a palindrome Figure 7 18 There are other methods probably much simpler of writing programs to test for palindromes However it is essential that you understand the use of arrays since they are important data structures in all fields of computing You will see more in
73. program will prompt the user to enter a number between 1 and 99 gt The program will test the number to see if it is less than 10 and print the message that it is a single digit number Tf it is gt 9 it will output double integer number otherwise out of range Dim testNumber As Integer testNumber InputBox Please input a number between 1 and 99 If testNumber gt 0 And testNumber lt 99 Then If testNumber lt 10 Then PicDisplay Print testNumber is a single digit number Else PicDisplay Print testNumber is a double digit number End If Else PicDisplay Print testNumber is out of range End If End Sub Private Sub ExitProgram_Click End End Sub This file NestealF txt can be downloaded from the course web site Code 6 12 Solution One variable testNumber is declared as an integer The user is prompted to enter a number between 1 and 99 and the value entered is stored in the variable number If the value is not within the specified range greater than O and less than 100 then the else part of the outer if statement is executed and the message Number is out of range is displayed on the screen and the program is finished On the other hand if the value is within range then the first part of the outer if statement is executed which contains several lines of code between if and End If Within this block of code is another if statement which tests if the number is less than 10 in which case the me
74. s robustness that a user might enter in a moment of confusion or mischief The HCI should be tested in respect of the operations a user might choose Whatever the user does the program should return to an active form The HCI should be tested in two respects e Normal user activity tests should be designed to answer such questions as do all the icons work are the forms properly connected are the forms consistent e Unusual user activity the HCI should be tested for unusual or potentially disastrous sequences of actions for example users get impatient and select things before the program s ready or select something over and over again because the program doesn t react quickly enough the program should cope if the user attempts to quit half way through a file operation and so on The program tester draws up a testlog This consists essentially of four columns input reason for choosing that input expected output expectations being formed on the basis of the specification and actual output Naturally the first three columns are filled in before testing and the fourth during testing When a program is highly interactive people often talk of its behaviour and the test log would record input reason expected behaviour and actual behaviour Faults that become evident during testing are known as bugs If bugs are identified the program is sent back with the test logs to the programming team for debugging This process is
75. second value End Sub Private Sub Command1_Click End End Sub This file RefParameter txt can be downloaded from the course web site Code 8 4 The first call of procedure GetNumbers produces the formal values for Numi and Num2 through user input These values are passed to the actual values Number1 and Number2 BlankLines 2 produces two clear lines before output of results HERIOT WATT UNIVERSITY 2006 236 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS The values are now swapped temp 20 valuei 40 value2 temp Notice the procedure BlankLines 1 is nested within procedure GetNumbers Results are displayed via procedure GetNumbers Typical output is shown in Figure 8 3 Numbers before swap 20 40 Numbers after swap 40 20 Figure 8 3 8 3 6 Review Questions Q6 The use of procedures in a program offers many advantages to the programmer Which one of the following would represent such an advantage They must have meaningful names Repetition of lines of code are avoided Procedures can be nested within procedures d They can work with or without parameters Q7 The structure of a procedure consists of three main parts Which one of the following is not one of these parts A heading A declaration An action a b c d A footer HERIOT WATT UNIVERSITY 2006 8 4 FUNCTIONS 237 Q8 Parameters can be classified as being IN OUT and IN OUT Which one of the follow
76. software is to minimise the number of errors introduced into the system A number of techniques can be used to help These include Use of static testing techniques also called desk checking and dry running These do not require the program to be run but instead examine the source code of the problem This has the advantage that each error can be considered in isolation and the error interactions are insignificant This is a surprisingly effective technique HERIOT WATT UNIVERSITY 2006 60 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION When using these techniques we strongly suggest that you examine a printout of the program and do not fiddle with it on screen If you are looking at a screen version the temptation is to make changes without thinking enough about their consequences So you go from a program which does not work well to a program which does not work at all At this point you find that you have probably not got a back up copy either Additional approaches include working with others to help identify errors For example reading code out to others in a group or explaining code to other people The problem is that many bugs are so hard to fix Staring at the screen and tinkering with the code does not help much with the more complex problems One reason for this is that modules are defined in one part of the code and called in another to check the progress of the program s execution you have to keep paging up and down I
77. tested until the condition fails i e Num becomes gt 10 and the loop exits with Num 10 The equivalent do while loop tests the condition in the first line and if false the loop will not be entered If true then the loop will run until Num 10 when the loop exits When should you use one and when the other If you know it is safe to run the code at least once probably you should use the do until loop If you must run the code at least once then again a do until loop is a good solution If there is any reason to doubt the value of any variables etc in the loop then you should always use the do while loop Menus often use do until loops as you know that the menu needs to be run at least once for the user to see it A number of worked solutions to problems are given here make sure you understand what is going on in these examples You may wish to try running these programs for yourself and to experiment with making changes to the code to ensure you fully understand what is happening Example 1 Guessing an age with do until and nested else 1f statement Problem A program is written to ask the user guess an age the value of which is stored as a program constant The program counts the number of tries needed to guess the correct age and declares whether the guesses are high or low Solution The algorithm is shown below set the number of guesses to 0 do request an age from the user if guess gt age output message el
78. the process then the entire model has to be revised to take HERIOT WATT UNIVERSITY 2006 13 14 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS these errors into account The model as it stands represents an ideal world rather than reality Developers do not know everything the client will need at the start of a project they make wrong decisions possibly based on incomplete information Even with perfect knowledge and infallible decisions the model could not stand as it is because as time goes by more information comes to light which changes how the software is to perform The model can be improved significantly if it is made to be iterative Ideally you would start a process with the analysis and work through the stages in turn doing everything only once In practice this happens rarely People make mistakes faults become apparent that can only be corrected by going back to an earlier stage of the process The model can be modified to represent this iteration Other models exist that are based on the waterfall method such as Structured Systems Analysis and Design Method SSADM This contains a comprehensive and rigorous set of standards that are implemented at the analysis and design stages only We will go into this method more fully later in the topic 2 3 1 Review questions Q6 In the process of software development the waterfall model emerged because a Software engineering dictated that such a method should exis
79. the running total to 0 display Give me your first number get number typed in at the keyboard do while user s number gt 0 add 1 to the running total display Give me the next number get input typed in at the keyboard loop display the total ON OOP WYN H The Visual Basic program is shown as Code 7 5 Option Explicit Private Sub Command1_Click 17th February 2004 gt Program by Fred Fink gt This program will illustrate the Do While loop program addPos gt This program will add a list of positive numbers typed in at the keyboard The program will stop when a negative number is entered and display the total Dim iNumber As Integer Total As Integer Total 0 iNumber InputBox Give me your first number Do While iNumber gt 0 Total Total iNumber iNumber InputBox Give me your Next number PicDisplay Print Your numbers add up to Total Loop End Sub This file DoWhile txt can be downloaded from the course web site Code 7 5 The program output is shown in Figure 7 7 HERIOT WATT UNIVERSITY 2006 7 4 DOLOOPS 189 Do While loop our numbers add up to 10 our numbers add up to 20 our numbers add up to 30 our numbers add upto 46 our numbers add up to 66 our numbers add up to 71 ournumbers add up to 71 our numbers add up to 71 Figure 7 7 Example 2 Validating character input Problem A program is written to prompt the user to enter a character The program continue
80. to pass Similarly the maintenance The maintenance is documentation only has to stand up to the probably going to be done by someone examiner s scrutiny who has not written the original program and knows nothing about the original design decisions unless they have been documented Programs are written for use by other The programs are not intended to be people who might have little used understanding of computers Real life programs are written for use by clients who require the software systems to help them do their jobs They probably expect them to work like any complicated electrical appliance such as a TV You switch it on and it works Change channels and the channels change The brightness and other controls do what they are supposed to do without stopping the TV from working or having some unexpected side effects The programmers goal is to produce software as robust and easy to use as a TV In reality this is going to be impractical but when you design programs this should be something you need to bear in mind For example keyboard input should be checked and incorrect input rejected But this is not enough you need to give a message to the user to help them type the correct information next time If you do not do this you leave them floundering they know what they typed is wrong but have no idea why or what the correct input should be Any other errors which arise in the program should HERIOT
81. value In this case the value 12345 is input to the program a caption appears in the title bar and the InputBox appears at coordinates 50 50 In most cases only the prompt is used Note that if a string contained 7902X7BMD then the Val function would return the value 7902 and ignore the other characters 2 Use of the Text Box The main advantage of a text box is that a user can type in much more information during the execution of a program Since text boxes can hold large amounts of text it is best that they are created using a vertical scroll bar Text Box THIS IS AN EXAMPLE OF ENTERINGALARGE A AMOUNT OF TEXT INTO A TEXT BOX NOTICE THAT A VERTICAL SCROLL BAR IS PRESENT TO ENSURE ALL THE TEXT IS READABLE SHOULD IT OVERFILL THE TEXT AREA 4 TEXT BOX CAN ALSO BE USED TO INPUT NUMERICAL VALUES INTO 4 PROGRAM 45 LONG 45 THE TEXT v By highlighting the text box and pressing function key F4 the properties window opens From this window the options Vertical scroll bar and Multiline True are set If numeric values have to be input then like InputBox the Val function is used Number2 Val Text1 text HERIOT WATT UNIVERSITY 2006 6 3 BUILDING APPLICATIONS 115 Exercise 1 Open a new Visual Basic project and experiment with adding buttons and text boxes to the form from the toolbox window Use the properties window to try out various settings and captions for the buttons and settings for the text box and form
82. value Setup Call procedures Populate_List List Search_for_max Pointer Maximum List End Sub Private Sub Setup Initialise variables 257 Randomize and clear output boxes PicList Cls PicResult Cls PicList Print Pointer 0 Maximum 0 End Sub Private Sub Populate_List ByRef List Fill array with Dim Fill As Integer 16 random numbers For Fill 0 To 15 List Fill Int 100 Rnd 1 PicList Print List Fill Next Fill End Sub Private Sub Search_for_max ByVal Pointer ByVal Maximum ByRef List Maximum List Pointer Do Pointer Pointer 1 If Maximum lt List Pointer Then find maximum Maximum List Pointer End If Loop Until Pointer gt 14 PicResult Print The maximum value in the list is Maximum HERIOT WATT UNIVERSITY 2006 258 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS End Sub Private Sub Command2_Click End End Sub This file Maximum txt can be downloaded from the course web site The above code can easily be modified to return the minimum value Maximum 84 41 22 64 53 36 53 47 95 56 76 55 72 48 59 59 The maximum value in the list is 95 HERIOT WATT UNIVERSITY 2006 8 7 SUMMARY 259 Finding the maximum and minimum value in a list of integers Write a program that will find the maximum and minimum values in a list of integers Use the algorithm you have seen in the maximum minimum animation to help you Remember to construct approp
83. where the name 30 min e does not appear in the list e appears at the start of the list e appears at the end of the list e appears within the list 8 6 2 Counting Occurrences Programs often have to count occurrences Examples include counting the number of e students who achieved particular marks in an examination e rainfall measurements greater than a particular level e words equal to a given search value in a text file The basic mechanism is simple 1 a counter is established 2 a list is searched for the occurrence of a search value 3 every time the search value occurs the counter is incremented You should notice that counting occurrences examines the entire list and so the algorithm is a variation of the linear search algorithm described above The general counting occurrences algorithm is Counting occurrences general algorithm 1 counter 0 2 prompt the user for the search value 3 set pointer to start of list 4 do 5 compare search item to list position 6 if equal then 7 increment count 8 end if 9 move to next position in the list 10 until until counter gt 15 11 report number of occurrences HERIOT WATT UNIVERSITY 2006 254 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS Below is the full Visual Basic implementation Option Explicit Dim SearchKey As Integer Pointer As Integer Fill As Integer Dim Occurrence As Integer Dim List 15 As Variant Private Sub Command1_Click Pr
84. 15 is out of range Try again 99 gade 68 gade B 50 gade C 49 gade D 15 gade E 10 is aut of range Try again End Program Figure 6 18 Example 3 Extending the testing for a weekend or weekday using text Input Problem Write a program to test whether a string variable Day holds text that represents a week day or a weekend Assume input can be in either lower or upper case Solution The statement in the previous example Code 6 14 could be extended to give the following program Code 6 16 Option Explicit Private Sub Command1_Click program use of case statement 3 16th February 2004 gt Program by Fred Fink To show the use of case with upper or lower case input Dim Day As String Dim FirstLetter As String Day InputBox Please enter the day FirstLetter Left Day 1 Pick off first character Select Case FirstLetter Case s S PicDisplay Print Day is the weekend Case m M PicDisplay Print Day is a weekday Case t T PicDisplay Print Day is a weekday HERIOT WATT UNIVERSITY 2006 6 16 THE SELECT CASE STATEMENT Case w W PicDisplay Print Day is a weekday Case f F PicDisplay Print Day is a weekday Case Else PicDisplay Print Day is not a day End Select End Sub Private Sub Command2_Click End End Sub This file Case3 txt can be downloaded from the course web site Code 6 16 Program output is shown in Figure 6 19
85. 2 Answer 5 8 3 2 d Answer 5 8 3 2 Q3 If the value of 1 represents TRUE and 0 represents FALSE which one of the following statements is true a 1 AND 0 TRUE b NOT 1 FALSE c 1 OR 1 FALSE d 0 AND 0 TRUE Q4 Consider the following segment of programming code For x 1t03 For y 1 to 3 Sum X y Next y Next x Print Sum When run what would be the final value of the variable Sum a0 0 D ZT om FM Q5 Which one of the following statements represents a valid string assignment Name Bert Number 12345 Paper Scots man All of the above Q O 0 9 HERIOT WATT UNIVERSITY 2006 108 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 6 1 Introduction In this topic you will be introduced to the Visual Basic programming environment Variables and data types are discussed with reference to local and global forms and scope together with fundamental programming statement structures Formatted input and output constructs are described and exemplified using respective Visual Basic code More advanced techniques involve conditional statements such as nested IF statements and the CASE construct Each Visual Basic construct is exemplified using pseudo code and high level equivalent 6 2 The Programming Environment In this topic and others all language features are exemplified using Visual Basic 6 Users of Visual Basic NET should find few incompatible problems
86. 2006 Topic 4 Personnel Contents 4 1 introduction a pia 2645 2 SE be orm Dad ma mare Phd AE L o 4 2 Personnel 25 nement AA 4 3 The Clients v8 paa Pe eS SRS Sete ele a a 4 4 The Project Manager 4 5 The Systems Analyst 4 5 1 Collection of Information 4 5 2 Analysis of the information 4 5 3 Review Questions 4 5 4 Production of the problem specification 4 6 The Programming Team 4 7 Independent Testing Group 4 7 1 Review Questions 4 8 Summary 444444 ee 4 9 End ortopic test ans ns amp amp amp 4 ane ae 2e ve a a a a ane te eee ie BR AK ae ae act a Prerequisite knowledge There are no prerequisites for this topic Learning Objectives e Identify the personnel at each stage of the Software Development Process e understand the role of each person 68 68 68 69 70 71 72 73 73 74 75 76 77 77 67 68 TOPIC 4 PERSONNEL 4 1 Introduction The Software Development Process involves many people throughout a computer system s lifecycle In this topic you will meet the personnel involved with a brief outline of their activities 4 2 Personnel The software development process is initiated by one of two processes e eit
87. 24 One disadvantage of using an interpreter is a Looping structures have to be interpreted each time they are entered b It stops execution when an error is encountered c It helps the user to debug programs d An interpreter is ideal for beginners Q25 High level languages have to be translated because choose one Computers can only understand machine code Source code is faster to run than object code Programs run faster when converted to binary All of the above 5 11 Summary The following summary points are related to the learning objectives in the topic introduction e there are numerous types of programming languages in use today e they are difficult to organise into discrete categories because of overlapping properties e features of procedural languages lend themselves to most of the programming tasks of the Higher computing course e high level languages have to be translated to machine code by compiler or interpreter e syntax and semantics of the language are part of the translation process e types of errors can be picked up by translators e scripting languages are now of great use in web page design 5 12 End of topic test An online assessment is provided to help you review this topic HERIOT WATT UNIVERSITY 2006 Topic 6 High Level Language Constructs 1 Contents 6 1 Introduction 6 2 The Programming Environment 6 3 Building applications 6 3 1
88. 24 When high level language code is compiled the code produced is called choose one a Executable b Object c Machine d All of these Q25 Data processed by computers must be structured in some way Which one of the following reasons is true To allow for faster processing So that databases can be used Since there might not be sufficient external storage space a b c d To cater for different data structures 2 7 Testing in closer detail Testing has several purposes It should check that e the software meets the specification e itis robust e itis reliable Commercial software is not exhaustively tested at the testing stage Software can be complicated and the available time is limited There must be a balance between creating a product for the market and exhaustive testing If errors become apparent after release the company will fix them and release with an updated version Test data preparation Testing can never show that a program is correct Even with extensive testing it is almost certain that undetected errors exist Testing can only demonstrate the presence of errors it cannot demonstrate their absence A program can be regarded as succeeding if it passes a test the test can be regarded as succeeding if it makes the program fail HERIOT WATT UNIVERSITY 2006 2 7 TESTING IN CLOSER DETAIL Unit Testing Module Testing Sub system Testing Integration Testing Acce
89. 6 3 BUILDING APPLICATIONS 117 PicDisplay Print numberi number2 number3 Sum PicDisplay Print End Sub Run the program using your own values of number1 number2 and number3 Your output should look like the following Formatted output Output using commas 1 2 Output using semi colons 1236 Find out what the output would be if the Val function is removed from the InputBox statement Use of TAB and SPC Two valuable print functions are TAB and SPC that allow for more formal results TAB 6 will begin output 6 units from the left margin SPC 6 will output 6 units from the previous output Exercise 5 Modify the previous code as follows and run the program PicDisplay Print PicDisplay Print Tab 2 number1 Tab 14 number2 Tab 26 number3 Tab 38 Sum PicDisplay Print PicDisplay Print Spc 4 number1 Spc 9 number2 Spc 9 number3 Spc 7 Sum HERIOT WATT UNIVERSITY 2006 118 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 This time you end up with the output that should look like the following Formatted output number number2 numbers Sum 1 2 3 6 You will learn more about formatting values later 6 4 Program Structure A typical Visual Basic program takes the form shown in Code 6 1 Option explicit General area Public or Global variables declared here Private Sub cmdClick_Click constant definitions gt the constants used in the program variable definitions
90. 61 e You start testing if the variable number is greater than or equal to 1000 in which case there are 4 digits you must be assuming that the variable number is not greater than 999 and the variable n_digits is set to 4 If it is not greater than or equal to 1000 then you move onto the next branch of the if statement e The next condition tests the variable number to see if it is greater than or equal to 100 If this is true then you know the variable number has a value between 100 and 999 and so it must have 3 digits and the variable n_digits is set to 3 Again if this condition is not fulfilled then you move onto the next branch of the if statement e The next condition tests the variable number to see if it is greater than or equal to 10 If this is true then you know the variable number has a value between 10 and 99 and so it must have 2 digits and the variable n_digits is set to 2 Again if this condition is not fulfilled then you move onto the next branch of the if statement e The next condition tests the variable number to see if it greater than or equal to 0 If this is true then you know that the variable number has a value between 0 and 9 and so it must have one digit The variable n_digits is set to 1 e The next branch of the if statement is not an elseif branch but an else branch and so does not have a condition but is the branch that is executed if none of the other conditions are met Execution of this branch of the
91. 81 Q31 a value_1 0 Hello Q32 b 10 HERIOT WATT UNIVERSITY 2006 282 ANSWERS TOPIC 8 8 Procedures and Standard Algorithms Revision page 223 Q1 Q2 Q3 Q4 Q5 b That the input data is within specified limits d All of the above b 5 b A sequence of instructions that can be used to solve a particular problem a Linear search Answers from page 236 Q6 b Repetition of lines of code are avoided Q7 d A footer Q8 d All three options are true Q9 b Anything that happens to the formal parameter happens to the actual parameter Q10 c 56153 Turning a procedure into a function page 241 function getValidNumber as integer Dim numberOk as boolean Dim number as integer do number Inputbox Input a number numberOK number gt 0 if not numberOK then Print The number must be greater than 0 end if loop until numberOK getValidNumber number end function Using procedures or functions page 242 Using the procedures program sumi dim first as integer second as integer sub getValidNumber ByRef number as integer var numberOk as boolean HERIOT WATT UNIVERSITY 2006 ANSWERS TOPIC 8 do number Inputbox Input a number numberOK number gt 0 if not numberOK then Print Make it positive end if loop until numberOK end sub function sum a as integer b as integer as integer sum a b getValidNumber first getValidNumber second Print The total is
92. A a te ee ae SD at dr aaa de de En eee A aS 8 89 End OftOpic test s s bee firmes rte ee ae EE URSS se eS Prerequisite knowledge Before studying this topic you should be able to e describe and exemplify pre defined functions e recognise appropriate use of the following standard algorithms input validation find min max count occurrences linear search 223 224 225 226 226 227 229 232 236 237 242 247 248 249 253 256 259 259 221 222 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS Learning Objectives understand and be able to use procedures in programs understand and be able to use functions and user defined functions in programs understand how the use of procedures and functions aids modularity of programs understand parameters and how they are passed in out in out understand parameter call by value and call by reference be able to describe in pseudocode and implement standard algorithms linear search counting occurrences and finding maximum minimum HERIOT WATT UNIVERSITY 2006 8 1 INTRODUCTION 223 Revision e Q1 Apiece of programming code contains a validation routine This is to ensure a That the program produces the correct output b That the input data is within specified limits c That the output is within specified limits d That the input data is restricted to characters only Q2 Programming languages usually contain a collection of pre defined functions Which one o
93. E CHARACTERISTICS 63 As examples of an unexpected condition we could take something going wrong with a printer it jams or it runs out of paper or a disc drive not being available for writing because it simply isn t there the user s forgotten to put in the floppy disc 3 9 2 Reliability A reliable program is able to react to the unexpected without crashing It should possess the ability to cope with errors and unexpected events during its execution Possible outcomes of error encounter could be e inform the user e die gracefully e recover reasonably within a minimum time period 3 9 3 Portability A portable program can run on a variety on machine architectures under different operating systems with little or no modification A portable program is one which is machine independent However the problem of porting programs from one operating system to another still exists The problem became acute with the development of the Internet which is meant to enable communication between all sorts of computers and operating systems A solution was devised by Sun Microsystems which introduced another layer of software called Java Programs written in Java are compiled into bytecode that can be run using a Java interpreter This is available for different machine platforms eg Apple Macs PCs etc A machine with a Java interpreter installed is Java enabled A Java enabled machine can run Java bytecode produced on any another kind of machi
94. Example ABS X Returns the absolute value of X ABS 5 6 5 INT X Returns truncated integer part of X INT 34 5 34 SQR X Returns the square root of X SQR 25 5 RND Generates a random number X 100 RND will give between 0 and 1 random numbers from 1 to 100 TAB X Outputs at print position X Print TAB 5 SPC X Outputs number of spaces between Print SPC 3 last printed position and the next ASC X Returns the ASCII value of a Print ASC A returns 65 character X CHR X Returns an ASCII value into a Print CHR 68 returns character D VAL X Returns the value of string X VAL 76923 76923 STR X Returns the string of value X STR 1234 1234 User defined functions work in exactly the same way as Visual Basic in built functions and extend the range of programming possibilities Here as a simple example is a little function that simply doubles the value sent to it function double number as integer as integer double number 2 end function The function would then be called as DoubleNumber double 10 We could combine this in a section of a program with a procedure to get a valid positive number Program getNumbers Dim number integer getValidNumber number print Twice that is double number sub procedure getValidNumber ByRef number as integer do number inputbox Enter a number loop until number gt 0 end sub function double number as
95. Exercise 2 Open a new Visual Basic project and produce the following form that shows text boxes labels and buttons Use the properties window to create captions for the objects labels and buttons are in bold Number addition Number 1 Number 2 Result Output methods 1 The MsgBox The MsgBox function is useful in situations where the user requires for example confirmation of an action In its simplest form the format of the function is MsgBox The value entered was within the required range The output screen would look like The full format of the MsgBox statement is MsgBox Prompt Buttons Title HERIOT WATT UNIVERSITY 2006 116 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Prompt is the message to be displayed in the MsgBox Buttons is a numeric expression that specifies which buttons to display with or without icons The values are 0 default 1 2 3 4 5 16 32 48 and 64 Title The string message displayed in the title bar Exercise 3 Experiment with MsgBox button values and create your own messages 2 The Print command The print statement is probably the most used output command since it can be used on its own or in combination with other objects and functions Used on its own the print statement with no explicit destination will produce output to the current window which in most cases is the Visual Basic form For example if X 5 and Y 7 the following statement will output
96. For example test data will be drawn up on the basis of the specification The specification can be used as a checklist to ensure that the development process remains on target A systems analyst s main task can be summarised as follows e translating client requirements into highly specified project briefs e identifying options for potential solutions and assessing them for both technical and financial suitability e presenting proposals to clients e working closely with programmers and a variety of end users to ensure technical compatibility and user satisfaction e ensuring that budgets are adhered to and deadlines met e drawing up a testing schedule for the complete system e overseeing the implementation of the new system e providing training to users of the new system 4 6 The Programming Team The programming team is responsible for the second part of the project creation the coding phase of the software development process They work to the design created by the systems analyst They are also responsible for testing the software and for maintaining it once it has been installed The team will report to the systems analyst As a rule at least in large projects the programming team reports to the systems analyst and tends not to have much contact with the project manager The analyst schedules the work keeps an eye on performance and oversees the HERIOT WATT UNIVERSITY 2006 4 7 INDEPENDENT TESTING GROUP develo
97. ITY 2006 8 TOPIC 1 INTRODUCTION TO SOFTWARE DEVELOPMENT PROCESS you need to consider the background and capabilities of intended system users There is often a trade off between these factors and the cost of producing the software This is illustrated in the diagrams in Figure 1 1 As you can see costs increase dramatically as developers attempt to provide software that is 100 percent reliable Making software more efficient also increases the amount of money that needs to be invested cost cost efficiency 100 Reliability Figure 1 1 Cost of Software Systems 1 7 Summary The following summary points are related to the learning objectives in the topic introduction e software development has its roots in software engineering e software development is a complex process involving many facets of professional expertise e no matter how simple or complex a program is the elements of software development are almost mandatory to ensure well planned programs e well planned programs take time to evolve e no matter how rigorous the software development processes are errors can still occur in large commercial software systems 1 8 End Of Topic Test An online assessment is provided to help you review this topic C HERIOT WATT UNIVERSITY 2006 Topic 2 Features of Software Development Process Contents 2 1 Introduction 2 2 Preamble 2 3 The Waterfall Method 2 3
98. IVERSITY 2006 212 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Average temperature Loop values Anay value 0 l 2 3 4 5 6 8 Run Program Lnmnnnonnrencscsencsssoscscscscscssseses Figure 7 15 Simulations Using arrays makes it easy to simulate many numerical activities that otherwise would be fairly tedious to do manually For example analysing the results of tossing a coin 1000 times throwing die or spinning a roulette wheel can all be dealt with in one dimensional arrays Such simulations make use of random numbers that can be generated between upper and lower limits for example tossing a coin random values 1 for heads or 2 for tails throwing a die random values between 1 and 6 roulette random values between 0 and 49 Random numbers Visual Basic has a built in function RND that produces a random number from O to 1 The randomise function allows the RND function to start from a seed value and to produce a series of numbers based on the seed Random numbers are generated internally using the computer s internal clock Since the random values produced are real they must be converted into integers before being stored in the array This can be achieved using another function INT Values are rounded down to the nearest integer HERIOT WATT UNIVERSITY 2006 7 5 ARRAYS 213 For example Int 7 3 Int 6 8 7 7 Example 2 Simulation of throwing a coin Problem Write a program to simu
99. Input and Output Controls 6 4 Program Structure 6 4 1 Example program 6 5 Datatypes 6 6 Visual Basic Nomenclature 6 6 1 Review Questions 6 7 Declaring Variables 6 7 1 Implicit and Explic 6 8 Declaring constants 6 8 1 Example program 6 8 2 Example program it declaration 1 Calculating the circumference of a circle 2 Use of a boolean variable 6 8 3 String variables and functions 6 8 4 Concatenation 6 9 Variables and scope 6 9 1 Review Questions 6 10 Operators 6 10 1 Operator precedence 6 11 Programming constructs 6 11 1 Sequence 6 11 2 Selection 6 12 The IF Statement 6 13 The If Then Else Statement 6 13 1 Comparison Operators 6 13 2 Relational operators 6 13 3 Logical Operators 6 13 4 Logical AND 6 13 5 The Logical OR Inclusive 6 13 6 Logical XOR Exclusive OR 6 13 7 Logical Not 6 13 8 Review Questions 108 108 110 112 118 119 121 122 123 124 125 128 128 130 131 132 135 137 138 139 141 141 142 142 145 149 150 151 151 153 155 156 156 105 106 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 6 14 Nested IF Statements
100. Mark gt 85 And iMark lt 100 Then sGrade A Else PicDisplay Print iMark is out of range Try again End If If iMark gt 0 And iMark lt 100 Then PicDisplay Print iMark grade sGrade End If End Sub Private Sub Command2_Click End End Sub This file Grades txt can be downloaded from the course web site Code 6 13 Figure 6 16 shows the program output HERIOT WATT UNIVERSITY 2006 6 15 IF THEN ELSEIF Form 105 is out of range Try again 95 gade 81 gade B 55 gade C 43 gade D 23 gadeE 5 is out of range Try again End Program Execute Figure 6 16 Calculating the number of digits in a number Learning Objective Refining an existing program to make it user friendly Write a program which will calculate the number of digits in a number The error messages should be helpful and user friendly The program should deal correctly with numbers having four or more digits by giving the error message Value out of range Maximum of three digits numbers please Calculating Leap Years Learning Objective Be able to use the if statement Be able to make us of constants where appropriate A leap year is a year which is exactly divisible by 4 unless it is exactly divisible by 100 in which case it is only a leap year if it is exactly divisible by 400 Write a program which prompts the user for a year and then displays if it is a leap year or
101. PicDisplay Print Both words pass are identical Else PicDisplay Print Wordi and Word2 are not identical End If End Sub Private Sub Command2_Click End End Sub This file Password txt can be downloaded from the course web site Code 6 10 Program output is seen in Figure 6 13 HERIOT WATT UNIVERSITY 2006 6 13 THE IF THEN ELSE STATEMENT Form Both words Daffodil are identical Daffodil and Tulip e not identical Daffodil and daffodi are not identical End Program Execute Figure 6 13 Notice from the third entry that the input is case sensitive How could this be resolved Using the logical and operator in an if statement Construct an if statement that displays a message if both the variables number1 and number2 are greater than 10 Validating numeric input and program testing Use this fragments of code you have just seen in this section to help you write a program which will accept a value from the keyboard and print yes if it is positive and even Test your program with positive and negative numbers odd and even numbers and make sure it passes all the tests Make a tabulated list of the numbers you use and the results the program gives for each input Use both positive and negative numbers not neglecting zero 6 13 5 The Logical OR Inclusive If either the expression before the or or after the or is true then the whole expression is true This also means that if both
102. Prerequisite knowledge 173 174 174 179 184 185 186 186 187 192 198 200 202 203 204 208 209 220 220 Before studying this topic you should be able to describe and use the following constructs in pseudo code and a suitable high level language e fixed loops e conditional loops using simple and complex conditions e nested loops e 1 D arrays 171 172 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Learning Objectives e Be able to declare a 1 dimensional array e Be able to access array elements e Be able to manipulate data within arrays using iterative structures HERIOT WATT UNIVERSITY 2006 7 1 INTRODUCTION Revision Q1 An array is described as a structured data type This means that a Data items are all in order b Data items will take up a lot of computer memory c Data items of the same type are grouped together d None of the above Q2 What occurs when a 1 D array is initialised All array elements are set to the same value All array elements are put into order Only the first array element is set to some value Nothing occurs when an array is initialised a b c we a a d Q3 A 1 D array string called Days 0 6 hold the days of the week The 4th array element is assigned the value Wednesday The correct statement for this is a Days 4 Wednesday b Days 3 Wednesday c Days 4 Wednesday d Days 3 Wednesday Q4 An array called List 5 contains the integers 1 to 6
103. SCHOLAR Study Guide SQA Higher Computing Unit 2 Software Development David Bethune Heriot Watt University Andy Cochrane Heriot Watt University Tom Kelly Heriot Watt University lan King Heriot Watt University Richard Scott Heriot Watt University Heriot Watt University Edinburgh EH14 4AS United Kingdom First published 2004 by Interactive University This edition published in 2007 by Heriot Watt University Copyright 2007 Heriot Watt University Members of the SCHOLAR Forum may reproduce this publication in whole or in part for educational purposes within their establishment providing that no profit accrues at any stage Any other use of the materials is governed by the general copyright statement that follows All rights reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means without written permission from the publisher Heriot Watt University accepts no responsibility or liability whatsoever with regard to the information contained in this study guide SCHOLAR Study Guide Unit 2 Computing 1 Computing Printed and bound in Great Britain by Graphic and Printing Services Heriot Watt University Edinburgh Acknowledgements Thanks are due to the members of Heriot Watt University s SCHOLAR team who planned and created these materials and to the many colleagues who reviewed the content We would like to acknowledge the assistance of the
104. Stage This stage and also design is extremely crucial to the entire cycle of events Any problems occurring at this stage will be propagated through the system and will become increasingly costly to rectify when discovered Analysis is an attempt to understand a given problem clearly and exactly and to generate a solution The outcome will be a specification that is used as the basis for all subsequent work Sometimes this stage begins with a vague idea or rough outline of the problem and ends with a precise problem specification On other rather more formal occasions it will start with a full requirements specification that serves as a legal contract between the client organisation and the development team and end with a system specification This will include hardware and software specifications and notes on project issues such as objectives constraints costs and schedule It may also include a full functional specification which will describe exactly how the system is meant to behave The functional specification is what the development team will follow in creating the software system Questions to be asked at this stage would include e What are the new system requirements e What are the costs involved e How long will it take to implement Details would be gathered by a variety of methods such as interviews and questionnaires 2 3 3 The Design Stage Once the precise problem specification has been agreed by both client a
105. The programming structure required to produce the above message could best be achieved using choose one A case statement A for loop A while loop a b c d An until loop Q30 An array numbers is declared with 6 elements and initialised to contain the following values 030259 During a program run the array elements are changed as follows numbers 2 6 numbers 5 7 numbers 1 4 The array contents are now a 030259 b 430259 c 460270 d 046257 HERIOT WATT UNIVERSITY 2006 7 5 ARRAYS 209 Q31 An array value_1 has been declared in Visual Basic to be of type single and to hold 5 values Which one of the following statements would produce an error when the program is run a value_1 0 Hello b value_1 4 89 45 c Neh a ae d value_1 2 16 Q32 What is the least positive value of the variable index that will cause the following code to fail Dim array_1 19 As integer Dim X As integer index As integer array_1 index array_1 index index a 9 b 10 c 11 d 12 7 5 5 Worked example programs A number of worked solutions to problems are given here make sure you understand what is going on in these examples Run these programs for yourself and experiment with making changes to the code to ensure you understand what is happening It is important that you do this programming is a skill which is learned by doing Just reading the examples will not give you that skill
106. UNIVERSITY 2006 249 250 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS 3 34 is compared to key Not equal so pointer moves on 4 76 compared with key Success Key found at position 4 in the list _ One method is to search the entire list from start to finish and stop only when the end of the list is reached This algorithm is shown below Linear search 1 searching the entire list prompt the user for the search value start at the first element in the list do while not end of list if the current element lt gt search value then move onto the next element in the list else output search value and position end if loop oo OO TF WN FE This is not a very efficient way of doing things Why bother to search the remainder of a list when the item has been found There are instances when you will want to search the entire list e g if you wish to replace all words in a list that begin with L to words that begin with P then the search would stop when you reach the end of the list The counting occurrences algorithm that you will meet next will accomplish this scenario The following algorithm makes use of a complex condition and a boolean variable Linear search 2 stopping when the search value is found 1 set found to false 2 prompt the user for the search value 3 start at the first element in the list 4 do while not end of list and found is false 5 if the current element search value then 6
107. VERSITY 2006 7 2 ITERATION 177 For Next Inches Centimeteres D 0 5 12 7 10 25 4 15 38 1 20 50 8 25 63 5 30 76 2 35 88 9 40 101 6 45 114 3 50 127 Figure 7 2 Note that the output of this program is in tabular form This was achieved using the TAB O function first to output the heading then the results Tab is short for tabulate and the output items are separated by the values within the tab statements If the value of step is not specified it is assumed by Visual Basic to be the value 1 by default Example 2 Displaying integers using negative step Problem Write a program that will output integers from 100 to 65 together with the corresponding characters that the numbers represent Use a for next loop with ve step and output the results in tabular form Solution 1 display The integers from 100 to 65 2 for counter 100 to 65 step 1 3 display the value of the integer and character 4 next counter The Visual Basic program is shown in Code 7 2 Option Explicit Private Sub Commandi_Click 16th February 2004 Program by Fred Fink This program will illustrate the For Next loop using ve step HERIOT WATT UNIVERSITY 2006 178 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Dim Counter As Integer Dim Char As String PicDisplay Print Spc 3 Integer Spc 12 Character PicDisplay Print For Counter 90 To 65 Step 1 Char Chr Counter PicDisplay Print Spc 5 Counter Spc 15 Char
108. WATT UNIVERSITY 2006 1 4 COMPUTING DISASTERS be clearly notified to the user in common sense language A Windows exception error an example of an intimidating and aggravating error message which provides no useful information to anyone except a dyed in the wool Windows programmer 1 4 Computing disasters It has been said Computers make very fast very accurate mistakes While this may be undeniably true it has to be said that complacency still exists in the use of computers and the programs running on them Software development is important because in its absence you are bound to have a disaster in a project of any great size Large projects demand a large investment of money time and resources before any returns are possible Consider the following e One in five software systems fail to deliver to the agreed specification e Software maintenance is the single highest computer related cost for many companies e Some systems can take many years to develop running the risk of obsolescence before they are even commissioned Naturally a fair bit of planning goes into them But perhaps the planning is not all it might be because even with the best will in the world things can go terribly wrong The list below contains a few examples of computing disasters that could be attributed to complexity and the need for better planning 1 Ariane 501 on the 4th June 1996 Ariane 501 exploded 40 seconds after takeoff due to a software bu
109. a text string and value to the form Print The sum of the two variables X and Y is X Y If the form is populated with many objects it may be difficult to see the above output It is much better therefore if the output is directed to a specified window such as a MessageBox or PictureBox Although the latter object is meant for graphics it is also ideal for the output of lists of text Using a PictureBox the previous print statement would become PictureBox Print The sum of the two variables X and Y is X Y Usually the term PictureBox is changed to PicBox PicOutput PicDisplay Picture1 or whatever name is suitable for the output Exercise 4 Create a new project and place a command button and PictureBox on the form Rename the PictureBox as PicDisplay F4 then change property Name Double click on the command button and enter the following code The first and last lines are present by default so they can be ignored when entering the text Private Sub Command1_Click Dim numberi As Integer number2 As Integer number3 As Integer Dim Sum As Integer numberi Val InputBox Please enter a value number2 Val InputBox Please enter a value number3 Val InputBox Please enter a value Sum numberi number2 number3 PicDisplay Print PicDisplay Print Output using commas PicDisplay Print numberi number2 number3 Sum PicDisplay Print PicDisplay Print Output using semi colons HERIOT WATT UNIVERSITY 2006
110. all the stubs are properly linked Then the detailed work can begin It may have occurred to you that if top down design exists then what about bottom up analysis Bottom up design begins with the lower levels of detail for example a device driver for a peripheral that will require to be written around the program codes needed to operate the device The emphasis here is to write the individual modules and knit them all together to form the final program With object oriented programming the bottom up approach has been partially revived HERIOT WATT UNIVERSITY 2006 3 3 DESIGN METHODOLOGIES 3 3 2 Structure charts An important approach in practically all methods of analysis is to draw a picture of some kind Analysts use pictures to present a synopsis of a system which shows e the main elements of the solution e how they fit together It is not enough for the analyst to have a design in mind It must be represented in a form that can be used by all members of the team One method is to use structure charts which are sometimes called structure diagrams A structure chart gives a picture of the design Structure charts depict programs or parts of programs Styles vary in detail but in essence structure charts consist of boxes lines arrows and text A box represents a block of code and has a name Usually it is a descriptive expression starting with a verb it shows the block s purpose Structure charts can be drawn accordin
111. an be used for event driven Windows style programming with AWT Abstract Window Toolkit This a large collection of resources for building graphical user interfaces within the Java environment Sentence completion languages On the Web is a interactivity You should now complete this task 5 7 Scripting languages A Scripting language is a style of programming that produces ASCII text based scripts which are usually designed for writing small programs like batch files Scripting languages support high level language control features such as selection and iteration syntax but they are not considered programming languages as such Often referred to as glue code they are instead seen as being an enhancement of particular software packages Scripting languages are not new Job Control Language JCL was one of the earliest scripting languages to be used in the 1960s and 1970 s on mainframe computers using punched card input The main program cards were preceded by cards containing JCL code that initialised system requirements such as memory buffers etc and formatted the input and output parameters For example the following code requests buffer memory and formats the input and output data streams for all subsequent program runs BUFFERS 64 FILE CARDS INPUT 2 10 LINES 1 2 17 Examples of present day scripting languages are VBScript JavaScript Perl Python TCL Tool Command Language etc Applications that provide script
112. and see how fast the relative costs soar the further along the project path you are This is because so much earlier work has to be undone and then re implemented to fix the errors This is another good reason for careful analysis and design HERIOT WATT UNIVERSITY 2006 54 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION Cost Number of residual errors Figure 3 4 Cost of Residual Error Removal Relative cost to fix error R Feasibility Design Code Test by Test by Operation Designers Customer Phase in which error detected Figure 3 5 Cost of errors in software projects The purpose of test data is to determine that the system behaves as expected and is correct according to the program specification Tests may be used for different purposes These include e module testing on components e integration testing components function as a unit HERIOT WATT UNIVERSITY 2006 3 4 TEST DATA e system testing black box e acceptance testing ensures system is ready for operational use 3 4 1 Test data preparation Testing can never show that a program is correct Even with extensive testing it is almost certain that undetected errors exist Testing can only demonstrate the presence of errors it cannot demonstrate their absence A program can be regarded as succeeding if it passes a test the test can be regarded as succeeding if it makes the program fail One thing you have to watch for is that errors may not cause im
113. application then run by activating a key press combination or clicking on an icon Maintenance The upkeep of a program by repair and modification Methodology A technique involving various notations that enables the design of software to be implemented HERIOT WATT UNIVERSITY 2006 264 GLOSSARY Module library A module library includes code for standard algorithms that can be re used by programmers Normal operation Running of a program under expected normal conditions Object A data item that can be manipulated by a computer system for example a database record or a file Object oriented design A method that centres on objects and the operations that can be performed on them Object oriented language An object oriented computer language like Java that uses objects rather than actions and data rather than logic An object is represented by a class that can be extended to involve inheritance Optimised Refinement of code to make it more efficient Parameter An argument of a procedure or function that represents a local variable Parameter passing The mechanism by which data is passed to and from procedures and the main program Perfective maintenance Takes place when a system has to be enhanced in some way e g program run faster Portable The ability of a program to run on different machine architectures with different operating systems Problem oriented The focus is on the problem and how it is to be solved r
114. aracters count count 1 Loop length count 1 gt to account for increment when is read in Now check for palindrome isPalindrome True count 1 Do While isPalindrome And count lt length 2 If Palarray count lt gt Palarray length count Then isPalindrome False Else count count 1 End If Loop If isPalindrome Then PicDisplay Print is a palindrome Else PicDisplay Print is not a palindrome End If End Sub This file Palindrome txt can be downloaded from the course web site HERIOT WATT UNIVERSITY 2006 218 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Code 7 13 Examine the do while statements carefully You will see that the conditions are compound e the character read in must not be a full stop AND there must still be space left in the array e if both these conditions are fulfilled then the loop continues e if either one or the other condition fails then the loop terminates The do while isPalindrome and count lt length 2 statement tests whether you have gone halfway through the array AND whether the boolean variable isPalindrome has been set to false This needs a bit more explanation notice that we initialised isPalindrome to true at the beginning of the program if you look at the output statements right at the bottom of the code you can see that if isPalindrone is still true then the array is a palindrome if isPalindrome has been set to false at any
115. arte te 5 10 2 Interpreter 5 10 3 Respective Advantages 5 10 4 Review Questions Bel die SUMMARY eA e a Paes HCL A Pago dhe ti a aha AAA 5 12 End of topic test Prerequisite knowledge Before studying this topic you should be able to e describe and compare machine code and high level languages e explain the need for translation of high level language e describe the function of a compiler e describe the function of an interpreter 81 82 82 85 86 87 88 90 91 93 94 94 95 96 98 99 99 100 102 102 103 104 104 79 80 TOPIC 5 LANGUAGES AND ENVIRONMENTS e describe the process of recording a macro e assign a keystroke to a macro e describe examples of the use of macros e describe the features of a text editor Learning Objectives e understand the differences between procedural declarative and event driven languages e be able to describe the uses of compilers and interpreters e understand the functions and efficiencies of compilers and interpreters e be able to describe the features and uses of scripting languages e understand how to create and edit a macro e understand the need and benefits of scripting languages e be able to describe the use of module libraries HERIOT WATT UNIVERSITY 2006 5 1 INTRODUCTION 81 Revision e Q1 Programs are written in high level lang
116. ary The use of comments within source code to describe what it does HERIOT WATT UNIVERSITY 2006 GLOSSARY 263 Internal documentation The use of comments within source code to describe what it does Interpreter A program that translates a high level program line by line which it then tries to execute No independent object code is produced Iterative An iterative process is one that incorporates feedback and involves an element of repetition Jackson Structured Programming A diagrammatic design method for small programs that focuses on sequence selection and iteration Java A language designed by Sun Microsystems The language is portable because Java interpreters are available for a wide range of platforms Keyword A reserved word with a special meaning in a computer language For example for if dim in Visual Basic Legal contract A contract set up between client and development team the details of which are set out in the requirements specification which becomes legally binding should anything go wrong Lexical analysis Part of the compilation process where the source code is tokenised into symbols and stored in the symbol table Linear search A standard algorithm that perform a sequential search on a list of data items Machine code Native computer code that can be understood without translation Macro A block of code that automates a repetitive task Rather like a batch file they are normally created within an
117. ather than on the hardware on which the program will run Problem specification A document outline of what is to be solved in terms of programming a solution to a given problem Procedural language Also known as imperative languages because the programs follow a sequence of steps until they terminate The code is made up of procedures and functions HERIOT WATT UNIVERSITY 2006 GLOSSARY Procedure A block of code that when called from within a program will perform a specific action Process An activity that is performed by a piece of software Programming team A section of the development team responsible for the coding testing implementation and maintenance of the software Project manager A member of the development team who is responsible for the supervision of the project The main tasks are to keep the project on schedule and within budget Pseudo code A notation combining natural language and code used to represent the detailed logic of a program i e algorithmic notation RAD Rapid Application Development An alternative software development model that uses event driven languages for its implementation Recursion A programming technique that is iterative in that a procedure or function can call itself It is very demanding of computer memory Reference parameter Here the address of the actual parameter is accessed by the formal parameter Information is passed OUT from the procedure to the main program Reliable A prog
118. can be seen in Figure 8 9 Counting Occurrences 18 22 13 6 13 32 13 25 12 25 24 31 29 25 25 34 ia item 25 found 4 times in the list End Program Figure 8 9 Counting names in a list Write a program that will count the number of times a search name appears in a list of names Use the algorithm you have seen in the counting occurrences animation to help you Remember to construct appropriate test cases in advance of coding You should consider tests which e check for boundary conditions e g occurrence of the search value at the beginning or end of the list e no occurrences of the search value within the list HERIOT WATT UNIVERSITY 2006 256 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS e asingle occurrence of the search value e multiple occurrences of the search value 8 6 3 Finding Maximum and Minimum Computers are often used to find maximum and minimum values in a list For example a spreadsheet containing running times for videos might make use of a maximum algorithm to identify the video with the longest running time or a minimum algorithm to identify the shortest running time A database containing personal details of club membership might make use of maximum and minimum algorithms to identify the oldest or youngest member We are certain you can think of a few more for yourself Clearly these algorithms are extremely useful and very widely used To find a maximum we set up a variable which will ho
119. can easily be altered by mistake The use of local variables is frowned upon HERIOT WATT UNIVERSITY 2006 138 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Q15 The scope of a variable is an important aspect in programming Scope is best described as a The range of values the variable can cope with b The amount of memory required by the variable c The extent to which the variable can be seen by the rest of the program d The number of times the variable can be used in the program Q16 Which one of the following describes a boolean variable It holds a numerical value It cannot be used in expressions It is only used in looping structures It can have only the values true or false 2 22 6 10 Operators Assignment operator The assignment operator in Visual basic is equals sign The general form for the assignment operator is variable expression This statement says make left hand side equal to the right hand side It makes the variable take on the same value as expression You have already seen this used in previous programs For example circumference 2 PI x r where the result of the expression 2 PI ris assigned to the variable circumference Arithmetic operators Table 6 8 list the main arithmetic operators in Visual basic Table 6 8 Arithmetic operators Example Result add 16 14 30 subtract 27 9 18 real division 27 83 3 9 27 multiply 12 65 5 63 23
120. ce in using simple variables page 133 Q11 The variable number2 has not been declared There will be no output since the variable sum has no value and has not been declared Also the Print statement is wrong Answers from page 137 Q12 Q13 Global All three statements above Q15 Q16 c d Q14 b They are hidden from other procedures and functions c The extent to which the variable can be seen by the rest of the program d It can have only the values true or false Answers from page 156 Q17 d NOT Q18 a 11 Q19 c The execution of program statements in order from beginning to end HERIOT WATT UNIVERSITY 2006 277 278 ANSWERS TOPIC 6 Q20 b The expression is TRUE when both conditions being tested are TRUE Q21 c Assignment HERIOT WATT UNIVERSITY 2006 ANSWERS TOPIC 7 279 7 High Level Language Constructs 2 Revision page 173 Q1 c Data items of the same type are grouped together Q2 c Only the first array element is set to some value Q4 c Q3 d Days 3 Wednesday 1 8 3 9 5 6 Q5 Cc Iteration Answers from page 184 Q6 d Control loop variable is increasing in value by a constant amount determined by the programmer Q7 d For loopCounter 3 4 16 to 5 5 6 step 1 Q8 a Calculating the total number of marks entered at a keyboard Q9 a Triangle Q10 c 18 Answers from page 192 Q11 The value of n within the loop is never incremented
121. code which can be used by HERIOT WATT UNIVERSITY 2006 2 6 IMPLEMENTATION IN CLOSER DETAIL the computer system The code is written in a high level language such as Pascal C or Java and converted into code which the computer understands A high level language is one that people find relatively easy to understand The code written at this stage is called source code The machine can understand machine code a translation of the source code into the binary instructions which the machine understands This code because it can be executed by a computer is also known as executable code The translation from source code into machine code is carried out by a program called a compiler The resultant machine code is portable to machines of the same type running under the same kind of operating system Compiling and debugging large programs can take a lot of time Another form of translation that can reduce development time is an interpreter When an error is encountered the interpreter immediately feeds back information on the type of error and stops interpreting the code This allows the programmer to see instantly the nature of the error and where it has occurred He or she can then make the necessary changes to the source code and have it re interpreted As the interpreter is also executing each line of code at a time the programmer is able to see the results of their programs immediately which can also help with debugging So
122. contain information about the hardware and software requirements of the program The hardware specification will include details of the processor type and speed RAM required RAM desired monitor resolution graphics and sound card specifications etc It will also contain instructions about configuring the program HERIOT WATT UNIVERSITY 2006 31 32 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS DOCUMENTATION Software designed to operate or run on networks can be very complicated and require a good deal of expertise Technical guides can be very large and cumbersome and difficult to navigate 2 9 Evaluation in more detail The evaluation is important for the user and the software author There are two reasons for conducting an evaluation e does the software meet the users requirements e how can the software house improve the SDP in future projects The performance of the system can be assessed in various ways e how closely does it fit the system design e how well does it answer the problem specification Questions may also be asked about matters such as e was the project within budget HERIOT WATT UNIVERSITY 2006 2 10 MAINTENANCE IN CLOSER DETAIL e was the project completed to schedule The development team will wish to review the project perhaps to learn from any mistakes to ensure they incorporate good points in future programmes Software houses aspire to produce new and better versions of thei
123. d com ariane html e From champagne to shock Ariane 5 explodes Science Online http www flatoday com space explore stories 1996 060496c htm e Ariane 5 Learning from Flight 501 and Preparing for 502 European Space Agency ESA http esapub esrin esa it bulletin bullet89 dalma89 htm 2 Y2K Problem The Millennium Bug e Looking at the Y2K Bug CNN http www cnn com TECH specials y2k 3 NASA Mars Lander e NASA Human error caused loss of Mars orbiter CNN including video of news reports http www cnn com TECH space 9911 10 orbiter 03 e Metric mishap caused loss of NASA orbiter CONN http www cnn com TECH space 9909 30 mars metric 02 HERIOT WATT UNIVERSITY 2006 1 6 WELL PLANNED PROGRAMS 4 Passport fiasco e http news bbc co uk 1 hi uk_politics 486821 stm 5 Asylum issue e http news bbc co uk 1 hi uk_politics 1171147 stm 6 Millennium bridge e http www arup com MilleniumBridge Some other general web sites on disasters are Risks Digest http catless ncl ac uk risks Horror stories http www cs tau ac il nachumd verify horror html No bugs in Win 95 Interview with Bill Gates http www cantrip org nobugs html One of the best books on computing disasters is The Mythical Man Month by F P Brookes Addison Wesley 1995 This describes a huge IBM disaster in the late 1960s early 1970s but is just a relevant for today It is also a very good read not filled with jargon and tiresome self
124. d product of the software development process and represents the efforts of the development team being realised lt may take many months or even years to arrive at a working solution to the initial problem so it must be designed with due care and attention HERIOT WATT UNIVERSITY 2006 23 24 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS The system specification and functional specification will form the basis of designing the program under the following headings e hardware specification e choice of high level language e how the software will finally behave e choice of operating system e portability of the system Depending on the client s requirements each of the above will have a significant part to play in the final project Hardware aspects will include processor speed does the program require multiple processor facilities for optimum performance as in networked database applications or maybe maximum memory for caching information on a regular basis How much external storage is required for say regular backing up procedures and on what medium This is an important issue especially on networked systems where users files are archived on a daily basis The choice of high level language will be chosen that is best suited to the problem but also one which the programming team is conversant with and proficient in its use Modularity will be an important issue where the team can share the workload by compiling module
125. data files The program may also contain data that is assigned directly to variables or constants during execution time The output of information may be achieved through a variety of Visual Basic control structures that are placed on the form at the design stage Output can also be directed to a printer or to an existing file Since file I O is beyond the scope of the Higher Computing course only the graphical methods will be discussed at this stage The stages in writing a program in Visual Basic involve the following aspects e Design stage the form is used to compose the graphical elements of the program Command buttons and control boxes objects can be placed anywhere on the form and these will dictate how the application is to run e Setting properties the form itself and the objects it contains can have various properties set thereby producing the visual effects required of the program Although there are numerous properties for each object the main ones would include HERIOT WATT UNIVERSITY 2006 6 3 BUILDING APPLICATIONS 113 Name of the object Colour Caption attached to object Height width Font used Position of object within the form Border style Properties are changed by highlighting the object and pressing function key F4 This opens up the Properties window from which changes can be made e Coding stage code is written for each object and when the main program is run each event will become part of t
126. day Monday Tuesday Wednesday Thursday Friday Days of the week Saturday 0 1 2 3 4 5 6 7 8 9 A B C D E F Hexadecimal digits 1 2 50p 20p 10p 5p 2p 1p Decimal coinage 1 Dimensional array Also called a Linear List the data items are simply stored in consecutive locations within a block of computer memory as follows O Sunday f Days of the week 0 gt 1 Days of the week 1 2 Tuesday f Days of the week 2 Index Values 3 Days of the week 3 4 Thursday f Days of the week 4 5 Days of the week 5 6 Saturday f Days of the week 6 Thus the data item Tuesday is stored in array location Days of the week 2 and the data item Saturday as Days of the week 6 Each data item therefore is uniquely identified as an index or subscript Note that the index values are not actual memory addresses as such but simply refer to the data positions within the array Imagine you were to process the average temperature data in Edinburgh for the last 30 days If each of the day s temperatures are stored as separate variables you HERIOT WATT UNIVERSITY 2006 7 5 ARRAYS 201 would require 30 distinct variables and the storage and manipulation of these variables becomes difficult To overcome the above problem you can define a variable called temperature which represents not a single value of temperature but an entire set of temperatures This is i
127. design File Edit View Insert Modify Control Help Olalla Design documentation will often include more than one notation eg structure charts for the higher levels to provide an overall picture and pseudo code for the detail Often the design notations are used at different stages in the design process and serve to provide information to different audiences HERIOT WATT UNIVERSITY 2006 3 3 DESIGN METHODOLOGIES 3 3 1 Top down design with stepwise refinement Stepwise refinement is associated with Nicholas Wirth the creator of the Pascal and Modula languages It is an approach used throughout computing and in many other fields as well The idea behind it is this 1 a problem might be difficult to solve as it stands So you try to break it down into a set of smaller problems which might be solved more easily This represents the first step of the process 2 you then take the smaller problems one at a time and break them down into still smaller problems 3 you keep repeating this process of breaking the problems down until all the problems facing you are small enough to handle At this point you are able to create detailed design specifications which can be turned into programming code This notion of breaking larger difficult problems down into smaller easier to solve ones is the refinement Stepwise refinement is sometimes called top down design for the obvious reason that yo
128. down design and stepwise refinement understand the need for systematic and comprehensive testing understand the terms robustness reliability portability efficiency and maintainability in the context of software evaluation HERIOT WATT UNIVERSITY 2006 3 1 INTRODUCTION 43 Revision e Q1 At the design stage of the software development process pseudocode may be used to represent a solution to a problem Which of the following best describes the use of pseudocode a It uses ordinary English words b Itis high level language dependant c Itis very useful in complex program designs d It mostly uses high level language key words Q2 A structure diagram is a valuable aid to the programming team This is because They are easy to use and look good They are well structured so allow for faster program execution They are the best used with programs that produce a lot of output They can reduce the overall development time of a program a b c YS er waa a d Q3 Pseudocode can be considered to be an intermediate stage between a High level language code and machine code b English and high level language code c English and machine code d None of these Q4 At what stage of the software development process could a running program be modified or updated to a newer version a Testing b Evaluation c Maintenance d Implementation Q5 A computer program is designed to accept input values between 0 and 99 as whole n
129. dure resets the variables to 0 since they have been re declared Call 2 produces the new values from the local procedure Therefore local variables always win Note Extensive use of global variables is bad practice the use of global variables should be kept to a minimum since their values can change from anywhere within a program as you have just seen Local variables on the other hand offer the following advantages 1 side effects caused by a subprogram altering the value of a variable used elsewhere in the program are greatly reduced 2 debugging is easier since access to variables is localised and so tracking errors can be faster 3 the transfer of procedures and functions from one program to another is simplified Sentence completion global and local variables On the Web is a interactivity You should now complete this task 6 9 1 Review Questions Q12 In high level language code a variable declared outside a procedure is choose one a Local b Constant c Global d Functional Q13 Which one of the following describes the relationship between main memory and program variables a Name of variable identifies memory location b Data type defines how much memory is needed c Values of variables are held in main memory d All three statements above Q14 Which one of the following describes a local variable Can be accessed anywhere in the program They are hidden from other procedures and functions Their values
130. e ES TT Bou B Formi SR Re A RN Se El True NR E SE O PE a True RIN CERRY SMART Ber te ON ph Project Project1 E Forma Formi Figure 6 1 The default screen that you can see is in design mode and consists of four main windows 1 a blank Form window which is the interface with the application program you create The visual design of the program is created on this form which has gridlines to help build objects like text boxes label boxes and control buttons etc What is placed on a form will be seen in a window when the program is executed 2 a Project window that displays the files that are created during the construction of the program These files could be forms modules blocks of code not attached to a form graphics or control structures such as Active X required for the successful running of your program Note that only one project can be open at any given time 3 a Properties window that displays the properties of the objects created in the program The form window itself has properties associated with it 4 a Toolbox window that consists of all the controls necessary for developing a program Boxes labels buttons and other objects can be drawn on the form as part of the visual interface and also to allow input and output of data At this stage it is important to realise that when you create a program each form module graphic and ActiveX control is saved as an individual file HERIOT
131. e classified as being close to assembly language Cobol Visual Basic a b C c d Prolog Q10 Choose one of the following that could refer to imperative languages a They employ procedures and functions b Programs written in the language are linear in structure c Programming instructions are explicit d All of these 5 5 Declarative languages Declarative languages or Logical languages model problem solutions very differently Programmers specify what the problem is rather than how to solve it In PROLOG for example a program represents propositional knowledge as facts and uses rules to test facts building more complex propositions Collectively facts and rules are called clauses A proposition is the smallest unit of knowledge that can be judged true or false such as a collie is a sheepdog or a beagle is a hound or George passed a ball to Steven In PROLOG these statements would be written as sheepdog collie fact that a collie is a sheepdog hound beagle fact that a beagle is a hound passed a ball George Steven A rule contains a condition Cats purr if they are stroked by humans This would be expressed in PROLOG as purr X stroked by X humans where X cats Facts and rules form the basis of PROLOG programs to represent knowledge that are stored in a database This database can then undergo querying HERIOT WATT UNIVERSITY 2006 88 TOPIC 5 LANGUAGES AND ENVIRONMENTS Example Usi
132. e conditions are false then statement 1is ignored and statement 2 is executed Example The Car wash program could easily be modified to include the XOR instead of OR Rewrite the code and run the program 6 13 7 Logical Not Use of the logical not operator is shown below if Vone 6 and not Vtwo 6 then statement i end if In this example if Vone is equal to 6 and Vtwo is not equal to 6 then statement 1 is executed The not operator inverts true false values e g if the value is true then not true false Complete the following table by dragging the TRUE FALSE boxes into their correct place Example The Word1 and Word program could easily me modified to include the NOT operator Rewrite the code and run the program 6 13 8 Review Questions Q17 Operators are used within expressions to assign values to variables and perform calculations Which one of the following operators has the highest precedence in Visual Basic see AND NOT Q18 What would be the result of evaluating the following expression 3 4 6 4 11 a b 14 c 23 d 38 HERIOT WATT UNIVERSITY 2006 6 14 NESTED IF STATEMENTS 157 Q19 Which one of the following describes sequencing a Alteration in the flow of control based upon the test of a condition b The repetitive execution of a sequence of instructions c The execution of program statements in order from beginning to end d Exiting a loop structure after a sequence o
133. e main program knows nothing about the local changes made within the procedure The following diagram should explain what is happening Procedure declaration Change ByRef number Test memory location accessed by procedure lt Memory location Test 10 Procedure call Change Test HERIOT WATT UNIVERSITY 2006 234 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS The process of events is as follows 1 The procedure call Change test is initiated 2 The procedure declaration Change is accessed 3 Procedure Change now accesses the memory location of variable Test and gets the numerical value 10 Formal parameter number now has the value 10 4 Procedure Change code is activated and both number and Test 20 Points to note In this case a change is made to the program variable Test since it is the address of the variable that is referenced and not a copy Since the formal parameter and the actual parameter have now been assigned the same memory address this means that any changes to the formal parameter are passed back to the main program It is important that you understand the differences between call by value and call by reference Don t worry if you have the material in this section difficult to follow first time round Remember e if a parameter is used only to transmit a value to a procedure then make it a value parameter e if a parameter represents a result that is produced by the procedure to b
134. e maintaining it Commercial software is meant to install itself more or less but advice on installation will also be included in either or both of these guides Other documentation is largely for the benefit of the development team and will include all the documents produced in the course of the development process This documentation is essential for certain kinds of maintenance or for future revisions of the software Final documentation will include a structured listing of the program Sentence completion Documentation On the Web is a interactivity You should now complete this task 2 3 8 The Evaluation Stage Evaluation is the formal monitoring of a system to ensure that it is performing its purpose accurately efficiently cost effectively and in a timely manner The performance of the system must be matched against a given set of criteria such as the initial project specification Evaluations of various kinds are an important aspect of the software development industry Evaluations are used to determine if systems are usable cost effective conforming to performance criteria etc The basis of evaluation is in social science methods using techniques such as observation interviews and questionnaires Additionally techniques such as automatic data logging are used Many organisations bring in consultants who design and carry out evaluations as the skills required to carry out effective evaluations are highly specialised There is n
135. e package is unlikely to fulfil all the organisations requirements and additional software may need to be written to meet these requirements 2 12 5 Spiral model This model was introduced by Barry Boehm in 1988 It is a risk driven approach rather than code driven It incorporates management and risk assessment components The development of a final product is based upon successive refinements 2 12 6 Open Source All the models described above are used to represent and enhance the production of commercial software As such it is envisaged that the client has a specific goal the company wishes to sell a product and make a profit and that programmers are employed to generate this software HERIOT WATT UNIVERSITY 2006 2 13 SUMMARY There is an alternative philosophy based on the Free Software Federation The philosophy is based on the following e The proliferation of the Internet and the increase in ease of communication has allowed geographically distant programmers to collaborate in ways not previously possible This in turn has allowed an increase in the development of many open source projects e The open software movement represents a growing body of users and programmers who have a totally different philosophy to the development and ownership of software Discussion of the open source movement is contained in the article The Cathedral and the Bazaar by Eric S Raymond e Aconsiderable amount of software has successfully been cr
136. e perfective Corrective maintenance is concerned with errors that escaped detection during testing but which occur during actual use of the program Users are encouraged to complete an error report stating the inputs that seemed to provoke the problem and any messages that the program might have displayed These error reports are invaluable to the development team who will attempt to replicate the errors and provide a improved solution Adaptive maintenance is necessary when the program s environment changes lt allows the authors to provide a program which responds to changes in the operating environment For example a change of operating system could require changes in the program or a new printer might call for a new printer driver to be added to the program A change of computer system will require the program to be ported to the new system Perfective maintenance occurs in response to requests from the user to enhance the performance of the program This may be due to changes in the requirements or new legislation Such maintenance can involve revision of the entire system and can be expensive Matching definitions Maintenance On the Web is a interactivity You should now complete this task 2 11 Weaknesses of the Waterfall Model Problems are usually encountered when you use the waterfall model 1 Real projects rarely follow a linear sequential flow Apart from any software problems people change their minds and often there
137. e program works properly and that it is reliable and robust Testing is often confused with the debugging of a program but these are not the same though they are very closely related e Testing establishes the presence of faults in a computer program e debugging is the finding and removing of these faults Also at this stage will be included internal documentation This is commentary within the program to explain the various stages and to record any changes that might be implemented in the coding during debugging One aspect of this is the use of meaningful variable names which we will cover later in the software development environment Standard Algorithms Most projects will use certain standard algorithms Programmers need to be familiar with these common algorithms Ones that you will become familiar with later include e linear searching e counting occurrences e finding maxima and minima Module Libraries It is often possible to use with or without alteration modules that have been previously written and have been retained in a module library A module library will include code for HERIOT WATT UNIVERSITY 2006 18 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS these standard algorithms Most development environments come with a large library of modules Programmers can use these in the code they are developing These libraries will include mathematical functions modules for converting text to numbers etc
138. e software systems produced without planning poorly performing software a A N difficulty in maintaining the software If you have been involved in any computer systems before you started this course you are probably nodding your head thinking of all the computing disasters you have seen But if you are new to computing then maybe the table in the next topic might help you to see the differences between real life programs and the sort of programs you are or will be writing We think that if you understand the problems of large scale programming the need for software development will be obvious Without this understanding it is all too easy to dismiss software development as a not very useful exercise but one which will give you a Higher credit It may seem to you that software development on this scale is overkill for the sort of programs you are going to be writing In many ways it is but then it is easier to learn about software development by tackling a small straightforward task than by starting out on a mammoth project Mistakes are easier to spot and easier to fix at this stage software problems in a commercial or industrial system are likely to be 100 to 500 times more costly to find and repair once the software has been installed and running HERIOT WATT UNIVERSITY 2006 4 TOPIC 1 INTRODUCTION TO SOFTWARE DEVELOPMENT PROCESS 1 3 Real life programs and classroom programming What are the differences between
139. e the array contents now array 8 23 5 9 3 0 4 52 array 8 23 5 19 9 4 7 52 array 8 23 5 9 3 4 7 52 Q O 0 D array 8 23 5 19 9 4 4 52 e none of the above Q25 Set up an array that can hold 4 values with a subscript range of 0 3 Initialise the array to hold all O values Now set the following values e array 1 9 e array 2 3 What are the contents of the array now express in format of array 3 2 5 0 HERIOT WATT UNIVERSITY 2006 208 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Q26 Set up an array that can hold 10 values with a subscript range of 0 9 Initialise the array to hold all O values Now set the following values e array 4 6 e array 8 2 e array 1 7 e array 7 3 What are the contents of the array now express in format of array 3 2 5 O Q27 Write a program that will set each element in an array called myarray of 10 elements to the value of its index The contents of the array are then printed out in a vertical line 7 5 4 Review Questions Q28 Initialising a 1 dimensional array means a Setting all locations of an integer array to O zero b Setting all locations of a string array to null c Setting all locations of a real array to pre determined values d All of the above options Q29 The contents of a string array message contain the following characters in successive memory locations HAPPYBIRTHDAY
140. e then it can be called from within the main program We will discuss procedures more fully later in the final topic Example Range checking using a boolean variable Problem A program is written to ask the user to enter a value If the value is outside the range expected the user will be prompted to enter another value This is another example of validation only in this program the use of a boolean variable is exemplified Solution The algorithm is shown below 1 input What size is needed 3 set value of ok to false 4 do while ok false 5 if size gt low value and size lt high value then 6 set ok to true 7 display This size in range 8 else 9 display This size is out of range 10 display Try entering another size HERIOT WATT UNIVERSITY 2006 7 4 DOLOOPS 11 input What size is needed 12 end if 13 loop 14 display Out of loop The Visual Basic program is shown in Code 7 7 Option Explicit Private Sub Command1_Click program RangeCheck 18th February 2004 gt Program by Fred Fink This program prompts the user to enter numeric value It uses a WHILE loop to repeatedly check that a value which is between LowValue and HighValue Const LowValue As Integer 10 Const HighValue As Integer 20 Dim size As Integer Dim OK As Boolean OK False size InputBox What size is required Do While Not OK If size gt LowValue And size lt HighValue Then OK True
141. e used elsewhere in the program then make it a reference parameter Call by reference is the default condition for Visual Basic Note for Visual Basic Net users the default condition is call by value Example 2 Program using reference parameters Problem A user enters two numbers at the keyboard Write a program that swaps the positions of the numbers Solution Consider the following procedural algorithm declare variables GetNumbers Number1 Number2 BlankLines 2 swap Number1 Number2 e NN Notice that we are using the procedure BlankLines the first procedure we met at the start HERIOT WATT UNIVERSITY 2006 8 3 PROCEDURES AND FUNCTIONS 235 The full Visual Basic program is shown in Code 8 4 Option Explicit Private Sub Exchange_Click Dim Numberi As Integer Number2 As Integer GetNumbers Number1 Number2 BlankLines 2 swap Numberi Number2 End Sub Private Sub BlankLines ByVal Num As Integer Dim count As Integer For count 1 To Num Display Print Next count End Sub Private Sub swap ByRef valuel As Integer ByRef value2 As Integer Dim temp As Integer Display Print Numbers before swap Tab 25 valuel value2 temp valuel valuei value2 value2 temp BlankLines 1 Display Print Numbers after swap Tab 25 valuel value2 End Sub Private Sub GetNumbers ByRef Numl As Integer ByRef Num2 As Integer Numi InputBox Input first value Num2 InputBox Input
142. e wake ie o do ete Se Des Gee 170 7 High Level Language Constructs 2 171 Tek CMMMOOUCHOM cet e a e Boasts BS we dd 173 Te MS oo et AR EA e 174 7 6 FOPMAaninG Opus dis aes ae PaaS 185 TA DOLOS c fos a ra ia a Shes aa ea ANN e o rd be 186 HERIOT WATT UNIVERSITY 2006 CONTENTS A AR Re AE 7 6 7 7 SUMMA sia Le pus ea esate eat E Me s plo oracion A II 8 ue 8 Procedures and Standard Algorithms 8 1 8 2 8 3 8 4 8 5 8 6 8 7 8 8 Introduction Modularity ono ve ar ie D cae Re Procedures and Functions FUNCIONS s a ia o a a Ge OR RA pee REGCUISION ils 4 4 4 aus a RAR MR a One NE ce More Standard Algorithms e 0 Led o tt SUMMA 000 aa a rs od ue Ad End Of tOpiGtest s syi L an i a edb la e bce eda ee Lis Glossary Hints for activities Answers to questions and activities 2 Y O O1 Y Features of Software Development Process Design notation data flow and evaluation Personnel ieri ads a a ade a Pe tra Languages and Environments High Level Language Constructs 1 High Level Language Constructs 2 Procedures and Standard Algorithms HERIOT WATT UNIVERSITY 2006 200 220 220 221 223 224 225 237 242 248 259 259 Topic 1 Introduction to Software Development Process Contents ET INTOQUCION lt p a
143. eated using this Open Source model eg examination of the Netcraft web site will illustrate the number of web servers globally which are operating using Apache 2 13 Summary The following summary points are related to the learning objectives in the topic introduction e understand the mechanism of the software development process e the process is iterative and involves a continual revision and evaluation at each phase of the process e itis a time consuming procedure from initial specification to a working program e various models exist to aid the software development process but none are perfect 2 14 End of topic test An online assessment is provided to help you review this topic HERIOT WATT UNIVERSITY 2006 39 40 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS HERIOT WATT UNIVERSITY 2006 Topic 3 Design notation data flow and evaluation Contents 3 1 Introduction 3 2 Tools and Techniques 3 3 Design methodologies 3 3 1 Top down design with stepwise refinement 3 3 2 Structure charts 3 3 3 Jackson Structured Programming 3 3 4 Pseudo code 3 3 5 Review questions 3 4 Test Data 8 4 1 Test data preparation 3 4 2 Review questions 3 5 S
144. ecome familiar with the syntax of a new language to the extent that they can write code as fluently as is it were the English language 3 6 3 Execution Run time Errors These are errors detected during the execution of the program eg division by zero They are also known as run time errors Even given that a program is translated into machine code and runs on the computer there is no guarantee that it will not generate errors For example a common mistake made by programmers is to divide by zero In most cases this will produce a run time error and cause the program to halt unexpectedly Another example includes attempting to read character data directly as numeric Array Bounds Exceeded is a common mistake in languages which support array data structures Here the programmer is attempting to access a position within the array which exceeds its predefined bounds 3 6 4 Logical Errors These are errors in the design of the program eg calling the wrong procedure or routine Even given that the program translates to machine code and does not halt unexpectedly due to run time errors there is no guarantee that it will not fail It may contain logical errors These are errors in the logic of the code itself For example writing code to add two numbers instead of multiplying them or forgetting to write code to do something when a condition that is being tested fails HERIOT WATT UNIVERSITY 2006 3 6 ERROR REPORTING Other exam
145. edule by whatever means possible Sometimes it may involve cracking the whip to make sure the work is up to standard and that important deadlines are met being a project manager means being accountable for the entire duration of the project Project managers are easy targets for criticism because the success or failure of a project is often dependent on their decisions Hence it can be a thankless task at times for this overworked person The most time consuming undertaking of all will be managing people whether they be clients or as members of the consultancy team With clients the project manager e needs to extract all the on going relevant information from the client and force him her to make decisions regarding software specification e has the ability to accommodate substantial changes to the original specification made by the client from the original specification and offer revised schedules and budgets at short notice With his her own team the project manager e adopts a counselling role for the members offering therapy to disgruntled or stressed out employees e promotes good welfare by raising team spirit through regular personal meetings and positive appraisal A job description for a typical project manager might involve the following requirements e have experience in dealing with a variety of clients the ability to manage a team e possess excellent verbal and written communication skills e have strong attent
146. edure can be individually tested e procedure code can be saved and re used in future projects Module libraries for instance are repositories for useful chunks of code that can be accessed by programmers who could save time by using such code instead of re inventing the wheel Procedures and functions are somewhat similar in their structure They both consist of e a heading e a declaration part where necessary e an action part a compound statement A procedure or function is activated by a call from the main program after which the procedure or function executes its block of code and then terminates The flow of data between procedures functions and the main program block is accomplished by the use of parameters which will be discussed later HERIOT WATT UNIVERSITY 2006 225 226 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS 8 3 1 Procedures Visual Basic offers a variety of procedure types The two that concern us here are e event procedures e general procedures Up to now most of all the programming code you have seen has been made up of event procedures that activate sections of code when say a command button is pressed These procedures are named by Visual Basic by concatenating the name of the object code and the name of the event according to the syntax Sub Command_Click End End Sub You will recognise this code which ends a Visual Basic program 8 3 2 General Procedures A general procedure unl
147. edure or function is called recursive Here is a simple example to print out the values from 1 to 10 Option Explicit Private Sub Commandi_Click 25th February 2004 gt Program by Fred Fink gt Program to illustrate recursion Counter 10 procedure call End Sub Private Sub Counter ByVal digit As Integer If digit gt O Then Counter digit 1 recursive call PicDisplay Print digit End If End Sub Private Sub Command2_Click End End Sub The procedure Counter calls itself with the value digit 1 which is 10 Counter digit 1 This is repeated until the value of digit is reduced to 1 The clever bit now starts The value of digit is output as 1 followed by the result of the procedure s previous call which HERIOT WATT UNIVERSITY 2006 8 5 RECURSION 243 was 2 This continues until the final call is output as 10 The first procedure call is the last to displayed For each activation of the procedure a new set of local loop variables and value parameters are created and are stored in a dynamic memory structure call a stack A stack is referred to as a LIFO Last In First Out Structure and can be created by the system for dealing with recursion and other arithmetical processes The educational language LOGO depends very heavily on recursion for its intuitive graphics displays Figure 8 4 shows the contents of the stack at the end of the procedure calls and Figure 8 5 shows program output lt Stack
148. ell application Finder if the count of folders in thisFolder gt O then repeat with innerFolder in every folder of thisFolder as list if file Mail Drop Preferences of innerFolder exists then delete file Mail Drop Preferences of innerFolder end if if file Email Startup of innerFolder exists then delete file Email Startup of innerFolder end if if file EmailSavePreferences of innerFolder exists then delete file EmailSavePreferences of innerFolder end if end repeat end if end tell end iterate Code 5 3 JavaScript perhaps the most publicised and well known scripting language was initially developed by Netscape as LiveScript to allow more functionality and enhancement to web page authoring that raw HTML could not accommodate A standard version of JavaScript was later developed to work in both Netscape and Microsoft s Internet Explorer thus making the language to a large extent universal This means that JavaScript code can run on any platform that has a JavaScript interpreter Typical uses of JavaScript include a Image or text rollovers If the user rolls the mouse over a graphic or hypertext then a text or graphic box will appear http scholar hw ac uk heriotwatt scholar2003 courses higher computing JavaScript Text Unit2 glossary asp 42 CTRL click to follow link b Creating a pop up window to display information in a separate window from the Web page that triggered it This is useful if the user requires to
149. emi colon Speed Another important difference is that interpreters can be 2 to 10 times slower than compilers One reason for this is that they translate the same statements within a loop over and over again Compilers can produce much more efficient object code than interpreters thus making the compiled programs to run faster Ease of use Interpreters however are more suitable for beginners to programming since errors are immediately displayed corrected by the user until the program is able to be executed On the whole compilers tend to be more difficult to use 5 10 4 Review Questions Q21 One of the main functions of a compiler in translating high level languages is to produce a symbol table containing reserved words and identifiers This part of the process is called a Program analysis b Lexical analysis c Semantic analysis d Syntax analysis Q22 Syntax analyses is rather more than just finding terms that are mis spelled In a computer program which one of the following will also be found HERIOT WATT UNIVERSITY 2006 103 104 TOPIC 5 LANGUAGES AND ENVIRONMENTS a Missing parenthesis b Use of a reserved word c Inappropriate data type d All of these Q23 One of the main differences between a compiler and interpreter is a An interpreter is faster then a compiler b Acompiler is better for beginners c Acompiler can produce more efficient object code d An interpreter is much harder to use Q
150. eneration Code Optimisation Code Generation Target Machine Code Lexical analysis takes the source program and constructs source program words and symbols invariably called tokens for all the identifiers reserved words like PRINT and arithmetic operators All comments and superfluous spaces are removed and the tokens stored in the symbol table Syntax analysis checks the symbol table contents to ensure that there are no grammatical or semantic errors in the source code The type of error will depend upon the syntax definition of the programming language For example some languages require semi colons to mark the end of statements blocks of code are defined within a BEGIN END etc Some compilers are also able to check that the correct number of parameters is being passed in the call to a subroutine and that they are of the appropriate data type HERIOT WATT UNIVERSITY 2006 102 TOPIC 5 LANGUAGES AND ENVIRONMENTS If any errors are detected then the compiler will pass control to the error handling routine and generate an error listing file containing descriptions of the offending statements and their line numbers within the source The programmers will then check through the error listing and use this as a basis for debugging the original source code The source code must then be recompiled Only when there are no errors will an object code file be generated for execution Intermediate code is produced for the target comput
151. ent of a mouse trackerball or other input device The WIMP environment My computer EJ Edit View Help Window Browse with Pro 5 Paint Menu Explore Find Scan for Viruses Add to Zip Create Shortcut Delete Rename briefcase 4 Properties Ico n A Close Pointer HERIOT WATT UNIVERSITY 2006 2 5 DESIGN IN CLOSER DETAIL The HCI must allow easy navigation Users should be able to move from one screen to another in a straightforward manner and to leave screens when they wish Some sites on the Internet for example include a site map to show the user how different forms are linked HCI must be consistent so that similar actions in different parts of the interface have similar responses throughout the program Prompts given to the user should be consistent Different screens should look as though they belong to the same software package The HCI should provide on line help offering intelligible prompts and send messages and warnings to the user about the consequences of choices made eg send a warning if a user chooses to delete data HCI design is based on an appreciation of what the user wishes to see The designer thinks in terms of the windows often called forms that are presented to the user Identifying characteristics of a good user interface On the Web is a interactivity You should now complete this task 2 5 2 Data structure A program
152. er and this is then optimised to produce more efficient code that might run faster if part of a network for example Once optimised the final object code is generated which can then be run or executed 5 10 2 Interpreter Another form of translation that converts source code into object code is an interpreter machine code program statement Interpreter errors Unlike a compiler an interpreter checks syntax and generates object code one source line at a time Think of this as very similar to a group of translators at a United Nations Conference who each have to convert sentences spoken by delegates into the native language of their representative When an error is encountered the interpreter immediately feeds back information on the type of error and stops interpreting the code This allows the programmer to see instantly the nature of the error and where it has occurred He or she can then make the necessary changes to the source code and have it re interpreted As the interpreter executes each line of code at a time the programmer is able to see the results of their programs immediately which can also help with debugging 5 10 3 Respective Advantages The main difference between an interpreter and a compiler is that compilation requires analysis and the generation of machine code only once whereas an interpreter may need to analyse and interpret the same program statements each time it meets them e g instructions a
153. erformance over the past few years has promoted a comparable increase in the power and sophistication of scripting languages that unlike conventional programming languages can even have certain security features built in Downloading web based content from a remote site to a user s local machine can include animations graphics MP3 audio files video clips and so on and this is authenticated by the scripting language However be warned Executable code can inadvertently be downloaded from a remote server to a web browser s machine installed and run using the local browser s interpreter This is easily done by visiting dubious web sites or downloading programs without valid authenticity The user is probably unaware of anything devious occurring This is a weakness in the formal rules defining scripting languages like JavaScript and VBScript 5 7 3 Creating a Macro A macro is a way to automate a task that you perform repeatedly or on a regular basis It is a series of commands and actions that can be stored and run whenever you need to perform the task Instructions can be simple such as entering text and formatting it or complex like automating tasks that would take several minutes to do manually Macro contents consist of ASCII text and can be created and edited in any simple text editor Many programs like Microsoft Word and Microsoft Excel can create macros easily All you have to do is record a set of actions as you perform them For e
154. evelopment The organisations creating software usually do so for profit Money time and people are involved The people involved have different points of view some are clients wanting to buy software some are developers concerned in creating software Managers are concerned with efficiency and profit within their organisation In the development of software the three aspects which the developer must consider are e data e processes e human computer interface In traditional structured design the primary tasks are to focus on the processes A process is the work that a program carries out on data or in response to certain inputs The software development process does not always start in the same place Sometimes there will only be an outline of the problem At other times a specification will be available The specification must be agreed with the clients Work on the problem and the solution is often carried out by a group of people called the development team The aim of the team is to produce a new software system that will solve the problem Software houses are in business to produce software and sell this to the world at large They develop software for sale to a market which they believe exists They also write HERIOT WATT UNIVERSITY 2006 2 3 THE WATERFALL METHOD bespoke software to meet specific needs These materials are concerned with projects that have definite clients however reference will be made to sof
155. f cells These packages make use of standard algorithms and it is worthwhile for every programmer to know them When implemented these standard algorithms may become key components in a module library This section introduces 3 common algorithms used by programmers Namely 1 linear search 2 counting occurrences 3 finding maxima and minima It would be advantageous for you to have prior understanding of arrays as examples given rely upon knowledge of accessing and manipulating such structures 8 6 1 Linear Search One task which computers frequently perform is to search through lists For example looking up a telephone number in a database finding and replacing a word in a text file or looking for a particular stock item in a warehouse etc The simplest way of doing this is to perform a linear search also called a sequential search where the search begins at the first item in a list and continues searching through each item of the list in turn Linear search is the simplest search method to implement and understand Starting with an array holding say 10 numbers with a pointer indicating the first item the user inputs a search key Scanning then takes place from left to right until the search key is found if it exists in the list Look at the list below A Suppose the search key is 76 1 16 is compared to 76 Not the key so pointer moves on one place 2 9 is compared to the key Not equal so pointer moves on HERIOT WATT
156. f instructions Q20 Which one of the following expressions represents the logical AND operator a Requires only one condition to be tested b The expression is TRUE when both conditions being tested are TRUE c The expression is TRUE if either the conditions being tested are TRUE d Can be used to test for values outwith a given range Q21 Which one of the following is NOT a control structure in programming Sequence Repetition Assignment Selection 6 14 Nested IF Statements If a condition has to be tested that depends on whether another condition is already True such as If its 6 30 p m and if I m logged on to SCHOLAR then nested If statements can be used A nested If statement is one that s enclosed within another If statement The format for a nested If statement is as follows If condition Then If another_condition Then statement Else another statement End If End If if statements can be nested but care should always be taken to ensure that the else statement is associated with the correct if The following examples exemplify the nested f statement Example 1 Testing for range and the number of digits in a number Problem Describe the operation of the following program as seen in Code 6 12 Option Explicit Private Sub Commandi_Click HERIOT WATT UNIVERSITY 2006 158 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 program nested_IF 15th February 2004 gt Program by Fred Fink gt This
157. f the following statements is true a Programming time can be saved b Functions produce a single value c Functions can be used with or without parameters d All of the above Q3 A linear search is performed on the following data contained in a 1 D array Glasgow Edinburgh Falkirk Perth Inverness Dumfries St Andrews Dundee How many comparisons are made before the search item Dumfries is found and TO gw 4 d N O O1 Q4 What is meant by the term standard algorithm a Universal code to solve all problems b A sequence of instructions that can be used to solve a particular problem c Code that makes a program more reliable d Any program written in a high level language Q5 Of the following standard algorithms which one is common to them all Linear search counting occurrences finding maximum minimum Linear search Counting occurrences Finding maximum minimum a b c d None of them 8 1 Introduction This final topic introduces further modular programming concepts Programs are built up from individual blocks of code that represent a procedure or function The main program will then consist of a series of procedure function calls and this in itself does much to make any program more readable and easier to maintain The fairly complex issue of parameters and parameter passing is covered in detail and exemplified by working solutions HERIOT WATT UNIVERSITY 2006 224 TOPIC 8
158. fed back in to a computer system Previous output becomes new input Fit for purpose The finished program runs to specification and is robust and reliable Function A block of code like a procedure but a value is returned when the function is used Functional language A language that utilises the evaluation of expressions rather than the execution of commands It is based on the use of functions from which new functions can be created Functional specification This will detail how the developed program will behave under specified conditions General purpose language The language can be used to program solutions covering a broad range of situations High level language A language designed to be easily understood by programmers They use commands and instructions based on English words or phrases Human computer interface Allows the program to interact with the outside world The interface is the only part of the program that users see Implicit declaration If a variable for example is not fully declared by the user then it is given default attributes by the Visual Basic language Independent test group Testing of software by a group out with the development team Inheritance The sharing of characteristics between a class of object and a newly created sub class This allows code re use by extending an existing class Intermediate code A form of compiled code that is specifically produced for a target computer Internal comment
159. from variables This is an individual preference This makes no difference to the program whatsoever its only purpose is to bring to your attention the fact that this particular name is being used for a constant and not a variable 6 8 1 Example program 1 Calculating the circumference of a circle Problem Write a program that calculates the circumference of a circle when supplied with the radius The value of Pl is defined as a constant Solution A typical solution to the problem is shown in Code 6 4 The circumference is calculated using the formula 2 x PI x r Note It is good programming practice to include comments in every program The information allows better readability of the program and also breaks the code listing into meaningful chunks The comment symbol is the single quote Visual Basic ignores all text that comes after the quote Comments can also be embedded within the lines of code Option Explicit Private Sub Command1_Click program circle 10th February 2004 Program by Fred Fink This program prompts the user to enter a value for the radius of a circle It then uses the formula 2 PI radius to calculate the circumference Const PI As Single 3 14159 Declare constant PI and assigns value Dim radius As Single HERIOT WATT UNIVERSITY 2006 6 8 DECLARING CONSTANTS 129 Dim circumference As Single radius InputBox Please enter the radius of the circle circumference 2 PI radius Pr
160. functions to compute values Also from the collection of primitive functions new functions can be defined and created Consider for example the simple problem of calculating the sum of the integers from 1 to 100 A simple loop structure could be used as seen in the following pseudo code Set total to 0 Set counter to O Repeat counter counter 1 total total 1 Until counter 100 OO O1 amp WN RE Using a functional language to solve the same problem the result can be calculated by evaluating the one line expression without the use of any variables sum 1 100 In this case the expression 1 100 represents the list of integers from 1 to 100 while sum is a function that can be used to calculate the addition of the integers Lisp The first functional language was Lisp which is a LISt Processing language A list is a data structure consisting of structured values arrays and records for example whereas the basic data in imperative languages are essentially unstructured integers for example Lisp is in fact one of the oldest programming languages older than any imperative language except Fortran and was first developed in the late 50s lt has widespread use in the field of artificial intelligence HERIOT WATT UNIVERSITY 2006 5 10 TRANSLATION METHODS 99 5 9 1 Review Questions Q16 One example of an object oriented language is a Prolog b Visual Basic c Java d COBOL Q17 The main concept
161. g This was an incidence of data conversion of a too large number 2 Y2K Problem The Millennium Bug problems with the way the date was stored on computers 3 NASA Mars Lander problems in software occurred when different measurement units were used there was confusion between pounds and kilograms 4 Home Office Immigration System Ordered in 1996 and supplied eighteen months late by Siemens in 1999 at a cost of 80 million It was supposed to speed the processing of asylum claims up but could not cope with the backlog and did the very opposite It was finally scrapped in 2001 Government ministers were blamed for ordering the over complex system in the first place 5 London Ambulance Service in 1992 they took on a despatch system that failed calamitously Ambulances were sent to the wrong place did not arrive when expected and the system generally caused major disruption to patient care and services 6 Passport Agency in 1999 anew system Siemens again that worked much less efficiently than the system it replaced Delays went up from two weeks to seven HERIOT WATT UNIVERSITY 2006 6 TOPIC 1 INTRODUCTION TO SOFTWARE DEVELOPMENT PROCESS with a backlog of more than half a million passports This cost the taxpayers 12 million and forced many people to cancel holidays The Government increased passport charges to recoup wasted money from this system 7 Post Office swipecard system a one billion pound project that
162. g characteristics in common e initialisation e acondition which evaluates either to TRUE or FALSE e a counter that increments or decrements by discrete values 7 2 1 The For Next loop The for keyword marks the beginning of the code which will be repeated according to the conditions supplied following the for When incrementing the general form of the statement is for counter initial value to final value step value statements Next counter When decrementing the general form of the statement is for counter initial value to final value step ve value statements Next counter HERIOT WATT UNIVERSITY 2006 7 2 ITERATION 175 Note 1 The initialisation statement is carried out only once when the loop is first entered i e initialise counter to initial value 2 The condition is tested before each run through the body of the loop The first test is immediately after initialisation so if the test fails the statements in the body are not run An incrementing loop terminates when counter gt final while a decrementing loop terminates when counter lt final 3 An increment or decrement of the counter variable is executed after the loop body and before the next test The value of the counter is incremented or decremented by the step value 4 the value of counter must not be changed in any statements within the body of the loop 5 changing the value of fina within the loop will have no effect on how many times t
163. g code It might be better to put the Print statements within a loop structure The following refinement should produce a more acceptable program Private Sub BlankLines print Message 1 for n 1 to 3 Print Next n print Message 2 End Sub The program is still not very flexible We should be able to tell the procedure how many blank lines to output This is achieved using parameters and we will come back to this section of code Exercise A user is asked to input numerical values between 1 and 30 Write a section of code as a procedure to validate user input between these two values Show how it would be called from the main program 8 3 3 Parameter passing Parameter passing is the main mechanism for transferring information between programs and sub procedures in Visual Basic Parameters can be classified into various types depending on how they deal with data values during a procedure call Other than using global variables parameter passing using local variables is the way in which information is transmitted to and or from called procedures in a program The formal parameters can behave in one of three ways HERIOT WATT UNIVERSITY 2006 227 228 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS 1 They can pass information to a sub program 2 They can receive information from a sub program 3 They can both send and receive information These three methods are described as 1 IN mode or use of a
164. g the system The first gives the analyst an idea of what the new system will have to produce and the second will help understanding of the workings of the current system e The What Where When Why Who approach The analyst seeks answers to the obvious questions beginning with these words what does the system do where are these things done when are they done why are they done and who does them Many of these techniques are essentially iterative The answers to questions often raise further questions which the analyst must go and ask and so on f Expert Knowledge The analyst has to try to gain understanding of the processes the new system is supposed to help This understanding is important because particular people tend to take their own special knowledge for granted and as a result don t mention important requirements to the analyst A basic understanding of the process will allow the analyst to ask more searching questions during the interviews with key informants 4 5 2 Analysis of the information When the analyst considers that enough information has been gathered work starts on the analysis However it may well be that the analysis reveals shortcomings in the information so far obtained In such a case iteration arises again the analyst has to go back for more information Having gathered information the analyst has to understand it All computer systems have three sub systems e input e processing e out
165. g to various sets of guidelines These are the basic graphical elements Module Module call O Data flow argument A structure chart for a program that simply gets in some data changes it in some way and produces output might look like Figure 3 2 Figure 3 2 Software Design Structure Structure charts are read from top to bottom The line joining two boxes indicates that the lower is called or brought into action by the upper The lower box represents one of the things the upper box has to do Along each line names and arrows describe the data that flow from one block to another and the direction in which they flow Each block in the structure chart represents a section of code to be written These sections have the generic name module The modules in a structure chart will become modules of code in the finished program The designer must give the modules meaningful names rather than Block 1 Block 2 etc which describe what the module does This makes the design easier to follow HERIOT WATT UNIVERSITY 2006 47 48 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION Structure charts emphasise modular design as they are hierarchical The project as a whole is at the top of the hierarchy A structure chart shows the relationship between modules and in particular shows which modules contain calls to modules lower down in the structure A complete structure chart of a large software system shows the
166. gram may also receive data internally during program execution The calculation is the heart of the program The input data is transformed to the output data This in short is all that a computer does The output phase is less straightforward There is no screen output in Visual Basic only windows called forms Output can also be directed to a file printer or disk You will see example output methods in the program exemplars 6 4 1 Example program Suppose for example that you were going to write a program to calculate the area of a rectangle where the user will input the dimensions and the program will return the area The program will take the general form as shown in Code 6 2 HERIOT WATT UNIVERSITY 2006 119 120 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Option Explicit Private Sub cmdDisplay_Click Dim Length As Integer Dim Width As Integer Dim Area As Integer Length Val Lngth Text Input length Width Val Wdth Text Input width Area Length Width Calculate area Ar Text Str Area Output result End Sub Code 6 2 This program uses text boxes to input and output the data 1 In the program the variables Length Width and Area are declared using the Dim statement see later 2 Values of Length and Width are input via text boxes The Visual Basic function Val changes text into numeric values 3 The area is calculated 4 Result output to a text box The function Str converts the numerical
167. h object in the form The code for each object is written in the form of a sub procedure A sub procedure or sub program is a block of code that is implemented when an event such as a mouse click is actioned Sub procedures can be used anywhere in the program by calling them by name Procedures can also be user defined More on procedures will be covered later in the next topic Double clicking on any of the objects in a form or even the form itself will open up the program editor and reveal the code for each event For example clicking on the Exit button will display the code editor as follows HERIOT WATT UNIVERSITY 2006 111 112 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 FA Projert1 Farm1 Cade Private Sub cmdExit Click End End Sub OLECompleteDrag All Visual Basic code is written between the lines that Visual Basic enters for you Private Sub cmdExit_Click End Sub On the right of the screen you can see a list of other events that are part of the Visual Basic environment 6 3 1 Input and Output Controls Visual Basic programs do not output to the computer screen as such Instead they use a form which is essentially a Visual Basic window that is the interface between the user and the application and allows information to be input by the user or displayed to the user There may be more than one form in a Visual Basic project Information may be input to a program via the keyboard or read directly from
168. hat you could write without having to bother with the details of how this is going to be implemented Or you could write convert entry to number without having to remember exactly how this is done in the chosen programming language Pseudo code frees us to get on with thinking about the details of program design without our having to stop and look things up in books or worry about whether we have got our syntax exactly right You use pseudo code to explain what a process will do in a clear and concise way One of the advantages of pseudo code is that it can be translated into programming language code fairly easily Very easily in fact if you are using languages HERIOT WATT UNIVERSITY 2006 51 52 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION such as C C Pascal Smalltalk or any of the family of block structured languages which descended from Algol in the 1960s Pseudo code also translates well into Cobol so by writing out your program in this way you are opening up the possibility of re writing itin a large number of different forms suitable for different machines Many designers use a numbering system for parts of the design Each block in the structure chart has its identifying number and each line of pseudo code is also numbered These numbers enable parts of the program to be related and show their dependencies For example a block number 3 1 in a structure chart might indicate that this is the first sub module
169. have two boolean variables booly1 and booly2 and you need to take actions for each of the possible combinations of true and false HERIOT WATT UNIVERSITY 2006 160 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Using nested if statements would produce If booly1 True Then If booly2 true Then statements for true true Else statements for true false End If Else If booly2 false Then statements for false true Else statements for false false End If End If Using ElseIF will produce the following more compact code If booly1 And booly2 Then statements for true true ElseIf booly1 And Not booly2 Then statements for true false ElseIf Not booly1 And booly2 Then statements for false true Else statements for false false End If The following examples will show the If EndIf statement in use Example 1 Using an elseif statement to calculate the number of digits in a number Problem How can an else if statement be used to find out whether an integer number is within a certain range a positive number and how many digits it contains Solution A typical solution to this problem is shown here if number gt 1000 then n_digits 4 elseif number gt 100 then n_digits 3 elseif number gt 10 then n_digits 2 elseif number gt O then n_digits 1 else print Value out of range The above code shows an example of how this could be achieved HERIOT WATT UNIVERSITY 2006 6 15 IF THEN ELSEIF 1
170. he code is run and the procedure then terminates Points to note 1 The original value of the variable ActualValue in the main program remains unchanged Any changes made by the procedure to the value passed are local to the procedure and not passed back to the main program In other words the procedure can only modify a copy of the variable value and not the variable ActualValue itself You will see more of this later 2 the number of actual and formal parameters must be the same in this there was only one 3 each parameter must be the same data type for the procedure call to work HERIOT WATT UNIVERSITY 2006 232 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS In a procedure call the word call may be omitted with only the procedure name and parameters required For example Call Square ActualValue becomes Square ActualValue This notation will be used from now on in all programs 8 3 5 Call by Reference One of the disadvantages of call by value is that a copy of the actual parameter is always made in order to produce the formal parameter during the procedure call A reference parameter does not pass a value of a variable but instead passes the address of the variable Call by reference is used when information has to be passed out from a procedure to the main program Here the variables inside the procedure body are allowed to reference the memory location of the actual variable that passed it This means that as the act
171. he loop is executed 6 after the loop has terminated the value of counter is undefined 7 counter may be any ordinal type e g integer char initialise test condition FALSE rest of program Figure 7 1 The initial and final states may be constants variables or expressions e g for counter min 7 to max 5 The following examples will show the for next loop in operation HERIOT WATT UNIVERSITY 2006 176 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Example 1 Converting inches to centimetres Problem Write a program that will convert inches to centimetres for a range of values and using an increment of 5 Use the for 1oop and output the results in tabular form Use the conversion factor 2 54 centimetres to the inch Solution The algorithm is shown below for each value from 1 to 50 step 5 calculate conversion to centimetres using the factor 2 54 tabulate output next counter oP N The full Visual Basic program is seen in Code 7 1 Option Explicit Private Sub Command1_Click 16th February 2004 gt Program by Fred Fink gt This program will illustrate the For Next loop Dim Inches As Integer Dim Cms As Single PicDisplay Print Tab 3 Inches Tab 12 Centimetres PicDisplay Print For Inches O To 50 Step 5 Cms Inches 2 54 PicDisplay Print Tab 5 Inches Tab 15 Cms Next Inches End Sub Code 7 1 The program output is shown in Figure 7 2 HERIOT WATT UNI
172. he overall effect Example events would include Clicking a command button Loading a form Clearing the contents of a text box Ending a program When Visual Basic is started Form shows by default You will see exemplar programs that make use of the following Visual Basic constructs later in this topic and others Input methods 1 InputBox function A program may ask for user input during its execution This can be accomplished using the InputBox function which by default allows text entry The full syntax for the InputBox function is InputBox Prompt Title xpos ypos Prompt is the displayed message Title is the optional text that will appear in the title bar xpos ypos coordinates for positioning the InputBox on the screen Note that in Visual Basic the screen is measured in Twips Twentieth of a point A point is a traditional measure used in printing which measures approximately 1 72 of an inch or 1 28 cm For example a program may require the user to enter a name The format is Name InputBox Please enter a name The user then complies with the request to enter a name Should a numerical value be required by the program then the input format is identical and the text input converted to numeric using the VAL function Numberi Val InputBox Please enter a value Number program 50 50 HERIOT WATT UNIVERSITY 2006 114 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Number program Please enter a
173. he user e makes them easy to learn and use e assumes minimum programming knowledge or experience e allows complex tasks to be performed in relatively few steps e allows simple creation and editing in a variety of text editors e allows the addition of dynamic and interactive activities to web pages Also scripting languages are generally portable across various hardware and network platforms and scripts can be embedded in HTML documents for added functionality Specialised scripting languages include Perl Practical Extraction and Report Language This is a popular string processing language for writing small scripts for system administrators and web site maintainers Much web development is now done using Perl Hypertalk is another example It is the underlying scripting language of HyperCard while Lingo is the scripting language of Macromedia Director an authoring system for develop high performance multimedia content and applications for CDs DVDs and the Internet AppleScript a scripting language for the Macintosh allows the user to send commands to the operating system to for example open applications carry out complex data operations An example script is shown in Code 5 3 HERIOT WATT UNIVERSITY 2006 92 TOPIC 5 LANGUAGES AND ENVIRONMENTS this simple Applescript will search recursively through folders in a shared volume removing certain unneeded files from every user s directory on iterate thisFolder t
174. her an old system is not working well or e an altogether new system has to be set up A new system is created by a project The creation of this of course is the work of people and it is important to say something about the personnel involved in the process Although many people may be involved the key personnel are discussed under the five main headings 1 client 2 project manager 3 systems analyst 4 programmers 5 independent testing group In a nutshell the process encompasses the following events The management who require the new or updated system represent the clients They approach external consultants the people who will create the system The consultants appoint a project manager who carries out a feasibility study If the feasibility study bodes well the management asks for a full system investigation This is carried out by a systems analyst from the consultants who works with the project manager It culminates in an operational requirements specification When the operational requirements have been agreed by both the consultants and the customer a contract for the system is drawn up The consultants put a team of programmers on the job to code the specification and the software development process begins Once the software has been implemented in a chosen language it undergoes rigorous testing by an independent testing group 4 3 The Client In this case the client is represented by the management of the compa
175. iable StringValue to be assigned the string 51 Two other useful functions are CHR and ASC The following examples show how they are used LetterValue ASC A will assign the value 65 to LetterValue This is the ASCII code for the letter A Letter CHR 66 will assign the string B to Letter since the ASCII code for B is 66 Table 6 7 summarises the string functions Table 6 7 Function Usage Examples VAL Converts string to value a Val 66 STR Converts value to string b Str 77 ASC Converts string to ASCII value c ASC D CHR Converts ASCII value to string d CHR 68 What are the results of each example 6 8 4 Concatenation Concatenation is simply joining string variables together to make longer strings The operator is the ampersand symbol amp When two or more strings are combined the second strings are added directly to the end of the preceding string The result is a longer string containing the full contents of both source strings The following example shows concatenation structure NewString StringOne amp StringTwo StringThree Here NewString represents the variable that contains the result of the concatenation HERIOT WATT UNIVERSITY 2006 6 8 DECLARING CONSTANTS 133 operation StringOne StringTwo and StringThree all represent string variables Note that the ampersand must be preceded and followed by a space Example of concatenation Examp
176. if statement results in the message Value out of range being displayed on the screen Example 2 Grades and Marks Problem Write a program using the ElseIf construct for a user to input a test result and output the corresponding grade Test scores range from 0 to 100 and the grades from A being the highest to E the lowest Solution Use the following algorithm 1 ask user to input a mark between O and 100 2 If mark gt 0 and lt 30 then grade E 3 elself mark gt 30 and lt 49 then grade D 4 elseif mark gt 49 and lt 65 then grade C 5 elseif mark gt 65 and lt 85 then grade B 6 elseif mark gt 85 and lt 100 then grade A 7 else number out of range 8 end if 9 If mark gt 0 and lt 100 10 display grade 11 end if HERIOT WATT UNIVERSITY 2006 162 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 The full Visual Basic program is shown in Code 6 13 Option Explicit Private Sub Command1_Click Marks and grades program 15th February 2004 Program by Fred Fink gt This program will prompt the user to enter a mark and a grade will be output Dim iMark As Integer Dim sGrade As String iMark InputBox Please input a test mark If iMark gt 0 And iMark lt 30 Then sGrade E ElseIf iMark gt 30 And iMark lt 50 Then sGrade D ElseIf iMark gt 50 And iMark lt 65 Then sGrade C ElseIf iMark gt 65 And iMark lt 85 Then sGrade B ElseIf i
177. ike an event procedure is user defined with its block of code being called from the main program The basic structure for a procedure is Sub ProcedureName formal parameters Declarations Statements End sub The name ProcedureName or identifier is what is used when the procedure is called and the name conforms to the same rules of naming variables Data is passed to and from the main program using the procedure parameters or arguments enclosed in parentheses Not all procedures however need do have parameters The declarations and statements follow an identical pattern to normal programming constructs Procedures are normally declared private and their scope is limited to other procedures and variables within the current form Here to get us started is a simple little procedure that prints blank lines on a form This might be useful for putting spaces into program output Private Sub BlankLines Print Print Print End Sub HERIOT WATT UNIVERSITY 2006 8 3 PROCEDURES AND FUNCTIONS This could be called in the action part of the main block as Call BlankLines lts use in a program could look like this Private Sub commandi_Click program lines Print Message 1 Call BlankLines Print Message 2 End Sub Private Sub BlankLines Print Print Print End Sub As it stands BlankLines isn t very well structured As programmers we should always be a little wary when we find ourselves repeatin
178. in an object oriented language is class Which one of the following represents a class a A word processing document b A printer that is on line c A database record d All of these Q18 Object oriented programming can involve inheritance Which one of the following best describes what is meant by inheritance a Data is passed from one part of the program to another b The behaviour of a class object cannot be changed c Itcan promote code re use by extending an existing class d It focuses mainly through data structures Q19 One of the earliest known functional languages was a Lisp b Fortran c Visual C d Java Q20 A functional language differentiates itself from other programming languages in that choose one It focuses on the execution of commands It is an easy language to learn It emphasises the evaluation of expressions a b c d It produces largely unstructured code YS ae na 5 10 Translation methods At the end of the implementation stage all going well a structured program listing will be produced complete with internal documentation This will be thoroughly checked against the design and against the original specification The high level code written at this stage is called source code which must be translated into machine code called object code that the computer understands There are two methods of translating source code into object code a compiler and an interpreter HERIOT WATT
179. ing capability allows the user to extend the functionality of the application by programming a sequence of actions For example in Filemaker Pro a database package it is possible to write scripts that open and close files copy data from records or enter a certain database mode such as browse or find An example script in Filemaker Pro is shown in Code 5 1 Enter Browse Mode Go to Layout Layout 1 Enter Find Mode Set Field Computing Course S3C8 Perform Find Sort Restore No Dialog Go to Layout S3 Report Final Code 5 1 HERIOT WATT UNIVERSITY 2006 5 7 SCRIPTING LANGUAGES Another example is VBScript which is a cut down version of Visual Basic used to enhance the features of web pages in Internet Explorer Below in Code 5 2 is an example of a section of VBScript embedded in HTML code lt HTML gt lt HEAD gt lt TITLE gt This is VBScript in action lt TITLE gt lt SCRIPT LANGUAGE VBScript gt MsgBox Welcome to VBScript lt P gt Click on the button below lt P gt lt INPUT TYPE Button NAME cmdClick VALUE Click gt lt SCRIPT gt Code 5 2 Note that the scripting language must be specified in the browser 5 7 1 Benefits of scripting languages One of the main benefits of scripted languages is that they require no compilation The language is interpreted at run time so the instructions are executed immediately Scripting languages also have a simple syntax which for t
180. ing statements is true regarding these parameters a In IN parameter is read only b An OUT parameter is write only c An IN OUT parameter is both read and write d All three options are true Q9 Ina procedure call by reference which one of the following is true a A reference parameter is an example of an IN parameter b Anything that happens to the formal parameter happens to the actual parameter c The memory address of the formal parameter is passed d All of the above Q10 What would be the output of the following Visual Basic code Dim x As Integer y As Integer x 5 y 6 Print x y result x y Print x y Sub result ByRef numi As Integer num2 As Integer numi numi 10 num2 num2 3 End Sub a 5653 b 5635 c 56153 d 56315 8 4 Functions A function is similar to a procedure except it returns a value to the calling code The basic structure for a function is Function functionName parameters As Data Type Declarations funcName expression End Function Since a function returns a value it is used within expressions The function name must in the action part of the function be assigned the value that is to be returned Some built in Visual Basic functions have been used in many of the programming examples up to now Table 8 1 shows some of the more common functions HERIOT WATT UNIVERSITY 2006 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS Table 8 1 Name Function
181. int The circumference of circle with radius radius is circumference End Sub This file Circle txt can be downloaded from the course web site Code 6 4 In this program the input and output commands are controlled using the nputBox function The program output Figure 6 5 and Figure 6 6 are shown below Circle Please enter the radius of the circle Figure 6 5 Formi The circumference of circle with radius 7 5 is 47 12385 Prete ee eee Calculate Circumference RCLTICOEE TELLE EEE CEE TELE EEE EEE EEE EE EP EEE CES EE EE EEE EE Figure 6 6 HERIOT WATT UNIVERSITY 2006 130 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Note that this method uses multiple windows Input is via an inputBox and output is on the form itself using the print command Compare this to the method used in the rectangle program 6 8 2 Example program 2 Use of a boolean variable Problem A program is written to display whether a number entered at the keyboard is greater than or equal to zero The program will prompt the user to enter a number read the number entered at the keyboard It will then display a message together with the value true or false depending on the value of the number entered Solution The algorithm is shown below 1 issue message to enter number 2 read the number typed in at the keyboard 3 set the boolean variable to true or false depending upon number gt or number lt 0 The
182. integer as integer double number 2 end function HERIOT WATT UNIVERSITY 2006 8 4 FUNCTIONS 239 Exercise Code the above section of code into a Visual Basic program and run it with different values Example 1 Use of a function Problem A program has to be written that uses a function to output the area of a circle given the radius Solution Consider the following algorithm declare variables function area area pi radius 2 display output e NN The Visual Basic program is seen in Code 8 5 Option Explicit Const Pi As Single 3 141592 Private Sub Commandi_Click Dim Radius As Integer PicResult Print Tab 4 Radius Tab 16 Area PicResult Print For Radius 1 To 10 PicResult Print Tab 6 Radius Tab 16 Format Area Radius Fixed Next Radius End Sub Function Area Radius As Single This function will calculate area of circle Area Pi Radius 2 End Function Private Sub EndProgram_Click End End Sub This file FunctionArea txt can be downloaded from the course web site Code 8 5 The function call Area Radius is highlighted and the output is formatted to two decimal places A loop structure is used to output the values between 1 and 10 Rewrite this procedure as a function It will return a valid integer It will no longer need a parameter HERIOT WATT UNIVERSITY 2006 240 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS Sub getValidNumber ByRef number As integer
183. ion Here the keyword To is used to represent values within a range Use the following algorithm ask user to input a mark between O and 100 select case mark case 85 to 100 output Grade A case 65 to 84 output Grade B case 50 to 64 output Grade C case 30 to 49 output Grade D case 0 to 29 output Grade E case else output mark outside range Try again end select ON OO O1 AUNE HERIOT WATT UNIVERSITY 2006 6 16 THE SELECT CASE STATEMENT 167 The full Visual Basic program is shown in Code 6 15 Option Explicit Private Sub Commandi_Click Use of the Case Select statement 15th February 2004 gt Program by Fred Fink This program will prompt the user to enter a date gt and the month will be output Dim iMark As Integer iMark InputBox Please input a test mark Select Case iMark Case 85 To 100 PicDisplay Print iMark grade A Case 65 To 84 PicDisplay Print iMark grade B Case 50 To 64 PicDisplay Print iMark grade C Case 30 To 49 PicDisplay Print iMark Case 0 To 29 PicDisplay Print iMark Case Else PicDisplay Print iMark is out of range Try again End Select End Sub grade D grade E Private Sub Command2_Click End End Sub This file Case2 txt can be downloaded from the course web site Code 6 15 Program output is shown in Figure 6 18 HERIOT WATT UNIVERSITY 2006 168 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Form 1
184. ion a number of keywords are reserved in Visual Basic for use as commands Some of these keywords are listed in Table 6 5 and must not be used as variable names Table 6 5 dim else true false to sub function while wend private const integer for string elseif case public repeat program and procedure boolean until clear or if string do print not A more complete list of keywords can be found in any good Visual Basic manual Sentence completion variables On the Web is a interactivity You should now complete this task 6 6 1 Review Questions Q6 Which one of the following variable names would not be allowed in Visual Basic a Hello b Number_1 c 17 5 Vat d SCHOLAR Q7 The choice of a variable name in programming is very important because choose one It is easier for programmers to locate and fix errors lt makes the programs more efficient Meaningful variable names make the program more reliable All of the above a0 0 gw HERIOT WATT UNIVERSITY 2006 124 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Q8 A program is written to input a person s age and calculate how old they will be in 10 years time Which of the following data types would be required in the program a String b Real c Boolean d Integer Q9 How many variables would the program require a 1or2 b 3or4 c 4or5 d greater than 5 Q10 A program is designed to generate prime numbers up
185. ion Tables 1 If Style lt gt Table Grid Then Style Table Grid End 1f ApplyStyleHeadingRows True ApplyStyleLastRow True ApplyStyleFirstColumn True ApplyStyleLastColumn True End With End Sub Code 5 4 5 7 5 Review Questions Q11 An event driven language differs from other languages in that choose one a Programs have no pre defined pathway b Programs are initiated entirely from mouse clicks c Program events cannot be nested d Programs are difficult to write Q12 One of the main benefits of a scripting language is a They are easy to learn and use b Allow complex tasks to be performed in relatively few steps c Web pages can be made more dynamic d All of the above 95 HERIOT WATT UNIVERSITY 2006 96 TOPIC 5 LANGUAGES AND ENVIRONMENTS Q13 The need for scripting languages has emerged from choose one a An increase in the speed of the Internet b Ease of developing of interactive web pages c The creation of JavaScript d All of the above Q14 Many software applications include a macro facility Which one of the options best describes a macro a Macros are not easy to edit b The creation of a macro can be time consuming c Macros automate repetitive tasks d A macro listing consists of complex code Q15 One of the tasks that a macro could NOT perform would be a Inserting special symbols or graphics into documents b Formatting a floppy disc c Creating headers and
186. ion is met then the program will continue and execute the for next statement and output results Note the output line which looks rather complex All it is doing is concatenating the output as a mixture if string and program variables Concatenation is not just reserved for strings Code and run the program You should end up with output as shown in Figure 7 5 HERIOT WATT UNIVERSITY 2006 7 2 ITERATION 183 Nested loops will gain 5 12 at 1 will gain 10 24 at 24 will gain 15 36 at 3 will gain 20 48 at 4 will gain 25 6 at5 will gain 30 72 at 6 will gain 35 84 at 74 will gain 40 96 at 8 will gain 246 08 at IZ will gain 51 2 at 10 Sum Enteied 512 Figure 7 5 Exercise Write a program that will output integer values representing the sides of right angled triangles that satisfy Pythagoras s theorem i e a2 b72 c72 Only output values that satisfy the equation Hint You will require three nested for next loops and experiment with loop values up to 10 for each loop otherwise the program may run out of memory Drawing right angled triangles Use a nested loop to draw right angled triangle as shown below 30 min KK oh KK OK OK 2 KK OK OK KK AS HERIOT WATT UNIVERSITY 2006 184 30 min TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Mowing meadows Use a nested loop to generate the following lines of a well known verse 1 man went to mow a meadow 2 men 1 man went to m
187. ion to detail e possess the ability to create schedules and budgets e show remarkable endurance under stress 4 5 The Systems Analyst The systems analyst carries out the system investigation In large systems the analysis might be carried out by a team of analysts The systems analyst is appointed by the project manager HERIOT WATT UNIVERSITY 2006 4 5 THE SYSTEMS ANALYST Systems analysts are active in the design testing and implementation phases of the project They often work in a team with significant liaison with external or internal clients Systems analysts will usually have learnt some programming but they won t necessarily be programmers It could not be taken for granted that an analyst would know anything about the programming language in which the system will be implemented Most systems analysts work with a specific type of system that varies with the type of organization they work for Examples would include business accounting or financial systems or scientific and engineering systems Some systems analysts also are referred to as systems developers or systems architects A requirements specification is the starting point and the analyst must proceed from there The aim is to produce a clear specification that the rest of the development team will use in the subsequent stages Analysts begin an assignment by discussing the systems requirements with company managers clients and users to determine the exact
188. is a interactivity You should now complete this task 5 6 Event driven languages Event driven programming languages have evolved to handle events Events can be initiated at two levels 1 at system hardware level events can include timers interrupts loading of files etc 2 at language system level events involve mouse clicks keyboard presses and cursor movements HERIOT WATT UNIVERSITY 2006 5 6 EVENT DRIVEN LANGUAGES 89 In Visual Basic each object has a set of events Here an event is an action that Visual Basic can detect and respond to by a user clicking on a command button for example The following examples show the action of clicking on two buttons in a Visual Basic program amm amm Pressing the clear button removes the message A typical event driven program has the effective structure do forever if event then if event caused by X then handle X else if event caused by Y then handle Y After each event is handled nothing happens until the next event occurs Note that event driven programs do not have a predefined pathway in the execution of the code as opposed to imperative programming style i e they have no beginning or end HERIOT WATT UNIVERSITY 2006 90 TOPIC 5 LANGUAGES AND ENVIRONMENTS Graphical user interface programs are typically programmed in an event driven style using languages such as Visual Basic and Visual C Even Java an object oriented language c
189. is is the only difference but a significant one between these looping constructs HERIOT WATT UNIVERSITY 2006 7 4 DOLOOPS test condition rest of program Figure 7 9 The general form of a do until loopis Do Until test condition statements loop The statements in the body of the loop are executed repeatedly until the test condition is FALSE See Figure 7 9 The do until loop is an example of a top tested while false structure The variant do loop until is an example of a bottom tested while false structure Do statements Loop until test condition The top tested loop can iterate between 0 and N times whereas the bottom tested loop may iterate between 1 and N This means that using the bottom tested loop the iteration must occur at least once so the condition can be tested immediately Some simple examples should clarify the situation Consider the simple lines of code representing a simple do until loop Dim Num As Integer Do Until Num 10 Num Num 1 Loop MsgBox Num HERIOT WATT UNIVERSITY 2006 193 194 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 The equivalent do while loop would be Dim Num As Integer Do While Num lt 10 Num Num 1 Loop MsgBox Num Although both loops end up with similar results their methods are different With the do until loop the condition Num 10 is set and the loop must be entered at least once to test this condition as true Num is continually
190. it positive loop until numberOk getValidNumber number end function function sum a as integer b as integer as integer sum a b end function Main program first getValidNumber second getValidNumber print The total is sum first second Turning a procedure into a function Rewrite this procedure as a function It will return a valid integer It will no longer need a parameter sub getValidNumber ByRef number as integer Dim number0K as Boolean do number Inputbox Input a number numberOK number gt 0 if not numberOK then Print The number must be greater than 0 end if loop until numberOK End sub 241 HERIOT WATT UNIVERSITY 2006 242 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS Using procedures or functions Write a program to add two validated numbers together First use the sum function and the getValidNumber procedure Then write another program using the sum and getValidNumber functions Functions On the Web is a interactivity You should now complete this task 8 5 Recursion Recursion is a powerful programming technique since it can use the minimum of code to achieve maximum output It should be used with care however since the action is an avid user of computer memory space Procedures and functions can be called from other procedures and functions they are said to be nested but calling a procedure or function within itself may seem strange This is recursion and the proc
191. justification Well worth getting Investigating computing disasters Several WWW sources of information about computing disasters have been given above For others we have not given any site details Try to find out more about any two or more that might interest you Alternatively try some of the general links to find two or more which are not in the list Write a summary of two disasters that you have found using around 500 words in total for both 1 6 Well planned programs The most basic notion of well planned programs is to produce software that does what the user wants This is easy to say but more than a little difficult to do If you have been involved in using a programming language to solve a problem then we are sure you know that this is the case from your own experience Other characteristics of well planned programs are 1 the software should be maintainable software with a long lifetime is likely to need changing This means that software must be written and documented in a way which makes change simple and straightforward 2 the software should be reliable 3 the software should be efficient It should not make unreasonable demands on the hardware on which it will run But higher efficiency can lead to less maintainable software as programmers use shortcuts which are effective but difficult to understand 4 the software should have an appropriate user interface Appropriate means that HERIOT WATT UNIVERS
192. ke sense with a few examples 1 Declare an array called MyName to hold 6 integer values Dim MyArray 5 As Integer 2 Declare a string array called Names to hold 3 string values Dim Names 1 to 3 As String 3 Declare a public array called Numbers to hold 50 decimal values Public Numbers 49 as single Note Visual Basic NET does not support declarations using to Errors Note that you cannot mix array types Once they have been declared as type then they cannot be used to store integer real or string variables together Arrays can be quite tricky and you will probably receive quite a few error messages that only occur at run time The most common error is to attempt to access an array element outwith the declared bounds e g accessing element 0 or 15 of an array with subscript range specified as Lo Td This type of error is so common that it has been given the name fencepost error It is HERIOT WATT UNIVERSITY 2006 7 5 ARRAYS not a minor error as it can crash the system If an array has an upper bound of 9 and you attempt to write something to item 10 then you could well be overwriting some variables which the computer has put in that location You may be lucky and there is nothing important there You may be unlucky It does not matter whether your program works or not it is flawed and incorrect Sooner or later it will fail Visual Basic traps this error and reports it to the user at run time 7 5 2 Initialising a
193. king about And if you actually uncover faults it means that you will have a lot more work to do and unpick lines of code that as much by luck as anything seem to work at present Like it or not the only way to test your programs and have a good chance of uncovering bugs is to prepare the test data beforehand Preparing test data A program is to be written which will read a list of examination marks typed in at the keyboard and find the average examination mark The program should reject examination marks which are not within a specified range and provide a suitable error message to the user HERIOT WATT UNIVERSITY 2006 55 56 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION 1 Write down what you think an acceptable range for an examination mark would be 2 Write down an algorithm in pseudo code notation to represent a solution to this problem 3 Copy the headings in the table below and construct at least 5 test data entries to demonstrate how you would verify the correctness of the program Test Case Reason Expected Result Actual Result Comments Sentence completion test data On the Web is a interactivity You should now complete this task 3 4 2 Review questions Q11 Which one of the following options states the main purpose of test data a To determine that the system meets the specification b To prove the absence of errors c To show that the programmers have been careles
194. late the tossing of a coin up to1000 times determined by the user and output the number of heads and tails produced The program can be done in several sections 1 Generate random numbers within the range 2 Store results of up to 1000 tosses 3 Display output The following code segment will generate the random numbers and convert them to integers within the range 1 and 2 Randomise for toss 0 to 999 HeadTails toss Int rnd 2 next toss This will fill the array called HeadsTails with either 1 s or 2s Rnd 2 is used since the full statement is HeadsTails toss Int upper value lower value rnd lower Counting heads and tails With 1000 numbers stored we can now scan the array and count the occurrences of 1 s and 2s that represent heads and tails The following code segment should accomplish this For toss 0 to 999 If HeadsTails toss 1 then heads heads 1 else tails tails 1 end if next toss Finally introduce the code to output the number of heads and tails What would you expect the two values to be Why Code the program and run it a few times to see if you are correct The full Visual Basic program is shown in Code 7 12 HERIOT WATT UNIVERSITY 2006 214 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Option Explicit Dim HeadsTails 1 To 1000 As Integer Private Sub Command1_Click 20th February Program by Fred Fink This program simulates the tossing of a coin Dim toss As I
195. ld be choose one a A corrupted floppy disc b A printer jam c A damaged keyboard key d A pointing device not attached Q24 Which one of the following actions will a reliable program NOT do a Inform the user that something is wrong b Produce output come what may c Recover from an error situation within a minimum time period d Die gracefully Q25 A language designed to be portable across different operating systems is choose one a Visual Basic b Pascal c Java d C 3 10 Summary The following summary points are related to the learning objectives in the topic introduction e much has to be done in terms of design and testing of software before the coding and implementation stages e various graphical design constructs are available e top down design and stepwise refinement is a well established technique e testing is an extremely time consuming process e the main aim is to produce software that contains the basic elements of reliability portability efficiency and maintainability e laudable as the efforts in the various phases of the software development process might be no piece of software can be considered to be error free HERIOT WATT UNIVERSITY 2006 3 11 END OF TOPIC TEST 3 11 End of topic test An online assessment is provided to help you review this topic HERIOT WATT UNIVERSITY 2006 65 66 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION HERIOT WATT UNIVERSITY
196. ld the value of the largest item that has been found so far usually the first data element If an element in the array exceeds this working maximum we give the working maximum that value Such algorithms sometimes have to return the index number of the largest or smallest element and sometimes the actual maximum or minimum value The algorithms to return the maximum and minimum values are shown below Finding the maximum set maximum to first item in the list set current position to 2 do compare maximum to item at current position if maximum lt item then set maximum to item set current position to next position in the list loop until end of list report maximum value ONO TF WN BE Finding the minimum set minimum to first item in the list set current position to 2 do compare minimum to item at current position if minimum gt item then set minimum to item set current position to next position in the list loop until end of list o ON OO O1 AUNDE report minimum value HERIOT WATT UNIVERSITY 2006 8 6 STANDARD ALGORITHMS The full Visual Basic program for maximum is shown below Option Explicit Dim SearchKey As Integer Pointer As Integer Fill As Integer Dim Maximum As Integer Dim List 15 As Variant Private Sub Command1_Click gt Program Maximum gt 29th February 2004 gt Program by Fred Fink gt This program will perform a search on an array holding 16 random integers and output the maximum
197. le 1 The statement Print Man chester would produce the string Manchester Example 2 Stringi This is String2 con String3 cat String4 en Strings nation Print Stringi amp String2 String3 String4 String5 will produce as output This is concatenation Practice in using simple variables Now let us put this to some practical use by having a look at an example program A Example Adding values Problem Describe the operation and the output of the following program Dim numberi As Integer Dim number2 As Integer Dim sum As Integer numberi 0 initialise the variables to some value number2 0 numberi InputBox Give me a number number2 InputBox Give me a second number Print sum numberi number2 Print The sum of number1 and number2 is sum This file add txt can be downloaded from the course web site Code 6 6 HERIOT WATT UNIVERSITY 2006 134 20 min TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Solution The program defines 3 integer variables Values are assigned to two of them These two variables are then added together with the result being stored in the third variable The result of the sum is then displayed Given number1 32 and number2 27 the output of the program is The sum of 32 and 27 is 59 In this program the variables value1 value2 and sum are declared to be of data type integer This declaration statement mu
198. likely to be iterative testing finds bugs they get fixed the program s tested again more bugs are found and so on It may be that bugs reveal flaws that were introduced at an earlier stage of the process at the design or even at the analysis stage If this is the case the documentation for each stage of the development process will need to be corrected A standard technique to identify potential errors is to conduct a dry run This involves taking test data and a listing of the relevant part of the code and calculating exactly what would happen to the data if it were to pass through that code It is a pencil and paper exercise HERIOT WATT UNIVERSITY 2006 2 7 TESTING IN CLOSER DETAIL 2 7 2 Beta testing Otherwise known as acceptance testing it takes place after alpha testing The idea is to subject a completed program to testing under actual working conditions If a program has been developed for use by particular clients it is installed on their site The clients use the program for a given period and then report back to the development team The process might be iterative with the development team making adjustments to the software When the clients regard the program s operation as acceptable the testing stage is complete If a program is being developed by a software house for sale to a market rather than an individual client the developers will provide an alpha tested version to a select group of expert users such as
199. llowed will accomplish a particular task The term algorithm derives from the name of the mathematician Mohammed ibn Musa al Khwarizmi c 825AD who was a mathematician and part of the royal court in Baghdad Al Khwarizmi s work is the likely source for the word algebra as well Figure 8 7 Cunieform tablet There is ample proof that the use of algorithms was evident around 2000 3000 BC by the ancient Sumerians whose work was inscribed on clay tablets using a cunieform cipher Translating this text revealed mathematical rules and astronomical data written in sexagesimal notation base 60 from which remains 360 degrees for circular measure HERIOT WATT UNIVERSITY 2006 8 6 STANDARD ALGORITHMS 60 minutes per hour 60 seconds per minute and so on A computer program can be viewed as an elaborate algorithm In mathematics and computer science an algorithm usually means a small procedure that solves a recurrent problem One major objective of this topic is to introduce you to common algorithms that have been tried and tested by programmers with knowledge of good algorithm design Many algorithms appear over and over again in program after program These are called standard algorithms or common algorithms Think about a word processing package which uses an algorithm to find all occurrences of a particular word in a block of text or a spreadsheet package which uses an algorithm to find the maximum value in a range o
200. llowing lines of code as shown Private Sub Form_Load Dim MyText MyText Sample program FirstNumber 5 SecondNumber 10 Total FirstNumber SecondNumber End Sub FirstNumber SecondNumber and Total have not been declared but Visual Basic has assigned them data types on the fly the first time they encountered Although My Text has been declared it has no type All variables have therefore been assigned the type variant But beware If a variant variable is mis spelled later in the program then a new variable will be created by Visual Basic This is a common error and can create program bugs that are difficult to find Explicit declaration In explicit declaration each variable is declared unambiguously using the Dim statement It is recommended that this option be used at all times This helps to prevent errors and allows the computer to work more efficiently If Visual Basic knows the data type through declarations then the requisite amount of memory can be assigned thus making memory management more effective Programs with defined variables also run around 3 times faster than those with variant data types Visual Basic can be forced to make variable declaration the default setting By clicking on Tools then Options a window like Figure 6 4 will open Checking the Require Variable Declaration box will ensure Visual Basic starts up in explicit declaration mode Note Visual basic NET does not support the type variant
201. llustrated in Figure 7 12 showing an array structure called temperature and elements with the subscript ranging from 1 to 8 temperature 1 temperature 6 Index or subscript Figure 7 12 Representation of an array and indices An individual array element can be used anywhere that a normal variable could be e g temp temperature 27 average temperature 5 temperature 6 2 0 It should be obvious from the above that temperature must be declared as a real Can you say why A value can be stored in an array simply by specifying the array element on the left hand side of the assignment operator equals sign e g temperature 2 18 0 assigns the value 18 0 to be stored in element with subscript 2 of the temperature array temperature 7 14 5 assigns the value 14 5 to be stored in element index number 7 of the temperature array This is illustrated in Figure 7 13 temperature fet ted 2 7 8 1 3 4 5 6 Index or subscript Figure 7 13 Representation of the temperature array with temperature 2 18 0 and temperature 7 14 5 More generally an integer variable can be declared and used as the subscript e g temp temperature i which will take the value assigned in element number i of the array temperature and HERIOT WATT UNIVERSITY 2006 202 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 assign it to the variable temp This means that if you want to access the elements of an array sequentially y
202. log is a procedural language used in artificial intelligence Q5 c A scripting language has to be translated Answers from page 86 Q6 Q7 Q8 Q9 Q10 b Languages have to be adapted so new versions are released c Basic Algol Pascal Comal d Moderation b C d All of these Answers from page 95 Q11 Q12 Q13 Q14 Q15 Programs have no pre defined pathway All of the above a d b Ease of developing of interactive web pages c Macros automate repetitive tasks d Changing audio CDs Answers from page 99 Q16 Q17 Q18 Q19 Q20 Java All of these c d c It can promote code re use by extending an existing class a Lisp c It emphasises the evaluation of expressions HERIOT WATT UNIVERSITY 2006 276 ANSWERS TOPIC 5 Answers from page 103 Q21 b Lexical analysis Q22 d All of these Q23 c A compiler can produce more efficient object code Q24 a Looping structures have to be interpreted each time they are entered Q25 a Computers can only understand machine code HERIOT WATT UNIVERSITY 2006 ANSWERS TOPIC 6 6 High Level Language Constructs 1 Revision page 107 Q1 b The FOR NEXT loop Q2 d Answer 5 8 3 2 Q3 b NOT 1 FALSE Q4 c 6 Q5 dj All of the above Answers from page 123 Q6 c 17 5 Vat Q7 a It is easier for programmers to locate and fix errors Q8 d Integer Q9 a ior2 Q10 c Integer long Practi
203. m Where there is a significant HCI the guide will show each form menu and icon and associated instructions about their use User guides may be supplied as paper manuals often with separate manuals for installation getting started and the user guide HERIOT WATT UNIVERSITY 2006 2 8 DOCUMENTATION IN CLOSER DETAIL User manual Increasingly software vendors supply the manuals on disc where they may be available in pdf or hypertext markup language HTML Paper manuals are costly to reproduce manufacturers frequently include electronic files which provide up to date amendments This lets the user read up to date information which could not be included in the original paper manual It is common for sample files to be included which complement the tutorial and provide the user with demonstration files The program should contain a help facility It is common for on line help to be presented in three tagged pages Contents Index and Search The contents present the help chapter by chapter the index refers to certain key words in the chapters and search offers the facility to locate key terms within the guide Onscreen help may be provided in Forms which have hints programmed into them so that if the cursor lingers on an icon or some other significant part of the form a message will be displayed explaining the icon s purpose or the significance of that part of the form 2 8 2 Technical guide The technical guide will
204. may be changes in legislation which mean that the program must be altered in order to comply with the new regulations No matter what the reason iteration always occurs and this creates problems because much of your work has to be re examined and revised 2 It is difficult for the customer to state all requirements explicitly at the start of developments The waterfall model depends on this and has difficulty incorporating customer uncertainty 3 Clients are frequently excluded from the development The working version of the program will not be available for the customer to see until late in the development cycle 4 Developers work in isolation from the clients often for months only for the clients HERIOT WATT UNIVERSITY 2006 2 12 ALTERNATIVE MODELS to be disappointed with the results Many developers value feedback from clients as the project progresses 5 Errors arising from incorrect requirements will not be obvious until late in the cycle by which time they will be difficult and expensive to fix There is nothing so depressing as delivering months sometimes years of work to the customer only to be greeted with the response That s not what wanted at all 6 The waterfall model does not address project management or software maintenance There are alternative models that have been developed for two reasons e perceived shortcomings in the traditional approach e advances in hardware and software 2 12 Alter
205. mediate failure or obvious corruption of your program Instead they may result in an incorrect output at some later stage To detect these errors the running of the program must be traced as the faulty output is only a symptom of the problem rather than the problem itself The easiest way to trace the program execution is to add print statements to the program at key points When you write your programs we are sure you will become very familiar with these Finally and most importantly tests should be devised against the specification so that you can see whether or not the program does what it s supposed to do In the full software development process now is the point at which test data should be prepared You do it before the coding That is before you have invested time and effort in writing the code It is often a temptation to leave making up the test data until you have written the program But experience shows that this is a mistake Once you have written the code you will tend to go easy on it and let the program s behaviour shape what you expect of it You are going to be too kind to it What you see becomes what you expect and what any reasonable person would expect This is a problem with all programmers but perhaps especially so if you are only beginning programming You may have only a hazy idea of what you are doing Getting the thing to work at all has been agony The idea that there are faults in it does not bear thin
206. metimes problems that arise at the implementation stage will call for a return to an earlier stage of the development process For example it might turn out that an algorithm runs too slowly to be useful and that the designer will have to develop a faster algorithm Or it might be that the slowness of operation is due not to a poor algorithm but to the hardware capability In such a case the development team might have to return to the analysis stage and reconsider the hardware specification At the end of the implementation stage a structured listing is produced complete with internal documentation This will be checked against the design and against the original specification to ensure that the project is remains on target There are many programming languages used for the implementation of software developments 2 6 1 Review questions Q21 One of the qualities of a good human computer interface is a It should be Windows based b It can make a program execute faster c Itcan make running a program a less irritable experience d It should have lots of colour Q22 Which one of the following elements is not part of software design The interface The requirements The data structures The main program a0 0 9 HERIOT WATT UNIVERSITY 2006 25 26 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS Q23 Which one of the following languages is not high level a Visual Basic b Pascal c Assembler d C Q
207. n IN parameter 2 OUT mode or use of an OUT parameter 3 IN OUT mode or use of an IN OUT parameter This is probably shown best in the following diagram Declared procedure Calling procedure Sub procedure a b c Information flow procedure x y Z Formal parameters a Cc Actual parameters x y Z os le B NS An OUT Mode call cj c IN OUT Mode return e In the diagram the declared procedure has three formal parameters a b and c while the calling procedure has actual parameters x y and z During a procedure call the formal and actual parameters will interact as follows IN mode information regarding x is passed to a OUT mode returning information from b to y IN OUT mode information regarding z is passed to c where it is updated and returned to z Make sure you understand the differences between the three modes The information that is passed can occur by two methods 1 Call by value 2 Call by reference HERIOT WATT UNIVERSITY 2006 8 3 PROCEDURES AND FUNCTIONS 229 8 3 4 Call by Value Call by value is the most common parameter passing mechanism and is also the easiest to understand Recalling the section of code that outputs blank lines we can now introduce a value parameter to make the procedure much more flexible Here is the Visual Basic code Code 8 1 Private Sub Command_Click Modified program lines Print Message 1 Call BlankLines 5 Print Message 1 ny End Sub
208. n the small It uses only the three control structures necessary for structured programming sequence selection and iteration The design is made up of boxes or nodes each of which represents a part of the process Boxes have names A plain box represents action of some kind This is sometimes called a normal node Boxes are always read and in the end executed from left to right order of execution A box with a circle in it is a selection node This means that it is part of a selection sequence It does not necessarily mean that it is a node that actually does any selection itself In this diagram a is the node where the selection takes place As a result of the selection b c or d happens Note that b c and d must all be selection nodes if one child of a node is a selection node they must all be The right most node in this case d will contain default behaviour A box with a star or asterisk in it is an iteration node The code it represents must be repeated a certain number of times HERIOT WATT UNIVERSITY 2006 49 50 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION To understand what a node is doing you need to investigate the next level down Many people feel this is a bad way of working and that some sort of sign should be present to indicate that a node involves rather than is involved in selection or repetition In fact some designers use these signs
209. n the topic introduction e introduction to the Visual Basic environment e existence of various data types including local and global forms e what is meant by the scope of a variable e discussion of formatted input output with coded examples e discussion of conditional statement structures with coded examples e exemplification of the CASE statement 6 18 End of topic test An online assessment is provided to help you review this topic HERIOT WATT UNIVERSITY 2006 Topic 7 High Level Language Constructs 2 Contents 1 AMrOCUCHI N a a 20 2 RRA A a ARA Poe METAN o AA A 72 11 The For Nextloop e omic a e ae ae dau 7 2 2 Nested For loops 7 2 3 Review Questions 143 FOrMatting Outputs 2 ede ti Ge dd send Bob EN es wt alae d TAa DO HOODS ut A keke Reiley Ae ok MR ER A AAA DOWIE MOOD 444 eee ee el ar er ae RB EE EAS A 7 4 2 Examples of Do While Loop 74 3 Do Until LOOP 2 2 ra i a eee we A As 7 44 Review Questions Ro EV A RO 7 5 1 Declaring arrays 7 5 2 Initialising arrays 7 5 3 Examples of using arrays 7 5 4 Review Questions 7 5 5 Worked example programs LO SUMMANY Li A e EN le pea AAA 1 7 End of topic test are w ea tt AA rt a A
210. native models The traditional model remains the basis for these alternative models and their subsequent refinements There are many models We will briefly describe the following structured systems analysis and design SSADM prototyping rapid application development RAD e commercial off the shelf software COTS spiral open source 2 12 1 SSADM The Structured Systems Analysis and Design Method SSADM concentrates on the analysis and design aspects lt deals with only part of the overall process and leaves the other aspects to other specialist models The stages addressed by SSADM are analysis requirements specification logical design physical design and program specification HERIOT WATT UNIVERSITY 2006 35 36 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS The following diagram outlines the typical structure of SSADM 1 Feasibility Study Systems Analysis System Design 4 Requirements 7 Physical Design specifications System Investigation Logical systems spec 2 Current environment 5 Technical option 3 Business system 6 Logical design This model was developed by Learmonte and Burchett and is widely used in the UK by government and public organisations where it first appeared at the Central Computer and Telecommunications Agency CCTA It is frequently used in conjunction with a planning process model eg PROMPT II a project management methodology where it is now regarded as a de facto s
211. nature of the problem They define the goals of the system and divide the solutions into individual steps and separate procedures Full systems analysis has three phases 1 collection of information 2 analysis of information collected 3 production of a problem specification or user requirements specification Identifying Personnel involved in a Systems Development On the Web is a interactivity You should now complete this task 4 5 1 Collection of Information There are various methods used for gathering information These include a Interviews The analyst talks face to face with clients to find out how the current system works and what is required of the new system b Questionnaires Where the current system has a large number of users the analyst might construct a questionnaire for everyone involved People often respond more frankly to an anonymous questionnaire On the other hand the response rate can be low c Observation The analyst studies the current system and observes how it works This is useful for bringing to light things that users take for granted d Document analysis Many different kinds of document are involved in a system the documents that the system produces the documents it uses i e source documents and the documents that HERIOT WATT UNIVERSITY 2006 71 72 TOPIC 4 PERSONNEL affect how the system works such as documents that spell out the procedures to be followed in usin
212. nce e understand the need for documentation at each stage of the software development process HERIOT WATT UNIVERSITY 2006 2 1 INTRODUCTION Revision Q1 The software development process consists of seven stages Three of the stages are analysis testing and maintenance Which one of the following statements correctly identifies the missing stages in order a Design documentation evaluation implementation b Design evaluation documentation implementation c Design implementation documentation evaluation d Design documentation implementation evaluation Q2 The software development process is an iterative process This means that choose one a Certain stages of the process are re written to improve quality b Certain stages of the process are re visited to make sure all is well c Certain stages of the process are ignored to save time d Certain stages of the process are very complex so more time is spent on them Q3 Which one ofthe following statements refers to an essential item of documentation that should be produced during the software development process a User Guide b Technical guide c Structured listing d All of these Q4 One of the characteristics of a computer program is the user interface Which one of the following is NOT a part of this aspect a Plenty of colour b Help screens c Instruction screens d Screen layout Q5 Which one of the following statements concerning a struc
213. nd development team then the design of the solution begins The design process is methodical using techniques such as structure charts and pseudo code The problem is approached by breaking it down into a collection of relatively small and simple tasks This approach is Known as top down design or stepwise refinement These techniques will be discussed more fully later on HERIOT WATT UNIVERSITY 2006 15 16 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS There are certain characteristics which all good software should possess e robustness e reliability e portability The development team will attempt to make the design of the program both robust and reliable In as much as the terms are distinguishable e areliable program is one that does not stop because of faults in its design e arobust program is one that can cope with errors when it is running To put it another way an unreliable program is one that hangs or crashes for no apparent reason whereas a non sturdy program is one that cannot cope with events that the world throws at it One of the matters for decision at this point is that of the language of implementation and the Software Development Environment eg should the program be written in C under Windows or in Java under Unix One of the factors which may affect this decision is the portability of the resulting code i e can the software be moved to a different hardware platform and still work effectively
214. ne For example you could create the bytecode on a PC running Linux and this will run under Windows or on a Macintosh computer This approach works very well for small programs or applets on the Web but interpreters tend to run slowly so the porting of large computer programs remains a problem A large and successful commercial system will generally outlast the hardware it was developed on When the hardware is changed the system will need to be transferred or ported to the new hardware If a program works well in one part of an organisation the decision is often made to set it up in other parts where for one reason or another the hardware might be different 3 9 4 Review questions Q21 Choose the correct response that relates to the term robust within software development a The program is strong and hardy b The program may be ported to a different machine architecture c The program can cope with mistakes that the user might make HERIOT WATT UNIVERSITY 2006 64 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION d The program runs to specification Q22 Using a module library can reduce software development time because choose one a Common programming modules can be used b Programmers do not need to write programs from scratch c Programmers can re use library code in their projects d All of the above Q23 An example of an unexpected condition that could cause a program to hang until user intervention wou
215. nesses to make the analysis and design stages of software development more manageable Before looking at some of these models we should take a brief look at why software development evolved as an engineering process This is best understood by looking at the sorts of things that have gone wrong in large software developments 1 2 1 Software engineering In this topic we want to consider good practice in developing programs within the software development environment To do so we think it is useful to put software development into a wider context as it is part of a subject known as software engineering HERIOT WATT UNIVERSITY 2006 1 2 OVERVIEW The ideas behind software engineering are to provide an approach to the development of software by designing and building software systems that are e of high quality e cost effective e produced to specification e delivered on time Rather than produce software on an arbitrary basis the idea is to bring together a variety of tools techniques and methods which will help create reliable software By these means programs can be designed to be maintainable that is they are presented and documented so clearly that they can be updated by another programmer at some future time 1 2 2 Software development There are many reasons why software development is required Some include 1 increased complexity and sophistication of computing systems escalating costs of software systems unreliabl
216. next i print sum a 16 b 17 c 18 d 19 7 3 Formatting output Up to this point it has been left to Visual Basic to output data in default mode However it is possible to have more control over how real values currency boolean variables are output by using the Visual Basic in built function Format The structure of the Format function is Format variable format expression Table 7 1 shows the formatting functions within Visual Basic Table 7 1 Format name Meaning Examples General Displays raw number without separators 12345 Fixed Displays at least one digit before the decimal 67 88 point and two digits after the point Scientific Uses scientific notation 6 023 E23 Standard Displays numbers with separators and two 1 234 56 digits after the decimal point Currency Same as standard Negative values are 1 234 56 enclosed within parentheses Percent Displays numbers multiplied by 100 with two 12345 67 digits after the decimal point followed by the sign Exercise Write a Visual Basic program to input a value and output the value in each of the formats in Table 7 1 Use the algorithm below to help you Make the value large enough so that all aspects of the formatting can be shown HERIOT WATT UNIVERSITY 2006 185 186 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Declare variable Input a real value Print Standard format Format value Standard repeat for othe
217. ng A process used in object oriented languages that identifies objects how they relate to one another and their manipulation Debugging The detection location and removal of errors in a program Declarative language Programmers use this type of language to specify what the problem is rather than how to solve it by writing code The language uses facts and rules to express relationships Desk checking Akin to a dry run where the running of a program is checked without a computer Development team Generic description of the personnel involved in developing the software solution Dry run A pen and paper exercise to debug a program Event driven A system that responds to an external event such as mouse click or a key press Event driven language An event driven language that is designed to handle external events like interrupts mouse clicks etc Exceptions testing Testing the robustness of a program by entering silly data character data instead of numeric data excessive values etc Executable code Independent machine code that can be run without translation Exhaustive testing Complete testing of a program under every conceivable condition An expensive method time wise HERIOT WATT UNIVERSITY 2006 262 GLOSSARY Explicit declaration Each variable for example is declared unambiguously by the user so there is much less room for error in running programs Visual basic Feedback A looping system where information is
218. ng examples are palindromes the sequence being the same when read from left to right or from right to left 2345432 madam im adam mas not a ton sam a man a plan a canal panama eve This program may seem more complicated than it really is If you follow the explanation you will see that by breaking it down into small steps each of which can be written in Visual Basic you will chip away at the problem until it is done HERIOT WATT UNIVERSITY 2006 216 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 The solution to this problem assumes that you do not know how many words are going to be input Solution The program does not know how big a sequence will be entered so an array of characters larger than required is declared The program reads in the sequence of characters one at a time into the array terminated by a full stop It also checks that the array bounds are not breached by testing the condition count lt Size using a do while loop This is important otherwise an array bounds error will likely occur The constant Size is initially set to 30 but may be altered if large strings are used The condition in the while do loop that checks whether was the last character entered is palindromeChar lt gt gt lt gt means not equal to Once it has completed reading in the characters you can determine the number of values read in This is count 1 not count since you are not interested in the last charac
219. ng facts rules and queries Problem Suppose we want to find out whether a person drives a fast car We start by building a set of facts and rules for our knowledge database Solution person judy this is the fact that Judy is a person person james drives_car james ford escort drives_car judy porsche this is the fact that Judy drives a Porsche drives_fast_car X drives_car X Y and Y porsche this is a rule for X driving a fast car In this example we could ask the program to tell us whether Judy drives a fast car by typing the goal drives_fast_car judy The result would be YES since the goal is satisfied If we asked drives_fast_car james then the result would be NO as drives_car james Y would evaluate Y ford escort This would then cause the rule drives_fast_car james to fail as Y does not equal porsche and the goal is not satisfied You can see from the code that there is no description of the type of data or its internal representation There are simply statements of facts and a rule Contrast this with a procedural language where the programmer would need to set up a structure to hold the knowledge and predefine its type string number etc Then they would need to describe the steps taken to search the structure in order to answer the query A declarative logical language is simplistically described as telling the computer what to do and not how to do it Goals and clauses On the Web
220. nguages 4 4 n saaa aaa eee oe desde Lave 85 5 5 Declarative languages 255 ute date en SEY aie a De Pe ke 2 87 5 6 Event driven languages waves Gi oe Sok a be tre Bk ey 88 5 7 Scripting languages lt o Bete ait ret de a oe eda BE ee 90 5 8 Object oriented languages 96 5 9 Functional languages veo ara kee eae a hee aie e 98 5 10 Translation methods seee ooo a a 99 ld Er SNS en A roda ne cit E 104 D 12 End OOPS test ia Ove id ie EA 104 6 High Level Language Constructs 1 105 6 1 Introduction 4 rats nee a a a da 108 6 2 The Programming Environment 108 6 3 Building applications 22584 44824 408 Late de e ee eS 110 6 4 Program Structure dans te eee MS OUR AE AS te sun dr Se 118 BO DANS Sr Gls Ae ia Sean he oe ee ee 121 6 6 Visual Basic Nomenclature 122 6 7 Declaring Variables ia ne Ep ee see ie me eS 124 6 8 Declaring constants 128 6 9 Variables and scope 422 428 0000 a bon Bee e let 135 6 10 Operators ea nant is DANS rent IA ee at 138 6 11 Programming constructs aces hee Duras Lu ewe ele peus 141 6 12 The IF Statement 44 722 A a ar 8 4 142 6 13 The If Then Else Statement 145 6 14 Nested IF Statements 157 6 1 Si A RRA 159 6 16 The Select Case Statement 164 AS ls A A AB as Bh oa hela ar hs ke aa es ep ar pha oh 170 6 18 End OMopic test co
221. nks more about the solution to the problem b Thinks more about the hardware c Thinks more about how the program will run d Thinks more the speed of execution of the program Q10 One disadvantage of NOT using stepwise refinement at the design stage is that it a b c d Reduces the chance of errors being introduced The designer does not have to bother with too much detail Makes the process more complex to novices The designer can concentrate on a small part of the problem at a time 3 4 Test Data When you design your program you should include fail safe mechanisms and anticipate user errors We know this is obvious but fewer bugs mean that you have to spend less time in fixing your code Designing your input routines so that they do not crash means that you do not have to spend time re writing them afterwards Fixing errors can be very expensive because as faults are removed the cost of finding and removing remaining faults increases exponentially as shown in Figure 3 4 and in Figure 3 5 The last few errors in a program are horrendously expensive to remove or even to find You may wonder why this is so but all the simple and straightforward tests have found all the simple and straightforward errors What are left are the more complex intermittent ones which require a very large expenditure of time and effort and hence money to fix Note that the cost scale in Figure 3 5 is logarithmic not linear Take a look
222. not Note Use else if in your code You will also need to be careful that you do the tests for leap years and leap centuries in the correct order If you test for leap years first then 1900 is divisible by 4 but as it is not a leap century it will not be a leap year either HERIOT WATT UNIVERSITY 2006 163 20 min 20 min 164 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 6 16 The Select Case Statement The Case statement is a special instance of the If Then ElseIf structure To implement multi way decisions the case statement provides a more concise and elegant representation than multiple else if and nested if statements which can get very difficult to follow Probably if you have more than three else if statements you should consider using the case statement instead The case statement is particularly useful when selection is based on a single variable or a simple expression This is called the case selector Note that the case selector must be an ordinal data type i e one whose values can be listed such as integer string Or boolean The structure of the Case statement is Select case test expression Case valuel Block of one or more statements Case value2 Block of one or more statements Case value3 Block of one or more statements Case Else Final block of one or more statements End Select The first statement of the Select Case block is the Select Case statement itself This statement identifies the value t
223. ns is not performed at this stage a They report directly to the project manager at all stages of programming b They are able to modify and repair existing programs c They are responsible for all test strategies concerning the software d They are overseen by the systems analyst at all stages of their work Q8 The completed project is usually tested by an independent group This is because choose one Independent test group will have better facilities for testing software Programmers will tend to test only within the functionality of their own code Independent test group will not test further than they have to so saving time Programmers are happy to test their programs to destruction 222 2 HERIOT WATT UNIVERSITY 2006 4 8 SUMMARY 77 Q9 If a project begins to run over budget then this will be the responsibility of one of the following personnel to change this state of affairs a The client b The programming team c The systems analyst d The project manager Q10 In beta testing which one of the following is true a Testing is done in house b Testing is done by specialist personnel at cost c Testing is done by external groups on a variety of computer platforms d Testing focuses on the problem specification 4 8 Summary The following summary points are related to the learning objectives in the topic introduction e personnel involved in the software development process e various levels professional exper
224. nteger heads As Integer tails As Integer Dim count As Integer Randomize PicHeads Cls PicTails Cls PicTosses Cls count InputBox Enter number of tosses For toss 0 To count 1 HeadsTails toss Int 2 Rnd 1 Generate numbers Next toss For toss 0 To count 1 Count 1 s and 2 s If HeadsTails toss 1 Then heads heads 1 Else tails tails 1 End If Next toss PicHeads Print heads Display results PicTails Print tails PicTosses Print count End Sub This file Heads Tails txt can be downloaded from the course web site Code 7 12 Note that to make the program easier to follow two for next loops are used but they could be combined into a single loop A typical output is shown in Figure 7 16 HERIOT WATT UNIVERSITY 2006 7 5 ARRAYS 215 w Form Number of heads Number of tals Number of tasses 1000 Run Program esosesoseeccsosssesaseeccsoseeccssseacoseecoose Figure 7 16 The program can easily be modified to simulate throwing a die Exercise Amend Code 7 12 to output the results of throwing a die about 50 times Example 3 Testing for Palindromes using an array Problem Write a program which will read in a sequence of words The characters will be read into an array and the program should then determine if the sequence is a palindrome Note A palindrome is a sequence of number characters words etc which is the same when read from either direction The followi
225. number end terminate program output message 6 13 Thelf Then Else Statement So far we have shown you the use of the if then statement when there is only one alternative i e if the expression is true then execute a single code fragment If the expression is not true you may want to execute a different code fragment This is known as an if statement with two alternatives and the general format becomes if condition then statements 1 else statements 2 End if Again the statements may be single or they can be multiple statements HERIOT WATT UNIVERSITY 2006 146 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 if expression TRUE FALSE statements 1 statements 2 rest of program If the expression is true then the code fragment following the then statements 1 will be executed If the expression is false the statements following the else statements 2 will be executed Example Single or double Problem A program is written to prompt the user for a number If the number entered by the user has a single digit then the program will display an appropriate message telling the user that this is single digit number Otherwise it will output the message double digit number The algorithm is shown below Solution 1 Ask for user to input number between 1 and 99 2 if the number lt 10 3 display single digit number 4 else 5 display double digit number The full Visual Basic program i
226. ny Management are responsible for overall business and strategic planning They choose the projects HERIOT WATT UNIVERSITY 2006 4 4 THE PROJECT MANAGER that will go ahead They review the progress of a project Obviously a project should benefit the organisation in some way but it s not always easy to assess and compare the benefits that different projects might bring One project might be relied upon to break even or show a small profit another might not be reliable at all but might make an enormous profit A project might not make much in itself but be worth doing because it could lead to future projects that would be immensely profitable Many projects are carried out not directly to make profit but to improve things in the organisation Non profit making organisations often have to assess projects in terms of the benefits they will confer rather than the money they will bring in It is important to note that the terms client and user do not necessarily mean the same thing but are sometimes used interchangeably A client is someone or a group such as management who buys or intends to buy some software for a particular purpose A user is someone who uses or will use the software Acting as the client or customer for the organisation the appropriate personnel will be concerned with the following activities e holding discussions with the consultants e review reports and negotiate contracts e ensure the provision of relevant info
227. o be tested against all possible results This value represented by the Value 1 Value 2 etc and can be any valid numeric or string expression a variable a logical expression or a function Each group of commands is initiated by the Case statement The Case statement identifies the expression to which the Value is compared The Case statement can express a single value or a range of values If the Value is equal to or within range of the expression the commands after the Case statement are run The program runs the commands between the current Case statement and the next Case statement or the End Select statement If the Value isn t equal to the value expression or doesn t fall within a range defined for the Case statement the program proceeds to the next Case statement A number of worked solutions to problems are given here make sure you understand what is going on in these examples Run these programs for yourself and experiment with making changes to the code to ensure you understand what is happening HERIOT WATT UNIVERSITY 2006 6 16 THE SELECT CASE STATEMENT 165 Example 1 Write a program to input an integer between 1 and 7 and the day of the week will be output Solution Use the following algorithm 1 ask user to input number between 1 and 7 inclusive 2 select case number 3 case is 1 output Sunday 4 case is 2 output Monday 5 case is 3 output Tuesday 6 case is 4 output Wednesday 7 case is 5
228. o limit to the number or type of criteria that are used in an evaluation A very important aspect of planning evaluations is defining the criteria Listed below are a number of evaluation criteria used in industry e the time it takes to install a piece of equipment e the number of errors an operator makes while doing a specific task e the time it takes an operator to complete a task e the number of times a computer crashes or hangs e the number of phone calls made to a help line e the number of times a user consults a manual The key criterion in evaluating a software product has to be whether it is fit for purpose i e does it meet the original specification and allow the client to carry out their tasks Main questions that may be asked are e how closely does the solution match the specification HERIOT WATT UNIVERSITY 2006 19 20 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS e is the solution what the clients were looking for Other matters for review will include cost and schedule Sentence completion Evaluation On the Web is a interactivity You should now complete this task 2 3 9 The Maintenance stage This as a rule is the most time consuming stage Software does not wear out but it usually needs subsequent modification Some bugs or design shortcomings only become apparent over time In addition changes might have to be made to adapt the system to new demands or legislation data protection guidelines fo
229. of a program limits the type and range of problems that can be solved Sequence is basic and essential but limited A program in simple sequence always does the same sort of thing and it can t easily do things more than once We want programs that can carry out tests and make decisions We want programs that can do things over and over again With the use of selection and repetition the range of problems that can be solved becomes much larger This is what we will look at next HERIOT WATT UNIVERSITY 2006 142 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 6 11 2 Selection A fundamental task in any program is the decision of what to do next Control constructs enable you to make decisions in your programs to determine when certain parts of the program will be executed In a similar manner to English you can make decisions using the if statement for example if it is raining then will take my umbrella These simple decisions can then be further extended as will be considered in this section In this topic you will look at the following control constructs and how to use them to enable decisions to be made in programs e the if statement e use of logical operators in decision making e the if else statement e nested if statements e multi way branching with elseif e the case statement 6 12 The IF Statement The general decision making capability in Visual Basic is provided by the if statement The format of this statement i
230. of the rules For example e inputs and outputs must be preserved from level to level e names must not be duplicated If the system is at all large the difficulties involved become significant CASE tools are used to help look after the very important details For example when we re refining a process the CASE tool will deal with the input and output flows automatically Likewise it may provide extensive support for drawing diagrams The CASE tool will also prevent the use of the same name for different things in the course of building up a data dictionary for the system 3 9 Software characteristics This section introduces the terms robustness reliability and portability A program is robust if it can cope with problems that come from outside and are not of its own making e g corrupt input data Reliability is an internal matter A program is reliable if it runs well and is never brought to a halt by a design flaw When the program is complicated the distinction between the two terms is not always clear When a machine hangs it is not always obvious whether this is due to a failure in robustness or reliability 3 9 1 Robustness The designer should try to ensure that the design is robust the resulting software should be able to cope with mistakes that users might make or unexpected conditions that might occur These should not lead to wrong results or cause the program to hang HERIOT WATT UNIVERSITY 2006 3 9 SOFTWAR
231. ogram Counting Occurrences 29th February 2004 gt Program by Fred Fink gt This program will perform a search on an array holding 16 random integers and output occurrences of an input value Setup Call procedures Populate_List List Enter_search_item SearchKey Search_for_item Pointer SearchKey Occurrence List End Sub Private Sub Setup Initialise variables Randomize and clear output boxes PicList Cls PicResult Cls PicList Print Pointer 0 Occurrence 0 End Sub Private Sub Populate_List ByRef List Fill array with Dim Fill As Integer 216 random numbers For Fill 0 To 15 List Fill Int 49 Rnd 1 PicList Print List Fill Next Fill End Sub Private Sub Enter_search_item ByRef SearchKey User input search item SearchKey InputBox Input search item to count End Sub Private Sub Search_for_item ByVal Pointer ByVal SearchKey ByVal Occurrence ByRef List Do If List Pointer SearchKey Then Occurrence Occurrence 1 HERIOT WATT UNIVERSITY 2006 8 6 STANDARD ALGORITHMS 255 End If Pointer Pointer 1 Loop Until Pointer gt 15 PicResult Print Search item SearchKey found Occurrence times in the list End Sub Private Sub Command2_Click End End Sub This file Occurrences txt can be downloaded from the course web site In this case the array is filled with values from 1 to 49 in order to increase the chances of multiple occurrences The output of this
232. ops terminate HERIOT WATT UNIVERSITY 2006 3 7 MODULE LIBRARIES b Has the programmer used meaningful variable names c Has the programmer used conditional statements d None of the above Q18 From the following list identify one other error to account for during a dry run a Initialisation of variables b Naming of constants c Correct conditional statements d All of the above Q19 A trace facility in a program will identify choose one a Compilation error b Syntax error c Logic error d Coding error Q20 Program errors can be categorised into types Which one of the following is NOT an error type a Compilation b De bugging c Execution d Design 3 7 Module libraries The use of previously written modules reduces the time spent creating the final software and minimises the cost Designers will incorporate if possible modules from the module library in the design For many software companies and programming departments one project will be similar to another Projects will have component parts which are similar for example many programs might require a sort routine to act on the contents of a database For many software companies and programming departments one project will be similar to another Projects will have components parts which are similar for example many programs will require a sort routine to act on the contents of a database As time goes by a collection of modules is built up
233. or example Dim numberi As integer number2 As integer sum As integer is equivalent to Dim numberi As integer Dim number2 As integer Dim sum As integer However the statement Dim numberi number2 sum As integer will assign sum as integer with number1 and number2 being assigned variant 6 8 3 String variables and functions A string is simply a collection of characters that are defined within quotes The following are examples of string values coffee This program is not working xyz February 16 2004 Visual Basic 6 HERIOT WATT UNIVERSITY 2006 132 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Shrove Tuesday is pancake day 51 The quotation marks are very important since they tell Visual Basic that the enclosed characters are a string variables Characters not enclosed in quotation marks are considered to be a numeric variable or some other part of the Visual Basic language Note The string value 51 does not equal the value 51 You might think that it s a value for an integer but it s not However there is a Visual Basic function VAL that will convert string variables to values The following statement NumericalValue VAL 51 will allow the variable NumericalValue to be assigned the integer value 51 Of course the reverse is also true Given a value it can be converted into a string using the Visual Basic STR function The following statement StringValue STR 51 will allow the var
234. ou can do it using a for next loop where the variable for the subscript is automatically incremented each time you go round the loop Remember that the subscript variable can only be an integer A real is not allowed The examples within this topic will show you how you can access an array using a loop This is the most common way of marching through an array from beginning to end and as you will probably use this technique a lot in your programs 7 5 1 Declaring arrays Before you can use an array it must be declared at the beginning of the program with the other variable declarations The declaration provides the name of the array the number of elements and the data type of the elements Like variables arrays can be declared using the Visual Basic keywords Dim Public and Private that determines their scope If Dim is used then the array is private to the procedure in which it is declared Public makes the array visible from anywhere in the program and Private within the General section of a form or module makes the array visible only to the form or module in which it s declared but if you use Dim in the module s Declarations section the array will be available to all procedures within the module Note that in Visual Basic when an array is declared the first element of the array is usually O zero if not declared It s possible however to force the first element of an array to be 1 by using the To statement All this will ma
235. output Thursday 8 case is 6 output Friday 9 case else output Saturday 10 end select Note the use of keyword is Whenever a condition is expressed within a statement the keyword is is used to impose the condition The full Visual Basic program is shown in Code 6 14 Option Explicit Private Sub Commandi_Click Use of the Case Select statement 1 15th February 2004 Program by Fred Fink This program will prompt the user to enter a number and the day will be output Dim iDay As Integer iDay InputBox Please input a number between 1 and 7 Select Case iDay Case Is 1 PicDisplay Print iDay Sunday Case Is 2 PicDisplay Print iDay Monday Case Is 3 PicDisplay Print iDay Tuesday Case Is 4 PicDisplay Print iDay Wednesday Case Is 5 PicDisplay Print iDay Thursday Case Is 6 PicDisplay Print iDay Friday Case Else PicDisplay Print iDay Saturday HERIOT WATT UNIVERSITY 2006 166 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 End Select End Sub Private Sub Command2_Click End End Sub This file Case1 txt can be downloaded from the course web site Code 6 14 The program output is shown in Figure 6 17 Form Wednesday Friday 7 1 5 2 3 4 6 End Program Figure 6 17 Example 2 Using the case select statement with a range of values Problem Rewrite the previous If Then ElseIf program Code 6 13 using Select Case Statement Solut
236. outputs Problem 2 Use of an If statement with nested For Next loop Problem Write a program that calculates bank interest on a sum of money that is input by the user Output the capital sum together with the interest Solution Consider the following algorithm 1 Ask user to input value 2 If value lt gt 0 3 for count 1 to 10 4 calculate interest on value 5 output value and interest 6 next count 7 else output message Value not valid try again 8 end if HERIOT WATT UNIVERSITY 2006 182 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 The Visual Basic Code 7 4 is shown Option Explicit Private Sub Command1_Click 16th February 2004 gt Program by Fred Fink gt This program will illustrate nested loop and IF Dim Capital As Integer Counter As Integer Dim Interest As Single Capital InputBox Please input capital amount SumDisplay Print Capital If Capital lt gt O Then PicDisplay Print For Counter 1 To 10 Interest Capital Counter 100 PicDisplay Print Tab 5 amp Capital Tab 12 will gain amp amp Interest amp at amp Counter amp 4 Next Counter Else PicDisplay Print amp Capital amp is not a valid input Please try again End If End Sub Code 7 4 The program involves an If statement with an embedded for next statement If the capital sum entered does not meet the initial condition then control will be passed to the else statement If the condit
237. ow a meadow 3 men 2 men 1 man went to mow a meadow N men N 1 men N 2 men 1 man went to mow a meadow for N 10 7 2 3 Review Questions Q6 Which one of the following describes correctly an incremental for loop Control variable is decreasing in value by a variable amount Control loop variable is increasing in value by 1 Control loop variable is increasing by a variable amount Control loop variable is increasing in value by a constant amount determined by the programmer sers Q7 Which one of the following statements is not permitted For loopCounter 3 4 to 5 6 step 1 For loopCounter 3 4 to 5 1 step 1 For loopCounter 3 4 to 5 2 step 1 For loopCounter 3 4 16 to 5 5 6 step 1 Q8 Which one of the following problems is best suited to the use of a FOR loop Calculating the total number of marks entered at a keyboard As an event loop that checks for keyboard input Calculating the average of marks held in a file d All of the above Q9 What shape will be displayed by the following Visual Basic program fragment for any value of N gt 1 for i 1 to N for j 1 to i print next j print next i Triangle Square Rectangle a b c d Circle HERIOT WATT UNIVERSITY 2006 7 3 FORMATTING OUTPUT Q10 What will be displayed by the following Visual Basic program fragment assuming N 3 sum 0 for i 1 to N for j 1 to N sum sum j next j
238. p Until NoOfTerms gt 0 And NoOfTerms lt 16 PicDisplay2 Print No0fTerms First InputBox Enter first number Second InputBox Enter second number Third 0 Count 0 PicDisplay Print First Second Do Third First Second First Third Second Third Second PicDisplay Print First Second Count Count 1 Loop Until Count NoOfTerms 2 2 End Sub This file Fibonacci txt can be downloaded from the course web site Code 7 9 The program input is restricted to values gt O and lt 15 otherwise the do until loop will never terminate until a value within the range is input If you find difficulty in following the logic of the program then perform a paper exercise running through the values of each variable as the program executes This is called a dry run and is best done by means of a trace table HERIOT WATT UNIVERSITY 2006 198 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Instructions First Second Third Output Starting 1 1 Values First Loop 2 3 2 1 1 Second Loop 5 8 5 2 3 Third Loop 13 21 13 5 8 The two starting values are 1 1 which are assigned to variables First and Second Variable Third then takes on the value of First Second which is 2 First now takes on the value of Third to become 2 Finally the variable Second takes on the value of Third Second to become 3 The values of First and Second are now displayed to give the output 1 1 2 3 Ge
239. pany the idea of starting a new project is mainly to a Make as large a profit as possible b Use up surplus capital otherwise it will diverted elsewhere c Give the users in the company something else to do d Benefit the organisation in some way Q3 Which one of the following statements does not refer to the systems analyst a The systems analyst is appointed by the project manager b The systems analyst discusses the system requirements with the clients c The systems analyst determines the exact nature of the problem d The systems analyst is responsible for the entire project Q4 There are three phases associated with systems analysis One of the main reasons for this is to a Allow the systems analyst to produce a clear specification of the problem b Allow the client to say how much the project will cost c Allow the project manager to dictate whether the project should go ahead d Allow the collection of information that the company will need anyway Q5 Should a project fall behind schedule then it is up to one of the following to get it back on track a The client b The project manager c The systems analyst d The project will eventually recover itself 4 5 4 Production of the problem specification When a system is accepted the system analyst will determine what computer hardware and software will be needed to set it up He she will coordinate tests and observe initial use of the system to ensure it performs as
240. ples include e making a call to the wrong module e passing incorrect data into a module e passing the wrong data out of a module 3 6 5 Coding Errors At implementation there are a number of error types that can occur You have already seen how translators will fail to convert the source code to object code if the grammatical rules of the programming language is not adhered to Other errors typical at the coding stage include e initialisation errors variables are not assigned an initial value e loop counter errors doing something too many times or not enough failing to increment a loop counter e failure to define or declare variables e incorrectly declaring structured data types and or dimensions in the case of arrays 3 6 6 Design errors Errors do occur at the design stage and some of the more typical ones include e incorrect interpretation of program specification e incomplete logic e neglect of special cases e poor error handling As you have already learned errors at the design stage can be very costly to correct Many months of development may have already been undertaken The re design of software can introduce more errors as existing code is altered to meet the specification As we have stated at the beginning of this section fixing errors can be very expensive because as faults are removed the cost of finding and removing remaining faults increases exponentially 3 6 7 Dry running One goal when preparing
241. pment of the system In respect of production a programmer s work is in two parts First the detailed logic of the modules in the system has to be worked out Data flow has to be identified at all stages Second the programmers write the code test it and debug it though testing is often done by a separate team The programmer is involved at all stages of integration of modules and follows a designed test strategy throughout In most cases several programmers work together as a team under a senior programmer s supervision Programmers often are grouped into two broad types applications programmers and systems programmers Applications programmers write programs to handle a specific job such as a program to track inventory within an organisation They may also revise existing packaged software Systems programmers on the other hand write programs to maintain and control computer systems software such as operating systems networked systems and database systems These workers make changes in the sets of instructions that determine how the network workstations and central processing unit of the system handle the various jobs they have been given and how they communicate with peripheral equipment such as terminals printers and disk drives Because of their knowledge of the entire computer system systems programmers often help applications programmers determine the source of problems that may occur with their programs Programmers
242. ppearing within a loop For example the following Visual Basic code would be interpreted each time the loop is entered HERIOT WATT UNIVERSITY 2006 5 10 TRANSLATION METHODS For iCountvar To 20 iSum iSum iCountvar Pic Display iSum Next iCountvar Errors This has implications for error reporting For instance when the interpreter encounters an error it reports this to the user immediately and halts further execution of the program Such instant feedback pinpointing the exact location of the error helps the programmer to find and remove errors Compilers on the other hand analyse the entire program taking note of where errors have occurred and places these in an error diagnostic file If errors have occurred then the program cannot run Programmers must then use the error messages to identify and remove the errors in the source code Some compilers assist by adding line numbers to the source listing to help pinpoint errors and all compilers will describe the nature of the error e g missing semi colon expected keyword etc although interpreting some compiler diagnostics is a skill in itself Error correction can be very time consuming and frustrating particularly in the case where spurious errors occur e g many errors are highlighted in the source but the cause of the error is a single simple mistake An example of this would be errors that are generated by say a compiler if a programmer simply misses out a s
243. ptance Testing One thing you have to watch for is that errors may not cause immediate failure or obvious corruption of your program Instead they may result in an incorrect output at some later stage To detect these errors the running of the program must be traced as the faulty output is only a symptom of the problem rather than the problem itself The easiest way to trace the program execution is to add print statements to the program at key points or use a trace facility Finally and most importantly tests should be devised against the specification so that you can see whether or not the program does what it is supposed to do In the full software development process now is the point at which test data should be prepared You do it before the coding That is before you have invested time and effort in writing the code All too often there is a temptation especially at classroom level to start coding a program as soon as possible without having produced adequate test data But experience shows that this is a mistake Once you have written the code you will tend to go easy on it and let the program s behaviour shape what you expect of it You are going to be too kind to it What you see becomes what you expect and what any reasonable person MURPHY s LAW 1 MURPHY s LAW 2 The quicker program coding is started the Murphy s Law 1 is correct longer the project will take Testing follows a test plan or
244. put The basic question is how to process the input to get the required output In small straightforward cases this can be answered by studying the information and giving it some thought More complicated cases are easier to understand if the analyst creates a model of the system This model focuses on the essential workings of the system and the connections between the component parts Common approaches to system modelling are data flow modelling object modelling structured analysis and information engineering These methods specify the inputs to be accessed by the system design the processing steps and format the output to meet the users needs They also may prepare cost benefit and return on investment analyses to help management decide whether implementing the proposed system will be financially feasible HERIOT WATT UNIVERSITY 2006 4 5 THE SYSTEMS ANALYST 73 Many designers consider that priority should be given to the data eg in cases where programs are needed to maintain a database of records or stock keeping Information engineering is a data centred technique that focuses on the data and uses structured design techniques to create the processes 4 5 3 Review Questions Q1 Inthe development process the client representative is best described as choose The group who will use the software The group who will test the software The group who will purchase the software The group who will write the software Q2 Ina com
245. r Gisplay result of condition End If Else Picbisplay Print testiumber is out of range display result of condition End If End Sub end of program block E fa 1 of Figure 3 6 3 6 Error Reporting Errors can occur at any of the stages in the development process Errors can be categorised in many ways This section will describe the following 3 categories of error e compilation e execution e design HERIOT WATT UNIVERSITY 2006 58 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION 3 6 1 Compilation Errors This is an error which is detected during compilation eg a syntax error Examples of typical errors that can occur at the compilation stage include e incorrect use of programming language syntax e wrong number of parameters used in the call to a module e incorrect type of parameter passed to a module e reference to undeclared variables 3 6 2 Syntax Errors These are errors which result from incorrect use of the programming language structure ie incorrect use of the language grammar They are detected during compilation and examples include e use of programming language keywords as variable identifiers e blocks that have a missing end marker e g in Visual Basic a missing End If statement e missing brackets semi colons These types of error can be very irritating as they prevent the generation of object code The program cannot run Those new to programming often take a long time to b
246. r example lt can be tempting to add patches as they are required However changes should be made in an organised manner having regard to the system as a whole and following good practice in software development Proper maintenance depends on accurate error reporting from users 2 3 10 Review questions Q16 Software testing and debugging are different because choose one Debugging finds faults and testing removes them Debugging takes longer to implement than testing Testing finds faults and debugging removes them Testing takes longer to implement than debugging a b c d Q17 Which statement is true about test data a It makes the program run faster b It makes the program more efficient c It makes the program run more reliably d It makes the programs run error free Q18 One of the main aspects of software evaluation is fit for purpose Which one of the statements reflect this a The final program runs error free b The final program meets the original specification c The final program is cheaper than originally planned d The final program runs more efficiently Q19 Documentation is an important aspect of the implementation stage This is because choose one lt makes programs more readable It documents what the code does lt records changes made to the program a b c d All of these HERIOT WATT UNIVERSITY 2006 2 4 ANALYSIS IN CLOSER DETAIL Q20 In the documentation stage of the
247. r formats e NN Run the program a few times with different values so that you understand the nature of each format 7 4 Do Loops With the for next loop the number of iterations must be known in advance so that the counter variable can be set There are many occasions in programming where the number of iterations is unknown so an alternative looping structure has to be used The Do Loop is a viable alternative to the for next statement In Visual Basic Do loops come in a variety of flavours and for any given program there will probably be more than one solution using a Do loop variant There are two main do 1oop constructs with two variants 1 Do While loop and variant Do loop While 2 Do Until loop and variant Do loop Until 7 4 1 Do While loop The do while loop repeats a given set of instructions while a given condition is true The general form of this statement is Do while test condition statements Loop The loop repeats itself until the condition becomes false If the condition is false to begin with then the do while loop will not be entered and control will pass to the rest of the program See Figure 7 6 While loops are used in situations where the number of times something has to be repeated is not known They are often used in data validation where the user is repeatedly asked to enter values when invalid data is detected HERIOT WATT UNIVERSITY 2006 7 4 DOLOOPS
248. r software They will study press reviews and note any contents and criticisms New or forthcoming changes in technology in operating environment and so on are also taken into account When the evaluation is complete work begins on the next version of the system 2 10 Maintenance in closer detail Once the software is operating the users will need support In the case of a bespoke system the development team or the organisation it works for will offer training in the use of the new system Creators of software systems often establish help desks so users can obtain advice about the software Software does not wear out in any physical sense but the presence of errors or omissions will give rise to the need for maintenance This doesn t appear to be working Software maintenance always involves a change in the software with the accompanying probability that additional errors may be introduced It is essential to ensure that adequate quality control is in place Maintenance documentation is designed for computer professionals rather than users and includes the documentation produced by the development process systems documentation such as the specification and the design documents and program HERIOT WATT UNIVERSITY 2006 33 34 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS documentation such as the structured listing There are three types of software maintenance e corrective e adaptive
249. ram is reliable if it runs well and is never brought to a halt by a design flaw Repetition A process that repeats itself a finite number of times or until a certain condition is met Requirements specification A document describing what the system must be able to do in order to meet user requirements Robust A program is robust if it can cope with problems that come from outside and are not of its own making Scripting language Used for writing small programs or scripts that enhances existing software The best example is JavaScript which is used to enhance web pages HERIOT WATT UNIVERSITY 2006 265 266 GLOSSARY Semantics Semantics is the meaning of a statement in a given language Simulation Replication of a process by computer that would not be possible to do manually For example studying the projected traffic analysis of an airport or throwing a die many hundreds of times Software development environment The high level language programming environment that offers tools and techniques to design and implement a software solution Software development process A series of stages involving defined methods to produce a software project according to an initial specification Software engineering A sphere of computing where the emphasis is on the development of high quality cost effective software produced on schedule and within agreed costs Source code The code for a program written in a high level language This code is
250. re are two loops that are controlled by the variables Outer and Inner For Outer For Inner Outer Loop Next Inner Inner Loop Next Outer The outer loop is initialised with the variable Outer 1 The inner nested loop is now executed 15 times and the first line of numbers are printed on the same line This is achieved by using the semi colon at the end of the first print statement Outer then takes on the value 2 and the process repeats itself until Outer 15 Each time the output is decreased by 1 as the outer loop is executed until the value 15 is reached The print statement on its own ensures that a new line is taken for the next row of output The print statement on its own basically means a line feed The output of the program is shown in Figure 7 4 Note that it is considered bad programming practice to jump out of loops without terminating them fully After the loops terminate the counter variables are discarded so if this is aborted prematurely program output may not be as expected HERIOT WATT UNIVERSITY 2006 7 2 ITERATION Nested loops 8 9 10 11 12 13 14 15 910 11 12 1314 15 1011 12 13 14 15 1 12 13 14 15 1121314 15 12131415 2 13 14 15 13 14 15 0 11 12 13 14 15 10 11 12 13 14 15 11 12 13 14 15 12 13 14 15 13 14 15 14 15 15 0 00 Nm O1 Le Co LO Y MM NM E Ly ND 2 3 4 5 6 8 9 f Figure 7 4 Experiment with the loops and range of numbers to arrive at different
251. re efficient HERIOT WATT UNIVERSITY 2006 8 3 PROCEDURES AND FUNCTIONS e debugging of the main body of the program is simplified since each procedure can be individually tested e procedure code can be saved and re used in future projects Module libraries for instance are repositories for useful chunks of code that can be accessed by programmers who could save time by using such code instead of re inventing the wheel 8 3 Procedures and Functions Procedures and functions provide a means of producing structured programs not only in Visual Basic but in other programming languages as well The more complex a program becomes the more reason to employ strategies to make it easier to read and maintain Procedures and functions help in this respect by breaking up what would be extensive lines of intricate code into more meaningful and logical sections As a consequence e the repetition of lines of code are avoided Rather than repeating the same operations several different times in a program the code can be placed in a procedure or function The procedure is then called as many times as necessary without re writing the code e it allows testing of the procedure code to take place in isolation from the main program Each functional unit can be written independently by programming teams thus making this part of the software development process more efficient e debugging of the main body of the program is simplified since each proc
252. relationship between all the modules in the system A structure chart conveys selected information with clarity rather than presenting all the information at once By convention structure charts are kept simple with no more than half a dozen blocks to each chart What matters is that the picture should be clear and easy to bear in mind If a block needs further refinement that is represented in another chart Describing a structure chart PRODUCE BEST SOLUTION Good Input Solution Good Solution Input GET GOOD go PUT OUT INPUT SOLUTION SOLUTION Formatted Raw Input Formatted Output READ EDIT FORMAT DISPLAY INPUT INPUT OUTPUT OUTPUT Figure 3 3 Sample structure chart Figure 3 3 shows a structure chart Make a list of all the modules and all the data flows Remember to make a sensible guess at what each block is supposed to do its name should be a good indication of this What sort of program do you think is represented by the whole structure chart 3 3 3 Jackson Structured Programming Other methods for structured programming were developed One explicitly for use on small projects was developed by a man called Michael Jackson in the 1970 s and his HERIOT WATT UNIVERSITY 2006 3 3 DESIGN METHODOLOGIES book on the subject came out in 1975 His method became known fairly enough as Jackson Structured Programming JSP JSP is designed for use with relatively small programs for program design i
253. riate test cases in advance of coding You should consider the following tests e anormal test where maximum and minimum are as expected e atest where the maximum and minimum values are the same Sentence completion algorithms On the Web is a sentence completion task on algorithms You should now complete this task 8 7 Summary The following summary points are related to the learning objectives in the topic introduction e understand and exemplify modularity in programming e understand and exemplify user defined procedures and functions in programming e understand procedure function parameters and how they are used e understand and exemplify parameter passing methods e understand and exemplify the following standard algorithms 1 linear search 2 counting occurrences 3 finding maximum minimum 8 8 End of topic test An online assessment is provided to help you review this topic HERIOT WATT UNIVERSITY 2006 260 GLOSSARY Glossary Acceptance testing Testing of software outside the development organisation and usually at the client site Adaptive maintenance Takes place when a program s environment changes for example a different operating system Algorithm A detailed sequence of steps which when followed will accomplish a task Alpha testing Testing of software within the development organisation Beta testing Testing of software outside the development organisation using clients or selected
254. rmation to the project manager and other members of the consultancy team e deciding whether or not to carry on e paying the consultants The client of course can t simply leave things up to the consultants The client must provide detailed direction to develop the project They have to promote support for the study within the organisation and ensure that the relevant resources are available to the investigators They must make sure that people with a stake in any possible development are involved in the study They must agree with the investigators on the description of the problem and on the assignment of priorities They represent the organisation as client and must make sure that all relevant information is given to the consultants When the study is completed they have to evaluate the possibilities presented Sentence completion software development On the Web is a interactivity You should now complete this task 4 4 The Project Manager The project leader is responsible for the project So far as these notes are concerned the project manager will be appointed by the consultants The project manager supervises the project and carries out the initial stages If it goes ahead the project manager will take charge of the project from the first brainstorming HERIOT WATT UNIVERSITY 2006 69 70 TOPIC 4 PERSONNEL session to the software launch and implementation It s up to the project manager to keep the process on sch
255. rrays In computer programming arrays are used to manipulate data and the actions include e initialising the array e reading data into the array e searching the array for data items e sorting data items For this topic we will focus on the first three only Initialising an array simply means setting all the array elements to zero null or a specified value Suppose we have an integer array called Numbers that can hold 7 values To set all the locations to zero we can use the following statements Numbers 0 0 olo Numbers 1 0 110 Numbers 2 0 210 Numbers 3 0 gt 310 Numbers 4 0 410 Numbers 5 0 51 0 Numbers 6 0 6 0 To initialise an array of say 1000 data elements this would be a very impractical way of doing it A much shorter method would be to use a loop structure as in the following piece of code Set Index to 0 Initialising Do until Index 6 Numbers Index 0 Index Index 1 Loop Initialisation is also useful to clear arrays of old data which otherwise might corrupt the new data being processed Whereas initialisation sets all array elements to be identical the same method can be used to input data For example to read the days of the week into the array called Days HERIOT WATT UNIVERSITY 2006 203 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Set Index 0 Initialising Do Until Index 6 Input Days Index Index Index 1 Loop The following days would be input
256. s if condition then statement or if condition then statements end if HERIOT WATT UNIVERSITY 2006 6 12 THE IF STATEMENT 143 if expression FALSE TRUE rest of program The program statement may be a single statement or may be a block of statements When the expression is true the statements following are executed When the expression is false then none of the statements are executed and control passes to the remainder of the program Example 1 Using a simple IF statement Problem A program is written to ask the user for a number If the number entered by the user has the same value as a value stored in a constant then the program will display a suitable response The algorithm is shown below Solution request a number from the user get number typed in at the keyboard IF the number typed in the program constant THEN display I like 99s display Program End So you don t like 99s oP Ne The full Visual Basic code for this program is as follows Option Explicit Private Sub cmdExecute_Click program simplelf_Then 13th February 2004 Program by Fred Fink A program to show a simple if then statement Const Ice As Integer 99 HERIOT WATT UNIVERSITY 2006 144 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Dim userno As Integer userno InputBox Give me a number If userno Ice Then PicDisplay Print I like Ice s End If PicDisplay Print Program
257. s d To minimise the number of errors in the program Q12 Error detection can be time consuming Which one of the following could be added to a program to help detect errors a Suitable commentary throughout the program b Output statements at key points in the code c Specific error detecting code d Nothing can be added Q13 Choose the statement that best describes testing for errors a There is a certainty that undetected errors will always exist b Testing can never show that a program is correct c Testing can demonstrate the absence of errors d All of the above Q14 One example of a fault avoidance technique in developing software is a Take more time to design better software b Hire more programmers so that errors will be easier to detect c Design input routines that will not crash when presented with unexpected data d Make sure that that the code is specifically written to avoid errors Q15 The last remaining errors in a program are not easy to remove because They could remain hidden until the program is run under all conditions The compiler is not very efficient De bugging procedures are not effective enough a b c d They will not affect the running of the program since most errors have been found HERIOT WATT UNIVERSITY 2006 3 5 STRUCTURED LISTING 57 3 5 Structured Listing A structured listing is a hard copy of the program source code It is important that the source code is laid out
258. s independently thereby reducing the overall development time Module libraries can be a rich source of standard algorithms that be used in software projects of many types How the system behaves will be determined by the reliability and robustness of the program Actual and expected outputs should be in agreement as far as possible and this can only be ascertained by rigorous testing at the implementation stage Choice of operating system will relate to the functionality and feel of the HCI Windows might offer much in the way of colourful screens interactive help and dialogue boxes etc It must also affect how the program runs and behaves is the OS software stable enough for the developed program to behave normally without crashing or does the OS offer a true multi tasking environment as in UNIX with the added benefits of in built security Nowadays Linux is being seen as a viable operating system which is both stable and not difficult to use cf UNIX If the developed software can be moved to different machine architecture and still run to specification then it will be deemed to be portable In some cases this might not be required but it is a characteristic that good software should possess 2 6 Implementation in closer detail If the design has been thorough the implementation should be straightforward It should be a matter of translating the pseudo code into code line by line The design is implemented when it has been converted into
259. s seen in Code 6 9 Option Explicit Private Sub Command1_Click program simple_If_Then_Else 15th February 2004 Program by Fred Fink gt This program will prompt the user to enter a number gt The program will test the number to see if it is HERIOT WATT UNIVERSITY 2006 6 13 THE IF THEN ELSE STATEMENT 147 less than 10 and print the message that it is a single digit number Otherwise it will output double integer number Dim testNumber As Integer testNumber InputBox Please input a number If testNumber lt 10 Then PicDisplay Print testNumber is a single digit number Else PicDisplay Print testNumber Is this double digit number End If End Sub Private Sub EndProgram_Click End End Sub This file IfThen txt can be downloaded from the course web site Code 6 9 Note that this program has an extra procedure Sub EndProgram_Click You have probably found that Visual Basic programs do not terminate by default By adding an extra button on the form and programming this with End between the lines of code this will terminate the program This will be used on all subsequent programs Sample output is shown in Figure 6 11 Form 8 is a single digit number D is a single digit number 86 ls this double digit number 99 Is this double digit number End Program Figure 6 11 HERIOT WATT UNIVERSITY 2006 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 148 30 min Further examples
260. s to prompt until it receives a character other than a Y or a y Solution The algorithm is shown below 1 display Continue 2 get input from the keyboard 3 do while user enters Y or user enters y 4 display Continue 5 get input from the keyboard 6 loop 7 display Out of loop The Visual Basic program is shown in Code 7 6 Option Explicit Private Sub Command1_Click 217th February 2004 HERIOT WATT UNIVERSITY 2006 190 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Program by Fred Fink gt This program will illustrate the Do While loop Program CharEntry This program prompts the user to enter a character It uses a WHILE loop to repeatedly check that a character other than a Y or a y has been entered Dim Response As String PicDisplay Print Do you want to continue Response InputBox Y or y Do While Response Y Or Response y Response InputBox Continue Loop PicDisplay Print Out of loop End Sub This file Validate txt can be downloaded from the course web site Code 7 6 The program output is minimal since it only responds to the correct input then the program will simply accept the character that is entered Only when the incorrect character is entered will the program fail to enter the loop and come up with the message Out of loop This code can be used as part of a larger program to validate input If coded as a procedur
261. s to identify all the objects you want to manipulate and how they relate to each other an exercise often known as data modelling Once you ve identified an object you generalize it as a class of objects For example there may be a class Cat and the cat Kitty is an object she is an instance of the class Cat The objects are created and destroyed but the class continues to exist For example Kitty may die but the class of Cat still exists or could get another cat called Puss and then have 2 objects both of type cat The class is the data type and HERIOT WATT UNIVERSITY 2006 5 8 OBJECT ORIENTED LANGUAGES the object is the variable One of the main benefits of object oriented programming is the creation of subclasses of a class that share some or all of the main class characteristics Called inheritance the subclass then inherits all the properties and methods of the superclass In this way inheritance can promote code reuse instead of recreating all the code common to both classes you can simply extend an existing class Another subclass in turn could extend the Cat class and so on In a complex application determining how to structure the hierarchy of your classes is a large part of the design process For example a Mammal class could be created that defines the properties and behaviours common to all mammals The Cat class would then be an extension of the Mammal class with similar traits This is shown diagrammatically
262. scientific and engineering applications and is still in use today Commercial COBOL COmmon Suitable for data processing applications Business Oriented So widely used COBOL 97 is the latest Language version in use Education Pascal Developed from ALGOL developed in the 1970 s to teach structured programming BASIC Beginners All One of the first interpreted languages Symbolic Instruction designed for beginners to programming Code in the 1960 s COMAL COMmon The language promoted the use of Algorithmic Language structured code as opposed to the spaghetti code from using BASIC Artificial PROLOG PROgramming Used in the construction of Al Intelligence in LOGic applications expert systems and in the teaching of Al Operating C Derived from UNIX as the C shell it now systems has many uses in programming being very close to assembly language Alternatively high level languages can be classified according to their structure and purpose Although quite an extensive list for the purposes of this topic the following categories are of importance HERIOT WATT UNIVERSITY 2006 83 84 TOPIC 5 LANGUAGES AND ENVIRONMENTS 1 Imperative procedural Declarative logical Event driven Pb OO ND Scripting Two other types that tend to be associated with the above categories in present day programming techniques are 5 Object oriented 6 Functional A table based on this language classification is shown
263. se input marks next times For each loop the user will be asked to input a mark After four marks have been entered the loop will terminate and the array mark will be storing the four value HERIOT WATT UNIVERSITY 2006 205 206 30 min 20 min TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Using arrays Learning Objective Initialising printing and putting data into arrays Several examples using arrays have been illustrated in the course notes Incorporate these program fragments into a working program which can do three things 1 initialise each element of an array to zero 2 allow you to input data in the form of floating point numbers directly into the array 3 print out the contents of the array Try to make the program user friendly by putting relevant information on the screen Finally add a section to the above program which will print the array in reverse order after it has printed it conventionally Indexing arrays Learning Objective To understand how the index numbers are used in arrays An online array interaction is available to help you Answer the following questions Use the arrays interaction on the course web site to help you find out the answers Q19 Begin with an array of 4 elements with a subscript range of 0 3 All values are initialised to O i e array 0 O O 0 Set array 1 3 What are the arrays contents array array 0 0 0 3 f none of the above
264. set found to true 7 display message 8 else 9 move onto the next element in the list 10 end if 11 loop 12 if not found then 13 display message 14 end if The full Visual Basic program is shown in Code 8 7 Examine it carefully to see how it operates based on the algorithm The output of this can be seen in Figure 8 8 HERIOT WATT UNIVERSITY 2006 8 6 STANDARD ALGORITHMS 251 Option Explicit Dim Found As Boolean Dim SearchKey As Integer Pointer As Integer Fill As Integer Dim List 15 As Variant Private Sub Command1_Click gt Program Linear_Search 29th February 2004 gt Program by Fred Fink This program will perform a linear search on an array holding 16 random integers between gt the values 1 and 99 Setup Call procedures Populate_List List Enter_search_item SearchKey Search_for_item Pointer SearchKey List End Sub Private Sub Setup Initialise variables Randomize gt and clear output boxes Found False PicList Cls PicResult Cls PicResult Print Pointer 0 End Sub Private Sub Populate_List ByRef List Fill array with Dim Fill As Integer 16 random numbers For Fill 0 To 15 List Fill Int 99 Rnd 1 PicList Print List Fill Next Fill End Sub Private Sub Enter_search_item ByRef SearchKey User input search item SearchKey InputBox Input search key End Sub Private Sub Search_for_item ByVal Pointer ByVal SearchKey ByRef List Do While Pointer lt 15
265. sif guess lt age output message endif add 1 to the number of guesses loop until guess age display The number of times guessed DO OO OO O1 amp WN FE HERIOT WATT UNIVERSITY 2006 7 4 DOLOOPS The Visual Basic program is shown in Code 7 8 Option Explicit Private Sub Command1_Click program MyAge 217th February 2004 gt Program by Fred Fink This program will prompt the user to guess an age which is stored gt in the program as a constant It will display the number of attempts needed to guess the correct age Const MyAge As Integer 21 again Dim ThisGuess As Integer guesses As Integer guesses 0 Do ThisGuess InputBox Guess my age guesses guesses 1 If ThisGuess lt MyAge Then PicDisplay Print ThisGuess is too low Elself ThisGuess gt MyAge Then PicDisplay Print ThisGuess is too high End 1f Loop Until ThisGuess MyAge PicDisplay Print Ok so its MyAge but it took you guesses tries End Sub This file GuessAge txt can be downloaded from the course web site Code 7 8 You may wonder why the elseif statement is used since by default if ThisGuess lt MyAge is false then ThisGuess must be true within the if endif statement This is so but when the initial condition is met MyAge ThisGuess an error occurs stating that the value 21 is too low followed by the correct statement as the loop exits The output is shown in Figure 7 10 HERIOT WATT UNIVERSITY 2006
266. sive process to look after all the details Here s a program that works in this way It s set up to move a stack of only four discs Note that within the machine s limits the moveTower procedure would work without alteration for any number of discs Note also that there s only one if statement involved You might like to use strings instead of the integer parameters left right and centre In terms of numbers the program is moving discs from rod 1 to rod 2 using rod 3 Option Explicit gt Program by Fred Fink 1st March 2004 gt This program emulates the Tower of Hanoi using recursive procedure calls Private Sub Command1_Click moveTower 4 1 2 3 End Sub Sub moveDisc ByVal left As Integer ByVal right As Integer PicOutput Print Move a disc from left to right End Sub Sub moveTower ByVal discs As Integer ByVal left As Integer ByVal right As Integer ByVal centre As Integer If discs 1 Then moveDisc left right Else moveTower discs 1 left centre right recursive call moveDisc left right moveTower discs 1 centre right left recursive call End If End Sub Private Sub Command2_Click End End Sub This file Hanoi txt can be downloaded from the course web site Typical output is shown in Figure 8 6 HERIOT WATT UNIVERSITY 2006 8 5 RECURSION 247 Towers of Hanoi Move a disc from 1 to3 Move a disc from 1 to 2 Move a disc from 3 to 2 Move a disc from 1 to 3 Move a disc
267. ssage single digit number is displayed on the screen otherwise else the message double digit number is displayed on the screen The program output is shown in Figure 6 15 HERIOT WATT UNIVERSITY 2006 6 15 IF THEN ELSEIF 159 w Formi Dis a single digt number 9 is a single digt number 10 is a double digit number 99 is a double digit number 5 is out of range 105 is cut of range giseeeerrmenereceecessossvmsnesooeesesecnsssmesenaes Exit Program E Execute RTTELTELE CITE TETE TELE EEE TEE TELE LEE EE EEE TETE EC Figure 6 15 Please take time to follow this explanation through If you can see the how and why of it you will be able to program if statements nested or plain without any worries 6 15 If Then Elself Nested if statements can be fairly complex to follow and can give rise to what is known as spaghetti code The ElseIf statement can simplify expressions to a certain extent The structure of the statement is if expressioni then statements 1 elseif expression2 then statements 2 elseif expression3 then statements 3 else statements 4 These expressions are evaluated in order if any expression is true the statement associated with it is executed and this terminates the whole chain As many decisions as desired may be included within the chain As always the code for each statement is either a single statement or a group of statements Consider the situation where you
268. st occur before the variables are used in the program since it instructs the compiler to allocate sufficient memory storage for each of the data items on the list This is important You cannot use a variable unless you have declared it first Also remember that variables may not be initialised when they are declared They may not be set to zero but have random numbers in them In the case of this program you either gave the variables specific values by reading values from the keyboard or you gave sum a value which was calculated by the program In either case the variable had been given a value before it was used Q11 What is wrong with this Visual Basic program program subtract Dim numberi As Integer Dim result As integer numberi InputBox Please enter the first number number2 InputBox please enter the second number result numberi number2 Print Number 1 take away number 2 sum Calculating minutes Learning Objective Be able to use get input from the user Be able to use arithmetic operators Be able to display output on the screen Write a program which prompts the user to enter a number of days hours and minutes The program will then calculate and display this as a total number of minutes HERIOT WATT UNIVERSITY 2006 6 9 VARIABLES AND SCOPE 135 6 9 Variables and scope Variables have another important characteristic called scope This determines which parts of a program are able to see
269. sting Alpha testing This is where the software usually with minimum functionality at this stage is passed to personnel in house who will undertake full exhaustive testing under varying circumstances The test group focus on the implementation of the program specification and provide feedback to the programmers on specific aspects of the software Beta testing From the alpha testing phase beta testing represents the pre release version of the software which is made available to a large number of selected users in the outside world The software will be run on a variety of computer platforms under real conditions After successful beta testing the software is then released for general use usually with a version number For more on beta testing have a look at the following web site http beta intuit com public upcomingBetalnfo cfm Roles within Software Development On the Web is a interactivity You should now complete this task 4 7 1 Review Questions Q6 The program specification is an important document in the software development process The main reasons for this is choose one a It can be used as a checklist to ensure the project is on target b Test data will be drawn up on the basis of this document c It describes all the inputs outputs and processes involved in the project d All of the above Q7 Once the program has been designed it is then passed to the programming team Which one of the following actio
270. strategy With most software projects the usual strategy is to test the software twice The methods are called e alpha testing where the software is tested by clients within the organisation e beta testing where the software is tested by personnel outside the organisation or by certain members of the public This is sometimes called acceptance testing Matching definitions Testing On the Web is a interactivity You should now complete this task HERIOT WATT UNIVERSITY 2006 27 28 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS 2 7 1 Alpha testing Test data is based on the specification Data will be designed to test three aspects of the program e normal operation data that the program has essentially been built to process all outputs should be satisfactory e boundary testing data to test that the program functions properly with data at the extremes of its operation for example if a number entered is meant to be limited the program s performance is tested just within the limit on the limit and just beyond the limit as another example if a table is supposed to have a maximum number of elements the program is tested to see if it can cope with exactly the maximum and if it can cope when an attempt is made to exceed the maximum e exceptions testing data that lie beyond the extremes of the program s normal operation these should include a selection of what might be called silly data to test the program
271. t b The model is easy to understand c The evolution of software systems were disorganised d Using It is an error free process Q7 Which one of the following statements regarding the order of the stages in the waterfall model is correct a Design implementation testing documentation b Analysis testing implementation design c Design testing evaluation implementation d Analysis design testing evaluation Q8 The waterfall model can involve iteration Which one of the following statements is true a The model will be more realistic b Use of the model will become error free c Use of the model will be simpler to understand d The model will be easier to implement Q9 Software developers cannot get the software correct at the first attempt This is because a Software systems can be very complex b Unforeseen errors always creep in that take time to solve c There could be problems with the client changing his her mind d All of the above HERIOT WATT UNIVERSITY 2006 2 3 THE WATERFALL METHOD Q10 Regular feedback of information to members of the development team is important This is done in order to To speed up the development process To enable personnel to discuss progress To keep the team happy To lower the costs on a regular basis Sentence completion waterfall model On the Web is a sentence completion task on the waterfall model You should now complete this task 2 3 2 The Analysis
272. t is often much simpler to get a listing of the code and settle down to work with that You sort out the listing so that the relevant modules and module calls are in front of you and you do a static test of the program You ask yourself What should it do next What state should the data be in These are the most common errors to look for e are all variables initialised before use remember that some translators do not initialise variables to zero e are all constants named e do all loops terminate e is the end of an array overwritten a very common mistake in programming e are the conditions correct in conditional statements e are there misplaced or missing statement terminators 3 6 8 Trace facilities Trace facilities are built into many languages A trace facility is used to identify the path taken through the program Trace facilities may help to identify logical errors The facility is implemented by toggling between TRACE ON and TRACE OFF or by running a debugging facility which will allow the program to be run step wise line by line 3 6 9 Review questions Q16 Acompilation error is best described as choose one a An error which occurs during execution of a program b An error generated by the source translator c Anerror in the logic of the code d An error made by the translator Q17 When carrying out a dry run which one of the following would represent common errors to look for a Do all program lo
273. tVariable 55 HERIOT WATT UNIVERSITY 2006 136 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 TestString Hello 1 Print In main program Testvariable TestVariable Print In main program TestString TestString End Sub Private Sub ExecuteLocal_Click Dim TestVariable As Integer Dim TestString As String Print Print Call 1 gives TestVariable TestVariable Print Call 1 gives TestString TestString Print TestVariable 110 TestString Hello 2 Print Call 2 gives TestVariable TestVariable Print Call 2 gives TestString TestString End Sub This file Scope txt can be downloaded from the course web site Code 6 7 TestVariable and TestString are declared Public They are given values in sub procedure ExecuteMain_Click They are re declared in sub procedure ExecuteLocal_Click and assigned new values Figure 6 9 shows the program output The program is called twice by activating the two buttons Form In main program Testvariable 55 In main program TestString TestString Cal 1 gives TestVariable O Cal 1 gives TestString Cal 2 gives TestVariable 110 Cal 2 gives TestString Hello 2 grteeemseessensscsssemesseeensensssenmersenses s Execute Loca Execute Public eecceaceccecceeccecceaceccecccecceeceeacceceeee Figure 6 9 Public gives the original values that can change HERIOT WATT UNIVERSITY 2006 6 9 VARIABLES AND SCOPE 137 In call 1 local proce
274. tandard 2 12 2 Prototyping A prototype is a small scale representation of a proposed design In prototyping the primary focus is the interface The interface can be put together quickly and shown to the clients Prototyping involves clients in the software development process The clients can make suggestions which can in turn be incorporated into a revised version of the prototype As such it involves feedback and is said to be iterative This iterative process can be repeated to make further refinements When the prototype has been suitably refined and agreed work on the full project will begin HERIOT WATT UNIVERSITY 2006 2 12 ALTERNATIVE MODELS STOP Prototyping had its proponents in the old days of text based screens but it has further developed since the appearance of the Graphical User Interface GUI Programming languages such as Delphi Visual Basic and Kylix make it easy to construct graphical user interfaces Amendments suggested by the clients are easier to incorporate at the prototype stage rather than later When the prototype has been amended it is again submitted to the clients The process continues until the clients are satisfied with the interface When the HCI has been agreed work starts on the detailed processing Disadvantage of prototyping Users often perceive the interface to be the program Clients having seen a prototype one week find it hard to understand why the entire program is not ready the
275. te between the various types of data objects Although not essential It is good programming practice to do so and also to use meaningful variable names so that values can be easily identified in programs Alternatively the initial letters of the prefix can be used instead as long as readability is not compromised The main data type prefixes are summarised in Table 6 6 Table 6 6 Data type Prefix Boolean bin or b Integer int or i Long Ing or String str Single sng Double dbl or d Constant conorc Exercise Which of the following variable assignments match a intValue 89 sNumber1 3 1417 T strName Hello Number2 25 683 strString 65 310 f lonBig_Number 5 6432e10 O o e g bFound false 6 7 1 Implicit and Explicit declaration Visual Basic offers two levels of variable type declarations 1 Implicit declaration 2 Explicit declaration Implicit declaration HERIOT WATT UNIVERSITY 2006 126 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 In implicit declaration if the dim statement is used on its own without assigning type to a variable or a variable is assigned a value then Visual Basic will assign the data type variant This is the default setting that Visual Basic will assign variables if not declared as some other type Visual Basic does not force you to declare data types but it is much better if you do For example consider the fo
276. ted by specialist companies HERIOT WATT UNIVERSITY 2006 29 30 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS Q29 Testing can never show that a program is correct Which option best describes why a Itis far too exhausting b You cannot account for all possible errors c It is too time consuming d Perfect programs do not exist Q30 During alpha testing the program is usually subjected to exceptions testing This means a The input of silly data b The input of large numbers c The input of small numbers d All of these 2 8 Documentation in closer detail Documentation is intended to describe a system and make it more easily understood Documentation will consist of 1 user guide 2 technical guide Some information may appear in both guides eg system specification Internal documentation such as remarks or comments in the code are for the benefit of the development team It will help if changes have to be made to the software in the future Other documentation for the development team includes all the documents produced in the software development process requirements specification program design documents for the HCI and for the structure and logic of the underlying code a structured listing of the code and a test history 2 8 1 User guide The user guide contains information about how to install start and use software It should also contain a list of commands and how to use the
277. ter All it contains is the termination character which you do not want to use in the rest of the program Now you are ready to see whether the string is a palindrome The array is searched through comparing the 1st element with the last the 2nd element with the 2nd last etc As soon as you find that they do not match you can terminate the search as you know that the sequence is not a palindrome It is not necessary to continue searching the whole list of numbers as we know what we set out to find out Note that you only have to loop for count lt length 2 as you compare the first half of the array to the second half See following Figure 7 17 0 1 2 3 length 1 length compare 2 Y and 2 last compare 1 and last Figure 7 17 Comparing array elements for a palindrome A possible solution is shown in Code 7 13 HERIOT WATT UNIVERSITY 2006 7 5 ARRAYS 217 Private Sub Commandi_Click program Palindrome 20th February 2004 gt Program by Fred Fink This program will test an input string for a palindrome Const sizeArray As Integer 30 Dim Palarray 1 To sizeArray As String Dim palindromeChar As String Dim length As Integer count As Integer Dim isPalindrome As Boolean count 1 Do While palindromeChar lt gt And count lt sizeArray palindromeChar InputBox Enter your characters one at a time Terminate by full stop Palarray count palindromeChar PicDisplay Print palindromeChar Output ch
278. the expressions are true the or expression will evaluate to true So or means either one or the other or both Hence the term inclusive HERIOT WATT UNIVERSITY 2006 153 ICO 20 min 154 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Use of the logical OR operator is shown below if Vone 6 or Vtwo 6 then statement 1 else statement 2 end if This code means that when either Vone or Vtwo is equal to 6 then statement 1 is executed If both of the conditions are false then statement 1 is ignored and execution passes onto statement 2 Example 1 Wash the car Problem A program is written to prompt the user to enter two conditions a temperature and a weather forecast If either or both of the conditions are met then the program will display a suitable message to go and wash the car If no conditions are met the user will be informed that washing the car is not a good idea The conditions are compared to program constants The algorithm is shown below Solution 1 request a temperature from the user 2 request weather condition from user 3 if the first input gt 15 or the second input Sunny then 4 display Wash the car 5 else 6 display Not a good idea The Visual Basic code for this program is shown in Code 6 11 Option Explicit Private Sub Command1_Click program using the OR operator 15th February 2004 gt Program by Fred Fink gt This program will prompt the user to enter
279. the two Table 1 1 should give you an indication Table 1 1 Real programs vs classroom programs Real life Programs Classroom programs are large and complex It is difficult to are small and simple They can be hold their details in your mind Because of described in a few sentences and this you have to specify them formally probably understood in minutes The main difficulty is with a The main difficulty you have is with writing understanding the problem b ensuring the solution in a programming language that your understanding actually matches which you are just learning and getting the users requirements c designing a your program to work correctly solution Development time is long Maybe as long Development time is short You should be as 5 years It is impossible to remember able to get the core of the solution all aspects of a program for this length of working in a few hours Consequently you time so you have to document the design can hold details of all aspects of the decisions and all your changes program in your head Documentation is skimpy or non existent Testing is going to be long intensive and Your testing is likely to be fairly basic exhaustive It will be done by a separate team whose function is solely to test programs and find faults A program s lifetime may be decades and The life of the program is short only long it may undergo changes called enough for you
280. the use of arrays in the final topic Sentence completion arrays On the Web is a interactivity You should now complete this task Comparing arrays and encoding the results Declare three 20 element arrays X Y Z Write a program to read 20 integers into each of the two integer arrays X and Y The program will prompt the user to enter the values 30 min into each of the arrays The program will then compare each of the elements of X to the corresponding element in Y Then in the corresponding element of a third array Z store the following values Table 7 2 Table 7 2 A aie ih Condition 1 if the element in X is larger than the element in Y 0 if the element in X is equal to the element in Y 1 if the element in X is less than the element in Y Then print out a three column table displaying the contents of the arrays X Y and Z Make up your own test data and write down in three columns the number you input for X the number you input for Y and the result you got for Z HERIOT WATT UNIVERSITY 2006 220 TOPIC 7 HIGH LEVEL LANGUAGE CONSTRUCTS 2 Comparing arrays extension If you found the previous exercise absurdly easy then you can follow up with this one 30 min Extend the above program by adding two further columns to the output giving each line five columns This is what you add column 4 a count of the number of elements of X that exceed Y and column 5 a count of the number of elements of X that are
281. then translated into machine code Special purpose language Languages designed for specific tasks such as prolog for artificial intelligence or C for writing operating systems Specification A document outlining the program requirements set by the client SSADM Structured Analysis and Design Model An alternative to the waterfall model that deals only with the analysis and design phases of software development Standard algorithm An algorithm that appears over and over again in many programs Also called common algorithms Stepwise refinement Similar to top down design of sectioning a large and complex system into smaller and more easily manageable components Structure charts A diagrammatic method of designing a solution to solve a software problem Structured data Data that is organised in some way for example an array or database HERIOT WATT UNIVERSITY 2006 GLOSSARY Structured listing Program listing clearly showing the modules involved complete with commentary and meaningful variable and procedure names Stub A temporary addition to a program used to assist with the testing process Symbol table Part of the compilation process where the tokens created by the lexical analysis phase are stored Syntax Syntax means structure or grammar of a statement in a given language Systems analyst The person responsible for analysing and determining whether a task is suitable for pursuit using a computer They are also responsible
282. tise required at each stage of the process e itis an iterative process involving on going communication at all stages e the final program may not meet client specification for various reasons 4 9 End of topic test An online assessment is provided to help you review this topic HERIOT WATT UNIVERSITY 2006 78 TOPIC 4 PERSONNEL HERIOT WATT UNIVERSITY 2006 Topic 5 Languages and Environments Contents 5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 5 9 MOGUCOM lt a a AS Ge Programming Languages Classification of High Level Languages Imperative languages 5 4 1 Review Questions Declarative languages Event driven languages Scripting languages 5 7 1 5 7 2 5 7 3 5 7 4 5 7 5 Benefits of scripting languages The need for scripting languages Creating a Macro Running A Macro 6 00 ace te e a al KE Review Questions Object oriented languages Functional languages 5 9 1 Review Questions 5 10 Translation methods 5 10 31 Compilet lt a a ft ee LR ny a Re MN
283. to do that Conditions are indicated by the letter C and a number alongside the box The number is used to distinguish between the different conditions that might be involved in a program The conditions in turn need to be spelled out somewhere on the diagram C1 ifN 1 C2 ifN 2 C3 until count 100 Each box represents a block of code either a procedure or a function When the JSP diagram is complete the corresponding pseudo code is then written for each box Characteristic of good software design On the Web is a interactivity You should now complete this task Structured design ES ES On the Web is a interactivity You should now complete this task HERIOT WATT UNIVERSITY 2006 3 3 DESIGN METHODOLOGIES 3 3 4 Pseudo code Another method is to describe the design in terms of pseudo code This is mostly used for working out the details of a design At this level pictures don t really help Pseudo code is a terse way of writing that lies somewhere between code and natural language such as English lt represents an understanding of the solution that can be turned into code but can still be understood by people Pseudo code follows the indenting conventions of the programming language to be used for the project This indentation makes the pseudo code easier to follow and to understand Pseudo code is a way of writing about a process without having to bother about details which are simply a matter of coding So t
284. to the maximum value possible with precision The results are stored in a variable called prime In order to perform the calculation the variable prime would need to be declared as a Integer b Real double c Integer long d Real single 6 7 Declaring Variables Within Visual Basic variables are used to represent and identify values within a program The values are held in temporary storage locations in the computers memory Each memory location is identified by a unique variable name and the value of its contents can change during the execution of a program Once the program has ended variables will be reset all numeric values become zero and strings become empty For this reason it is important that all variables are assigned initial values before a program run To use a variable in Visual Basic three quantities must be specified 1 Name of the variable 2 Type of variable 3 Value of the variable Variables are declared using the Dim statement which allocates temporary storage to them It is usual to use Dim statements before any other code so that total memory can be allocated at run time HERIOT WATT UNIVERSITY 2006 6 7 DECLARING VARIABLES 125 Examples of Dim statements are Dim binFound As boolean Dim intMaximum As integer Dim db Precision As double Dim siMyname As string Notice that each variable name has a prefix attached This is a Visual Basic construct that allows the programmer to differentia
285. tructured Listing 3 6 Error Reporting 3 6 1 Compilation Errors 3 60 20 Synta XENO S 2 2e wi eign anes abattre dot Gog PRBS na e 3 6 3 Execution Run time Errors 3 6 4 Logical EmO S nc 6 Oa ee ae ne RE ram ie eee a e AA 3 6 5 CodingErrors 3 6 6 Design errors 3 60 77 DIV UNI ase oe oe edi Ee ey es dater RR EME ae EM dt A 3 6 8 Trace faciliti S 0 uti na LL Papi A HAA Hae eS 3 6 9 Review questions 3 7 Module libraries 3 8 CASE tools 3 9 Software characteristics 3 9 1 RODUSINESS ma acs img a a a a AS A a 3 9 2 Reliability 3 9 3 Portability 3 9 4 Review questions 3 10 Summary 3 11 End of topic test 43 44 44 45 47 48 51 52 53 55 56 57 57 58 58 58 58 59 59 59 60 60 61 62 62 62 63 63 63 64 65 41 42 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION Prerequisite knowledge Before studying this topic you should be able to describe and use pseudocode describe and use a graphical design notation structure diagram or other suitable method Learning Objectives understand the nature of graphical design notations be able to use a graphical design construct understand the nature of pseudo code be able to use pseudo code understand the nature of top
286. tured listing is true It makes the program run faster It is part of the design stage of the software development process It is used to spot possible errors in a program a b c d None of the above 2 1 Introduction This topic introduces the various mechanism of the software development process From the initial client specification to the production of a working program can take considerable time and effort by the development team The process involves constant revision and evaluation at every phase of the project which makes it predominantly an iterative process This ensures quality and efficiency in the final product Various models are introduced that aid the software development process but you will find that the perfect solution does not exist HERIOT WATT UNIVERSITY 2006 11 12 TOPIC 2 FEATURES OF SOFTWARE DEVELOPMENT PROCESS 2 2 Preamble An individual may write a program for personal use If it does not work then it can be changed If more features or facilities are required then the individual can make amendments to their program This ad hoc method is not satisfactory in commercial environments where the goal is the creation of large scale software A more structured approach is necessary Some of the reasons are concerned with the commercial nature of the business others you have already met in previous topics The sole programmer Many unmanaged Managed software feverishly coding programmers d
287. tware development as it occurs in software houses 2 3 The Waterfall Method The traditional software development process contains a sequence of stages The precise names of the stages and even the number of stages are not universally agreed They differ from book to book and from developer to developer Much depends on the aspects of software development that a book wishes to emphasise or that a particular developer prefers Referred to as the waterfall model this was one of the first models designed for software engineering which arose as a response to the disorganised ways in which previous software systems evolved In this course we will consider the following stages Documentation dhe Installation Maintenence The idea here is that the development of the system flows down or cascades through the stages like water flowing down a fall As each stage is completed responsibility and control is passed down until the final section is completed We will look at each stage in turn very shortly An important aspect of the software development process is that it is an iterative process An iterative process is one that incorporates feedback and involves an element of repetition The reasons for this will soon become apparent You will meet iteration again in later topics dealing with the software development environment As you can see one of the main drawback to this model is the fact that if any unnoticed errors occur at any stage of
288. u start the process at the top with the problem as a whole and work downwards This is shown in Figure 3 1 One other advantage of this systematic approach is that it also automatically gives a structure to your solution HERIOT WATT UNIVERSITY 2006 45 46 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION DIFFICULT PROBLEM Less difficult Less difficult Fairly Easy Easy Problem Problem Problem Problem Easy Fairly Easy Problem Problem Easy Easy Easy Fairly Easy Problem Problem Problem Problem Easy Easy Problem Problem Easy Easy Easy Problem Problem Problem Figure 3 1 Stepwise refinement Stepwise refinement allows the designer to concentrate on one small part of the problem at a time If thinking about the problem as a whole the designer does not have to bother with details In thinking about a portion of the detailed design the designer does not have to bear in mind all the rest of the problem This makes the process manageable Once manageable parts have been identified the analyst can assign individual tasks to different teams of programmers The complex task is made more straightforward by the system of divide and conquer Programmers often use stubs when using a top down technique A stub is an outline of a module that does little more at run time than declare its presence or return a value of appropriate type When all the stubs are in place the program as it stands can be tested to make sure that
289. uages and then translated before they can be executed by a computer This is because a Computers do not understand English words b It is easier to write high level code c Computers only understand machine code d All of the above Q2 Two translator programs are a compiler and an interpreter Which one of the following statements is true a Acompiler produces object code whereas an interpreter is much faster b A compiler is much faster whereas an interpreter executes a line at a time c An interpreter produces object code whereas a compiler is much faster d An interpreter is much slower whereas a compiler executes a line at a time Q3 Which one of the following error situations would be picked up by a compiler or interpreter a Runtime error b Logic error c System error d Syntax error Q4 A problem may be implemented by using either a procedural language or a declarative language Which one of the following statements is true a Pascal is a procedural language used in education b Comal is a declarative language used in artificial intelligence c Prolog is a procedural language used in artificial intelligence d Visual Basic is declarative language used in education Q5 A scripting language differs from a macro in that a b c d A scripting language is difficult to use A macro must be run by pressing a key A scripting language has to be translated A macro can be used to automate simple tasks
290. ual parameters change as do the formal parameters It is important that you understand the difference between value and reference parameters Consider the following procedure codes where one uses call by value and the other call by reference Private Sub No_Change ByVal Number As Integer Number Number 10 End Sub Private Sub Change ByRef Number As Integer Number Number 10 End Sub If they are now executed within a program we can see the difference to the variable Test in the main program by calling each procedure The full Visual Basic program is shown in Code 8 3 Option Explicit Private Sub Command1_Click Dim Test As Integer Test 10 PicDispi Print Test Change Test No_Change Test PicDisp2 Print Test End Sub Private Sub No_Change ByVal Number As Integer Number Number 10 HERIOT WATT UNIVERSITY 2006 8 3 PROCEDURES AND FUNCTIONS 233 End Sub Private Sub Change ByRef Number As Integer Number Number 10 End Sub Code 8 3 Figure 8 2 shows the value of the variable Test before and after each call of the procedures Call by Value DER Call by Reference DER Value of Test before call 10 Value of Test before call 10 Value of Test after call 10 Value of Test after call 20 Run Program Run Program Figure 8 2 Each procedure call produces the correct value of 20 for Test but only in call by reference is this value passed back to the main program In call by value th
291. ugged and compiled Your own programs therefore however small they may be should embody the principles of modularity Visual Basic is an events driven programming language where the programming is done in a graphical environment Users can click on various objects where each object is programmed independently to be able to response to user actions A Visual Basic program is therefore modular being made up of many subprograms each having its own program code that can be executed independently These subprograms are called procedures and functions Procedures and functions provide a means of producing structured programs not only in Visual Basic but in other programming languages as well The more complex a program becomes the more reason to employ strategies to make it easier to read and maintain Procedures and functions help in this respect by breaking up what would be extensive lines of intricate code into more meaningful and logical sections As a consequence e the repetition of lines of code is avoided Rather than repeating the same operations several different times in a program the code can be placed in a procedure or function The procedure is then called as many times as necessary without re writing the code e it allows testing of the procedure code to take place in isolation from the main program Each functional unit can be written independently by programming teams thus making this part of the software development process mo
292. umbers If the value 56 8 was entered this would be an example of An input error An exceptional input Unacceptable output All of the above 3 1 Introduction In this topic you will learn about the various methods that are used to aid the system developers and programming team to implement solutions according to program specifications The first important issue you will come across is that program coding is only attempted after extensive and rigorous series of planning and design stages are completed beforehand Efforts at these initial stages pay dividends at the coding stage in terms of testing debugging and maintenance of the programs HERIOT WATT UNIVERSITY 2006 44 TOPIC 3 DESIGN NOTATION DATA FLOW AND EVALUATION 3 2 Tools and Techniques This section describes the tools and techniques used in the software development process Initially good program design will save much cost and time in the later stages of development such as testing debugging and maintenance You will see more of this later The main tools and techniques include e Design methodologies e Test data e Structured program listing e Comprehensive error reporting e Module libraries 3 3 Design methodologies The design of software is something of an art and normally follows a clear design methodology A methodology is an agreed technique used to design software It includes both approaches to designing software and the notations used to represent the
293. value back to a string value to be recognised by the text box Figure 6 3 shows a program run HERIOT WATT UNIVERSITY 2006 6 5 DATA TYPES 121 Form Input Length Input Width Area of rectanak is Figure 6 3 You can see that the form contains 3 labels and 3 text boxes for the input and output of data and a control button 6 5 Data types Visual basic has a number of in built data types the significant ones for this topic being integer single real boolean and string These are summarised with others in Table 6 2 HERIOT WATT UNIVERSITY 2006 122 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 Table 6 2 Data Type Optional Suffix Description Integer These are whole numbers positive or negative without a decimal point The range depends on the machine but if 16 bits long the range is 32 768 to 32 767 Long integer amp Extended range of integer from 2 147 483 648 to 2 147 483 647 Single real These are floating point numbers e g 3 33333 When 32 bits long their range is 3 4e 38 and referred to as single precision Double real Double precision floating point numbers within the range 1 7e 308 String Fixed length up to 65 400 characters Variable length up to 2 billion characters boolean This data type can represent two values true and false variant Any numeric value up to the range of a double precision number or
294. value between 1 and 100 Loop Until ActualValue gt 1 And ActualValue lt 100 Call Square ActualValue Call procedure PicDisplay Print Call SqrRoot ActualValue Call procedure End Sub Private Sub SqrRoot ByVal number As Integer Procedure declaration Dim Result As Single Result Sqr number PicDisplay Print The square root of number is Format Result Fixed End Sub Private Sub Square ByVal number As Integer Procedure declaration Dim Result As Integer Result number 2 PicDisplay Print The square of number is Result End Sub Private Sub Command2_Click End End Sub This file ValueParameter txt can be downloaded from the course web site Code 8 2 Examine this code carefully Make sure you understand it s structure The fixed format command is to output the square root to two decimal places Program output is shown in Figure 8 1 HERIOT WATT UNIVERSITY 2006 8 3 PROCEDURES AND FUNCTIONS 231 Form The square of 58 is 3364 The square root of 58 is 7 62 End Program Run Program i Figure 8 1 In this program the formal parameter number was passed the value 7 in each of the two procedures Consider the following diagram showing the procedure Square Procedure declaration Square number as integer Copy of ActualValue 7 passed to formal parameter number Procedure call Square ActualValue Once the value 7 has been sent to the procedure Square t
295. values 3 12 4 6 3 2 0 1 see Figure 7 14 then the information displayed would be HERIOT WATT UNIVERSITY 2006 7 5 ARRAYS Store BGC 0 1 2 3 4 5 Figure 7 14 Contents of a six element array Store This time one simple loop replaces 6 lines of code i e Print element 0 Store 0 Print element 1 Store 1 Print element 2 Store 2 Print element 3 Store 3 Print element 4 Store 4 Print element 5 Store 5 Look carefully and you can see that the array can only be written out element by element You cannot use one statement to print the entire array For example it is wrong to say Print Store and expect all elements of the array to be displayed A single element can be written or accessed at random you are not forced to process the entire array to do this Any one of the six lines of code above does the job of printing out that particular array element so the code Print element 5 Score 5 outputs the sixth element of the array the first element being element 0 Example 3 Reading user input into an array Problem How can data entered by the user at the keyboard be stored directly into the elements of an array Solution Consider the situation where you want to store 4 user entered integers in an array called mark You could use a for next loop to prompt and obtain input and to store the integers in the array e g for times 0 to 3 mark times InputBox Plea
296. ver moving a disc so that it lay on top of a smaller one There were 72 discs When the monks had finally moved all the discs from one rod to another the world would come to an end Our task is to write a program to spell out the moves that need to be made You might like to consider for a moment how you would set about the task using iteration We have three rods called left right and centre Our task is to move all the disks from the left to the right using the centre If we look at the matter recursively we could break down the problem into three steps First we move all the discs but the largest from left to centre using the right rod to help Then we move the largest from the left to the right Then we move the pile of smaller discs back on top of the largest from the centre onto the right using the left rod to help That s the general case The base case is when there s only one disc to move And that s it problem solved HERIOT WATT UNIVERSITY 2006 245 246 TOPIC 8 PROCEDURES AND STANDARD ALGORITHMS Note that the number of discs involved or whether that number is odd or even have no effect on the method of solution If you made much of an attempt to solve the problem by iteration you should be able to see that the recursive solution is at a higher level we are thinking of what the solution should be and not bothering too much about how exactly it will be implemented We trust to our analysis and to the powers of the recur
297. will update repair and modify existing programs When making changes to a section of code they make other users aware of the changes by inserting comments in the coded instructions so others can understand the program Programmers test a program by running it to ensure the instructions are correct and it produces the desired information If errors do occur the programmer must make the appropriate change and recheck the program until it produces the correct results This process is called debugging Programmers may continue to fix these problems throughout the life of a program 4 7 Independent Testing Group Consider the following quote from computing expert in the field of software development No no no no no the people who develop and implement code should have absolutely no role in testing that code A test team should be TOTALLY independent from the implementation team Quite an adamant view with a clear message Programmers would be less inclined to test their software to destruction and take into effect test data that might cause unexpected results they have the knowledge of how the functionality of the code was designed and will test accordingly Also they probably don t have sufficient time to fully test the program under all conditions HERIOT WATT UNIVERSITY 2006 75 76 TOPIC 4 PERSONNEL The software is therefore passed to other groups of people independent test groups who will undertake impartial te
298. wnloaded from the course web site Code 8 6 From the local value of Number in the for next loop the first call of HERIOT WATT UNIVERSITY 2006 8 5 RECURSION factorial Num factorial Num 1 takes on the value 1 which is displayed Next the value 2 is passed and the result 2 1 displayed This continues until the loop value ends at 7 when factorial 7 will be displayed Exercise The previous program may be coded without recursion using a looping structure See if this alternative version can produce factorials of numbers higher than the recursion method Hint An other general rule for calculating factorials is factorial n n n 1 n 2 1 Base your program on the following algorithm 1 declare variables 2 do 3 input a value to get factorial 4 loop until n gt 0 5 factorial 1 6 do 7 factorial factorial n 8 n n t1 9 loop until n 0 10 display factorial Recursive procedures Recursive procedures are often used in programming for example in sorting arrays or in searching through them A famous example of a recursive procedure concerns the problem of the Towers of Hanoi This was a game or toy that came out in Victorian times consisting of three upright rods and a set of discs of graduated size that went on the rods The story that went with it was that in a temple in Hanoi the monks performed part of their devotions by moving similar discs of bronze from one rod to another ne
299. wo 6 then statement 1 else statement 2 End if This code means that when both Vone and Vtwo are equal to 6 then statement 1 is executed If either or both of the conditions is false then statement 1 is ignored and execution passes onto statement 2 Example 1 Passwords Problem A program is written which asks the user to enter a password and to confirm it by entering it again If both words are equal to a program constant then the program will display a suitable comment If not or only one instance of the password is entered the user will be informed HERIOT WATT UNIVERSITY 2006 151 152 TOPIC 6 HIGH LEVEL LANGUAGE CONSTRUCTS 1 The algorithm is shown below Solution request ist password from the user request 2nd password from the user if the first password constant and the second password constant then display the word entered both times else display the two words and that they are different OO O1 amp WN EB The full Visual Basic code for this program is as follows Option Explicit Private Sub Command1_Click program using the AND operator 15th February 2004 gt Program by Fred Fink gt This program will prompt the user to enter two words gt and compare them to a string constant Dim Wordi As String Dim Word2 As String Const pass As String Daffodil Wordi InputBox Please input password Word2 InputBox Password again please If Wordi pass And Word2 pass Then
300. xample you could record opening a new document using a specific template inserting a header and inserting a name and address and greeting Each time you replayed the macro it would perform those tasks For programs that don t include a macro facility there are numerous shareware macro programs that can be downloaded and used in any application Such a program is Macro Express 2 1 which is ideal for beginners 5 7 4 Running A Macro A macro can be initiated by e pressing selected key combination hot keys e clicking an icon on the toolbar that has been created for the macro e running the macro from the Tools menu of the application Example tasks could include inserting your name and address on documents e formatting text with specified font and size e accessing websites from a list of favourites e inserting special symbols or graphics into documents e automate playing of audio CDs while you work on the computer HERIOT WATT UNIVERSITY 2006 5 7 SCRIPTING LANGUAGES e formatting of spreadsheet cells e creating headers and footers Code 5 4 is an example VBScript listing for a macro to create a table in Microsoft Word Macro to create a table in Word 2 Sub Macro1 2 Macroi Macro Macro recorded 05 01 2004 by John Smith 2 ActiveDocument Tables Add Range Selection Range NumRows 7 NumColumns _ 4 DefaultTableBehavior wdWord9TableBehavior AutoFitBehavior _ wdAutoFitWindow With Select
301. y of the actual parameter is passed in to the formal parameter Information is passed IN to the procedure form the main program Waterfall model One of the earliest models for software development that incorporates 7 stages from analysis to implementation and maintenance HERIOT WATT UNIVERSITY 2006 HINTS 269 Hints for activities Topic 6 High Level Language Constructs 1 Calculating minutes Hint 1 This problem naturally breaks up into four sections 1 declare the variables 2 get input 3 calculate the minutes 4 output results The input must consist of three numbers the days the hours and the minutes So you need three variables to hold these figures What will you name them What type will they be integer real How do you work out the total number of minutes from these figures You have to design a section of code to do this Hint 2 There are 60 minutes in one hour and 24 hours in a day hence 720 24 60 1440 minutes in a day Hint 3 For example days 1 hours 12 minutes 15 Total number of minutes 2175 days 3 hours 4 mins 5 total minutes 4565 days 17 hours 10 mins 0 total mins 25080 Calculating the number of digits in a number Hint 1 It helps the user to know what type of number to type in and what range of numbers is allowable before they type the wrong input This should be in addition to any checks you do on the length of the number Calculating Leap Years
302. ystems are now an important aspect of everyday life Indeed it would be difficult to visualise a world without the day to day impact that computers have on our lives cash machines supermarket tills petrol pumps travel tickets payslips and bills the Internet and e commerce and so on In the 1960 s 70 s when mainframe computers were at the heart of large commercial and industrial computer systems mostly for batch processing tasks companies relied on vast teams of programmers to implement software solutions that required system specifications Today s computing systems offer much more complex scenarios and their development requires well thought out plans and sophisticated software tools for defining each stage of the process in a much more formal manner than previously attained The first few topics of this unit describe the development of software The development of software follows a definite process known as the software development process SDP It introduces a few of the models which are used to represent the software development process and describes in detail the traditional model A model allows users to understand the development process and the stages involved in the development sequence The model aids management and good management helps produce a higher quality product possibly in a shorter period of time and at less cost In the last thirty years or so a number of models have evolved each with particular strengths and weak

SQA Higher Computing Unit 2 Software Development

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