INF110 Visual Basic Programming AUBG Spring semester 2011

1. INF110Visual Basic ProgrammingAUBG Spring semester 2011Reference books:Schneider D., An Introduction to Programming Using Visual Basic, Prentice Hall, Pearson Education Inc., 7th Ed. 2008, 6th Ed. 2006 Liberty J., Learning Visual Basic .NET, O’Reilly, 2002 Any Visual Basic book available in AUBG libraryCourse lecturer: Assoc. Prof. Svetla Boytcheva, PhD

2. INF110 Visual Basic Programming AUBG Spring semester 2011 Lecture 08 Title: Visual Basic (Repetition/Iteration statements 2)

3. Lecture Contents: • Reminder on Decisions/Selections • Reminder on Repetitions/Iterations • Endless Loops • Loops with GOTO • Demo programs • Practical session

4. INF110 Visual Basic Programming Iterations Demo programs by J.Liberty, Chapter 06, 0609-0617 Plus Practical Session

5. Reminder On Decisions/Selections

6. VBasic selection statements include If condition Then statement sequence End If If condition Then statement sequence1 Else statement sequence2 End If

7. VBasic selection statements include If condition1 Then statement sequence1 ElseIf condition2 statement sequence2 • ElseIf condition3 • statement sequence3 • Else • statement sequence4 End If

8. VBasic selection statements include Select Case expression Case value1 Block of one or more VB statements Case value2 Block of one or more VB Statements Case value3 Block of one or more VB statements Case value4 . . . Case Else Block of one or more VB Statements End Select

9. Reminder On Iterations/Repetitions

10. Visual Basic supports the following loop structures: • Do … Loop • While … End While • For … Next

11. For i = 1 To 5 ... Next And its corresponding Do While equivalent i = 1 Do While i <= 5 ... i = i + 1 Loop

12. Examples (a) For counter=1 to 10 Console.Writeline(counter) Next (b) For counter=1 to 100 Step 10 Console.Writeline(counter) Next (c) For counter=100 to 5 Step -5 Console.Writeline(counter) Next

13. Variations of the Do…Loop control structure: • Do … Loop • 1/ Pre test loops • with While and Until • 2/ Post test loops • with While and Until

14. Pre test loops with While and Until

15. Do Loops • All the variations use the same basic model. A pretest loop is executed either • While condition is True. Uses While reserved word Do While condition statement-block Loop • Until condition becomes True. Uses Until reserved word Do Until condition statement-block Loop

16. Examples I = 1 Do While (I <= 10) Console.WriteLine(I) I = I + 1 Loop How many iterations are to be run? (10) Try it

17. Examples I = 1 Do Until I <= 10 Console.WriteLine(I) I = I + 1 Loop How many iterations are to be run? (0) Try it

18. Examples to achieve the same effect I = 1 Do While (I <= 10) Console.WriteLine(I) I = I + 1 Loop ======================= same effect I = 1 Do Until Not(I <= 10) Console.WriteLine(I) I = I + 1 Loop How many iterations are to be run? (10) Try it

19. Examples to achieve the same effect I = 1 Do WhileNot(I <= 10) Console.WriteLine(I) I = I + 1 Loop ======================= same effect I = 1 Do Until (I <= 10) Console.WriteLine(I) I = I + 1 Loop How many iterations are to be run? (0) Try it

20. Post test loops with While and Until

21. Do Loops • All the variations use the same basic model. A posttest loop is executed either • While condition is True. Uses While reserved word Do statement-block Loop While condition • Until condition becomes True. Uses Until reserved word Do statement-block Loop Until condition

22. Examples I = 1 Do Console.WriteLine(I) I = I + 1 Loop While (I <= 10) How many iterations are to be run? (10) Try it

23. Examples I = 1 Do Console.WriteLine(I) I = I + 1 Loop Until (I <= 10) How many iterations are to be run? (1) Try it

24. Examples to achieve the same effect I = 1 Do Console.WriteLine(I) I = I + 1 Loop While (I <= 10) =================== same effect I = 1 Do Console.WriteLine(I) I = I + 1 Loop UntilNot(I <= 10) How many iterations are to be run? (10) Try it

25. Examples to achieve the same effect I = 1 Do Console.WriteLine(I) I = I + 1 Loop WhileNot(I <= 10) =================== same effect I = 1 Do Console.WriteLine(I) I = I + 1 Loop Until (I <= 10) How many iterations are to be run? (1) Try it

26. Endless loops with While … End While andDo … Loop

27. Endless loops - examples While True statement-block End While

28. Endless loops - comments The endless loops should be avoided. They must be terminated from within the own loop body with an Exit statement While True statement-block if condition Then Exit While statement-block End While

29. Endless loops - examples Do statement-block Loop

30. Endless loops - comments The endless loops should be avoided. They must be terminated from within the own loop body with an Exit statement Do statement-block If condition Then Exit Do statement-block Loop

31. Example 6-9 • Creating Loops with Goto • Using Goto

32. Example 6-9 Option Strict On Imports System Module Module1 Sub Main( ) Dim counterVariable As Integer = 0 repeat: ' the label Console.WriteLine("counterVariable: {0}", counterVariable) ' increment the counter counterVariable += 1 If counterVariable < 10 Then GoTo repeat ' loop implemented: control transferred back to label repeat End If End Sub 'Main End Module

33. Example 6-10 • The Do Loop • Using Do While

34. Example 6-10 Option Strict On Imports System Module Module1 Sub Main( ) Dim counterVariable As Integer = 0 Do While counterVariable < 10 Console.WriteLine("counterVariable: {0}", counterVariable) counterVariable = counterVariable + 1 Loop ' While counterVariable < 10 End Sub 'Main End Module

35. Example 6-11 • The Do Loop • Using Do Until

36. Example 6-11 Option Strict On Imports System Module Module1 Sub Main( ) Dim counterVariable As Integer = 0 Do Until counterVariable = 10 Console.WriteLine("counterVariable: {0}", counterVariable) counterVariable = counterVariable + 1 Loop ' Until counterVariable = 10 End Sub 'Main End Module

37. Example 6-12 • The Do Loop • Do … Loop While

38. Example 6-12 Option Strict On Imports System Module Module1 Sub Main( ) Dim counterVariable As Integer = 100 Do Console.WriteLine("counterVariable: {0}", counterVariable) counterVariable = counterVariable + 1 Loop While counterVariable < 10 End Sub 'Main End Module

39. Example 6-13 • The Do Loop • Breaking out of a Do Loop • Using Exit Do

40. Example 6-13 Option Strict On Imports System Module Module1 Sub Main( ) Dim counterVariable As Integer = 0 Do Console.WriteLine("counterVariable: {0}", counterVariable) counterVariable = counterVariable + 1 ' test whether we've counted to 9, if so, exit the loop If counterVariable > 9 Then Exit Do End If Loop End Sub 'Main End Module

41. Example 6-14 • The For Loop • Using a For loop

42. Example 6-14 Option Strict On Imports System Module Module1 Sub Main( ) Dim loopCounter As Integer For loopCounter = 0 To 9 Console.WriteLine("loopCounter: {0}", loopCounter) Next End Sub 'Main End Module

43. Example 6-15 • The For Loop • Loop with a Single counter

44. Example 6-15 Option Strict On Imports System Module Module1 Sub Main( ) Dim loopCounter As Single For loopCounter = 0.5 To 9 Console.WriteLine("loopCounter: {0}", loopCounter) Next End Sub 'Main End Module

45. Example 6-16 • The For loop • Adjusting the step counter

46. Example 6-16 Option Strict On Imports System Module Module1 Sub Main( ) Dim loopCounter As Single For loopCounter = 0.5 To 9 Step 0.5 Console.WriteLine("loopCounter: {0}", loopCounter) Next End Sub 'Main End Module

47. Example 6-17 • The For Loop • Controlling a For Loop using Next • Multiple updates with one Next statement

48. Example 6-17 Option Strict On Imports System Module Module1 Sub Main( ) Dim outer As Integer Dim inner As Integer For outer = 3 To 6 For inner = 10 To 12 Console.WriteLine("{0} * {1} = {2}", outer, inner, outer * inner) Next inner, outer End Sub 'Main End Module

49. Example Run the program. Test the program. Modify the program and rerun it again.

50. Practical session 3Loops,Iterations, Repetitions