1. Recursion and Branching By: Engr. Faisal ur Rehman CE-105T Spring 2007 By: Engr. Faisal ur Rehman CE-105T Spring 2007

2. Call, Function, Property, SubUse procedures. Choose, If...Then...Else, Select Case, SwitchMake decisions. Do...Loop, For...Next, For Each...Next, While...End While, WithLoop. End, Exit, StopExit or pause the program. GoTo, On ErrorBranch. Language elementAction

3. Recursion It is the process of repetition of a particular statement Also know as iteration Achieved by Control Structure or Loop Also achieved by recursive functions It is the process of repetition of a particular statement Also know as iteration Achieved by Control Structure or Loop Also achieved by recursive functions

4. Loops Running a set of statements until a condition becomes true

5. Loop Types While Loop Do Loop For Loop For Each Loop While Loop Do Loop For Loop For Each Loop

6. While Loop Runs a series of statements as long as a given condition is True. While condition [ statements ] [ Exit While ] [ statements ] End While Runs a series of statements as long as a given condition is True. While condition [ statements ] [ Exit While ] [ statements ] End While

7. While Loop Dim counter As Integer = 0 While counter < 20 counter += 1 debug.writeline counter ‘if counter = 10 then exit while End While MsgBox("While loop ran " & CStr(counter) & " times") Put code in form_load and also check debug window (Ctrl + G) after running the code Dim counter As Integer = 0 While counter < 20 counter += 1 debug.writeline counter ‘if counter = 10 then exit while End While MsgBox("While loop ran " & CStr(counter) & " times") Put code in form_load and also check debug window (Ctrl + G) after running the code

8. Do Loop Repeats a block of statements while a Boolean condition is True or until the condition becomes True. Do { While | Until } condition [ statements ] [ Exit Do ] [ statements ] Loop -or- Do [ statements ] [ Exit Do ] [ statements ] Loop { While | Until } condition Repeats a block of statements while a Boolean condition is True or until the condition becomes True. Do { While | Until } condition [ statements ] [ Exit Do ] [ statements ] Loop -or- Do [ statements ] [ Exit Do ] [ statements ] Loop { While | Until } condition Debug.WriteLine("Do Demo 1:") Do while i <= 10 debug.writeline i i = i+1 Loop Debug.WriteLine("Do Demo 2:") Do debug.writeline i i = i+1 Loop while i <= 10 Debug.WriteLine("Do Demo 1:") Do while i <= 10 debug.writeline i i = i+1 Loop Debug.WriteLine("Do Demo 2:") Do debug.writeline i i = i+1 Loop while i <= 10

9. For Next Loop Repeats a group of statements a specified number of times. For counter [ As datatype ] = start To end [ Step step ] [ statements ] [ Exit For ] [ statements ] Next [ counter ] Repeats a group of statements a specified number of times. For counter [ As datatype ] = start To end [ Step step ] [ statements ] [ Exit For ] [ statements ] Next [ counter ]

10. For Next Loop For i = 1 to 10 Debug. writeline i Next i For i = 1 to 10 step 2 Debug. writeline i Next i For i = 1 to 10 Debug. writeline i Next i For i = 1 to 10 step 2 Debug. writeline i Next i For i = 1 to 10 step -1 Debug.writeline i ‘if i = 8 then exit for Next i For i = 1 to 10 step -1 Debug.writeline i ‘if i = 8 then exit for Next i

11. For Next Loop Code for Prime Composite number: Dim n As Double = 0 n = CDbl(txtNo.Text) For i As Integer = n - 1 To 2 Step -1 If n Mod i = 0 Then MsgBox("Composite number!") Exit Sub End If Next MsgBox("Prime number!") Code for Prime Composite number: Dim n As Double = 0 n = CDbl(txtNo.Text) For i As Integer = n - 1 To 2 Step -1 If n Mod i = 0 Then MsgBox("Composite number!") Exit Sub End If Next MsgBox("Prime number!")

12. For Each Loop Repeats a group of statements for each element in a collection. For Each element [ As datatype ] In group [ statements ] [ Exit For ] [ statements ] Next [ element ] Repeats a group of statements for each element in a collection. For Each element [ As datatype ] In group [ statements ] [ Exit For ] [ statements ] Next [ element ]

13. For Each Loop Dim found As Boolean = False Dim thisCollection As New Collection For Each thisObject As String In thisCollection If thisObject = "Hello" Then found = True Exit For End If Next thisObject Dim found As Boolean = False Dim thisCollection As New Collection For Each thisObject As String In thisCollection If thisObject = "Hello" Then found = True Exit For End If Next thisObject

14. Loops How to: Improve the Performance of a Loop

15. Recursive Function Self calling function is called recursive function Function factorial(ByVal n As Integer) As Integer If n <= 1 Then Return 1 Else Return factorial(n - 1) * n End If End Function Self calling function is called recursive function Function factorial(ByVal n As Integer) As Integer If n <= 1 Then Return 1 Else Return factorial(n - 1) * n End If End Function

16. Other Control Structures With object [ statements ] End With With btn1.text = “Test button”.Forecolor = vbblue.heght =40.width = 30 End with With object [ statements ] End With With btn1.text = “Test button”.Forecolor = vbblue.heght =40.width = 30 End with btn1.text = “Test button” btn1.Forecolor = vbblue btn1.heght =40 btn1.width = 30 btn1.text = “Test button” btn1.Forecolor = vbblue btn1.heght =40 btn1.width = 30

17. Branching / Decision Structure

18. If Condition Select case Try catch Goto On Error If Condition Select case Try catch Goto On Error

19. IF Condition If condition [ Then ] [ statements ] [ ElseIf elseifcondition [ Then ] [ elseifstatements ] ] [ Else [ elsestatements ] ] End If -or- If condition Then [ statements ] [ Else [ elsestatements ] ] If condition [ Then ] [ statements ] [ ElseIf elseifcondition [ Then ] [ elseifstatements ] ] [ Else [ elsestatements ] ] End If -or- If condition Then [ statements ] [ Else [ elsestatements ] ]

20. IF Condition Code for Even / Odd: Dim n As Double = 0 n = CDbl(txtNo.Text) If n Mod 2 = 0 Then MsgBox("Even number!") Else MsgBox("Odd number!") End If Code for Even / Odd: Dim n As Double = 0 n = CDbl(txtNo.Text) If n Mod 2 = 0 Then MsgBox("Even number!") Else MsgBox("Odd number!") End If

21. Select Case Select [ Case ] testexpression [ Case expressionlist [ statements ] ] [ Case Else [ elsestatements ] ] End Select Select [ Case ] testexpression [ Case expressionlist [ statements ] ] [ Case Else [ elsestatements ] ] End Select

22. Select Case Dim S as string = txtCode.text Select case S Case “A”, “a” Msgbox “Afghanistan Case “B”, “b” Msgbox “Brazil” Case else Msgbox “Unknown Code” End select Dim S as string = txtCode.text Select case S Case “A”, “a” Msgbox “Afghanistan Case “B”, “b” Msgbox “Brazil” Case else Msgbox “Unknown Code” End select

23. Try Catch Finally Try [ tryStatements ] [ Exit Try ] [ Catch [ exception [ As type ] ] [ When expression ] [ catchStatements ] [ Exit Try ] ] [ Catch... ] [ Finally [ finallyStatements ] ] End Try Try [ tryStatements ] [ Exit Try ] [ Catch [ exception [ As type ] ] [ When expression ] [ catchStatements ] [ Exit Try ] ] [ Catch... ] [ Finally [ finallyStatements ] ] End Try

24. Try Catch Finally Code for factorial: Try Dim n As Integer = InputBox("Enter a number for factorial:") MsgBox("Factorial is:" & vbCrLf & factorial(n)) Catch ex As Exception MsgBox(Err.Description & vbCrLf & "Error Value:" & Err.Number) Finally Beep End Try Code for factorial: Try Dim n As Integer = InputBox("Enter a number for factorial:") MsgBox("Factorial is:" & vbCrLf & factorial(n)) Catch ex As Exception MsgBox(Err.Description & vbCrLf & "Error Value:" & Err.Number) Finally Beep End Try

25. Goto Sub gotoStatementDemo() Dim number As Integer = 1 Dim sampleString As String ' Evaluate number and branch to appropriate label. If number = 1 Then GoTo Line1 Else GoTo Line2 Line1: sampleString = "Number equals 1" GoTo LastLine Line2: ' The following statement never gets executed because number = 1. sampleString = "Number equals 2" LastLine: ' Write "Number equals 1" in the Debug window. Debug.WriteLine(sampleString) End Sub Sub gotoStatementDemo() Dim number As Integer = 1 Dim sampleString As String ' Evaluate number and branch to appropriate label. If number = 1 Then GoTo Line1 Else GoTo Line2 Line1: sampleString = "Number equals 1" GoTo LastLine Line2: ' The following statement never gets executed because number = 1. sampleString = "Number equals 2" LastLine: ' Write "Number equals 1" in the Debug window. Debug.WriteLine(sampleString) End Sub GoTo line

26. On Error On Error { GoTo [ line | 0 | -1 ] | Resume Next } On error goto handler: Dim n As Integer = InputBox("Enter a number for factorial:") MsgBox("Factorial is:" & vbCrLf & factorial(n)) Exit sub Handler: MsgBox(Err.Description & vbCrLf & "Error Value:" & Err.Number) Resume next On Error { GoTo [ line | 0 | -1 ] | Resume Next } On error goto handler: Dim n As Integer = InputBox("Enter a number for factorial:") MsgBox("Factorial is:" & vbCrLf & factorial(n)) Exit sub Handler: MsgBox(Err.Description & vbCrLf & "Error Value:" & Err.Number) Resume next

27. Nested Control Structures Code for Prime / Composite Dim n As Double = 0 n = CDbl(txtNo.Text) For i As Integer = n - 1 To 2 Step -1 If n Mod i = 0 Then MsgBox("Composite number!") Exit Sub End If Next MsgBox("Prime number!") Code for Prime / Composite Dim n As Double = 0 n = CDbl(txtNo.Text) For i As Integer = n - 1 To 2 Step -1 If n Mod i = 0 Then MsgBox("Composite number!") Exit Sub End If Next MsgBox("Prime number!")

28. Q & A

29. Write structure of: For Next Loop For Each While Loop Do Loop With Structure If Condition Select case Try catch Goto On Error Write structure of: For Next Loop For Each While Loop Do Loop With Structure If Condition Select case Try catch Goto On Error

30. Q & A Define Branching and Recursion. Name components of Control Structure Name components of Decision Structure Define Branching and Recursion. Name components of Control Structure Name components of Decision Structure