Revision #3

What the heck is a loop???

A loop is a repetitive procedure that is designed to repeat a given set of instructions.

Loops are absolutely essential for getting work done. You know how computer software saves you so much time, by doing the tedious repetition of tasks? Our good hero the loop is the one to blame.

Other terms associated with loops: Looping, Iterating, Iteration, Enumerating, Enumeration, Cycling

What kind of loops can you make in Visual Basic?

• The most primitive loop(GOTO) in the basic programming language involves the use of 2 components:

• ) A numeric label for the parser
• ) A GOTO command

• Example of a simple GOTO Loop
• Option Strict On

  Public Class Form1

      Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

  1:      Dim Counter As Integer = 0

  2:      Counter = Counter + 1

  3:      'You can put

  4:      'code in-between

  5:      If Counter < 100 Then GoTo 2

  6:      MsgBox("We have reached " & Counter & ", so the loop is complete!")

      End Sub

  End Class

• Never use this, there are better ways!
• The good ol' Do-Loop Loop, this loop has several different ways it can be used:
  • ) Do-Loop-Until
    • Example
    • Option Strict On

      Public Class Form1

          Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

              Dim Count As Integer = 0

              Do

                  'You can put

                  'Code in here

                  Count = Count + 1

              Loop Until Count = 100

              MsgBox("We have reached " & Count & ", so the loop is complete!")

          End Sub

      End Class
  • ) Do-Loop-While
    • Example
    • Option Strict On

      Public Class Form1

          Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

              Dim Count As Integer = 0

              Do While Count < 100

                  'You can put

                  'Code in here

                  Count = Count + 1

              Loop

              MsgBox("We have reached " & Count & ", so the loop is complete!")

          End Sub

      End Class
  • ) Do-Loop-Exit Do
    • Example
    • Option Strict On

      Public Class Form1

          Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

              Dim Count As Integer = 0

              Do

                  'You can put

                  'Code in here

                  Count = Count + 1

                  If Count = 100 Then Exit Do

              Loop

              MsgBox("We have reached " & Count & ", so the loop is complete!")

          End Sub

      End Class
• There's yet another kind of loop! For-Next
  • For - Next
    • Example
    • Option Strict On

      Public Class Form1

          Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

              Dim Result As Integer

              For I As Integer = 0 To 100

                  'You can put

                  'Code in here

                  Result = I

              Next

              MsgBox("We have reached " & Result & ", so the loop is complete!")

          End Sub

      End Class
  • ​Fo​r-Next-Step
    • Example
    • Option Strict On

      Public Class Form1

          Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

              Dim Result As Integer

              For I As Integer = 500 To 100 Step -2

                  'You can put

                  'Code in here

                  Result = I

              Next

              MsgBox("We have reached " & Result & ", so the loop is complete!")

          End Sub

      End Class
  • ​​Fo​r-Next-Exit For
    
    • Example
    • Option Strict On

      Public Class Form1

          Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

              Dim Result As Integer

              For I As Integer = 0 To 500000

                  'You can put

                  'Code in here

                  Result = I

                  If I = 100 Then Exit For

              Next

              MsgBox("We have reached " & Result & ", so the loop is complete!")

          End Sub

      End Class
  • ​​Fo​r-Next-Continue For
    • Example
    • Option Strict On

      Public Class Form1

          Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

              Dim Result As Integer

              For I As Integer = 0 To 200

                  Select Case I Mod 2

                      Case 1

                          Result = Result + 1

                          Continue For

                  End Select

                  'Only arrive here when I is an odd number

              Next

              MsgBox("We have reached " & Result & ", so the loop is complete!")

          End Sub

      End Class
  • Fo​r-Each-Next
    • Example
    • Option Strict On

      Public Class Form1

          Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

              Dim Array() As Integer = {25, 25, 25, 25}

              Dim Result As Integer

              For Each Number As Integer In Array

                  Result = Result + Number

              Next

              MsgBox("We have reached " & Result & ", so the loop is complete!")

          End Sub

      End Class
• While
  • While-End While
    • Example
    • Option Strict On

      Public Class Form1

          Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

              Dim Result As Integer

              While Result < 100

                  'You can put

                  'Code in here

                  Result = Result + 1

              End While

              MsgBox("We have reached " & Result & ", so the loop is complete!")

          End Sub

      End Class
• Last, but not least, I want to add a very interesting method of looping which I will call "Function Looping"(for lack of a better term)
  • I first really noticed it with Euclid's algorithm for calculated the greatest common divisor of 2 numbers. So here it is, Euclid's Algorithm utilizing "Function Looping". This function will call itself until the remainder is 0, effictivelty creatinting a loop without using any of the conventional methods listed above!
    • Example
    • Function EuclidGCD(Number1 As Integer, Number2 As Integer)

          Dim Remainder As Integer = Number1 Mod Number2

          If Remainder = 0 Then Return Number2

          Return EuclidGCD(Number2, Remainder)

      End Function

There are many many uses of looping in Visual basic, and programming in general would not be complete without the ability to iterate.

• MSDN - http://msdn.microsoft.com/en-US/
• MSDN Forums - http://social.msdn.microsoft.com/Forums/en-US/categories

I hope you find this helpful, Please update this article if I left anything out!