In VB programming, a sequence of instructions that is repeated until a certain condition is met is called looping. For example, we can write VB code that adds a series of numbers until the sum exceeds a certain value or a VB program that asks the user to enter data repeatedly until he or she enters the word ‘Finish’. In Visual Basic 2010, we have three types of Loops, they are the For…..Next loop, the Do loop. and the While…..End while loop
To exit a For…..Next Loop, you can place the Exit For statement within the loop; and it is typically used together with the If….Then…..statement. For its application, you can refer to example 11.1 d.
Dim counter, sum As Integer sum = 1000 For counter = 100 To 5 Step -5 sum - = counter ListBox1.Items.Add(sum) Next
*Notice that increment can be negative.The program will compute the
subtraction as follow:
Dim n as Integer For n=1 to 10 If n>6 then Exit For End If Else ListBox1.Items.Add ( n) Next End If Next
The process will stop when n is greater than 6.
Do Until condition Block of VB2010 statements Loop
Do Block of VB 2010 statements Loop Until condition
Let’s examine the following examples
Do while counter <=1000 TextBox1.Text=counter counter +=1Loop
* The above example will keep on adding until counter >1000.
The above example can be rewritten as
Do TextBox1.Text=counter counter+=1 Loop until counter>1000
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.ClickDim sum, n As IntegerListBox1.Items.Add("n" & vbTab & "Sum") ListBox1.Items.Add("----------------------") Do n += 1 sum += n ListBox1.Items.Add(n & vbTab & sum) If n = 100 Then Exit Do End If Loop End Sub