Loops in Visual Basic

The while loop uses a Boolean expression to determine when to end the loop:
The format of a while loop is:

While <Boolean expression>
<statements>
Wend

The examples below compares a For and a While Loop. Both examples generate the values 1, 2, 3, 4, 5.

 

For Loop:

 

While Loop:

 

For N = 1 To 5

Next

 

N = 1 'Initial value in line 1 of For loop
While N<=5 'Test is in line 1 of For loop

N = N + 1 'Increment is in line 3 in For loop
End While

(One advantage of the while loop is that the Boolean expression can include AND and OR.)

Modify the program to generate powers of 2 using the code shown below:

'Programmer: Janet Joy
'While loop generates 1,2,4,8,...512
Public Class Form1
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Dim Num As Integer
        ListBox1.Items.Add("Powers of 2")
        Num = 1
        While Num < 1000
            ListBox1.Items.Add(Num)
            Num = Num * 2
        End While
    End Sub
End Class

NEXT: While, cont.