Visual Basic 2012 Lesson 11- Looping

Visual Basic 2012 allows a procedure to be repeated as many times as long as the processor and memory could support. This is generally called looping . Looping is required when we need to process something repetitively until a certain condition is met. For example, we can design a program that adds a series of numbers until the sum exceeds a certain value, or a program that asks the user to enter data repeatedly until he/she keys in the word ‘Finish’. In Visual Basic 2012, we have three types of Loops, they are the For…..Next loop, the Do loop. and the While…..End while loop

11.1 For….Next Loop in Visual Basic 2012 The format is: For counter=startNumber to endNumber (Step increment) One or more VB statements Next To exit a For…..Next Loop, you can place the Exit For statement within the loop; and it is normally used together with the If….Then…..sstatement. For its application, you can refer to example 11.1 d.

Example 11.1 a Dim counter as Integer For counter=1 to 10 ListBox1.Items.Add (counter) Next * The program will enter number 1 to 10 into the list box.	Example 11.1b Dim counter , sum As Integer For counter=1 to 100 step 10 sum+=counter ListBox1.Items.Add (sum) Next * The program will calculate the sum of the numbers as follows: sum=0+10+20+30+40+……
Example 11.1c 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: 1000-100-95-90-……….	Example 11.1d 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.

11.2 Do Loop The Do Loop formats are a) Do While condition Block of one or more Visual Basic 2012 statements Loop b) Do Block of one or more Visual Basic 2012 statements Loop While condition c) Do Until condition Block of one or more Visual Basic 2012 statements Loop d) Do Block of one or more Visual Basic 2012 statements Loop Until condition * Exiting the Loop Sometime we need exit to exit a loop prematurely because of a certain condition is fulfilled. The syntax to use is known as Exit Do. Lets examine the following examples

Example 11.2(a) Do while counter <=1000 TextBox1.Text=counter counter +=1 Loop * 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

Example 11.2(b) Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim sum, n As Integer ListBox1.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