BREAKING OUT OF LOOPS

Sometimes you may find situations in which you will want to break out of a loop before it finishes processing, based on some condition that occurs. To deal with this type of situation, you can use either of two types of Exit statements to force an immediate termination of a loop. Once executed, the Exit statement transfers control to the next statement following the loop within the application.

Exit For

You can use the Exit statement to break out of any For…Next or For Each…Next loop. The syntax for this form of the Exit statement is shown below.

 Exit For 

The following example demonstrates how to use the Exit For statement to break out of the processing of a loop.

 Private Sub Form1_Load(ByVal sender As System.Object, _       ByVal e As System.EventArgs) Handles MyBase.Load         Dim intCounter As Integer         Dim strResponce As String         Dim UserArray(4) As String         For intCounter = 0 To 4             strResponce = InputBox("Enter a name or type Quit to exit.")             If strResponce.ToLower = "quit" Then                 MessageBox.Show("Data collection has been terminated.")                 Exit For             End If             UserArray(intCounter) = strResponce         Next End Sub 

In this example, a For…Next loop has been set up to collect five names that the user supplies by entering them into a pop-up window generated by an InputBox() function. However, if at any point during the collection process the user decides to enter the word "Quit," the Exit For statement executes and terminates the data collection process.

Exit Do

You can also use the Exit statement to break out of any Do…Until or Do…While loop. The syntax for this form of the Exit statement is shown below.

 Exit Do 

The following example demonstrates how to use the Exit Do statement to break out of the processing of a loop.

 Private Sub Form1_Load(ByVal sender As System.Object, _   ByVal e As System.EventArgs) Handles MyBase.Load      Dim intCounter As Integer = 0      Dim intOverFlow As Integer = 50      Dim strResponce As String =""      Dim blnTerminate As Boolean = False      Dim UserArray(49) As String       Do Until blnTerminate = True            strResponce = InputBox("Enter a name or type Quit to exit.")            If strResponce.ToLower = "quit" Then                 MessageBox.Show("Data collection has been terminated.")                 blnTerminate = True            Else                 UserArray(intCounter) = strResponce                 intCounter += 1                 If intCounter = intOverFlow Then                     MessageBox.Show("Error: Array overflow, max size = 50")                     Exit Do                 End If            End If      Loop End Sub