You can use Do...Loop statements to run a block of statements an indefinite number of times. The statements are repeated either while a condition is True or until a condition becomes True.

Repeating Statements While a Condition is True

Use the While keyword to check a condition in a Do...Loop statement. You can check the condition before you enter the loop (as shown in the following ChkFirstWhile example), or you can check it after the loop has run at least once (as shown in the ChkLastWhile example). In the ChkFirstWhile procedure, if myNum is set to 9 instead of 20, the statements inside the loop will never run. In the ChkLastWhile procedure, the statements inside the loop run only once because the condition is already False.

The following examples illustrates the use of the while:

Example 1:

Sub ChkFirstWhile()
	Dim counter, myNum
	counter = 0
	 myNum = 20
	Do While myNum > 10
	   myNum = myNum - 1
	   counter = counter + 1
	Loop
	'This loop made 10 repetitions."
End Sub

Example 2:

Sub ChkFirstWhile()
    Dim counter, myNum
    counter = 0
    myNum = 9
    Do While myNum > 10
        myNum = myNum - 1
        counter = counter + 1
    Loop
    'This loop made 0 repetitions.
End Sub

Example 3:

Sub ChkLastWhile()
    	Dim counter, myNum
    	counter = 0
    	myNum = 9
    	Do
        	myNum = myNum - 1
        	counter = counter + 1
    	Loop While myNum > 10
    	'This loop made 1 repetition.
End Sub

Example 4:

Sub ExampleWithDoWhile()
    	Dim counter, myNum
    	counter = 0
    	myNum = 15
    	Do While myNum > 10
        		myNum = myNum - 2
        		counter = counter + 1
    	Loop
' This loop reduced myNum to 9 and made 3 repetitions
End Sub

Example 5:

Sub ExampleWithDoLoopWhile()
   	 Dim counter, myNum
    	counter = 0
    	myNum = 5
    	Do
        		myNum = myNum + 1
        		counter = counter + 1
    	Loop While myNum < 10
' This loop increased myNum to 10 and made 5 repetitions.
End Sub

Example 6:

Sub ChkLastWhile()
   Dim counter, myNum
   counter = 0
   myNum = 9
   Do
      myNum = myNum - 1
      counter = counter + 1
   Loop While myNum > 10
   'This loop made 1 repetition.
End Sub

Repeating a Statement Until a Condition Becomes True

There are two ways to use the Until keyword to check a condition in a Do...Loop statement. You can check the condition before you enter the loop (as shown in the following ChkFirstUntil example), or you can check it after the loop has run at least once (as shown in the ChkLastUntil example). As long as the condition is False, the looping occurs.

The following examples illustrates the use of the until:

Example 1:

Sub ChkFirstUntil()
   Dim counter, myNum
   counter = 0
   myNum = 20
   Do Until myNum = 10
      myNum = myNum - 1
      counter = counter + 1
   Loop
   'This loop made 10 repetitions.
End Sub

Example 2:

Sub ChkLastUntil()
   Dim counter, myNum
   counter = 0
   myNum = 1
   Do
      myNum = myNum + 1
      counter = counter + 1
   Loop Until myNum = 10
'This loop made 9 repetitions.
End Sub

Example 3:

Sub ExampleWithDoUntil()
    	Dim counter, myNum
    	counter = 0
    	myNum = 20
    	Do Until myNum < 15
        		myNum = myNum - 2
        		counter = counter + 1
    	Loop
'This loop reduced myNum to 14 and made 3 repetitions.
End Sub

Example 4:

Sub ExampleWithDoLoopUntil()
    Dim counter, myNum
    counter = 0
    myNum = 5
    Do
        myNum = myNum + 2
        counter = counter + 1
    Loop Until myNum >= 15
    'This loop increased myNum to 15 and made 5 repetitions.
End Sub

Exiting a Do...Loop Statement from Inside the Loop

You can exit a Do...Loop by using the Exit Do statement. Because you usually want to exit only in certain situations, such as to avoid an endless loop, you should use the Exit Do statement in the True statement block of an If...Then...Else statement. If the condition is False, the loop runs as usual.

In the following example, myNum is assigned a value that creates an endless loop. The If...Then...Else statement checks for this condition, preventing the endless repetition.

The following examples illustrates the use of the do loop statement:

Example 1:

Sub ExitExample()
   Dim counter, myNum
      counter = 0
      myNum = 9
      Do Until myNum = 10
         myNum = myNum - 1
         counter = counter + 1
         If myNum < 10 Then Exit Do
      Loop
      'This loop made 1 repetition.
End Sub

Example 2:

Sub PreventEndlessLoop()
    	Dim counter, myNum
    	counter = 1
    	myNum = 0
    	Do
        		myNum = myNum + 1
        		counter = counter + 1
        		If counter > 10 Then 
            			Exit Do   ' Avoids endless loop by exiting after 10 iterations.
        		End If
    	Loop
    	'This loop made 11 repetitions.
End Sub

Example 3:

Sub ExampleWithDoWhile()
    Dim counter, myNum
    counter = 0
    myNum = 20
    Do While myNum > 10
        myNum = myNum - 2
        counter = counter + 1
        If myNum < 15 Then Exit Do   ' Exit the loop early if myNum is less than 15.
    Loop
    'This loop reduced myNum to 14 and made 3 repetitions.
End Sub

Example 4:

Sub NestedLoopsExample()
    Dim i, j
    For i = 1 To 3
        j = 0
        Do
            j = j + 1
            If j > 2 Then Exit Do   ' Exit inner loop after 2 iterations.
        Loop
    Next
End Sub