Using Do...Loop Statements

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

There are two ways to use the While keyword to check a condition in a Do...Loop statement. You can check the condition before you enter the loop , or you can check it after the loop has run at least once.

In the following ChkFirstWhile procedure, you check the condition before you enter the loop. 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 before the condition becomes False.

Sub ChkFirstWhile()
    counter = 0
    myNum = 20
    Do While myNum > 10
        myNum = myNum - 1
        counter = counter + 1
    Loop
    MsgBox "The loop made " & counter & " repetitions."
End Sub

Sub ChkLastWhile()
    counter = 0
    myNum = 9
    Do
        myNum = myNum - 1
        counter = counter + 1
    Loop While myNum > 10
    MsgBox "The loop made " & counter & " repetitions."
End Sub

Repeating Statements 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 ChkFirstUntil procedure), or you can check it after the loop has run at least once (as shown in the ChkLastUntil procedure). Looping continues while the condition remains False.

Sub ChkFirstUntil()
    counter = 0
    myNum = 20
    Do Until myNum = 10
        myNum = myNum - 1
        counter = counter + 1
    Loop
    MsgBox "The loop made " & counter & " repetitions."
End Sub

Sub ChkLastUntil()
    counter = 0
    myNum = 1
    Do
        myNum = myNum + 1
        counter = counter + 1
    Loop Until myNum = 10
    MsgBox "The loop made " & counter & " repetitions."
End Sub

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

You can exit a Do...Loop using the Exit Do statement. For example, to exit an endless loop, use the Exit Do statement in the True statement block of either an If...Then...Else statement or a Select Case statement. If the condition is False, the loop will run 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, and then exits, preventing endless looping.

Sub ExitExample()
    counter = 0
    myNum = 9
    Do Until myNum = 10
        myNum = myNum - 1
        counter = counter + 1
        If myNum < 10 Then Exit Do
    Loop
    MsgBox "The loop made " & counter & " repetitions."
End Sub

Note   To stop an endless loop, press ESC or CTRL+BREAK.