Use the While keyword to verify a condition in a Do...Loop statement. You can verify the condition before you enter the loop (as illustrated in the following ChkFirstWhile instance), or you can verify it after the loop has run at least once (as illustrated in the ChkLastWhile instance). In the ChkFirstWhile procedure, if myNum is set to 9 rather than 20, the statements inside the loop will never run. In the ChkLastWhile process, the statements inside the loop run only once since the condition is already False.
Sub ChkFirstWhile() Dim counter, myNum 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() Dim counter, myNum counter = 0
myNum = 9
Do
myNum = myNum - 1 counter = counter + 1
Loop While myNum > 10
MsgBox "The loop made " & counter & " repetitions." End Sub
The above figure illustrate two example code fragments illustrating the do... loop and do while ... loop statements. In the first loop the condition is verified before executing the code however in the second loop the statements are first executed once and after that the condition is verified. In the first loop the instructions given in the loop's body will never be executed if the condition initially fails but in the second loop these instructions would be executed at least once. The following flow chart illustrates the execution plan of the second procedure i.e. CheckLastWhile:
Figure: Execution Plan of the Second Loop