Using Do Loops in QTP

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.

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

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.

Sub ChkFirstUntil()

   Dim counter, myNum

   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()

   Dim counter, myNum

   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 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.

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

      MsgBox "The loop made " & counter & " repetitions."

End Sub