BUG: Do Until Loop Evaluates "True" as -1 Exclusively

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 5.0

SYMPTOMS

A Do Until loop that uses a literal or a variable of type Integer as a conditional will execute endlessly if the value is not -1.

RESOLUTION

Use a variable of type Variant or Long as the conditional argument for the loop.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Visual Basic defines "True" to mean "non-zero." Any value that is not zero should be evaluated as True. The Do Until loop in Visual Basic 5.0, however, evaluates only -1 as True if a literal value or a variable of type integer is used for the conditional argument.

Steps to Reproduce Behavior

Method 1:

1. Place the following code on a CommandButton on a Visual Basic 5.0 form:

         Debug.Print "A"
         Do Until 3
            Debug.Print "B"
         Loop
         Debug.Print "C"
   
   

2. Click the button. This loop will print "B" endlessly. (Press CTRL-BRK to stop execution.)

1. Place the following code on a CommandButton on a Visual Basic 5.0 form:

         Dim i As Integer
         i = 3
         Debug.Print "A"
         Do Until i
            Debug.Print "B"
         Loop
         Debug.Print "C"
   
   

2. Click on the button. This loop will print "B" endlessly. (Press CTRL-BRK to stop execution.)

   Note that, in both cases, the loop that prints "B" should not execute.