Knowledge Base

PRB: Run-Time Overflow Error w/Byte Type Counter in For Loop

Article ID: 129709

Article Last Modified on 12/9/2003

Microsoft Visual Basic 4.0 Standard Edition
Microsoft Visual Basic 4.0 Professional Edition
Microsoft Visual Basic 4.0 Professional Edition
Microsoft Visual Basic 4.0 16-bit Enterprise Edition
Microsoft Visual Basic 4.0 32-Bit Enterprise Edition

This article was previously published under Q129709

SYMPTOMS

Using a byte variable as a counter in a For loop with a negative Step value causes an Overflow error at run-time.

CAUSE

In a For loop in Visual Basic for Windows, the Start, Limit and Step values are all coerced to the type of the For loop counter. Since the byte data type cannot be negative, it cannot have a negative step value.

RESOLUTION

This is a limitation of the implementation of the byte datatype and For loop. The solution is to never use byte type variables in For loops where the step is negative or a variable (since the variable may contain a negative number at some future time.)

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior in Visual Basic Version 4.0

Start a new project in Visual Basic. Form1 is created by default.

Add the following code to the Command1_Click procedure:

      Dim ByteVar As Byte

      For ByteVar = 10 To 5 Step -1
         Debug.Print ByteVar
      Next

Additional query words: increment decrement counter

Keywords: kbprogramming kbprb KB129709