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

ID: Q129709

The information in this article applies to:

Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0

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

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

2. 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          : kbprg kbVBp400 PrgOther VB4WIN vbwin 
Version           : WINDOWS:4.00
Platform          : WINDOWS
Issue type        : kbprb

Last Reviewed: October 1, 1997