Q130128: PRB: MOD Function w/ Negative Number May Give Different Answer

Article: Q130128
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0
Operating System(s): 
Keyword(s): kbcode
Last Modified: 09-FEB-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 3.0 
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SYMPTOMS
========

If negative numbers are used with the MOD function, it is possible that the
answer returned will be different from the answer given by other applications
that also incorporate a MOD function.

CAUSE
=====

The correct definition of MOD is as follows:

     x MOD y = z where z + y * int(x/y) = x
     z = x - y * int(x/y)

Therefore:

     x MOD y = x - y * int(x/y)

In the Microsoft MOD function, we do the same as above except we use the FLOOR()
function instead of INT() in order to be backward compatible with other products
that use the FLOOR() function.


RESOLUTION
==========

Below are two functions. The first function (FLOORMOD) implements the MOD with a
FLOOR() function, and the second function (INTMOD) implements the MOD with an
INT() function. Sometimes you may want to use the INTMOD function.

     **** MOD with FLOOR() ****
     FUNCTION FLOORMOD
        PARAMETER x,y
        z = x - FLOOR(x/y)*y
     RETURN z
     **************************

     **** MOD with INT() ******
     FUNCTION INTMOD
        PARAMETER x,y
        z = x - INT(x/y)*y
     RETURN z
     **************************

STATUS
======

This behavior is by design.

Additional query words: VFoxWin

======================================================================
Keywords          : kbcode 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300
Version           : WINDOWS:3.0

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