DOCUMENT:Q174155  11-JAN-2001  [vbwin]
TITLE   :PRB: Format Function May Return Incorrect Values
PRODUCT :Microsoft Visual Basic for Windows
PROD/VER:WINDOWS:4.0,5.0
OPER/SYS:
KEYWORDS:kbVBp400 kbVBp500 kbVBp600fix

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Visual Basic Control Creation Edition for Windows, version 5.0 
 - Microsoft Visual Basic Learning Edition for Windows, version 5.0 
 - Microsoft Visual Basic Professional Edition for Windows, version 5.0 
 - Microsoft Visual Basic Enterprise Edition for Windows, version 5.0 
 - Microsoft Visual Basic Standard Edition, 32-bit, for Windows, version 4.0 
 - Microsoft Visual Basic Professional Edition, 16-bit, for Windows, version 4.0 
 - Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0 
 - Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows, version 4.0 
 - Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

Decimal values rounded by the Format function may be incorrect. For a specific
decimal number, the rounded value returned by the Format function may differ for
different data types and between different versions of Microsoft Visual Basic.

CAUSE
=====

When a variable is passed into the Format function, an algorithm is used to
determine the most appropriate numeric data-type to convert the value to, and
how to format it. This algorithm may not evaluate certain decimal values as
expected.

RESOLUTION
==========

To avoid these unexpected conversions, explicitly convert the value to the
desired data type before using the Format function. For instance, use the CCur
function to convert the decimal value to a currency data-type that maintains
more accuracy in rounding.

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products listed at
the beginning of this article. This problem does not occur in Visual Basic 6.0.

MORE INFORMATION
================

Decimal values stored in single and double data-types are binary representations
of the number. Certain decimal values cannot be exactly represented in binary
and are approximately represented. When evaluated by the Format function, these
values may not be rounded as expected.

There are two methods recommended to minimize these errors:

1. Use the Currency data type rather than singles or doubles. Currency values
   are actually stored as integers with the decimal point scaled four places.

2. Convert the values to Currency before evaluation by the Format function.

Steps to Reproduce Behavior
---------------------------

1. In Microsoft Visual Basic, create a new Standard EXE project. Form1 is
   created by default.

2. On Form1, add a textbox (Text1) and three labels (Label1, Label2, and
   Label3).

3. Set the Text property of Text1 to a zero and the Caption property of each of
   the labels to nothing.

4. Add the following code to the Change event of the textbox:

         Dim dblValue As Double
         Dim sngValue As Single
         Dim curValue As Currency

         dblValue = Text1.Text
         sngValue = Text1.Text
         curValue = Text1.Text

         Label1.Caption = Format(dblValue, "#.000")
         Label2.Caption = Format(sngValue, "#.000")
         Label3.Caption = Format(curValue, "#.000")

5. Run the project, and enter some decimal values in the textbox, such as:

   0.9125
   0.7125
   0.0915

   Note that the values displayed in the labels are different. The Format
   function rounds some values up and some down based upon the data-type. For
   instance, 0.9125 may be displayed as .912 and .913.

To correct this problem and to keep all values consistent, do one of the
following:

1. Use the CCur() function to convert the values to a Currency data type before
   using the Format() function: (This should not be used if the values will have
   more than 13 digits.)

   TextDblCur = Format(CCur(dblValue), "#.000")
   TextSngCur = Format(CCur(sngValue), "#.000")

2. Declare the variables as Currency.

REFERENCES
==========

For additional information, please see the following articles in the Microsoft
Knowledge Base:

(Complete) Tutorial to Understand IEEE Floating-Point Errors

HOWTO: Work Around Floating-Point Accuracy/Comparison Problems

Additional query words: Precision

======================================================================
Keywords          : kbVBp400 kbVBp500 kbVBp600fix 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVBA500Search kbVBA500 kbVB500 kbVB400Search kbVB400 kbZNotKeyword3 kbVB16bitSearch
Version           : WINDOWS:4.0,5.0
Issue type        : kbbug kbprb
Solution Type     : kbfix

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 2001.