Microsoft KB Archive/114136

= BUG: FoxPro Math-Precision Problems with SET DECIMALS =

Article ID: 114136

Article Last Modified on 5/6/2003

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APPLIES TO


 * Microsoft Visual FoxPro 3.0 Standard Edition
 * Microsoft Visual FoxPro 3.0b Standard Edition
 * Microsoft Visual FoxPro 5.0 Standard Edition
 * Microsoft Visual FoxPro 5.0a
 * Microsoft Visual FoxPro 6.0 Professional Edition
 * Microsoft FoxPro 2.0

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This article was previously published under Q114136



SYMPTOMS
SET DECIMALS TO 2 changes the result when a numeric expression that evaluates to a decimal value is used in a comparison. For example, type the following in the Command window: SET DECIMAL TO 18 ? 12/8888888 = 0    && FoxPro returns FALSE SET DECIMALS TO 2 ? 12/8888888 = 0    && FoxPro returns TRUE Under dBASE IV, both of these expressions will return FALSE.

In FoxPro version 2.6a, a similar decimal-precision problem occurs when any whole number is used in math problems. For example: SET DECIMALS TO 18 ?12/8888888      && dBASE returns 0.00000135... but FoxPro returns 0 ?12/88888888     && dBASE returns 0.0000000000... but FoxPro returns 0 ?12.0/8888888    && dBASE returns 0.00000135... but FoxPro returns 0 However the behavior of FoxPro versions 2.5x, 2.6 and Visual FoxPro is closer to that of dBase. For example: SET DECIMALS TO 18 ?12/8888888      && FoxPro returns 0.000001350000135000 ?12/88888888     && FoxPro returns 0 ?12.0/8888888    && FoxPro returns 0.000001350000135000



RESOLUTION
If you need greater precision in FoxPro, set the SET DECIMALS command to a higher value. For greater precision with constants, replace the constants with memory variables, so that FoxPro performs the calculation at run time.

If you must use constants, express them in the precision that is desired. For example, use this expression ?12.0000000/88888888 && FoxPro returns 0.00000135... rather than this one: ?12/88888888 && FoxPro returns 0.0000000000...



STATUS
Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article.



MORE INFORMATION
NOTE: FoxPro returns a zero when the first significant digit is in the seventh position to the right of the decimal; for example, 0.0000001.

Additional query words: math set decimal kbFP250 kbFP260 kbvfp300 kbvfp500 kbvfp600

Keywords: kbbug KB114136

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