On 22 March 2004 10:31, Paul Hopkins wrote:
> Here's the code:
>
> <?php
> $a = 676.6;
> $b = 0.175;
>
> $y = $a * (1 + $b);
> echo("y: " . $a . " * (1 + " . $b . ") = $y<BR>");
>
> $z = $a + ($a * $b);
> echo("z: " . $a . " + ( " . $a . " * " . $b . ") = $z<BR>");
>
> echo("number format(y)=".number_format($y, 2)."<BR>");
> echo("number format(z)=".number_format($z, 2)."<BR>");
> >
>
>
> Here's the output:
>
> y: 676.6 * (1 + 0.175) = 795.005
> z: 676.6 + ( 676.6 * 0.175) = 795.005
> number format(y)=795.01
> number format(z)=795.00
This is because of the inherent minor imprecision in the way floating point numbers
are represented in a computer -- please see the big fat note headed "Floating point
precision" at http://www.php.net/manual/en/language.types.float.php. You should never
rely on the absolute accuracy of floating point numbers -- even very simple
calculations can be off by an infinitesimal but nonetheless significant amount (for
example, 10.0/3*3 almost never equals 10.0 ;).
Cheers!
Mike
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Mike Ford, Electronic Information Services Adviser,
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