Peculiar behaviour with number_format()

[pesback]

First time poster - hope this is the right place!

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

In other words, using two logically equivalent (?) formulae to derive exactly the same result from the same two values results in somehow different results (I guess it's not an issue with number_format() per se, but with associativity or summat...).

Hope it's not an obvious schoolboy error - any ideas?

PHP 4.2.2
Apache 2.0.40
Redhat 7.3

[weekender]

Hi Paul, welcome to the board!

i think it's something to do with accuracy of different data types - i remember doing something about this at school a long way back.

i know that some accounting packages store currency values in pence (or cents) ie £192.77 is stored as 19277 and then divide by 100 for display - this means the number is stored as an integer not a float and guarantees accuracy

adam