Re: Weird results of "=="

Brian P. O'Donnell wrote:

<? $a = 252.73; $b = 252.73; $c = 0; if ($a == ($b + $c)) { // do the first thing } elseif ($a > ($b + $c)) { // do the second thing } elseif ($a < ($b + $c)) { // do the third thing } ?> Each of the three variables is derived by some earlier calculation, but for testing purposes I have made sure that they end up being $a = $b and $c = 0. I have tested for three different values (of $a) and gotten all three results. That is, once the first block has executed, once the second block and once the third block. Am I missing something really obvious here?

This is an inherent problem with floating-point operations, especially comparison, and is not unique to PHP. Often numbers will be off by some miniscule amount, just enough to make them not equal. What I would do in this situation is create a function float_equals(), after deciding what delta is acceptable for your situation, like this: define('MAX_FLOAT_DELTA', 0.001); // Or whatever is acceptable for you function float_equals($a, $b) { return (abs($a - $b) <= MAX_FLOAT_DELTA); } Then use float_equals($x, $y) instead of $x == $y. Jasper