Possible Duplicate:
Compare floats in php
I have the following piece of code:
$a = 1.49;
$b = 1.50;
echo $b - $a; // Outputs 0.01, which is ok
if (($b - $a) != 0.01) {
echo "Not ok";
} else {
echo "Ok";
}
The problem is that if statement echoes "Not ok", although the subtract result is 0.01.
Any idea why?
it's because some floating point operations. the result isn't exactly 0.01. your output is rounded by the system.
just try var_dump(($b-$a)-0.01). this should be float(8.673617379884E-18)
a solution would be if (round($b - $a,2) != 0.01)
The PHP doc on floating point numbers shows how to compare them
As noted in the warning above, testing floating point values for equality is problematic, due to the way that they are represented internally. However, there are ways to make comparisons of floating point values that work around these limitations.
To test floating point values for equality, an upper bound on the relative error due to rounding is used. This value is known as the machine epsilon, or unit roundoff, and is the smallest acceptable difference in calculations.
<?php
// $a and $b are equal to 5 digits of precision.
$a = 1.23456789;
$b = 1.23456780;
$epsilon = 0.00001;
if(abs($a-$b) < $epsilon) {
echo "true";
}
?>
Applied to your example:
$c = $b - $a;
$epsilon = 0.00001;
if (abs($a-$b-0.01) < $epsilon) {
echo "Not ok";
} else {
echo "Ok";
}
Outputs OK