Problem with Floats! (in PHP)

Question

What's wrong with php floats?

$v = 5.2 * 3;

if($v==15.6) {
    echo 'Everything is fine =)';
} else {
    echo 'Okay something is wrong :S';
    var_dump($v); // float 15.6
}

Check this out too:

$v = 5.2 * 3;

if($v>15.6 AND $v<15.60000000001) {
    echo 'We are doomed :S';
    var_dump($v); // float 15.6
} else {
    echo 'Everything is fine =)';
}

I guess it has something to do with the internal representation or some obscure low level stuff? If that's the case, how do I get around this issue? Anything else I should know before using this to calculate real money transactions?

Answer 1

I am sure this is a duplicate, so I'm making this a CW

$v = 5.2 * 3;
if (bccomp($v, 15.6) === 0) {
    echo 'Everything is fine =)';
} else {
    echo 'Okay something is wrong :S';
    var_dump($v); // float 15.6
}

will give 'Everything is fine =)'

Answer 2

It has to do with the internal representation indeed :). Never compare float values. I think there will exists php classes/modules that work around this problem, but you can also store your money values as integers and multiply them by 100. Before display you can divide them again :)