This question already has an answer here:
Somehow PHP thinks that 3.57 + 0.01 equals 3.5799999999999996 in my script.
I tested about 10 other sums like this (e.g. 10.51 + 0.01) and then PHP gave me the correct answer (10.52 in the latter case). So, weirdly enough it only seems to make this mistake with these specific floats.
Code: (simplified for readability)
$users = array();
$IDs = [1,2,3];
foreach($IDs as $ID)
{
$user = (object) array();
$user->ID = $ID;
$users[] = $user;
}
$initialAmount = 3.57;
$chosenIDs = [1,3];
foreach ($users as $key => $value)
{
$users[$key]->amount = $initialAmount;
if(in_array($key, $chosenIDs))
{
//the following returns 3.5799999999999996
$users[$key]->amount = $users[$key]->amount + 0.01;
//even if I do it like the following, it returns the wrong answer
$users[$key]->amount = 3.57 + 0.01; //according to PHP equals 3.5799999999999996
//the following actually gives the correct answer though
//$users[$key]->amount = ($users[$key]->amount * 100 + 1) / 100;
}
}
Is this some weird error in my configuration, or what is going on here?
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As others have mentioned, it's a problem with Floating Point Math, not php.
http://php.net/manual/en/language.types.float.php
You can avoid it by using the BC Math extension when working with numbers where Floating Point errors would be a problem. It supports arbitrary precision.