[RESOLVED] Strange script behaviour, is this a PHP bug?

[Jak-S]

Hi, can someone explain to me whats wrong with this script. Looking at the code it all seems pretty simple, but what php outputs is really unexpected:

header('content-type: text/plain');
$d = 2;

for($i = 0.01; $i <= 10; $i += 0.01)
{
	$a = $i;
	$a = $a / 1.175;
	$a = round($a, $d);
	$a = $a * 1.175;
	$a = round($a, 2);
	$r = ($i == $a) ? 'ok' : 'error';
	echo $i."\t".$a."\t".$r."\n";
}

As you should be able to see, every number after 0.16 says error, even though you can quite clearly see that the two numbers do match, and then once $i gets to
4.43 it completly screws up.

Im sure there is no error in the script and there is nothing that tells the value of $i to be any more than two decimals long.

Im running PHP 4.4.2. Here is some sample output:

4.36	4.36	error
4.37	4.37	error
4.38	4.38	error
4.39	4.39	error
4.4	4.39	error
4.41	4.41	error
4.42	4.42	error
4.43	4.43	error
4.4399999999999	4.44	error
4.4499999999999	4.45	error
4.4599999999999	4.47	error
4.4699999999999	4.47	error
4.4799999999999	4.48	error
4.4899999999999	4.49	error
4.4999999999999	4.5	error
4.5099999999999	4.51	error

Thanks in advance.
Jack

[Installer]

Read up on some of the foibles of floating-point numbers here (text and user notes).

To constrain to one decimal place, use round().

[Jak-S]

Hmmm, that’s a shame, that floats pretty much don’t work properly (or at least, not as expected). Good thing this was just a test script and wasn’t for any real site.

For anyone that’s interested, I had to use the BCMath functions to get this to work properly:

header('content-type: text/plain');

$d = 2;

for($i = 1; $i <= 100000; $i++)
{
	$t = bcdiv($i, 100, 2);
	$a = $t;
	$a = bcdiv($a, 1.175, 11);
	$a = round($a, $d);
	$a = bcmul($a, 1.175, 11);
	$a = round($a, 2);
	$r = (bccomp($t, $a, 2) == 0) ? 'ok' : 'error';
	echo $t."\t".$a."\t".$r."\n";
}