php - Why does `intval(19.9 * 100)` equal `1989`?

Question

Boy, this one is really weird. I expect the following code to print 1990, but it prints 1989!

$val = '$19.9';

$val = preg_replace('/[^d.]/','',$val);
$val = intval($val * 100);

echo $val;

Why on earth is this happening?

Edit: and this code:

$val = '$19.9';
$val = preg_replace('/[^d.]/','',$val);
echo $val . "<br>";
$val = $val * 100;
echo $val . "<br>";
$val = intval($val);
echo $val;

Prints:

19.9
1990
1989

Why does intval(1990) equal 1989???

Answer 1

This is a precision issue inherent to floating point numbers in PHP, and lots of other languages. This bug report discusses it a bit, in the context of casting as an int:

http://bugs.php.net/bug.php?id=33731

Try round($val * 100) instead.