Why are floating point numbers printed so differently?

Question

It\'s kind of a common knowledge that (most) floating point numbers are not stored precisely (when IEEE-754 format is used). So one shouldn\'t do this:

0.3 -         


        

Answer 1

PHP automatically rounds the number to an arbitrary precision.

Floating-point numbers in general aren't accurate (as you noted), and you should use the language-specific round() function if you need a comparison with only a few decimal places. Otherwise, take the absolute value of the equation, and test they are within a given range.

PHP Example from php.net:

$a = 1.23456789;
$b = 1.23456780;
$epsilon = 0.00001;
if(abs($a - $b) < $epsilon) {
  echo "true";
}

As for the Ruby issue, they appear to be using different versions. Codepad uses 1.8.6, While Ideaone uses 1.9.3, but it's more likely related to a config somewhere.