Check whether a value is 'not-a-number' in PHP

Description

The following code shows how to check whether a value is 'not-a-number'.

Example

  /* w  ww.  j  a v  a2 s.co  m*/
<?php
    echo is_nan(200) . "<br>";
    echo is_nan(acos(1.01));
?>

The code above generates the following result.