PHP code - 13 lines

Link:

PHP, pasted on Feb 6:

<?php

error_reporting(E_ALL);

function func($a)
{
  if ( isset($a) )
    echo 'Ok';
  else
    echo 'Not ok';
}

func($_GET['a']);

Output:

1
2
3


Notice: Undefined index:  a in /t.php on line 13
Not ok