3v4l.org - online PHP & HHVM shell, execute code in 100+ different versions!

<?php $a = 0; echo $a + ++$a;
Output for 5.1.0 - 5.6.0, php7@20140507 - 20140901, hhvm-3.0.1 - 3.2.0
2
Output for 4.3.0 - 5.0.5
1