3v4l.org

run code in 300+ PHP versions simultaneously
<?php $arr = array ( 0 => 'nested array', 1 => 'nested array', 2 => 'nested array', 3 => 'nested array', 4 => 'nested array', 5 => 'nested array', ); for ($key = 0, $end = max(array_keys($arr)) + 1; array_key_exists($key, $arr); $key++); var_dump($key);
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.24 - 5.5.35, 5.6.8 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.20, 7.2.6 - 7.2.33, 7.3.12 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
int(6)

preferences:
203.35 ms | 406 KiB | 312 Q