3v4l.org

run code in 300+ PHP versions simultaneously
<?php $array = array('a' => '…', 'b' => '…', 'c' => '…', 'd' => '…', 'e' => '…', 'f' => '…'); foreach ($array as $key => $val){ echo "current key: $key, next key: ".key($array)."<br>"; }
Output for 4.3.0 - 4.3.11, 4.4.0, 4.4.2 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.3, 7.0.0 - 7.0.20, 7.1.0 - 7.1.20, 7.2.0 - 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 - 8.3.7
current key: a, next key: a<br>current key: b, next key: a<br>current key: c, next key: a<br>current key: d, next key: a<br>current key: e, next key: a<br>current key: f, next key: a<br>
Output for 5.2.4 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.0 - 5.5.36, 5.6.0 - 5.6.28
current key: a, next key: b<br>current key: b, next key: b<br>current key: c, next key: b<br>current key: d, next key: b<br>current key: e, next key: b<br>current key: f, next key: b<br>
Output for 4.4.1
current key: a, next key: b<br>current key: b, next key: c<br>current key: c, next key: d<br>current key: d, next key: e<br>current key: e, next key: f<br>current key: f, next key: <br>
preferences:
210.95 ms | 402 KiB | 349 Q