3v4l.org

run code in 300+ PHP versions simultaneously
<?php $x = array( 'a' => array('1' => 2, '2' => 3), 'b' => array('4' => 5, '5' => 6)); print_r($x); foreach ($x as $k => $v){ if (isset($v['1'])) {$x[$k]['1'] = 10; } } print_r($x);
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 - 7.1.10, 7.2.0 - 7.2.33, 7.3.16 - 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
Array ( [a] => Array ( [1] => 2 [2] => 3 ) [b] => Array ( [4] => 5 [5] => 6 ) ) Array ( [a] => Array ( [1] => 10 [2] => 3 ) [b] => Array ( [4] => 5 [5] => 6 ) )

preferences:
256.61 ms | 406 KiB | 310 Q