3v4l.org

run code in 300+ PHP versions simultaneously
<?php $master = array(); $arrColors = array('R', 'B', 'G' ,'Y'); $arrNumbers = array('1', '2', '3', '4'); foreach($arrColors as $color) { foreach($arrNumbers as $num) { array_push($master, $color); //$master += array($color => $num); //echo $color.' => '.$num; //echo "\n"; } } print_r($master);
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, 5.5.0 - 5.5.38, 5.6.0 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.25, 7.2.0 - 7.2.33, 7.3.0 - 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 ( [0] => R [1] => R [2] => R [3] => R [4] => B [5] => B [6] => B [7] => B [8] => G [9] => G [10] => G [11] => G [12] => Y [13] => Y [14] => Y [15] => Y )

preferences:
225.75 ms | 406 KiB | 368 Q