3v4l.org

run code in 300+ PHP versions simultaneously
<?php $strings = [ "test string", "lado lomidze needs a solution", "i made some research and found 'good' answers here; they really helped me." ]; // if not already all lowercase, use strtolower() foreach ($strings as &$string) { for ($i = 0, $len = strlen($string); $i < $len; $i += 2) { $string[$i] = strtoupper($string[$i]); } } var_export($strings);
Output for 5.6.38, 7.1.0 - 7.1.33, 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 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.25, 8.4.1 - 8.4.12
array ( 0 => 'TeSt sTrInG', 1 => 'LaDo lOmIdZe nEeDs a sOlUtIoN', 2 => 'I MaDe sOmE ReSeArCh aNd fOuNd \'GoOd\' AnSwErS HeRe; ThEy rEaLlY HeLpEd mE.', )
preferences:
149.78 ms | 408 KiB | 5 Q