String lower and upper in php

We can change all characters to lower case by using strtolower. The following code is an example.

<?php
$string = 'I am ThEt NainG WiN!';
$string_low = strtolower($string);
echo $string_low;
?>

We can also change all characters to upper case by using strtoupper. The following is an example.

<?php
$string = 'I am ThEt NAInG win!';
$string_up = strtoupper($string);
echo $string_up;
?>