Untitled

<?php
function changeLower($upper): string
{
    $lower = '';
    for ($i = 0; $i < strlen($upper); $i++) {
        
        if ($upper[$i] <= "Z" and ord($upper[$i]) > 64)
            $lower .= chr(ord($upper[$i]) + 32);
        else
            $lower .= $upper[$i];
    }
    return $lower;
}
$upper = 'MARY HAD A LITTLE LUMP AND She Is 25 bUtty';
echo changeLower($upper);