<?php
function romanNumerals($num){
    $n = intval($num);
    $res = '';

    /*** roman_numerals array  ***/
    $roman_numerals = array(
        'M'  => 1000,
        'CM' => 900,
        'D'  => 500,
        'CD' => 400,
        'C'  => 100,
        'XC' => 90,
        'L'  => 50,
        'XL' => 40,
        'X'  => 10,
        'IX' => 9,
        'V'  => 5,
        'IV' => 4,
        'I'  => 1);

    foreach ($roman_numerals as $roman => $number){
        /*** divide to get  matches ***/
        $matches = intval($n / $number);

        /*** assign the roman char * $matches ***/
        $res .= str_repeat($roman, $matches);

        /*** substract from the number ***/
        $n = $n % $number;
    }

    /*** return the res ***/
    return $res;
}

echo romanNumerals(2523);
?>

MMDXXIII