IBAN\Core\IBAN::getNumericRepresentation PHP Method

    private function getNumericRepresentation($letterRepresentation)
    {
        $numericRepresentation = '';
        foreach (str_split($letterRepresentation) as $char) {
            if (array_search($char, Constants::$letterMapping)) {
                $numericRepresentation .= array_search($char, Constants::$letterMapping) + 9;
            } else {
                $numericRepresentation .= $char;
            }
        }
        return $numericRepresentation;
    }