PHP 產生指定長度的亂數字串，數字

function randomStr($length) {

    $chars  = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';

    $result = '';

    for ($i = 0; $i < $length; $i++) {

        $result .= $chars[ mt_rand(0, strlen($chars) - 1) ];

    }

    return $result;

}

function randomNum($length) {

    $result = '';

    for ($i = 0; $i < $length; $i++) {

        $result .= mt_rand(0, 9);

    }

    return $result;

}