[Dylanblitz]

If you are going to split it up and give messages I'd do something like this and split it a bit more, otherwise the user might get confused with one message for multiple conditions.

PHP Code:

    if (!$vbulletin->GPC['quote'] OR !$vbulletin->GPC['name'] OR !$vbulletin->GPC['letter'])
    {
        print_stop_message('cannot_have_null_values');
    }

    if (strlen($vbulletin->GPC['letter']) != 1)
    {
        print_stop_message('only_1_character_allowed');
    }

    if (!preg_match('/^[a-zA-Z0-9]+$/', $vbulletin->GPC['letter'])
    {
        print_stop_message('only_numbers_letters_allowed');
    }