<?php

$error = array();
$error['login'] = array();

if (empty($_POST['user']))
{
    $error['login']['mf_user'] = 'Username missing';
}

if (empty($_POST['pass']))
{
    $error['login']['mf_pass'] = 'Password missing';
}

if (empty($error['login']))
{
    $user = $_POST['user'];
    $pass = $_POST['pass'];

    if (!preg_match('/^[a-zA-Z0-9]/', $user))
    {
        $error['login']['chr_user'] = 'Username can only contain A-Z and 0-9';
    }

    if (!preg_match('/^[a-zA-Z0-9]/', $pass))
    {
        $error['login']['chr_pass'] = 'Password can only contain A-Z and 0-9';
    }

    if ((strlen($user) < 6) || (strlen($user) > 16))
    {
        $error['login']['user_length'] = 'Username is shorter than 6 or longer than 16 characters.';
    }

    if ((strlen($pass) < 6) || (strlen($pass) > 16))
    {
        $error['login']['pass_length'] = 'Password is shorter than 6 or longer than 16 characters.';
    }

    if (empty($error['login']))
    {

    }
}