PHP

<?php

require "db.php";

function reg($hfuser, $user, $email, $pass) {

$hfuser = $_POST['hfuser'];
$user = $_POST['username'];
$email = $_POST['email'];
$pass = md5($_POST['password']);
$errors = array();

$qry = mysql_query("INSERT INTO `users`(`hfuser`, `user`, `email`, `pass`)
VALUES('$hfuser', '$user', '$email', '$pass') ");

$result = mysql_query($qry);

mysql_close();

$check = mysql_query("SELECT `user` FROM `users` WHERE `user`=$user");

$user_ex = mysql_query("$check");


if (!$user) {

	$errors[] = "Username is not defined!";

}

if (!$pass) {

	$errors[] = "Password is not defined!";

}

if (!$email) {

	$errors[] = "E-mail is not defined!";

}

if ($user) {

	if (!ctype_alnum($user)) {

		$errors[] = "Username can only contain numbers & letters!";

	}

}

$range = range(1,15);

if (!in_array(strlen($user), $range)) {

	$errors[] = "Username must be between one and fifteen characters!";

}

if($email){
			$checkemail = "/^[a-z0-9]+([_\\.-][a-z0-9]+)*@([a-z0-9]+([\.-][a-z0-9]+)*)+\\.[a-z]{2,}$/i";

}

			if(!@preg_match($checkemail, $email)){
				$errors[] = "E-mail is not valid, must be name@server.tld!";
			}

if ($user_ex) {

	echo "I am sorry, but that username is not available.";
	unset($user);

}

}
?>