if( empty( $_POST['register'] ) === false ) {

    $errors = array();

    $username = clean( $_POST['username'] );
    $password = encrypt( $_POST['password'] );

    if( !$_POST['username'] || !$_POST['password'] ) {

        $errors[] = 'You left a field blank';

    }

    if( strlen($username) > 30 ) {

        $errors[] = 'Your username cannot exceed 30 characters.';

    }

    $query = mysql_query( "SELECT username FROM users WHERE username = '$username'" );
    $count = mysql_num_rows( $query );

    if($count > 0 ) {

        $errors[] = 'That username is already taken. Please choose another one.';

    }

    if( $errors ) {
        foreach( $errors as $disperrors ) {

            echo $disperrors.'<br />';

        }

        echo 'Click <a href="register.php">here</a> to go back.';
        die();
    }