user if exists isn't working

I'm trying to do if user exists function but it isn't working.My other validation works fine. addnewuser.php

<?php
    include ('dbco.php');
    include('users.php');
    include('general.php');
    $newuser = $_POST['useameinput'];
    $password = md5($_POST['passwordinput']);

if (empty($errors) === true){
    if (user_exists($_POST['useameinput']) === true) {
        $errors[] = 'Sorry, the useame '' . $_POST['useameinput'] . '' is already taken.'; 
    }

users.php

function user_exists($newuser) {
    $newuser = sanitize($newuser);
  retu (mysql_result( mysql_query("SELECT COUNT(`user_id`) FROM `users` WHERE `useame` ='$newuser' "), 0) == 1) ? true : false;
  }

general.php

function sanitize($data) {
    retu mysql_real_escape_string($data);
    }