function login($username, $password)
{
    //returning user id error was you were returning the true or false
    $userid = user_id_username($username);
    $username = sanitize($username);
    $password = sha1($password);
    $query = "SELECT COUNT(`user_id`) FROM `lr` WHERE `username` = '{$username}' AND`password`='{$password}'";
    $run_query = mysql_query($query);
    if (mysql_result($run_query, 0) == 1) {
        return $userid;
    } else {
        echo mysql_error();
        return false;
    }
}
<?php

include 'core/init.php';
include 'includes/overall/header.php';
if ($_GET['username'] === true && empty($_GET['username']) === false) {
    $username = $_GET['username'];
    if (user_exists($username) === true) {
        $user_id = user_id_username($username);
        $user_data[] = user_data($user_id, 'firstname', 'lastname', 'email');
    }
} else {
    //echo "hey chud lo";
    header('location:index.php');
    exit;
}
?>
<td valign="top">
<h3>Name:-   </h3><?php 
echo $user_data['firstname'] . " " . $user_data['lastname'];
?>




</td>
<?php 
include 'includes/aside.php';
include 'includes/overall/footer.php';
?>