mysql_result to mysqli issue - php

Question

ive tried in vain for a good amount of time to convert this string from mysql to mysqli with no luck. here is what i had for mysql :
function user_exists($username) {
$username = sanitize($username);
$query = mysql_query("SELECT COUNT(`user_id`) FROM `users` WHERE `username` = '$username'");
return (mysql_result($query, 0) == 1) ? true : false;
}
ive tried:
function user_exists($username) {
$link = mysqli_connect("localhost", "username", "password", "table");
$username = sanitize($username);
$usernamequery = "SELECT COUNT(`userid`) FROM `table` WHERE `username` = '$username' ";
$query = mysqli_query($link, $usernamequery);
$queryarray = mysqli_fetch_array($query, MYSQLI_BOTH);
$queryarrayres = mysqli_num_rows($query) ;
if ($queryarrayres > 0) { true; } else { false;}
}
numerous hits of this issue on here from previous users but none of them seem to work for me.this and this for example. it all seems fine until i get to converting the mysql_result query and it goes to pieces. i understand that mysql_result in the above situation is essentially checking to see if theres one row selected and thats it equal to one, ie present, but i just cant seem to get something equivalent in the mysqli.
function login($username, $password) {
$link = mysqli_connect("localhost", "username", "pw", "db");
$username = sanitize($username);
$password = md5($password);
$loginquery = "SELECT COUNT(`user_id`) FROM `users` WHERE `username` = $username AND `password` = $password";
$query = mysqli_query($link, $loginquery);
$queryarray = mysqli_fetch_array($query);
$queryarrayres = $queryarray[0];
return ($queryarrayres > 0)? $userid :false;
}
in this instance, $queryarrayres prints as 1 at the right occasion, and zero the rest. so that bit works. the function actually contains a password element too, which ive added.
unfortunately when i use the function is continually returns false. i have tested on a test page, and if i change $username and $password to absolute variable its seems to work. the code is identical between the old version (not shown), and this version, aside from the obvious mysqli updates. this narrows the issue down to three possibilities. 1) something to do with $username and $password population. 2) the $usernamequery string. 3) the return of the function. i reckon its three given that no other code has changed, but i cant put my finger on whats going on here.

Answer 1

Use this function below, it works
function user_id_from_username ($username){
global $connect;
$username = sanitize($username);
$query = " SELECT user_id FROM users WHERE username = '$username' ";
$result = mysqli_query($connect, $query);
$row = mysqli_fetch_array($result, MYSQLI_ASSOC);
echo $row["user_id"];
}

Answer 2

Your new user_exists function is not returning anything.
change
if ($queryarrayres > 0) { true; } else { false;}
to
return ($queryarrayres > 0)?true:false;

Answer 3

You may use the following function and call the function
function mysqli_result($res, $row, $field=0) {
$res->data_seek($row);
$datarow = $res->fetch_array();
return $datarow[$field];
}