php - mysqli prepared statement not working in login -

i want login user, returns 0 in num rows. problem?

config.php

<?php  $hostname="localhost"; $titulo="config"; $user="root"; $pass=""; $bd="st";  $mysqli_link = new mysqli($hostname, $user, $pass, $bd);  if (mysqli_connect_errno()) {     printf("connect failed: %s\n", mysqli_connect_error());     exit(); }  ?> 

no error showing.

login.php

include("config.php"); $user = $_post['user']; $pass = $_post['pass'];  $stmt = $mysqli_link->prepare("select id, user cadastro binary user = ? , binary senha = ?"); $stmt->bind_param('ss', $user, $pass); $stmt->execute(); $stmt->store_result(); //it works!!**  $num = $stmt->num_rows; echo $num; //$num 0 why?  if($num > 0) {...  

i type user , pass correctly, im converting mysql mysqli.

edit-------------------------------------------------------

with $stmt->store_result(); works! have error in part:

        $i=$mysqli_link->prepare("update cadastro set `lastsession` = ? `user` = ? limit 1;");         $i=$mysqli_link->bind_param('ss', $sessionid, $user);         $i=$mysqli_link->execute(); 

fatal error: call undefined method mysqli::bind_param() in c:\xampp\htdocs\login.php on line 45

now have shown real code! , problem have use $stmt variable this:

$stmt = $mysqli_link->prepare("update cadastro set `lastsession` = ? `user` = ? limit 1"); $stmt->bind_param('ss', $sessionid, $user); //^^^ see here $stmt->execute(); $stmt->store_result();