xamp - fatal eror (notpad++) : 
Notice: Undefined variable: con in C:\xampp\htdocs\projekt\ps.php on line 34

Fatal error: Call to a member function query() on null in C:\xampp\htdocs\projekt\ps.php on line 34

This opened in my browser, i looked for other replay on this quedition but i cound't find a resolve..``                                                                     
Problem is here in index.html

    <?php
    $res -$con->query("SELECT * FROM studenti");
    while ($row=$res->fetch_array()){
    ?>

This is base:

    <?php

    $con =mysqli_connect('localhost', 'root','');
    if(!$con)
    {
	echo 'Not connected';
    }
    if(!mysqli_select_db($con,'studenti'))
    {
	echo 'database not selected';
    }
    ?>