function login($username,$password)
        $sql = "SELECT * FROM users WHERE username = '".esc($username)."' AND password = '".esc($password)."'";
        $res = mysql_query($sql);
        $row = mysql_fetch_object($res);
        if(mysql_num_rows($res) > 0){
            $_SESSION["username"] = $row->username;
        } else{
            echo "Login failed!";
        }

}