php - Warning: mysql_fetch_assoc() expects parameter 1 to be resource, object given

I cant seem to figure out what I'am doing wrong. So when I submit my form I get Warning error and the

Notice: Undefined variable: dbusername in /Library/WebServer/Documents/ArturoLuna_Final/loginCheck.php on line 30

$username = $_POST['username'];
$password = $_POST['password']; 

if($username&&$password)
{
    require 'conn.php';
    $query = "SELECT * FROM  users WHERE username='$username'";
    $result = $mysql->query($query) or die(mysqli_error($mysql));

    $numrows = $result->num_rows;

    if ($numrows!=0)
    {
        while($row = mysql_fetch_assoc($result))
        { 
            $dbusername = $row['username'];
            $dbpassword = $row['password']; 
        }


        //check to see if they match!
        if($username==$dbusername&&$password==$dbpassword)
        { 
            echo "youre In!";
        }
        else
        echo "incorrect password!";

    }
    else

        die("that user is dead");

    //echo $numrows;

}

else

    echo ("Please Enter Username")

what can I be possibly doing wrong?