Warning: mysql_fetch_assoc() expects parameter 1 to be resource, object given
$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")

while($row = mysql_fetch_assoc($result))

while($row = $result->fetch_assoc())

$row = $result->fetch_assoc();