Code:

if(isset($_POST['submit']))
{
    $username = mysqli_real_escape_string($con, $_POST['username']);
    $password = mysqli_real_escape_string($con, $_POST['password']);

    $query = "SELECT * FROM `users` WHERE username='$username' and password='$password'";

    $result = mysqli_query($con, $query) or die(mysqli_error($con));
    //$count = mysqli_num_rows($result);
    $row = mysqli_fetch_assoc($result);

    if (!empty($row))
    {
        if(password_verify($password, $row['password']))
        {
            $_SESSION['id'] = $username;
            $ip = $_SERVER["REMOTE_ADDR"];
            $q = "UPDATE users SET ip='$ip' WHERE username='$username'";
            mysqli_query($con, $q);
            header('Location: index.php');
        }
        else
        {
            echo '<script language = "javascript">';
            echo "alert('Invalid Password.');window.location.href='login.php'";
            echo '</script>';
        }
    }
    else
    {
        echo '<script language = "javascript">';
        echo "alert('Something went wrong, Enter real data.');window.location.href='login.php'";
        echo '</script>';
    }
}