signin Riwaj Parajuli

<!DOCTYPE html>
<html>
<head>
    <title></title>
    <!-- CSS only -->
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" integrity="sha384-9aIt2nRpC12Uk9gS9baDl411NQApFmC26EwAOH8WgZl5MYYxFfc+NcPb1dKGj7Sk" crossorigin="anonymous">

<!-- JS, Popper.js, and jQuery -->
<script src="https://code.jquery.com/jquery-3.5.1.slim.min.js" integrity="sha384-DfXdz2htPH0lsSSs5nCTpuj/zy4C+OGpamoFVy38MVBnE+IbbVYUew+OrCXaRkfj" crossorigin="anonymous"></script>
<script src="https://cdn.jsdelivr.net/npm/popper.js@1.16.0/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/js/bootstrap.min.js" integrity="sha384-OgVRvuATP1z7JjHLkuOU7Xw704+h835Lr+6QL9UvYjZE3Ipu6Tp75j7Bh/kR0JKI" crossorigin="anonymous"></script>
</head>
<body>
    <div class="container col-6">
    <form action="" method="post">
        <h1 class="display-4 text-center">FORM</h1>
<div class="container">
    <div class="form-group">
            <input type="text" name="user"  class="form-control"/>
    </div>
    <div class="form-group">
            <input type="text" name="pass"  class="form-control"/>
    </div>
    <input type="submit" name="submit">
</div>
</form>
<?php
$con = mysqli_connect('localhost', 'root', '', 'pdo');
if (isset($_POST['submit']))
{
    $user = $_POST['user'];
    $pass = $_POST['pass'];

    $sql = "SELECT * FROM user where user='$user' AND pass='$pass' ";
    $result = mysqli_query($con, $sql);
    $num = mysqli_num_rows($result);
    if ($num)
    {
        echo "successful";
    }
    else
    {
        echo "error";
    }
}
?>
</div>
</body>
</html>