conn.php

<?php
$username = filter_input(INPUT_POST, 'username');
$password = filter_input(INPUT_POST, 'password');
if (!empty($username)) {
    if (!empty($password)) {
        $host = "localhost";
        $dbusername = "root";
        $dbpassword = "";
        $dbname = "Travel_Agency";
        $conn = new mysqli($host, $dbusername, $dbpassword, $dbname);
        if (mysqli_connect_error()) {
            die('Connect Error (' . mysqli_connect_errno() . ')'
                . mysqli_connect_error());
        } else {
            $sql = "select C_Name, C_Pass from customer;";
            $result = mysqli_query($conn, $sql);
            $resultcheck = mysqli_num_rows($result);
            if ($resultcheck > 0) {
                while ($row = mysqli_fetch_assoc($result)) {
                    if ($row['C_Name'] == $username && $row['C_Pass'] == $password) {
                        echo "Log in succesful. Redirecting to Home page";
                        header("Location: timeout.html");
                    } else {
                        echo "Log in unsuccesful. Redirecting to Sign in page";
                        header("Location: signin.html");
                    }
                }
            }
            if ($conn->query($sql)) {
                echo "New Record is inserted succesfully";
            } else {
                echo "Error" . $sql . "<br>" . $conn->error;
            }
            $conn->close();
        }
    } else {
        echo "Password should not be empty";
    }
} else {
    echo "Username should not be empty";
}