process.php

<?php include 'database.php'; ?>
<?php
// Destroy the session.
session_destroy();
// Start the session.
session_start();
?>
<?php
// Check to see if score is set_error handler
if(!isset($_SESSION['score'])){
    $_SESSION['score'] = 0;
}

if($_POST){
    $number = $_POST['number'];
    $selected_choice = $_POST['choice'];
    $next = $number+1;

    /* 
    * Get total questions
    */

    $query = "SELECT * FROM `questions`";
    //Get results
    $results = $mysqli->query($query) or die($mysqli->error . __LINE__);
    $total = $results->num_rows;
    
    /* 
    * Get correct choice
    */

    $query = "SELECT * FROM `choices` 
            WHERE question_number = $number AND is_correct = 1";

    // Get result
    $result = $mysqli->query($query) or die ($mysqli->error . __LINE__);

    // Get row
    $row = $result->fetch_assoc();

    // Set correct choice 
    $correct_choice = $row['id'];

    // Compare
    if($correct_choice == $selected_choice){
        // Answer is correct
        $_SESSION['score']++;
    }
    // Check if last question
    if($number == $total){
        header("Location: final.php");
        exit();
    } else {
        header("Location: question.php?n=" . $next);
    }

}