submit_exams.php

<?php
session_start();
require 'config.php';
if (!isset($_SESSION['id']) || $_SESSION['role'] !== 'student') { header('Location:index.php'); exit; }

$user_id = $_SESSION['id'];
$exam_id = intval($_POST['exam_id'] ?? 0);

$qstmt = $pdo->prepare("SELECT * FROM exam_questions WHERE exam_id = ?");
$qstmt->execute([$exam_id]);
$questions = $qstmt->fetchAll(PDO::FETCH_ASSOC);

$total = 0;
$score = 0;

// create submission
$pdo->beginTransaction();
$ins = $pdo->prepare("INSERT INTO exam_submissions (exam_id, user_id, score, total) VALUES (?, ?, 0, 0)");
$ins->execute([$exam_id, $user_id]);
$submission_id = $pdo->lastInsertId();

$insertAns = $pdo->prepare("INSERT INTO exam_answers (submission_id, question_id, chosen) VALUES (?, ?, ?)");

foreach ($questions as $q) {
    $qid = $q['id'];
    $chosen = $_POST["q$qid"] ?? null;
    $insertAns->execute([$submission_id, $qid, $chosen]);
    $total += intval($q['points']);
    if ($chosen && $chosen === $q['correct_option']) {
        $score += intval($q['points']);
    }
}

$upd = $pdo->prepare("UPDATE exam_submissions SET score = ?, total = ? WHERE id = ?");
$upd->execute([$score, $total, $submission_id]);
$pdo->commit();

header("Location: exam_result.php?id={$submission_id}");
exit;