php checkbox array GET/POST

//Classes.php INITIAL TABLE OF CLASS CHOICES:
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 // Retrieve the class data from MySQL
  $query = "SELECT DATE_FORMAT(date, '%a, %d %b %Y') AS new_date, DATE_FORMAT(time, '%H:%i') AS new_time, venue, free_spaces, class_id FROM classes WHERE time_stamp > CURRENT_TIMESTAMP ORDER BY time_stamp ASC LIMIT 8";
  $data = mysqli_query($dbc, $query);

// Loop through the array of class data, formatting it as HTML
  echo '<table class="table table-striped table-hover">';
  echo '<thead><tr><th>Date</th><th>Time</th><th>Venue</th><th>Spaces available</th><th>Select to book</th></tr></thead>';

  while ($row = mysqli_fetch_array($data)) {
      echo '<tr><td>' . $row['new_date'] . '</td>';
      echo '<td>' . $row['new_time'] . '</td>';
      echo '<td>' . $row['venue'] . '</td>';
      echo '<td>' . $row['free_spaces'] . '</td>';
      echo '<form action="makebooking.php" method="get">';
      echo '<td><input type="checkbox" name="class_id[]" value=' . $row['class_id'] . '</td></tr>';
    }
    echo'</table>';

    // Make booking button
      echo '<input type="submit" class="btn btn-large btn-primary pull-right" value="Book classes">';
      echo '</form>';

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//Makebooking.php $_GET AND $_POST TO REFLECT CHOICES AND ALLOW USER TO CONFIRM BEFORE UPDATING DB WITH BOOKING
-------------------------------------------------------------------------------------------
<?php
//Start the session
require_once('startsession.php');
require_once('connectvars.php');
require_once('header.php');
?>
  <body>

<?php
//Insert the navigation bar
require_once('navbar.php');

//Check if the GET is set from classes.php
if (isset($_GET['class_id'])) {
// Grab the score data from the GET
    foreach($_GET['class_id'] as $class_id) {
        $_GET['class_id'] = $class_id;
    }
}
//---------------------------------------------------------------------------------
//Check if the shown bookings have been confirmed
    else if (isset($_POST['class_id'])){
        foreach($_POST['class_id'] as $class_id) {
            $class_id = $_POST['class_id'];
            $user_id = $_SESSION['user_id'];
        }
} else {
    echo '<div class="alert">
        <button type="button" class="close" data-dismiss="alert">&times;</button>
        Please tick the boxes next to the classes you want to book.</br>
        </div>';
}
//---------------------------------------------------------------------------------
//If the confirm button has been hit:
if (isset($_POST['submit'])) {
//-------------------------------------------------------------------------------
//Get user's ID from the users DB and set as $username
    $who = "SELECT first_name, last_name, user_id FROM users WHERE email = '" . $_SESSION['email'] . "'";
    $name = mysqli_query($dbc, $who);
    $row = mysqli_fetch_array($name);
    $username = $row['first_name'] . ' ' . $row['last_name'];

 // Connect to the database
  $dbc = mysqli_connect(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);

    //UPDATE the bookings table;
    $query = "INSERT INTO bookings (user_id, booking_name, class_id, time_stamp) VALUES ('$user_id', '$username', '$class_id', NOW())";
        mysqli_query($dbc, $query);
    // REDIRECT
          $home_url = 'http://' . $_SERVER['HTTP_HOST'] . dirname($_SERVER['PHP_SELF']) . '/classes.php';
    header('Location: ' . $home_url);
    mysqli_close($dbc);
    }

else if (isset($class_id)) {
//---------------------------------------------------------------------------------

//table header
echo '<table class="table table-bordered table-hover">';
  echo '<thead><tr><th>Date</th><th>Time</th><th>Venue</th><th>Who\'s going?</th><th>Add someone</th></tr></thead>';
//create the form
echo '<form method="post" action="' . $_SERVER['PHP_SELF'] . '">';

//Get the class IDs from the GET to use in the POST

    foreach ($_GET['class_id'] as $class_id) {
    $sql = "SELECT class_id, DATE_FORMAT(date, '%a, %d %b') AS new_date, DATE_FORMAT(time, '%H:%i') AS new_time, venue FROM classes WHERE class_id = '$class_id'";
    $data = mysqli_query($dbc, $sql);

//---------------------------------------------------------------------------------
//get table data
    while ($row = mysqli_fetch_array($data)) {
        $date = $row["new_date"];
        $time = $row["new_time"];
        $venue = $row["venue"];
        $class_id = $row["class_id"];
    }
    //---------------------------------------------------------------------------------
//Show a table of the selected classes

      echo '<input type="hidden" name="id" value= ' . $class_id . ' />';
      echo '<td>' . $date . '</td>';
      echo '<td>' . $time . '</td>';
      echo '<td>' . $venue . '</td>';
      echo '<td>' . $username . '</td>';
      echo '<td><button class="btn btn-mini" type="button"><i class="icon-user"></i><i class="icon-plus"</i></button></td></tr>';
}
 echo'</table>';

    //Go Back button
    echo '<a class="btn btn-link pull-left" href="classes.php"><i class="icon-arrow-left"></i> Go back</a>';

    // Make booking button
      echo '<input type="submit" name="submit" class="btn btn-large btn-primary pull-right" value="Confirm">';
      echo '</form>';

}

?>