public function list_courses()
 {
     $courses = $this->CoursesService->get_all_courses();
     $courses_count = count($courses);
     echo "<option value='-1' >" . "" . "</option>";
     for ($i = 0; $i < $courses_count; $i++) {
         $hashed_course_id_local = hash_val($courses[$i]->get_course_id());
         echo "<option value= {$hashed_course_id_local}  >" . $courses[$i]->get_course_name() . "</option>";
     }
 }
echo $_SESSION['user_name'] . "...";
?>
 Theses are courses you <?php 
if (un_hash_val($_SESSION['current_user_type']) == constantss::$user_type_instructor) {
    echo "teaches";
} else {
    echo "have enrolled in";
}
?>
                    </h3></div> </div>
            <div class="list-group center_class" >
                <?php 
foreach ($courses as $course) {
    ?>
                    <h3> <a href= <?php 
    echo "\"course_materials.php?course=" . hash_val($course->get_course_id()) . "\"";
    ?>
 class="list-group-item"><div class="bg-primary"><?php 
    echo $course->get_course_name();
    ?>
</div></a></h3>
                        <?php 
}
?>
            </div>
        </div>

        <!-- jQuery (necessary for Bootstrap's JavaScript plugins) -->
        <script src="js/jquery.min.js"></script>
        <!-- Include all compiled plugins (below), or include individual files as needed -->
        <script src="js/bootstrap.min.js"></script>
<?php

include_once 'service/MaterialsService.php';
include_once 'function.php';
session_start();
$MaterialsService = unserialize($_SESSION['material_service']);
$file_name = urldecode($_GET['file']);
$section_id = $_GET['section_id'];
$MaterialsService->delete_material($file_name, $section_id);
$course_id = $MaterialsService->get_course_id();
header('location:course_materials.php?course=' . hash_val($course_id));
 public function select_user($user_id, $user_password)
 {
     $this->openDb();
     $user_rec = mysql_query("SELECT * FROM " . $this->user_table . " where user_id = '{$user_id}' and user_password=md5('{$user_password}');") or die('<span class="error_span"><u>MySQL error:</u> ' . htmlspecialchars(mysql_error()) . '</span>');
     if (mysql_num_rows($user_rec) == 1) {
         $user = mysql_fetch_object($user_rec);
         $_SESSION['user_id'] = $user->user_id;
         $_SESSION['user_name'] = $user->user_name;
         $_SESSION['current_user_type'] = hash_val($user->user_type);
         $_SESSION['change_password'] = $user->change_password;
         $_SESSION['change_old_password'] = -1;
         echo $_SESSION['current_user_type'];
         return 1;
     } else {
         return 0;
     }
     $this->closeDb();
 }