public function addSubject()
 {
     $this->load->model('Subjects_model');
     $p = new Academic_year_model();
     $p->subject_code = $this->input->post('subject_code');
     $p->subject_title = $this->input->post('subject_title');
     $result = $p->addSubject();
     if (!$result) {
         echo mysqli_error($result);
     } else {
         if ($this->session->userdata('role_id') == 0) {
             redirect('admin', 'refresh');
         } else {
             redirect('staff', 'refresh');
         }
     }
 }