public function attendance($centre)
 {
     try {
         $centre = Crypt::decrypt($centre);
         $centre = Centre::find($centre);
     } catch (Exception $e) {
         return View::make('layouts.error');
     }
     Excel::create($centre->name, function ($excel) use($centre) {
         $excel->setTitle('Attendance Sheet');
         $excel->setCreator('Technothlon')->setCompany('Technothlon');
         $excel->setDescription('Attendance Sheet for ' . $centre->name);
         $excel->sheet('Offline', function ($sheet) use($centre) {
             $sheet->appendRow(array('Name 1', 'Name 2', 'School', 'Roll'));
             $users = array();
             foreach (User::where('centre_id', $centre->id)->wherePaid(1)->orderBy('school_id')->get() as $user) {
                 $users[] = array($user->name1, $user->name2, $user->school->name, $user->roll);
             }
             $sheet->rows($users);
         });
         $excel->sheet('Online', function ($sheet) use($centre) {
             $sheet->appendRow(array('Name 1', 'Name 2', 'School', 'Roll'));
             $users = array();
             foreach (User::where('centre_id', $centre->id)->wherePaid(0)->orderBy('school_id')->get() as $user) {
                 $users[] = array($user->name1, $user->name2, $user->school->name, $user->roll);
             }
             $sheet->rows($users);
         });
     })->export('xlsx');
 }