I have done the example and installed everything.
The read or display method of table works correctly, but whenever I try to add, delete or edit a registry a windows appears and say:
404 Page Not Found
The page you requested was not found.
Here is my Controller
class Welcome extends CI_Controller {
    public function __construct()
    {
        parent::__construct();
        $this->load->model('grocery_CRUD_model');
        $this->load->database();
        $this->load->helper('url');
        $this->load->library('grocery_CRUD');
    }
    public function index()
    {
        $crud = new grocery_CRUD();
        $crud->set_theme('datatables');
        $crud->set_table('students');
        $crud->set_relation('class','class','class');
        $crud->display_as('name','Name of Student');
        $crud->set_subject('Students');
        $crud->columns('name','class','roll_no');
        $crud->add_fields('name','class','roll_no');
        $crud->required_fields('name','class','roll_no');
        $crud->unset_export();
        $crud->unset_print();
        $output = $crud->render();
        $this->load->view('home', $output);
    }
}
when i click ADD button URL becomes
http://localhost/index.php/add
what is missed? i am new in codeigniter and Grocery Crud...