How to get checkbox value in controller codeigniter?,

Also note that if a checkbox is not checked it has no value at all.

Unchecked boxes have no value and are not sent to the server. Given 5 checkboxes, if only two are checked then the return from $this->input->post('category') will be an array with two items. If no boxes are checked the return from $this->input->post('category') would be null.