php - Codeigniter error Missing argument -

i've concatenated id of user , pass paramater controller addquestion($id) keep getting these errors:

a php error encountered  severity: warning message: missing argument 1 questions::addquestion() filename: controllers/questions.php line number: 49  php error encountered severity: notice message: undefined variable: id filename: controllers/questions.php line number: 67  database error occurred error number: 1048 column 'question_user_id' cannot null insert `questions` (`question_user_id`, `question`) values (null, 'sdf') filename: c:\xampp\htdocs\webdev\askme\system\database\db_driver.php line number: 330 

here's view:

<h1>ask users</h1> <ul class="list_items"> <?php foreach ($users $user):?>     <li>         <div class="list_name"><b><?php echo $user->username;?></b></div>         <div class="list_body"><?php echo $user->register_date;?> </div>         <div class="list_body">              <a href="<?php echo base_url(); ?>questions/addquestion/<?php echo $user->id; ?>">ask question</a>             <!--<?php //echo anchor(//'questions/addquestion/'.$user->id, //'ask question'); ?> -->         </div>     </li> <?php endforeach; ?> </ul> 

and here's addquestion function in controller:

public function addquestion($id) // line 49  {     $this->form_validation->set_rules('question','your question','trim|required|xss_clean');      if($this->form_validation->run() == false)     {         //load view , layout         $data['main_content'] = 'questions/add_question';         $this->load->view('layouts/main',$data);       }      else      {         //validation has ran , passed           //post values array         $data1 = array(                'question_user_id'      => $id,                 'question'      => $this->input->post('question')         );        if($this->questions_model->create_question($data1))        {             $this->session->set_flashdata('question_created', 'question sent');            // redirect index page notification above             redirect('home/index');        }     } } 

please me, dont know what's wrong

you sending null values db field , it's can not null or try make question_user_id can null $id can not empty it's required value use check this

 else {        if(empty($id))            redirect('home'); // redirect page         $data1 = array(                'question_user_id' => $id,                 'question' => $this->input->post('question')         );