submit multiple inputs within a forloop in codeigniter

My code is to fetch questions of users saved in the database by a foreach loop and let the admin answer each question and save the answer of each question after checking of validation rules in the database , Here we go :

Model is :

public function get_questions(){

 $this->db->select('id,user_name, question, date');
 $this->db->order_by("id", "desc");
 $query=$this->db->get('t_questions');
 return $query->result();

}

My view is:

foreach ($questions as $id => $row) :
           ?>
       <?php

               echo "<h5>".$row->question;
               echo "<br>";

               echo "from : ".$row->user_name."</h5>";
               echo date('Y-m-d H:i');
               echo "<br>";
               $q_no='save'.$row->id;
               $ans_no='answer'.$row->id;
               echo  "<h4> Answer:</h4>";
               echo form_open('control_panel');
               ?>
               <textarea name='<?php echo 'answer'.$row->id; ?>'  value="set_value('<?php echo 'answer'.$row->id; ?>')" class='form-control' rows='3'> </textarea>
               <input type='hidden' name='<?php echo $q_no ; ?>' value='<?php echo $q_no; ?>' />
               <input type='hidden' name='<?php echo $ans_no ; ?>' value='<?php echo $ans_no ; ?>' />
               <?php
               echo form_error($ans_no);
               echo "              
           <div class='form-group'>
                           <div >
                               <label class='checkbox-inline'>

                               <input type='checkbox' name='add_faq' value='yes' />
                                     Adding to FAQ page .
                               </label>
                           </div>
                       </div>




         <p>";

          ?>
         <input type='submit' name='<?php echo 'save'.$row->id; ?>' value='<?php echo 'save'.$row->id; ?>' class='btn btn-success btn-md'/>
           <?php
           echo 'answer'.$row->id;
           ?>
           <hr>

           <?php endforeach; ?>

and my controller is :

$this->load->model('control_panel');
   $data['questions']=$this->control_panel->get_questions();
   $data['no_of_questions']=count($data['questions']);



   if($this->input->post($q_no))
   {

     $this->form_validation->set_rules($ans_no,'Answer','required|xss_clean');  
       if($this->form_validation->run())
     {  

     /* code to insert answer in database */
     }

   }

of course it did not work with me : i get errors :

       Severity: Notice

   Message: Undefined variable: q_no

i do not know how to fix it

I am using codeigniter as i said in the headline.



to explain exactly what i want to do : it is supposed for users to ask the admin , so their questions are saved t_questions table in the database , then i got them in the view by a foreach loop and i wrote a code under each fetched question for a textbox to let the admin answer each question do to validate each answer through the validation rules i differ each answer by the id of the question which is a column in the table t_question and also i am doing the same for the submit button to differ which submit button is clicked that is it