fetch values not correctly?

Code:

I want to store checkbox value,two textbox value in array.

public function valinsert()
{
$certids = $this->input->post('certid');  
$nocs = $this->input->post('noc1');   
$amtt = $this->input->post('txt');

$result = array();
  foreach ($certids as $index=>$certid) 
  {
     $result[] = $certid . '_' . $nocs[$index] .'_' . $amtt[$index];
  }

but it displays

Code:

Array
(
   [0] => 1_2_1700
   [1] => 2_3_900
   [2] => 3_0_0
   [3] => 4_0_0
   [4] => 5_3_900
   [5] => 6_3_900
   [6] => 7_3_900
)

how to display those checked checkbox with corresponding row details. some times its working but most of the time return "o". how to solve this