Codeigniter - Edit Form with Checkbox

I'm using codeigniter and have a problem with my edit form in checkbox. The checkbox have 2 values 1 and 0, if checked then the value is 1 and if unchecked then the value is 0.

here is my controller:

function updatepost($id=0){
    $data = $_POST;
    $this->db->where('id_post',$id);
    $outp = $this->db->update('post',$data);
}

And here is my view

sport <input type="checkbox" name="sport" value="1" <?php if($data['sport'] == '1'){echo 'checked';}?> />

tekno <input type="checkbox" name="tekno" value="1" <?php if($data['tekno'] == '1'){echo 'checked';}?>/>

game <input type="checkbox" name="game" value="1" <?php if($data['game'] == '1'){echo 'checked';}?>/>

if i unchecked the checkbox, value should be '0';

My question is how to get value if the checkbox is uncheked?

Many thanks for the answer..