Validate input fields with dynamic names

[eluser]Prophet[/eluser]
Okay I might have just found a solution to my own problem. It definitely works but is it good coding practice to do things like this?

Creating the inputs:

Code:

<input name="count_<?=$stock['id']?>" value="<?=$stock['count']?>" size="3" />

Form validation:

Code:

foreach ($_POST as $key => $val)
{
    if (substr($key, 0, 6) == 'count_')
    {
        $this->form_validation->set_rules($key, 'Count', 'required|is_natural|maxlength[7]');
    }
}