checking a form

Hi everybody. First be patiently with my English.I am from Galiza country.

I am a new php-postgresql user. I am making a form. After submit this form,
it will take us to an archive.php. Firts i would do is to check if every
form'elements  are not-white.It is, if everyone have been selected.
I was tryng  so using  $HTTP_POST_VARS) and cheking if every slots where not
-white.

$comprova_form=comprovaformulario($HTTP_POST_VARS)
function comprovaformulario($var)
 {
  $num=count($var);
  for ($i=1;$i<$num;$i++)
   {
    if (empty($var[$i]))
     {
      return false;
     }
   }
 }



 But it is wrong  for example in the case of a checkbox: it does not must be
on all off then.

How can i do this???.

Thank you.