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.