//recuperation des champs du formulaire
$nom=$_POST['nom'];
$prenom=$_POST['prenom'];
$ville=$_POST['ville'];
$cp=$_POST['cp'];
$email=$_POST['email'];

	//test champs vides
	if (($full=!empty(($nom) && ($prenom) && ($ville) && ($cp) &&  ($email)) && ( $reg=(ereg("^(.+)@(.+)\.(.+)$", $email)) && ($num=is_numeric($cp) )))
		{
		$connect=mysql_connect("localhost", "root", "") or die ("connection bdd impossible ");
		mysql_select_db("essai", $connect) or die ("<br>selection table impossible </br>");
		$requete="insert into rens (nom, prenom, ville, cp, email) values ('$nom', '$prenom', '$ville', '$cp', '$email')";
		$ok=mysql_query($requete);

$vars = array( 'nom', 'prenom', 'ville', 'cp', 'email' );

$allowed = true;

foreach ( $vars as $var )
{
    if ( ! isset( $_POST[ $var ] ) or empty( $_POST[ $var ] ) )
    {
        $allowed = false;
    }
}

if ( $allowed )
{
    // etc
}