<?

$tablica1 = Array(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16);
$tablica2 = Array(1,3,7,12);
$ile_1 = count($tablica1);

$diff=array_diff($tablica1,$tablica2);

?>

<select name="user_id">

<?
$n=0;
while ($n < $ile_1){
?>

<option value="<? echo $diff[$n]; ?>"> <? if ($diff[$n]!='') {echo $diff[$n];} ?> </option>

<?
$n++;
}
echo "</select>";
?>