$sayi = count($_POST["istek"]);

for($i = 0; $i <= $sayi; $i++) {

$istek = $_POST["istek"][$i];
$adet = $_POST["adet"][$i];

        $kaydet=$db->prepare("INSERT INTO istek_durum SET isd_istekid=:iid, isd_Hesapid=:hid, isd_hafta=:hft, isd_adet=:adt");
        $al=$kaydet->execute(array('iid'=> $istek,'hid'=> $Hid, 'hft'=>$hafta, 'adt'=>$adet));

}