A Little help with Code needed

I have alittle PHP snippet in a While loop and i am getting into problems while converting it

$sql = "select rating from r_ratings where iid = $iid";

$result3 = mysql_query($sql ,$db);

if ($myrow2 = mysql_fetch_array($result3)) {

do {
$ratetotal = $ratetotal + $myrow2["rating"];
$ratecount++;
} while ($myrow2 = mysql_fetch_array($result3));

}

$newrate = $ratetotal / $ratecount;