[RESOLVED] running number ih php

[chinna]

<?
include "db1.php";
$sql="select * from voucher";
$result=mysql_query($sql)or die(mysql_error());
 $id_index=date('dmy');
$r=mysql_num_rows($result);
$c=$r+1;
$t_id="EP".$id_index."-".$r;
echo $t_id;
?>

i use this code to generate ID...out i get is EP100407-1...how to change the output to this EP100407-0001....already try in google but cannot get the answer...thanks in advanced

[NogDog]

$t_id = sprintf("EP%s-%04d", $id_index, $r);