Why won't this loop variable increment? - php

Question

I'm trying to write code that will count the number of users returned by a sqlite query and then split a 'bill' between those users, but for some reason my counter won't increment and I am getting a division by zero error. My code is here:
<?php
session_start();
require 'database.php';
$db = new Database();
$name = $_POST['name'];
$amount = $_POST['amount'];
$due = $_POST['due'];
$gid = $_GET['gid'];
$uid = $_SESSION['id'];
$count = 0;
$users = $db->query("select * from members where(gid='$gid');");
while($data = $users->fetchArray()) {
$count++;
}
$amount = $amount / $count;
while($data = $users->fetchArray()) {
if($data['uid'] == $uid) {
continue;
} else {
$temp = $data['uid'];
$db->exec("insert into bills values(NULL,'$gid','$uid','$temp','$amount','$due','false','$name');");
}
}
header('Location:grouppage.php?gid='.$gid.'');
?>
Anyone have any ideas on how to fix this?

Answer 1

Regardless of the loop not seeming to work, you can't have two while(... fetchArray()) loops without something resetting the internal pointer.
In this case, however, you don't need that:
$users = $db->query("select * from members where(gid='$gid')");
$count = $users->numRows();
if( $count == 0) die("No users found!");
$amount /= $count;
while($data = $users->fetchArray()) {
...
}

Answer 2

You don't handle case, when select doesn't return any record.
Just look at your code:
$users = $db->query("select * from members where(gid='$gid');");
while($data = $users->fetchArray()) {
$count++;
}
No data selected -- no while-body
executed, $count not incremented and left zero, with "divide by zero" error in following line as consequence.
$amount = $amount / $count;