Syntax error,plz help

[cty]

1)Error display in cart.php page:
PHP Notice: Undefined offset: 0 in C:\test\kelly.php on line 16 PHP Notice: Undefined variable: totalCost in C:\test\kelly.php on line 61
2)Error show when i try to remove item form cart:
PHP Notice: Undefined variable: db in C:\test\kelly.php on line 43 PHP Fatal error: Call to a member function query() on a non-object in C:\test\kelly.php on line 43

--------------------------------------------------------
//This is "db.php"
<?php
function GetCartId()
{
// This function will generate an encrypted string and
// will set it as a cookie using set_cookie. This will
// also be used as the cookieId field in the cart table
if(isset($_COOKIE["cartId"]))
{
return $_COOKIE["cartId"];
}
else
{
// There is no cookie set. We will set the cookie
// and return the value of the users session ID
session_start();
setcookie("cartId", session_id(), time() + ((3600 * 24) * 30));
return session_id();
}
}
?>
-------------------------------------------------------------------
//This is "product.php"
<?php

include("db.php");
$db=new mysqli('localhost','root','','test');
$db->select_db('test');

$query="select * from items order by itemName asc";
$result = $db->query($query);
?>
<?php
while($row =$result->fetch_assoc())
{
?>
<table border=2>
<tr>
<td width="30%" height="25">
<font face="verdana" size="2" color="black">
<?php echo $row["itemName"]; ?>
</font>
</td>
<td width="10%" height="25">
<font face="verdana" size="2" color="black">
<?php echo $row["itemPrice"]; ?>
</font>
</td>
<td width="50%" height="25">
<font face="verdana" size="1" color="black">
<?php echo $row["itemDesc"]; ?>
</font>
</td>

<td width="10%" height="25">
<font face="verdana" size="2" color="black">
<a href="cart.php?action=add_item&id=<?php echo $row["itemId"]; ?>&qty=1">Add Item</a>
</font>
</td>
</tr>
<br />

<?php }?>
<tr>
<td width="100%" colspan="4">
<hr size="1" color="red" NOSHADE>
</td>
</tr>

<tr>
<td width="100%" colspan="4">
<font face="verdana" size="1" color="black">
<a href="cart.php"> View Your Shopping Cart &gt;&gt;</a>
</font>
</td>
</tr>
</table>
</body>
</html>

---------------------------------------------------------
//This is "cart.php"
<?php
include("kelly.php");
include("db.php");
?>

<?php
switch($_GET["action"])
{
case "add_item":
{
AddItem($_GET["id"], $_GET["qty"]);
ShowCart();
break;
}
case "update_item":
{
UpdateItem($_GET["id"], $_GET["qty"]);
ShowCart();
break;
}
case "remove_item":
{
RemoveItem($_GET["id"]);
ShowCart();
break;
}
default:
{
ShowCart();
}
}
?>

-----------------------------------------------
//This is "kelly.php"

<?php

function AddItem($itemId, $qty){

$db=new mysqli('localhost','root','','test');
$db->select_db('test');
$query="select count(*) from cart where cookieId = '" . GetCartId() . "' and itemId = $itemId";
$result=$db->query($query);

$row =$result->fetch_assoc();
$numRows = $row[0];
if($numRows == 0)
{
// This item doesn't exist in the users cart,
// we will add it with an insert query
$query="insert into cart(cookieId, itemId, qty) values('" . GetCartId() . "', $itemId, $qty)";
$result=$db->query($query);
}
else
{
// This item already exists in the users cart,
// we will update it instead
UpdateItem($itemId, $qty);
}
}

function UpdateItem($itemId, $qty){
$query="update cart set qty = $qty where cookieId = '" . GetCartId() . "' and itemId = $itemId";
$result=$db->query($query);
}
function RemoveItem($itemId){
$query="delete from cart where cookieId = '" . GetCartId() . "' and itemId = $itemId";
$result=$db->query($query);
}

function ShowCart(){
$db=new mysqli('localhost','root','','test');
$db->select_db('test');

$query="select * from cart inner join items on cart.itemId = items.itemId where cart.cookieId = '" . GetCartId() . "' order by items.itemName asc";
$result=$db->query($query);
while($row = $result->fetch_assoc())
{
// Increment the total cost of all items
$totalCost += ($row["qty"] * $row["itemPrice"]);
?>

<td width="55%" height="25">
<font face="verdana" size="1" color="black">
<?php echo $row["itemName"]; ?>
</font>
</td>
<td width="20%" height="25">
<font face="verdana" size="1" color="black">
$<?php echo number_format($row["itemPrice"], 2, ".", ","); ?>
</font>
</td>
<td width="10%" height="25">
<font face="verdana" size="1" color="black">
<a href="cart.php?action=remove_item&id=<?php echo $row["itemId"]; ?>">Remove</a>
</font>
</td>
</tr>
<br />
<?php } ?>
<tr>
<td width="100%" colspan="4">
<hr size="1" color="red" NOSHADE>
</td>
</tr>
<tr>
<td width="70%" colspan="2">
<font face="verdana" size="1" color="black">
<a href="products.php">&lt;&lt; Keep Shopping</a>
</font>
</td>
<td width="30%" colspan="2">
<font face="verdana" size="2" color="black">
<b>Total: $<?php echo number_format($totalCost, 2, ".", ","); ?></b>
</font>
</td>
</tr>
<?php } ?>

--------------------------------------------------end//