Not getting Get Variables form Url

[eluser]kalpesh[/eluser]
Hi,
I try to get variables from Url which like as follow

http://localhost/Site/index.php/Offer?City=NewYork&Id=1

and try to print that variables

Code:

$data['city']=$_GET['City'];
  $data['pid']=$_GET['Id'];
  echo $data['pid'];
   echo $data['city'];

But I get this error:

Code:

A PHP Error was encountered
Severity: Notice

Message: Undefined index: City

Filename: controllers/Offer.php

Line Number: 15

A PHP Error was encountered
Severity: Notice

Message: Undefined index: Id

Filename: controllers/Offer.php

Line Number: 16

I am just new in CI.
So please Help me.
Thanks.