Undefined Variable

Hello Mr. /Mrs./Ms. Webmaster, I'm Eben Ezer Sinaga from Indonesia, I'm sorry to bother you.. I have html link like this : <a href=http://localhost/test/index.php?page=1&experience=0>My Text</a> and my php is : $experience = $_GET['experience']; but I have found notice says: *Notice*: Undefined index: experience in C:\xampp\htdocs\test\index.php on line 4 I conclude that if I set my 'experience' value to *0* it means my $_GET['experience'] come to undefined variable! Is it true??? Can you give me an explanation how to get *0 *value from my url, I desperately need it to run my program?? Thanks Mr. /Mrs./Ms Webmaster for your attention... *sorry I'm not good in English....