comparing random number?

how do I compare a random number or is it possible?

the scenario is I have a function using $_GET method and it is visible on URL. so any user can store this link to use it later. this is a PHP game so any one can cheat the game very easily. so what will be the best w开发者_开发百科ork around to prevent the same? I was thinking about a random number to use each time when user calls the link and compare it so user cant use the same link to access the game later.

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Do you have access to a database for the site? If so, you can log the user's IP address and the random number and perform a check each time the page is accessed.

If not, you can store the numbers in the $_SESSION variable and check to see if it was already used:

session_start();
if(!isset($_SESSION['codes'])) $_SESSION['codes'] = array();

if(in_array($_GET['code'], $_SESSION['codes']) {
   // code to execute if this code was already used by the user
} else {
  $_SESSION['codes'][] = $_GET['code'];
}