Why is $x a undefined variable for switch statement?
===

It is display $x as undefined. What is wrong with my switch statement?

    http://localhost/add.php?price_error=1

    switch(isset($_GET['price_error']) && $_GET['price_error'] == $x){
    		
    			case 1:
    				echo '<span class="error_msg">Discount price cannot be greater than original price</span><br/>';
    				break;
    		
    			case 2:
    				echo '<span class="error_msg">Discount cannot be less than 30% of original price</span><br/>';
    				break;
    			
    			case 3:
    				echo '<span class="error_msg">Discount price and original price cannot be greater than $30000 HKD</span><br/>';
    				break;
    		
    			default: 
    				false;
    				break;
    		}