Global variables in If statements - PHP

Question

I was looking for examples of using global variables in IF statements, found few but I still cannot make my code to work. I'm declaring variable globally and tried to assign values inside if statement and later to check if the variable contains certain value. When I echo the variable, it is not updated with the value I'm assigning within if statement. My code:

<?php
    $cart = 0;

    if ((isset($_POST["b1"]) && $_POST["b1"] === "Add to cart")) { 
        global $cart; 
        $cart = 1;
        $query_HOD = "INSERT INTO orderLine 
                      (LINE_ID, PRODUCT_ID, QUANTITY, AMOUNT)
                      VALUES 
                      ('LINE1', '00001', 1, 6.99)";

        if ((isset($_POST["add"]) && $_POST["add"] === "Go to cart")) {
            echo $cart;
            if($cart === 1) {
                echo $cart;
                header("location:cart.php");
            }
            else {
                echo "<script type='text/javascript'>alert('Your cart is empty');</script>";
            }
        }
?>

isset methods are working fine, I have checked those, it seems to me that the variable is updated but only locally and does not affect the global variable.

Answer 1

Perhaps you're expecting a global variable to mean a variable that persists between requests; that's not what they are. A global is just a variable that is accessible anywhere in your code for that request . As @user1231958 stated, you'll want a cookie or some other way to persist state.