如何获得问号后的PHP值回声

I need the value of add_cart after the question mark?

echo "<a  href='index.php?add_cart=<?php echo $pro_id; ?>' name='shto' class='sp' '><button style='float:right;'>Cart</button></a>  ";

Something like this

$value = add_cart;

use $_GET

example:

$value = $_GET['add_cart'];

Try something like:

$value = 4544545; //the item number
echo "<a  href='index.php?add_cart=$value' name='shto' class='sp' '><button style='float:right;'>Cart</button></a>  ";

And in index.php you get the value with:

$valueFromAddCart = $_GET['add_cart'];