Advertising in a product category?

Question

PHP

Good afternoon, please tell me how they put ads in the list of goods that most likely goes through foreach?

Answer 1

foreach ($goods as $index => $good) {
    if ($index % 3 == 0) {
        print_ad();
    }
    print_cart($good);
}

Answer 2

There is a counter in the loop, and the condition after such a number to show ads, nothing complicated
. How to make a counter in foreach?