Automatically add products to cart when visit page

added_to_cart.php

add_action( 'template_redirect', 'add_product_to_cart' );
function add_product_to_cart() {
    if ( ! is_admin() ) {
        $articles = array(64);
        $found = false;

        // check if product already in cart
        if ( sizeof( WC()->cart->get_cart() ) > 0 ) {
            foreach ( WC()->cart->get_cart() as $cart_item_key => $values ) {
                $_product = $values['data'];

                if (($key = array_search($_product->id, $articles)) !== false)
                    unset($articles[$key]);
            }

            // if product not found, add it
            if ( count($articles) > 0 ) {
                foreach ($articles as $article) {
                    WC()->cart->add_to_cart($article);
                }
            }
        } else {
            // if no products in cart, add it
            foreach ($articles as $article) {
                WC()->cart->add_to_cart( $article );
            }
        }
    }
}