Exclude certain post types from the search results

How do I exclude certain post types from the search results?
I have put this code at function.php to exclude the page from the search results but it doesn’t work:

/*START EXCLUDE PAGE FROM SEARCH RESULT*/
function remove_pages_from_search() {
    global $wp_post_types;
    $wp_post_types['page']->exclude_from_search = true;
}
add_action('init', 'remove_pages_from_search');
/*END EXCLUDE PAGE FROM SEARCH RESULT*/

Thank you