if ( ! empty( $_GET['affiliate'] ) ) {
    setcookie( 'is_aff', $_GET['affiliate'], time() + ( 30 * DAY_IN_SECONDS ), COOKIEPATH, COOKIE_DOMAIN );
}

if ( ! empty( $_GET['aff'] ) ) {
    setcookie( 'is_affcode', $_GET['aff'], time() + ( 30 * DAY_IN_SECONDS ), COOKIEPATH, COOKIE_DOMAIN );
}