code explanation and a question about signals

["Tralfas D" <tralfas gmail com>]

i was reading over the source for the range widget example and i was wonder why this was there 

#ifndef GTKMM_DISABLE_DEPRECATED
Gtk::OptionMenu m_OptionMenu;
#endif //GTKMM_DISABLE_DEPRECATED

why is it in ifndef? i looked up some stuff about it im guessing it means it is showing newer code for option menus and disabling old obselete code. 

and then another random thought i had was about signals. i wanted to make two buttons do different things when clicked but i dont know how to connect them to a on_button_clicked. can there be multiple on_button_clicked signals or only one and then you have to use a new signal.

also thanks for the book murray.