Novice problem

I’m new in using ROOT, and beginner in object-oriented programming. But I can recognize a good program, and ROOT I think the best scientific implementation of OOP ever. I plan to use it in my engineering career. But apparently I’m the only one of Argentina to try to use it. Anyway, my problem is very basic: it refers to the use of Vertical Slider:


At that point the interpreter displays the following error:

Any help?
(I have included TGSlider.h at the beginning of the code)


For a TGVSlider, the signal is PositionChanged(Int_t pos), so you should call:

Cheers, Bertrand.