First as a new root user thanks to root authors to provide a free product 
adapted to Scientific (e.g. Particle Physics) Work!!!
My problem:
I call root in a C++ code. In there I succeed to open a canvas, fill histos 
and draw them in the canvas. Now when I go in the canvas and try to do 
anything interactively with the mouse, the canvas is not refreshed and 
the histograms don't appear any longer.
How to solve that?
I am working with root
   Version   1.01/04       4 June 1997 
on HP-UX 9.x 
thanks in advance for help.
                             Pascal Perrodo.