how to display window(Window A), when clicked on a button of another window(Window B)

[aurora]

I hav created two windows, window_A and window_B
I hav button "SHOW" on window_B, when i click on that i want to display window_A.
How can i do that?
I hav files
window_A.h
window_B.h
window_A.cpp
window_B.cpp
main.cpp

where should i write that code?