declaring global variables

Define it inside the dialog source file and declare it as extern in all the other source files allowed to access it, e.g.

// MyDialog.cpp
int g_counter = 0; // variable definition (and initialization, here)

// MyOtherDialog.cpp
extern int g_counter;
//...
g_counter = 5; // access global variable defined in MyDialog.cpp

:-)

If the need is a global variable available to all the dialogs in your app... I'd go for a variable declared in your app class... then you'll be able to get access to it from everywhere...

I'd use getters and setters in order to acces to it...

HTH! :thumbsup:

I suggest not to use global variables because they just bring too many problems:
Global Variables Are Bad[^]

Niklas's answer is probably the best choice.