Normal way to visualize the structure of a program source-code?

[Pooya <Input Pooya de>]

Dear Dia-users,

For my thesis, I would like to visualize the structure of my developed program. Before starting to mention 
some of the most important methods, I´d like to give the reader an overview about the system.

But I don´t know, what the normal way to put this into practice would be.

What would you recommend or is there a "normals" way? And how would it be done in Dia?

Would it even be visualized, e.g. by a graph?

thanks in advance!