Changing horizontal window split default to vertical?

[Stephan Kuhagen]

My dear Emacs Wizards!

Although I'm using the mighty Emacs for nearly 16 years now, I encountered a
new problem with its behaviour (of course, this is not the guilt of Emacs,
but of the now mainstream 16:10 displays): When I start Emacs with two
files (often a *cpp, and its *h), Emacs opens the two buffers in two
windows, one above and one below a horizontal splitter. I like to have them
left and right from a vertical splitter. Is there a switch or some magic
lisp setting, I can add to my .emacs to make Emacs do this?

Regards and thanks
Stephan