How to tell emacs is running under term or windows?

[Corsair]

Hi everybody!  I have a setting concerning the frame size in my
.emacs:

    (set-frame-size (car (frame-list)) 100 45)

However, when started in a term, emacs will display an error:

    X windows are not in use or not initialized.

So the `set-frame-size' function should be called only when running
under windows system.  The problem is, how to tell that emacs is
running under a term or a windows system, or, to be simple, how to
tell if the `-nw' option is issued when starting emacs?

Thanks.

-- 
Fear is the path to the Darkside.
Fear leads to anger,
Anger leads to hate,
Hate leads to suffering.