Emacs : abbrev mode

[geenux]

Hello.
I'm a new emacs user and I have problems whith my emacs configuration.
I'm trying to call a skeleton named "for-skel" when I write "_for" in a buffer.
I did the skeleton:

(define-skeleton for-skel
"Insert a for loop"
nil
"for(int i=0;i<" _ ";i++)\n{\n\n}\n")

It work when I call it with M-x for-skel.
I've read a lot of things about abbrev-mode but all I tried failled...

thanks a lot.