automatic rank assigning

is thr any way to give a rank to a new member automatically

I have a new user rank set, which all new members default to as they register.

Simply go to admin>users & groups>rank administration (which is were you do your rank setting anyway) and make a new rank with a '0' minimum post count.

it will work?

It works for my site, which is why I answered your question.

when you make the rank, be sure to set it to NOT SPECIAL RANK or this will not work