robots.txt and add-on domain

hi guys
i bought a domian name an added-on to my server in www (public html) directory.i had a forum in this directory and after adding a add-on domain i can see a folder named as domain name
if i want to prevent search engines to show this directory like sub.domian.com in their index, should i disallow subdomain folder in robot.txt which exist in main directory?
if so,can i still use robots.txt in subdomian directory to have crawling this directory with spiders with new domain name?
sorry for bad english

 

bump
i need answer :d
plz help guys
thanks

 

Just put robots.txt in the addon domain folder,

 

tnx for reply
yes i will do that
but in robots.txt in main directory should i disallow the addon folder?

 

NO, just think of the addon folder as its own website and put the disallow in that folder