>I am not sure but i think rebuilding clustered index will not rebuild non-clustered automatically..
You're right on this. Please see Books Online.
"Rebuilding a clustered index does not rebuild associated nonclustered indexes unless the keyword ALL is specified."
http://msdn.microsoft.com/en-us/library/ms188388.aspx
>If clustered index need to be rebuild then don't we need to rebuild all non-clusted index on same table
As I understand it we only need to rebuild non clustered indexes if they are fragmented.
Ola Hallengren