As n can be upto 100, you cannot store 100! in int variable. You need use array or strings to store the answers. You can use link.
can you guide me how to get star in codechef\
Participate in rated contests and you will get stars according to your performance.
can suggest me some?
Participate in Long Challenge( 10 day event), or short contests like Lunchtime, Cook-Off or CC Starters
sorry i am taking your time but can you suggest how to prepare for that.
Learn basic Data Structures and Algorithms. Learn about time constraints and complexity of your code. See if your approach can fit in the given constraints or not. Try past problems, you will get an idea where you need to focus on.
cool, thank you