How can assign large numbers in c++

Answer 1

If you already have a boost dependency (which many people these days do), you can use the boost multi-precision library. In fact, it already has an example of a factorial program that can support output up to 128 bits, though extending it further is pretty trivial.

Answer 2

Yes

Answer 3

long long int

Answer 4

is it available for number with 100 digits

Answer 5

long double.