Factorial

- [Instructor] According to Wikipedia,…the factorial of a non-negative number, n,…is the product of all positive integers…less than or equal to n.…So, the factorial of five is equal to five times four…times three times two times one, or 120.…Let's see how to implement this…using template metaprogramming.…We have our include iostream, include vector,…using namespace std.…We have some commented out code…that's going to print the results,…but before we get to that let's first…write a regular C++ function,…and it's going to be recursive, to do factorials…so we get an idea of what it looks like…with something that's more familiar to us.…

We're going to say factorial const int input…const int sum, and we're going to get…sum a default value of one.…So if no sum is called it has a value of one…because one times anything is the number.…Then we're going to say if input is greater than one…we're going to return, and we're going to do a recursive call.…So we're going to call factorial,…and we're going to say input minus one.…