HW#8
 Due Friday, 10/5/7, hw8.cpp
 Implement a factorial function using for loops. 

Factorials are only defined on positive integers and result in
positive integers. It is the product of all non-negative integers less
than the argument. Examples follow.

0! = 1
1! = 1
2! = 2 * 1 = 1 * 2 = 2
3! = 3 * 2 * 1    =  1 * 2 * 3    = 6
.
.
.
5! = 120
6! = 720
7! = 5040
.
.
.
11! = 39916800