Calculating n!

Exercise Type: Implementation

Instructions

The factorial of a natural number (n!) is defined as such:

0! = 1
1! = 1
2! = 1 * 2
3! = 1 * 2 * 3
n! = 1 * 2 * 3 * ... * n

Part 1 - backbone

Write a bit of code using a while() loop to calculate n!! Calculate 12!

Part 2 - function

Make the code you produced in Part 1 a function that has the following characteristics:

name:	Fact()
argument(s):	n (numeric)
return	numeric, the factorial of n

Part 3 - defense

Make a list of cases when the function has no meaning. Make sure that the function returns missing values when this is the case!