Definitions

   The factorial of   0   (zero)   is defined as being   1   (unity).
   The   Factorial Function   of a positive integer,    n,    is defined as the product of the sequence:
                 n,   n-1,   n-2,   ...   1 



Task

Write a function to return the factorial of a number.

Solutions can be iterative or recursive.

Support for trapping negative    n    errors is optional.



Related task

   Primorial numbers


using System;
 
class Program
{
    static int Factorial(int number)
    {
        if(number < 0) 
            throw new ArgumentOutOfRangeException(nameof(number), number, "Must be zero or a positive number.");
 
        var accumulator = 1;
        for (var factor = 1; factor <= number; factor++)
        {
            accumulator *= factor;
        }
        return accumulator;
    }
 
    static void Main()
    {
        Console.WriteLine(Factorial(10));
    }
}