This program calculates the factorial of an integer:

using System;

public class Program
{
    static long Factorial(long number)
    {
        long p = 1;

        if (number > 1)
            for (long i = 2; i <= number; i++)
                p *= i;
        return p;
    }

    static int Main(string[] args)
    {
	Console.WriteLine("The factorial of 5 is: {0}\n", Factorial(5));

        return 0;
    }
}

The factorial of 5 is: 120

Press any key to continue . . .