Novahq.net Forum - C#: Factorials, Combinations, and Permutations Class

Code:
    // Class Name: Basic Counting Theory

    // Author: Bullet Magnet

    // Version: 1.0

    // Copyright: 2010 Bullet Magnet



    public class BasicCountingTheory

    {

        #region CaclulateFactorial

        // Factorial method

        // Accepts one parameter of type long

        public static long CalculateFactorial(long x)

        {

            long fact = 1; 

            long i = 1; // Lowest possible term in a factorial



            // Loop through each subsequent terms of x

            while (i <= x)

            {

                fact = fact * i; 

                i++;

            }

            return fact;

        }

        #endregion



        #region Permutation

        // This method calculates permutations, in which the order of a selection matters

        // Accepts 2 parameters for use in the main formula

        public static long Permutation(long a, long b)  

        {

            // Variable used to store result

            long result;

            // Main formula: (n!/((n-r)!))

            result = ((CalculateFactorial(a))/(CalculateFactorial(a-b)));



            return result;

        }

        #endregion



        #region Combination(long a, long b)

        // This method calclulates combinations, in which order of a selection doesn't matter

        public static long Combination(long a, long b)

        {

            // Variable used to store result

            long result;

            // Main formula: (n!/((n-r)!)r!)

            result = ((CalculateFactorial(a)) / ((CalculateFactorial(a - b) * CalculateFactorial(b))));



            return result;

        }

        #endregion

    }