using System;

​

public class Program

{

    static private ulong fact(ulong a)

    {

        ulong factorial = 1;

        ulong i = 1;

        do

        {

            factorial = factorial * i;

            i++;

        }

        while (i <= a);

        return factorial;

    }

​

    static private double DectoPer(double a)

    {

        return a * 100;

    }

​

    static private double PertoDec(double a)

    {

        return a / 100;

    }

​

    static private ulong nPR(ulong a, ulong b)

    {

        ulong afact = fact(a);

        ulong abfact = fact(a - b);

        return afact / abfact;

    }

​

    static private ulong nCR(ulong x, ulong y)

    {

        ulong xfact = fact(x);

        ulong sub = x - y;

        ulong xyfact = fact(sub);

        ulong yfact = fact(y);

        return xfact / xyfact * yfact;

    }

​

    static private double mean(double a, double b, double c, double d, double e)

    {

        double avg = (a + b + c + d + e) / 5;

        return avg;

    }

​

    public static void Main()

    {

        string repeat = "h";

        while (repeat != "q" && repeat != "Q")

        {

            start:

                Console.Clear();

            Console.WriteLine("Enter 1 for factorial calculator, enter  2 to convert from decimal to percent, enter 3 to convert from percent to decimal, enter 4 to calculate the Permutation, enter 5 to calculate the combination, enter 6 for mean.");

            string choice = Console.ReadLine();

            if (choice == "1")

            {

                Console.Clear();

                Console.WriteLine("What number would you like to calculate the factorial of?");

                ulong fac = ulong.Parse(Console.ReadLine());

                ulong fa = fact(fac);

                Console.WriteLine("The factorial of " + fac + " is " + fa + ".");

            }

            else if (choice == "2")

            {

                Console.Clear();

                Console.WriteLine("Please enter a decimal");

                double dec = double.Parse(Console.ReadLine());

                double per = DectoPer(dec);

                Console.WriteLine("The decimal " + dec + " would convert to a percentage of " + per + "%.");

            }

            else if (choice == "3")

            {

                Console.Clear();

                Console.WriteLine("Please enter a percentage");

                double pe = double.Parse(Console.ReadLine());

                double de = PertoDec(pe);

                Console.WriteLine("The percentage " + pe + "% would convert to a decimal of " + de + ".");

            }

            else if (choice == "4")

            {

                Console.Clear();

                Console.WriteLine("Please enter the total number of items.");

                ulong it = ulong.Parse(Console.ReadLine());

                Console.WriteLine("Please enter the number you would like them to be arranged");

                ulong arr = ulong.Parse(Console.ReadLine());

                ulong perm = nPR(it, arr);

                Console.WriteLine("The Permutation of a total number of items " + it + " and the number of items arrangered " + arr + " is " + perm + ".");

            }

            else if (choice == "5")

            {

                Console.Clear();

                Console.WriteLine("Pleae enter How many items do you have?");

                ulong i = ulong.Parse(Console.ReadLine());

                Console.WriteLine("Pleae enter How many items you want to choose?");

                ulong choose = ulong.Parse(Console.ReadLine());

                ulong comp = nCR(i, choose);

                Console.WriteLine("The Combination of a total number of items " + i + " and the number of items chosen " + choose + " is " + comp + ".");

            }

            else if (choice == "6")

            {

                Console.Clear();

                Console.WriteLine("Please enter the first number");

                double num1 = double.Parse(Console.ReadLine());

                Console.WriteLine("Please enter the second number");

                double num2 = double.Parse(Console.ReadLine());

                Console.WriteLine("Please enter the third number");

                double num3 = double.Parse(Console.ReadLine());

                Console.WriteLine("Please enter the fourth number");

                double num4 = double.Parse(Console.ReadLine());

                Console.WriteLine("Please enter the fifth number");

                double num5 = double.Parse(Console.ReadLine());

                double m = mean(num1, num2, num3, num4, num5);

                Console.Clear();

                Console.WriteLine("The mean of the numbers " + num1 + ", " + num2 + ", " + num3 + ", " + num4 + ", " + num5 + " is " + m);

            }

            else

            {

                Console.WriteLine("Please enter a vaild number. Press enter to continue");

                Console.ReadLine();

                goto start;

            }

​

            Console.WriteLine("Please enter q to quit or any other key to continue.");

            repeat = Console.ReadLine();

        }

    }

}