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 ulong nPr(ulong n, ulong r)

    {

        return fact(n) / fact(n - r);

    }

​

    static private ulong nCr(ulong n, ulong r)

    {

        return fact(n) / fact(n - r) * fact(r);

    }

    static private decimal PtD(decimal p)

    {

        decimal d = p/100;

        return d;

    }

    static private decimal DtP(decimal d)

    {

        decimal p = d * 100;

        return p;

    }

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

    {

        decimal m = a+b+c+d+e;

        decimal me = m/5;

        return me;

    }

    public static void Main()

    {

        string restart = "Chicken Nugget";

        while (restart != "q")

        {

            Console.WriteLine("Stat Calculator.");

            Console.WriteLine("Press 1 for factorial, 2 for permuations, 3 for combination.");

            Console.WriteLine("4 for Percent to Decimal, 5 for Decimal to Percent, 6 for mean.");

            string choice = Console.ReadLine();

            if (choice == "1")

            {

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

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

                Console.WriteLine(input + "! = " + fact(input));

            }

            else if (choice == "2")

            {

                Console.WriteLine("How many objects do you have in total?");

                ulong input1 = ulong.Parse(Console.ReadLine());

                Console.WriteLine("How many objects do you want to arrange?");

                ulong input2 = ulong.Parse(Console.ReadLine());

                Console.WriteLine(input1 + "P" + input2 + " = " + nPr(input1, input2));

            }

            else if (choice == "3")

            {

                Console.WriteLine("Press q to quit or anything else to continue the program.");

                restart = Console.ReadLine();

            }

            else if (choice == "4")

            {

                Console.WriteLine("What is your percent that you want as a decimal? (No need to add %)");

                ulong input3 = ulong.Parse(Console.ReadLine());

                Console.WriteLine(input3 + " as a decimal is: " + PtD(input3));

            }

            else if(choice == "5")

            {

                Console.WriteLine("What is your decimal that you want to be a percent?");

                decimal input4 = decimal.Parse(Console.ReadLine());

                Console.WriteLine(input4 + " as a percent is: " + DtP(input4) + "%");

            }

            else if (choice == "6")

            {

                Console.WriteLine("Please enter the 5 numbers you want the mean of");

                decimal input5 = decimal.Parse(Console.ReadLine());

                decimal input6 = decimal.Parse(Console.ReadLine());

                decimal input7 = decimal.Parse(Console.ReadLine());

                decimal input8 = decimal.Parse(Console.ReadLine());

                decimal input9 = decimal.Parse(Console.ReadLine());

                Console.WriteLine("The mean of all 5 numbers is: " + mean(input5, input6, input7, input8, input9));

            }

            Console.WriteLine(" ");

            Console.WriteLine("Type 'q' to quit, type anything else to restart");

            restart = Console.ReadLine();

            Console.Clear();

        }

    }

}