using System;

​

public class Program

{

    static private double fact(double a)

    {

        double factorial = 1;

        double i = 1;

        do

        {

            factorial = factorial * i;

            i++;

        }

        while (i <= a);

        return factorial;

    }

​

    static private double mean(double a, double b)

    {

        return a / b;

    }

​

    static private double nPr(double n, double r)

    {

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

    }

​

    static private double pd(double a)

    {

        return a / 100;

    }

​

    static private double dp(double a)

    {

        return a * 100;

    }

​

    public static void Main()

    {

        string restart = "Chicken Nugget";

        while (restart != "q")

        {

            Console.Clear();

            Console.WriteLine("Press 1 for factorial. 2 for permuations. 3 for percent to decimal. 4 for decimal to percent. 5 for mean");

            string choice = Console.ReadLine();

            if (choice == "1")

            {

                Console.Clear();

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

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

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

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

                restart = Console.ReadLine();

            }

            else if (choice == "2")

            {

                Console.Clear();

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

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

                Console.WriteLine("How many objects would you like to arrange?");

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

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

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

                restart = Console.ReadLine();

            }

            else if (choice == "3")

            {

                Console.Clear();

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

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

                Console.WriteLine("Your percentage into a decimal is " + pd(pdinput));

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

                restart = Console.ReadLine();

            }

            else if (choice == "4")

            {

                Console.Clear();

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

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

                Console.WriteLine("Your decimal into a percentage is " + dp(dpinput) + "%");

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

                restart = Console.ReadLine();

            }

            else if (choice == "5")

            {

                Console.Clear();

                Console.WriteLine("How many numbers would you like to put in");

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

                double e;

                double i = 1;

                double meann = 0;

                do

                {

                    Console.WriteLine("Enter a number");

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

                    meann += e;

                    i++;

                }

                while (i <= u);

                Console.WriteLine("Your mean is " + mean(meann, u));

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

                restart = Console.ReadLine();

            }

            else{

            Console.WriteLine("What you inputed is not valid, please enter something else.");

            restart = Console.ReadLine();

            }

        }

    }

}