using System;

​

public class Program

{

    static private ulong fact(ulong a) //Method to calculate factorial 

    {

        ulong factorial = 1;

        ulong i = 1;

        do

        {

            factorial = factorial * i;

            i++;

        }

        while (i <= a);

        return factorial;

    }

​

    static private double DectoPer(double a) //decimal to percent

    {

        return a * 100;

    }

​

    static private double PertoDec(double a) //percent to decimal

    {

        return a / 100;

    }

​

    //Method for permutations

    //Method for combinations

    public static void Main()

    {

        Console.WriteLine("Please choose which option you would like to calculate");

        Console.WriteLine("Press 1 for factorial, 2 to convert from decimal to percent, 3 to convert from percent to decimal.");

        string choice = Console.ReadLine();

        if (choice == "1")

        {

            Console.WriteLine("what number do you want the factorial of?");

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

            Console.WriteLine("the Factorial of " + number+ " is " + factorial);

        //ask the user to enter what they want the factorial of stored as a ulong

        //Call the factorial method and output in a complete sentence

        }

        else if (choice == "2")

        { //ask the user to enter a decimal

        //Call the dectoper method and output in a complete sentence

        }

        else if (choice == "3")

        { //ask the user to enter a percent

        //Call the pertodec method and output in a complete sentence

        }

        else

        { //tell the user to enter a valid choice

        //send them back to the beginning using a goto

        }

    }

}