using System;

public class Program

{

     public static void Main()

        {       

            start: 

            Console.Clear(); 

            Console.WriteLine("Please Choose an option from the menu!");

            Console.WriteLine("If you would like to calculate n!, please press 1. ");

            Console.WriteLine("If you would like to calculate nPr, please press 2. ");

            Console.WriteLine("If you would like to calculate nCr, please press 3. ");

          int choice = int.Parse(Console.ReadLine());

            if (choice == 1)

                 {  Console.Clear();

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

                    long ans = long.Parse(Console.ReadLine());

                    Console.WriteLine("The Factorial of " + ans + "= " + Fact(ans));

                 }

            else if (choice == 2)

                {   Console.Clear();

                    Console.WriteLine("Please enter your first value");

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

                    Console.WriteLine("Please enter your second value");

                    long num2 = int.Parse(Console.ReadLine());

                    Console.WriteLine(num1+ "P"  + num2 + "= " + nPr(num1, num2));

                }

         else if(choice == 3)

         {

             Console.WriteLine("What is the total amount of objects being cosen from?");

            long comb1 = long.Parse(Console.ReadLine());

            Console.WriteLine("How many objects are being chosen?");

            long comb2 = long.Parse(Console.ReadLine());

            Console.WriteLine("There are " + nCr(comb1, comb2) + " possible outcomes");

         }

            else

            {Console.WriteLine("Please Enter a Valid Choice");

            goto start;

            }

        Console.ReadLine();

        }

​

​

        static public long Fact(long a)

            { long fact = 1;

              for(long i = 1; i <= a; i++)

                    {fact *= i;}

              return fact;

            }

        static public long nPr(long n, long r)

            {   long perm = Fact(n) / Fact(n - r);

             return perm;

            }

        static private long nCr(long x, long y)

    {

        long nCr = (Fact(x) / (Fact(x - y) * Fact(y)));

        return nCr;

    }

​

}

​

​

​