This program is useful for learning the basics of the function and action.

Arithmetics with Func & Action

using System;
using System.Linq;

namespace AppliedArithmetics
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] input = Console.ReadLine()
                .Split()
                .Select(int.Parse)
                .ToArray();

            string command = Console.ReadLine();

            Func<int, int> add = x => x += 1;
            Func<int, int> multiply = x => x *= 2;
            Func<int, int> subtract = x => x -= 1;
            Action<int[]> print = x => Console.WriteLine(string.Join(" ", x));

            while (command != "end")
            {
                switch (command)
                {
                    // We have to change the collection each time we have to do a function on it
                    // Therefore we use the input = input.Select ..., otherwise input.Select alone doesnt work!
                    case "add":
                        input = input.Select(add).ToArray();
                        break;
                    case "multiply":
                        input = input.Select(multiply).ToArray();
                        break;
                    case "subtract":
                        input = input.Select(subtract).ToArray();
                        break;
                    case "print":
                        print(input);
                        break;
                    default:
                        break;
                }
                command = Console.ReadLine();
            }
        }
    }
}