Rx_FizzBuzz.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;

namespace ConsoleApplication4
{
    class Program
    {
        static void Main(string[] args)
        {
            var source = Observable.Range(1, 100);

            var consoleObserver = Observer.Create<string>(Console.WriteLine);
            var debugObserver = Observer.Create<string>(n=>Debug.WriteLine(n));

            var connected = source.FizzBuzzLogic().Publish();
            connected.Subscribe(consoleObserver);
            connected.Subscribe(debugObserver);
            using(connected.Connect())
            {
                Console.ReadLine();
            }
        }
    }

    public static class FizzBuzzExtentions
    {
        public static IObservable<string> FizzBuzzLogic(this IObservable<int> source)
        {
            return source.Select(number =>
            {
                if (IsFizzBuzz(number))
                    return "FizzBuzz";
                else if (IsFizz(number))
                    return "Fizz";
                else if (IsBuzz(number))
                    return "Buzz";
                return number.ToString();
            });
        }


        public static bool IsBuzz(int number)
        {
            return (number % 5 == 0);
        }
        public static bool IsFizz(int number)
        {
            return (number % 3 == 0);
        }
        public static bool IsFizzBuzz(int number)
        {
            return ((number % 5 == 0) && (number % 3 == 0));
        }
    }
}