using System;

using System.Collections.Generic;       

​

public class Program

{

    public static void Main()

    {

        foreach (int f in fib(6))

        {

            Console.Write(f + " ");

        }

        Console.WriteLine("\r\nFibonocci for Even Numbers");

        foreach (int f in EvenNoOnly(fib(6)))

        {

            Console.Write(f + " ");

        }

​

    }

    public static IEnumerable<int> fib(int fibcount)

    {

        for (int i=0,prefib=1,currfib=1; i<fibcount;i++)

        {

            yield return prefib;

            int newfib=prefib+currfib;

            prefib=currfib;

            currfib=newfib;

        }

    }

    public static IEnumerable<int> EvenNoOnly(IEnumerable<int> n)

    {

        foreach(int i in n)

        {

            if( (i%2) ==0)

                yield return i;

        }

    }

}