yield return

public class DaysOfTheWeek : System.Collections.IEnumerable
{
    string[] m_Days = { "Sun", "Mon", "Tue", "Wed", "Thr", "Fri", "Sat" };

    public System.Collections.IEnumerator GetEnumerator()
    {
        for (int i = 0; i < m_Days.Length; i++)
        {
            yield return m_Days[i];
        }
    }
}

class TestDaysOfTheWeek
{
    static void Main()
    {
        // Create an instance of the collection class
        DaysOfTheWeek week = new DaysOfTheWeek();

        // Iterate with foreach
        foreach (string day in week)
        {
            System.Console.Write(day + " ");
        }
    }
}

******************************************

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;

namespace yeildTST
{
    public class List
    {
        public static IEnumerable Power(int number)
        {
            while (number< 100)
            {
                number = number + number;
                yield return number;
            }
        }

        static void Main()
        {
            foreach (int i in Power(1))
            {
                Console.Write("{0} ", i);
            }

            Console.ReadLine();
        }
}