using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        string[] stringArray = { "abc", "def", "ghi" };

​

        // 2 separate methods       

        IEnumerable<string> q1 = stringArray.ConvertCollectionToUpperCase();

        IEnumerable<string> q2 = q1.AppendString("!!!");

        // 2 methods chained together

        IEnumerable<string> q3 = stringArray.ConvertCollectionToUpperCase().AppendString("!!!");

        foreach (string str in q3)

        {

            Console.WriteLine("Main: str >{0}<", str);

            Console.WriteLine();

        }

        Console.ReadLine();

    }

}

    public static class LocalExtensions

    {

        public static IEnumerable<string>

            ConvertCollectionToUpperCase(this IEnumerable<string> source)

        {

            foreach (string str in source)

            {

                Console.WriteLine("ToUpper: source >{0}<", str);

                yield return str.ToUpper();

            }

        }

        public static IEnumerable<string>

            AppendString(this IEnumerable<string> source, string stringToAppend)

        {

            foreach (string str in source)

            {

                Console.WriteLine("AppendString: source >{0}<", str);

                yield return str + stringToAppend;

            }

        }

    }

​

​