using System;

​

public class Program

{

    public static void Main()

    {

        PhoneCustomer phoneCust = new PhoneCustomer();

        phoneCust.CustomerID = 123;

        phoneCust.FirstName = "Joe";

        phoneCust.LastName = "Smith";

        Console.WriteLine("{0} {1} {2}", phoneCust.CustomerID, phoneCust.FirstName, phoneCust.LastName);

        Console.WriteLine(phoneCust.UpperCaseLastName("Mr."));

    }

    class PhoneCustomer

    {

        public const string DayOfSendingBill = "Monday";

        public int CustomerID;

        public string FirstName;

        public string LastName;

​

        public                  // method modifier 

            string              // type of the return value

            UpperCaseLastName   // name of the method

            (string prefix)     // list of input arguments

        {                       // body of the method

            return string.Format("{0} {1}", prefix, this.LastName.ToUpper());

        }

    }

}