// WorkItem implicitly inherits from the Object class. 
public class WorkItem
{
    // Static field currentID stores the job ID of the last WorkItem that 
    // has been created. 
    private static int currentID;

    //Properties. 
    protected int ID { get; set; }
    protected string Title { get; set; }
    protected string Description { get; set; }
    protected TimeSpan jobLength { get; set; }

    // Default constructor. If a derived class does not invoke a base- 
    // class constructor explicitly, the default constructor is called 
    // implicitly.  
    public WorkItem()
    {
        ID = 0;
        Title = "Default title";
        Description = "Default description.";
        jobLength = new TimeSpan();
    }

    // Instance constructor that has three parameters. 
    public WorkItem(string title, string desc, TimeSpan joblen)
    {
        this.ID = GetNextID();
        this.Title = title;
        this.Description = desc;
        this.jobLength = joblen;
    }

    // Static constructor to initialize the static member, currentID. This 
    // constructor is called one time, automatically, before any instance 
    // of WorkItem or ChangeRequest is created, or currentID is referenced. 
    static WorkItem()
    {
        currentID = 0;
    }


    protected int GetNextID()
    {
        // currentID is a static field. It is incremented each time a new 
        // instance of WorkItem is created. 
        return ++currentID;
    }

    // Method Update enables you to update the title and job length of an 
    // existing WorkItem object. 
    public void Update(string title, TimeSpan joblen)
    {
        this.Title = title;
        this.jobLength = joblen;
    }

    // Virtual method override of the ToString method that is inherited 
    // from System.Object. 
    public override string ToString()
    {
        return String.Format("{0} - {1}", this.ID, this.Title);
    }
}

// ChangeRequest derives from WorkItem and adds a property (originalItemID)  
// and two constructors. 
public class ChangeRequest : WorkItem
{
    protected int originalItemID { get; set; }

    // Constructors. Because neither constructor calls a base-class  
    // constructor explicitly, the default constructor in the base class 
    // is called implicitly. The base class must contain a default  
    // constructor. 

    // Default constructor for the derived class. 
    public ChangeRequest() { }

    // Instance constructor that has four parameters. 
    public ChangeRequest(string title, string desc, TimeSpan jobLen,
                         int originalID)
    {
        // The following properties and the GetNexID method are inherited  
        // from WorkItem. 
        this.ID = GetNextID();
        this.Title = title;
        this.Description = desc;
        this.jobLength = jobLen;

        // Property originalItemId is a member of ChangeRequest, but not  
        // of WorkItem. 
        this.originalItemID = originalID;
    }
}

class Program
{
    static void Main()
    {
        // Create an instance of WorkItem by using the constructor in the  
        // base class that takes three arguments.
        WorkItem item = new WorkItem("Fix Bugs",
                                     "Fix all bugs in my code branch",
                                     new TimeSpan(3, 4, 0, 0));

        // Create an instance of ChangeRequest by using the constructor in 
        // the derived class that takes four arguments.
        ChangeRequest change = new ChangeRequest("Change Base Class Design",
                                                 "Add members to the class",
                                                 new TimeSpan(4, 0, 0),
                                                 1);

        // Use the ToString method defined in WorkItem.
        Console.WriteLine(item.ToString());

        // Use the inherited Update method to change the title of the  
        // ChangeRequest object.
        change.Update("Change the Design of the Base Class",
            new TimeSpan(4, 0, 0));

        // ChangeRequest inherits WorkItem's override of ToString.
        Console.WriteLine(change.ToString());

        // Keep the console open in debug mode.
        Console.WriteLine("Press any key to exit.");
        Console.ReadKey();
    }
}
/* Output:
    1 - Fix Bugs
    2 - Change the Design of the Base Class
*/