// Base Class
class Control
{
	// Properties
    // These members are private and thus invisible
    // to derived class methods; we'll examine this
    // later in the chapter
    private int top;
    private int left;

    // Constructor takes two integers to
    // fix location on the console
    public Control(int top, int left)
    {
        //The this keyword refers to the current instance of the class 
        this.top = top;
        this.left = left;
    }
    // Simulates drawing the window
    public void DrawControl()
    {
        Console.WriteLine("Drawing Control at {0}, {1}",
        top, left);
    }
}

// DERIVED Class
//TextBox class inherits from class Control
//The derived class "Textbox" has the properties and methods of the base class (Parent class) Control    
class TextBox : Control
{
    //TextBox has the following properties:
    // top and left that are inherited from the class Control
	//      only accessed via accessors (set and get)
    // mTextBoxContents which is defined in the class TextBox
    private string mTextBoxContents;  // new member variable

    // Constructor adds a parameter
    public TextBox(
        int top,
        int left,
        string theContents) :
        base(top, left) // call base constructor (constructor of Control)
    {
        mTextBoxContents = theContents;
    }


    // A new version (note keyword) because in the
    // derived method we change the behavior
    //When an instance of type "TextBox" calls the method DrawControl, this method will be executed
    // and not the one in the Control class
    public new void DrawControl()
    {
        base.DrawControl();  // invoke the base method
        Console.WriteLine
            ("Writing string to the textbox: {0}", mTextBoxContents);
    }
}

//TESTING
class Tester
{
    public static void Main()
    {
        // Create a base instance
        Control contr = new Control(5, 10);
        contr.DrawControl();

        // Create a derived instance
        TextBox txt = new TextBox(20, 30, "Hello world");
        txt.DrawControl();

        Console.ReadLine();
    }
}