Assume the existence of a window class with a function getwidth that returns the width of the window. define a derived class windowwithborder that contains a single additional integer instance variable named borderwidth, and has a constructor that accepts an integer parameter which is used to initialize the instance variable. there is also a function getuseablewidth, that returns the width of the window minus the width of the border.

Following are the code in the C++ Programming Language.

//define class and inherited the parent class

class WindowWithBorder : public Window

{

//access modifier

private:

//set integer variable

int borderWidth;

//set integer variable

int windowWidth;

//access modifier

public:

//definition of the constructor that accept an integer type argument

WindowWithBorder(int);

//definition of the function

int getUseableWidth();

};

//set constructor outside the class

WindowWithBorder::WindowWithBorder(int y)

{

//initialization in integer variable from function

windowWidth = getWidth();

//initialization in integer variable from the argument list

borderWidth = y;

}

//set function from outside the class

int WindowWithBorder::getUseableWidth()

{

//return output

return windowWidth - borderWidth;

}

Explanation:

Here we define a class "WindowWithBorder" which inherit their parent class "Window", inside the class.

Then, we define constructor outside the class which accept the integer type argument list "y" inside it.

Finally, we define function in which we perform the subtraction of the variable "windowWidth" from the variable "borderWidth" and return it.