29 The Power of Inheritance and Polymorphism

Implementation: Windows classes 1045fWidth = width;fHeight = height;fFramed = framed;}fBkgd = new char* [height];fCurrentImg = new char* [height];for(int row = 0; row < height; row++) {fBkgd[row] = new char[width];fCurrentImg[row] = new char[width];for(int col = 0; col < width; col++)fBkgd[row][col] = bkgd;}Naturally, the main task of the destructor is to get rid of the image arrays:Window::~Window(){for(int row = 0; row < fHeight; row++) {delete [] fCurrentImg[row];delete [] fBkgd[row];}delete [] fCurrentImg;delete [] fBkgd;}Functions like Clear(), and Set() rely on auxiliary routines Valid() andChange() to organize the real work. Function Valid() makes certain that thecoordinates are within the window's bounds. Function Change() is given thecoordinates, and the new character. It looks after details like making certain thatthe window frame is not overwritten (if this is a framed window), arranging for arequest to the WindowRep object asking for the character to be displayed, and theupdating of the array.void Window::Clear(int x, int y){if(Valid(x,y))Change(x,y,Get(x,y,fBkgd));}void Window::Set(int x, int y, char ch){if(Valid(x,y))Change(x, y, ch);}(Function Change() has to adjust the x, y values from the 1-based scheme used forreferring to screen positions to a 0-based scheme for C array subscripting.)void Window::Change(int x, int y, char ch){if(fFramed) {if((x == 1) || (x == fWidth)) return;if((y == 1) || (y == fHeight)) return;