//global parameters
#define DRAW_RECT 1
#define DRAW_CIRC 2

int DrawMode;

//drawing functions of each class - dispatch the WM_PAINT nessage
RectClass::DrawShape(RECT rct)
{
	DrawMode = DRAW_RECT;
	InvalidateRect(hwnd, &rct, TRUE);
}

CircClass::DrawShape(RECT rct)
{
	DrawMode = DRAW_CIRC;
	InvalidateRect(hwnd, &rct, TRUE);
}

//in the main file
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	int wmId, wmEvent;
	PAINTSTRUCT ps;
	HDC hdc;
	
	switch (message)
	{
		.
		.
		.
	case WM_PAINT:
		hdc = BeginPaint(hWnd, &ps);
		switch (DrawMode)
		{
		case DRAW_RECT:
			DrawingARect(hdc, RectClassObj.getCoordinates());
			break;
		case DRAW_CIRC:
			DrawingACircle(hdc, CircClassObj.getCoordinates());
			break;
		}
		EndPaint(hWnd, &ps);
	break;
		.
		.
		.
	}
}

class DrawingObject
{
...
    virtual void Draw() = 0; // implemented by subclass
};
 
class Circle : public DrawingObject
{
...
    virtual Draw() ; // implenentation of base class
};
 
class Rectangle : public DrawingObject
{
...
    virtual Draw() ; // implenentation of base class
};
 
// creation of this vector is not shown here
vector<DrawingObject> theList;
 
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	int wmId, wmEvent;
	PAINTSTRUCT ps;
	HDC hdc;
 
	switch (message)
	{
		.
		.
		.
      case WM_PAINT:
            hdc = BeginPaint(hWnd, &ps);
            for(int i = 0; i < theList.size(); i++)
                  theList[i].Draw();