initgraph(&gdriver, &gmode, "");

case WM_LBUTTONDOWN:
    fDraw = TRUE;
    ptPrevious.x = LOWORD(lParam);
    ptPrevious.y = HIWORD(lParam);
    return 0L;
 
case WM_LBUTTONUP:
    if (fDraw)
    {
        hdc = GetDC(hwnd);
        MoveToEx(hdc, ptPrevious.x, ptPrevious.y, NULL);
        LineTo(hdc, LOWORD(lParam), HIWORD(lParam));
        ReleaseDC(hwnd, hdc);
    }
    fDraw = FALSE;
    return 0L;
 
case WM_MOUSEMOVE:
    if (fDraw)
    {
        hdc = GetDC(hwnd);
        MoveToEx(hdc, ptPrevious.x, ptPrevious.y, NULL);
        LineTo(hdc, ptPrevious.x = LOWORD(lParam),
          ptPrevious.y = HIWORD(lParam));
        ReleaseDC(hwnd, hdc);
    }
    return 0L;