YOU LOOK HAPPY TO MEET ME

#define DIVISIONS 5

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR  szCmdLine, int iCmdShow)
{
     static TCHAR szAppName[] = TEXT ("Checker1") ;
     HWND         hwnd ;
     MSG          msg ;
     WNDCLASS     wndclass ;
    
     wndclass.style         = CS_HREDRAW | CS_VREDRAW ;
     wndclass.lpfnWndProc   = WndProc ;
     wndclass.cbClsExtra    = 0 ;
     wndclass.cbWndExtra    = 0 ;
     wndclass.hInstance     = hInstance ;
     wndclass.hIcon         = LoadIcon (NULL, IDI_APPLICATION) ;
     wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;
     wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
     wndclass.lpszMenuName  = NULL ;
     wndclass.lpszClassName = szAppName ;
    
     if (!RegisterClass (&wndclass))
     {
          MessageBox (NULL, TEXT ("Program requires Windows NT!"),
                      szAppName, MB_ICONERROR) ;
          return 0 ;
     }
    
     hwnd = CreateWindow (szAppName, TEXT ("Checker1 Mouse Hit-Test Demo"),
                          WS_OVERLAPPEDWINDOW,
                          CW_USEDEFAULT, CW_USEDEFAULT,
                          CW_USEDEFAULT, CW_USEDEFAULT,
                          NULL, NULL, hInstance, NULL) ;
    
     ShowWindow (hwnd, iCmdShow) ;
     UpdateWindow (hwnd) ;
    
     while (GetMessage (&msg, NULL, 0, 0))
     {
          TranslateMessage (&msg) ;
          DispatchMessage (&msg) ;
     }
     return msg.wParam ;
}

LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
     static int  fState[DIVISIONS][DIVISIONS] ;
     static int  cxBlock, cyBlock, Counting ;
     HDC         hdc ;
     int         x, y ;
     PAINTSTRUCT ps ;
     RECT        rect ;
    
     switch (message)
     {

     case WM_SIZE :
          Counting = 3 ;
          cxBlock = LOWORD (lParam) / DIVISIONS ;
          cyBlock = HIWORD (lParam) / DIVISIONS ;
          return 0 ;
         
     case WM_LBUTTONDOWN :
          Counting++;
          x = LOWORD (lParam) / cxBlock ;
          y = HIWORD (lParam) / cyBlock ;
         
          if (x < DIVISIONS && y < DIVISIONS && !fState [x][y])
          {
               switch(Counting%2)
               {
               case 0 :
                   fState [x][y] ^= 1 ; break;
               case 1:
                   fState [x][y] ^= 2 ; break;
               }

               rect.left   = x * cxBlock ;
               rect.top    = y * cyBlock ;
               rect.right  = (x + 1) * cxBlock ;
               rect.bottom = (y + 1) * cyBlock ;
              
               InvalidateRect (hwnd, &rect, FALSE) ;
          }
          else
               MessageBeep (0) ;
          return 0 ;
         
     case WM_PAINT :
          hdc = BeginPaint (hwnd, &ps) ;
         
          for (x = 0 ; x < DIVISIONS ; x++)
          for (y = 0 ; y < DIVISIONS ; y++)
          {
               Rectangle (hdc, x * cxBlock, y * cyBlock,
                         (x + 1) * cxBlock, (y + 1) * cyBlock) ;
                   
               if (fState [x][y] == 1)
               {
                    MoveToEx (hdc,  x * cxBlock,  y * cyBlock, NULL) ;
                    LineTo   (hdc, (x+1) * cxBlock, (y+1) * cyBlock) ;
                    MoveToEx (hdc,  x * cxBlock, (y+1) * cyBlock, NULL) ;
                    LineTo   (hdc, (x+1) * cxBlock,  y * cyBlock) ;
               }
               if (fState [x][y] == 2)
               {
                    Ellipse (hdc, x * cxBlock, y * cyBlock,
                         (x + 1) * cxBlock, (y + 1) * cyBlock) ;
               }
          }
          EndPaint (hwnd, &ps) ;
          return 0 ;
              
     case WM_DESTROY :
          PostQuitMessage (0) ;
          return 0 ;
     }
     return DefWindowProc (hwnd, message, wParam, lParam) ;
}