変数のスコープ

まずは，変数のスコープを狭める。さらに，変数は宣言と同時に値を代入するように変更。

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    static HBITMAP hBitmap;

    switch (message) 
    {
    case WM_COMMAND:
    {
        int wmId    = LOWORD(wParam); 
        int wmEvent = HIWORD(wParam); 
        // 選択されたメニューの解析 :
        switch (wmId)
        {
        case IDM_ABOUT:
            DialogBox(hInst, (LPCTSTR)IDD_ABOUTBOX, hWnd, (DLGPROC)About);
            break;
        case IDM_EXIT:
            DestroyWindow(hWnd);
            break;
        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
        }
        break;
    }
    case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hWnd, &ps);
        HDC hBufdc = CreateCompatibleDC(hdc);
        SelectObject(hBufdc, hBitmap);
        BITMAP bmp;
        GetObject(hBitmap, sizeof(BITMAP), &bmp);
        BitBlt(hdc, 0, 0, (int)bmp.bmWidth, (int)bmp.bmHeight, hBufdc, 0, 0, SRCCOPY);
        DeleteDC(hBufdc);
        EndPaint(hWnd, &ps);
        break;
    }
    case WM_CREATE:
        hBitmap = (HBITMAP)LoadImage(hInst,
                                     MAKEINTRESOURCE(IDB_BITMAP1),
                                     IMAGE_BITMAP,
                                     0, 0,
                                     LR_DEFAULTCOLOR);
        break;
    case WM_DESTROY:
        DeleteObject(hBitmap);
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}