[PIU] Tworzenie okna + MessageBox v2

#include <Windows.h>
//-------Zmienne i funkcje globalne.
//-------Zmienne globalne.
TCHAR EndCaption[] = TEXT("Zamykanie aplikacji");
TCHAR EndText[] = TEXT("Czy chcesz zamknąć aplikację?");
TCHAR WindowText[] = TEXT("Nowa nazwa okna");

//Komunikaty
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    HDC hdc;
    switch (msg)
    {
    case WM_PAINT:
    {
        PAINTSTRUCT ps;
        hdc = BeginPaint(hwnd, &ps);
        //Rysowanie:
        EndPaint(hwnd, &ps);
        break;
    }

    case WM_LBUTTONDOWN:
        hdc = GetDC(hwnd);
        SetWindowText(hwnd, WindowText);
        ReleaseDC(hwnd, hdc);
        break;

    case WM_CREATE:
        break;

    case WM_CLOSE:
        if (MessageBox(hwnd, EndText, EndCaption, MB_YESNO) == IDYES) {
            DestroyWindow(hwnd);
        }
        break;

    case WM_DESTROY:
        PostQuitMessage(0);
        break;

    default:
        return DefWindowProc(hwnd, msg, wParam, lParam);
    }

    return 0;
}

//Main
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR ilCmdLine, int nCmdShow)
{
    WNDCLASSEX window;
    HWND hwnd = NULL;
    MSG msg;
    TCHAR Class_Name[] = TEXT("OKNO_TEST");
    TCHAR Title[] = TEXT("Typowa Aplikacja WinAPI");

    window.cbClsExtra = NULL;
    window.cbSize = sizeof(WNDCLASSEX);
    window.cbWndExtra = NULL;
    window.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    window.hCursor = LoadCursor(NULL, IDC_ARROW);
    window.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    window.hIconSm = NULL;
    window.hInstance = hInstance;
    window.lpfnWndProc = WndProc;
    window.lpszClassName = Class_Name;
    window.lpszMenuName = 0;
    window.style = CS_VREDRAW | CS_HREDRAW;

    RegisterClassEx(&window);

    hwnd = ((CreateWindowEx(WS_EX_WINDOWEDGE, Class_Name, Title,
        WS_OVERLAPPEDWINDOW | WS_VISIBLE, CW_USEDEFAULT, CW_USEDEFAULT,
        800, 600, NULL, NULL, hInstance, NULL)));

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    UnregisterClass(Class_Name, hInstance);
    return msg.wParam;
}