I changed my code from this:

    if (!RegisterClassEx(&wc)) {
        MessageBox(NULL, "Window Registration Failed!", "Error!", MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

to this:

    if (!RegisterClassEx(&wc)) {
        MessageBox(NULL, "Failed to register window class.", "Error", MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

and it causes failure of window creation

    hwnd = CreateWindowEx(
        WS_EX_CLIENTEDGE,
        g_szClassName,
        "The title of my window",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 240, 120,
        NULL, NULL, hInstance, NULL);

    if (hwnd == NULL) {
        MessageBox(NULL, "Failed to create a window.", "Error", MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

I honestly have no idea what to do