The Beginning

If you are the Window programmer, you know that everything begins from here:

#define WIN32_LEAN_AND_MEAN        // Exclude rarely-used stuff from Windows headers

#include <windows.h>

LPCWSTR s_szWndClassName = L"Small Window";

ATOM                RegisterWndClass(HINSTANCE hInstance, LPCWSTR lpszWndClassName);
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);

int APIENTRY wWinMain(HINSTANCE hInstance, HINSTANCE, 
                      LPWSTR, int nCmdShow)
{
    HWND hWnd = NULL;
    MSG msg = { 0 };

    RegisterWndClass(hInstance, s_szWndClassName);

    hWnd = CreateWindow(s_szWndClassName, s_szWndClassName, 
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, 
        NULL, NULL, hInstance, NULL);

    if (hWnd != NULL)
    {
        ShowWindow(hWnd, nCmdShow);
        UpdateWindow(hWnd);

        // Main message loop:
        while (GetMessage(&msg, NULL, 0, 0))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }

    return (int)msg.wParam;
}


ATOM RegisterWndClass(HINSTANCE hInstance, LPCWSTR lpszWndClassName)
{
    WNDCLASSEX wcex = { 0 };
    wcex.cbSize            = sizeof(WNDCLASSEX);
    wcex.style            = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = WndProc;
    wcex.hInstance        = hInstance;
    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground    = (HBRUSH)(COLOR_WINDOW + 1);
    wcex.lpszMenuName    = NULL;
    wcex.lpszClassName    = lpszWndClassName;
    return RegisterClassEx(&wcex);
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    PAINTSTRUCT ps;
    HDC hdc;

    switch (message)
    {
    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);
        EndPaint(hWnd, &ps);
        break;

    case WM_DESTROY:
        PostQuitMessage(0);
        break;

    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}