Windows Tech Series: Simplest C code for Win32 Desktop with a BUTTON

 Just for copy/paste.

#include <windows.h>
#define IDC_BUTTON1 1001
const TCHAR* g_szClassName = TEXT("myWindowClass");
LRESULT CALLBACK OnCreate(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    HWND hwndButton = CreateWindow(
        L"BUTTON",  // Predefined class; Unicode assumed 
        L"OK",      // Button text 
        WS_TABSTOP | WS_VISIBLE | WS_CHILD | BS_DEFPUSHBUTTON,  // Styles 
        10,         // x position 
        10,         // y position 
        100,        // Button width
        100,        // Button height
        hwnd,     // Parent window
        (HMENU)IDC_BUTTON1,       // Control ID
        (HINSTANCE)GetWindowLongPtr(hwnd, GWLP_HINSTANCE),
        NULL);      // Pointer not needed.
    return 0;
}
LRESULT CALLBACK OnCommand(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    DWORD ctrID = LOWORD(wParam);
    DWORD notifyCode = HIWORD(wParam);
    if (notifyCode == BN_CLICKED && ctrID == IDC_BUTTON1) {
        MessageBox(NULL, TEXT("click"), TEXT("Info"), MB_OK);
    }
    return TRUE;
}
// Step 4: the Window Procedure
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg)
    {
    case WM_CREATE:
        return OnCreate(hwnd, msg, wParam, lParam);
    case WM_COMMAND:
        return OnCommand(hwnd, msg, wParam, lParam);
    case WM_CLOSE:
        DestroyWindow(hwnd);
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX wc;
    HWND hwnd;
    MSG Msg;
    //Step 1: Registering the Window Class
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = 0;
    wc.lpfnWndProc = WndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInstance;
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wc.lpszMenuName = NULL;
    wc.lpszClassName = g_szClassName;
    wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
    if (!RegisterClassEx(&wc))
    {
        MessageBox(NULL, TEXT("Window Registration Failed!"), TEXT("Error!"),
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }
    // Step 2: Creating the Window
    hwnd = CreateWindowEx(
        WS_EX_CLIENTEDGE,
        g_szClassName,
        TEXT("The title of my window"),
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 
        CW_USEDEFAULT, CW_USEDEFAULT,
        NULL, NULL, hInstance, NULL);
    if (hwnd == NULL)
    {
        MessageBox(NULL, TEXT("Window Creation Failed!"), TEXT("Error!"),
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }
    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);
    // Step 3: The Message Loop
    while (GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return Msg.wParam;
}