CheckMenuItem (hMenu, iSize, MF_UNCHECKED);

#include <windows.h>
#include "resource.h"

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM);
int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,PSTR szCL,int iCS){
    static TCHAR szAppName [] = TEXT ("HelloBit");
    HWND         hwnd;
    MSG          msg;
    WNDCLASS     wndclass;

    wndclass.style         = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc   = WndProc;
    wndclass.cbClsExtra    = 0;
    wndclass.cbWndExtra    = 0;
    wndclass.hInstance     = hInstance;
    wndclass.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW);
    wndclass.hbrBackground = (HBRUSH) GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName  = szAppName;
    wndclass.lpszClassName = szAppName;

    if(!RegisterClass(&wndclass)) {
        MessageBox(NULL,TEXT("Requires Windows NT!"),szAppName,MB_ICONERROR);
        return 0;
    }
    hwnd = CreateWindow(
        szAppName, TEXT("Escrever em Tela"), WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
        NULL, NULL, hInstance, NULL
    );
    ShowWindow(hwnd, iCS);
    UpdateWindow(hwnd);

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

LRESULT CALLBACK WndProc(HWND hwnd,UINT message,WPARAM wParam,LPARAM lParam) {
    static HBITMAP hBitmap;
    static HDC     hdcMem;
    static int     cxBitmap, cyBitmap, cxClient, cyClient, iSize = IDM_BIG;
    static TCHAR * szText = TEXT (" Inscreva-se ");
    HDC            hdc;
    HMENU          hMenu;
    int            x, y;
    PAINTSTRUCT    ps;
    SIZE           size;
    switch (message)     {
        case WM_CREATE:
            hdc = GetDC(hwnd);
            hdcMem  = CreateCompatibleDC(hdc);
            GetTextExtentPoint32(hdc, szText, lstrlen (szText), &size);
            cxBitmap = size.cx;
            cyBitmap = size.cy;
            hBitmap = CreateCompatibleBitmap(hdc, cxBitmap, cyBitmap);
            ReleaseDC (hwnd, hdc);
            SelectObject (hdcMem, hBitmap);
            TextOut (hdcMem, 0, 0, szText, lstrlen (szText));
            return 0;
        case WM_SIZE:
            cxClient = LOWORD (lParam);
            cyClient = HIWORD (lParam);
            return 0;
        case WM_COMMAND:
            hMenu = GetMenu (hwnd);
            switch (LOWORD(wParam)) {
                case IDM_BIG:
                case IDM_SMALL:
                    CheckMenuItem (hMenu, iSize, MF_UNCHECKED);
                    iSize = LOWORD (wParam);
                    CheckMenuItem (hMenu, iSize, MF_CHECKED);
                    InvalidateRect (hwnd, NULL, TRUE);
                    break;
            }
            return 0 ;
        case WM_PAINT:
            hdc = BeginPaint(hwnd, &ps);
            switch(iSize) {
                case IDM_BIG:
                    StretchBlt(hdc,0,0,cxClient,cyClient,hdcMem,0,0,
                               cxBitmap,cyBitmap,SRCCOPY);
                    break;
                case IDM_SMALL:
                    for (y = 0 ; y < cyClient ; y += cyBitmap)
                    for(x = 0; x<cxClient ; x += cxBitmap) {
                        BitBlt(hdc, x, y, cxBitmap, cyBitmap, hdcMem, 0, 0, SRCCOPY);
                    }
                    break;
            }
            EndPaint(hwnd, &ps);
            return 0;
        case WM_DESTROY:
            DeleteDC (hdcMem);
            DeleteObject(hBitmap);
            PostQuitMessage(0);
            return 0;
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}