Linguagem C - Temporizador

#include <windows.h>

#define ID_TIMER 1

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
void CALLBACK TimerProc(HWND, UINT, UINT, DWORD);

int WINAPI WinMain(HINSTANCE hI, HINSTANCE hPI, PSTR szCL, int iCS) {
    static char szAppName[] = "Temporizador";
    HWND     hwnd;
    MSG      msg;
    WNDCLASS wndclass;

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

    if(!RegisterClass(&wndclass)) {
        MessageBox(NULL, TEXT("This program requires Windows NT"),
                   szAppName, MB_ICONERROR);
        return 0;
    }

    hwnd = CreateWindow(
        szAppName, "Temporizador", WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
        NULL, NULL, hI, 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) {
    switch(message) {
        case WM_CREATE:
            SetTimer(hwnd, ID_TIMER, 1000, TimerProc);
            return 0;
        case WM_DESTROY:
            KillTimer(hwnd, ID_TIMER);
            PostQuitMessage(0);
            return 0;
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}

void CALLBACK TimerProc(HWND hwnd, UINT message, UINT iTimerID, DWORD dwTime) {
    static BOOL fFlipFlop = FALSE;
    HBRUSH hBrush;
    HDC    hdc;
    RECT   rc;

    MessageBeep(-1);
    fFlipFlop = !fFlipFlop;

    GetClientRect(hwnd, &rc);

    hdc    = GetDC(hwnd);
    hBrush = CreateSolidBrush(fFlipFlop ? RGB(0, 255,0) : RGB(11, 0, 255));

    FillRect(hdc, &rc, hBrush);
    ReleaseDC(hwnd, hdc);
    DeleteObject(hBrush);
}