Multiplicação com Saída em Arquivo Texto

#if defined(UNICODE) && !defined(_UNICODE)
    #define _UNICODE
#elif defined(_UNICODE) && !defined(UNICODE)
    #define UNICODE
#endif

#include <tchar.h>
#include <windows.h>
#include <math.h>
#include <stdio.h>

#define ID_BUTTON  1

static HWND num1, num2, t;


LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

void addMenus(HWND);
HMENU eMenu;

TCHAR szClassName[ ] = _T("CodeBlocksWindowsApp");


int WINAPI WinMain (HINSTANCE hThisInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR lpszArgument,
                     int nCmdShow)
{
    HWND       hwnd;       /** Evento de Janela */
    MSG        messages;   /*Here messages to the application are saved*/
    WNDCLASSEX wincl;      /** Dados e struturas para Classe de Janela */

    /* The Window structure */
    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure;
    wincl.style = CS_DBLCLKS;             /** Catch double-clicks */
    wincl.cbSize = sizeof (WNDCLASSEX);

    /* Use default icon and mouse-pointer */
    wincl.hIcon = LoadIcon (NULL, IDI_EXCLAMATION);
    wincl.hIconSm = LoadIcon (NULL, IDI_EXCLAMATION);
    wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;
    wincl.cbClsExtra = 0;
    wincl.cbWndExtra = 0;       /**Estrutura ou Instancia da Janela*/
    wincl.hbrBackground = GetSysColorBrush(COLOR_3DFACE);

    if (!RegisterClassEx (&wincl))
        return 0;



    hwnd = CreateWindowEx (
           0,                   /* Extended possibilites for variation */
           szClassName,         /** Nome da Classe */
           _T("Linguagem C com PHP"), /* Title Text */
           WS_OVERLAPPEDWINDOW, /* default window */
           CW_USEDEFAULT,       /* Windows decides the position */
           CW_USEDEFAULT,       /*where the window ends up on the screen*/
           500,                 /** Largura do Programa */
           200,                 /** Altura em pixels */
           HWND_DESKTOP,        /*The window is a child-window to desktop*/
           NULL,                /* No menu */
           hThisInstance,       /* Program Instance handler */
           NULL                 /** Nenhum dado de Criação da janela */
    );

    ShowWindow (hwnd, nCmdShow);

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

LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message,
                                  WPARAM wParam, LPARAM lParam) {
    switch (message) {
        case WM_CREATE:
            addMenus(hwnd);

            CreateWindow(
                TEXT("static"), TEXT("Linguagem C/C++ com PHP:"), WS_VISIBLE | WS_CHILD,
                30, 20, 480, 20,
                hwnd, NULL, NULL, NULL
            );

            num1 = CreateWindow(  /**Aqui está variável num1 para entrada de dados*/
                TEXT("edit"), TEXT(""), WS_VISIBLE | WS_CHILD | WS_BORDER,
                30, 50, 80, 20,
                hwnd, NULL, NULL, NULL
            );

            num2 = CreateWindow(  /**Aqui está variável num2 para entrada de dados*/
                TEXT("edit"), TEXT(""), WS_VISIBLE | WS_CHILD | WS_BORDER,
                120, 50, 80, 20,
                hwnd, NULL, NULL, NULL
            );

            CreateWindow(
                TEXT("button"), TEXT("Calcular"), WS_VISIBLE | WS_CHILD | WS_BORDER,
                220, 50, 80, 20,
                hwnd, (HMENU) ID_BUTTON, NULL, NULL
            );

            CreateWindow(
                TEXT("static"), TEXT("----Multiplicação----"),
                WS_VISIBLE | WS_CHILD,
                30, 90, 280, 20,
                hwnd, NULL, NULL, NULL
            );
            t = CreateWindow(   /**t é a caixa de texto vazia do lado do botão*/
                TEXT("edit"), TEXT(""), WS_VISIBLE | WS_CHILD | WS_BORDER,
                320, 50, 80, 20,
                hwnd, NULL, NULL, NULL
            );
            break;

        case WM_COMMAND:
            if(LOWORD(wParam)==ID_BUTTON) {
                int n1 = GetWindowTextLength(num1)+1; /**Captura a variável num1*/
                int n2 = GetWindowTextLength(num2)+1; /**Captura a variável num2*/

                static char t1[40];  /**Array de caracter t1 em modo estático*/
                static char t2[40];  /**Array de caracter t2 em modo estático*/

                GetWindowText(num1, t1, n1); /**Jogo n1 para dentro da variável t1*/
                GetWindowText(num2, t2, n2); /**Jogo n2 para dentro da variável t2*/

                int res = atoi(t1)*atoi(t2); /**Agora mudar para multiplicação*/


                char tam[40];  /**Declaro a variável tam(tamanho) do tipo array de 40 caracteres*/

                itoa(res, tam, 10); /**Converte res(resultado) para String tam(tamanho)*/

                SetWindowText(t, tam); /**Jogo a vaiável tam(tamanho) para t(text)*/

                FILE *arq;
                arq=fopen("C:\\xampp\\htdocs\\dashboard\\Arquivos\\TESTE.txt", "w+");
                fwrite(tam, sizeof(arq), 10, arq);
                fclose(arq);

                return 0;
            }
            break;

        case WM_DESTROY:
            PostQuitMessage(0); /** Saída padrão do Sistema */
            break;
        default:                /**for messages that we don't deal with*/
            return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}

void addMenus(HWND hwnd) {
    eMenu = CreateMenu();

    HMENU sub = CreateMenu();
    AppendMenu(sub, MF_STRING, NULL, "Copy");
    AppendMenu(sub, MF_STRING, NULL, "Paste");

    AppendMenu(eMenu, MF_STRING, 0, "Arquivo");
    AppendMenu(eMenu, MF_STRING, NULL, "Editar");
    AppendMenu(eMenu, MF_POPUP, (UINT_PTR) sub, "SubMenu");
    AppendMenu(eMenu, MF_STRING, 3, "Iniciar");

    SetMenu(hwnd, eMenu);
}