void a() {
 b();
}
void b() {
 a();
}

a();

//main.cpp
int main(int argc, char *argv[])
{
...
    MainWindow w;
    Second s;
    QObject::connect( &w,SIGNAL(go()),   &s,SLOT(go()) );
    QObject::connect( &s,SIGNAL(back()), &w,SLOT(back()) );
...
}


//mainwindow.h
class MainWindow : public QMainWindow
{
...
  private:
    int VALUE;
    int MAX_VALUE;

  private slots:
    void on_pushButton_clicked();

  public slots:
    void back();

  signals:
    void go();
};


//mainwindow.cpp
void MainWindow::on_pushButton_clicked()
{
    VALUE = 0;
    MAX_VALUE = 10000;

    emit go();
}


void MainWindow::back()
{
    qDebug() << VALUE;

    if(VALUE<MAX_VALUE)
    {
        VALUE++;
        emit go();
    }
}


//second.h
class Second : public QObject
{
...
signals:
    void back();

public slots:
    void go();
};


//second.cpp
void Second::go()
{
    emit back();
}