c++ gui qt4 chap01 age

<age.cpp>#include <QApplication>#include <QHBoxLayout>#include <QSlider>#include <QSpinBox>int main(int argc, char *argv[]){    QApplication app(argc, argv);    QWidget *window = new QWidget;    window->setWindowTitle("Enter Your Age");    QSpinBox *spinBox = new QSpinBox;    QSlider *slider = new QSlider(Qt::Horizontal);    spinBox->setRange(0, 130);    slider->setRange(0, 130);    QObject::connect(spinBox, SIGNAL(valueChanged(int)),                     slider, SLOT(setValue(int)));    QObject::connect(slider, SIGNAL(valueChanged(int)),                     spinBox, SLOT(setValue(int)));    spinBox->setValue(35);    QHBoxLayout *layout = new QHBoxLayout;    layout->addWidget(spinBox);    layout->addWidget(slider);    window->setLayout(layout);    window->show();    return app.exec();}