MainWindow::MainWindow(QWidget *parent) :

    QMainWindow(parent),

    ui(new Ui::MainWindow)

{    

    ui->setupUi(this);

    ui->label->setText("");

    num=0;

    QTimer *time=new QTimer(this);

    connect(time,SIGNAL(timeout()),this,SLOT(UpdateText()));

    time->start(100);

}

void MainWindow::UpdateText()

{

    QTime time=QTime::currentTime();

    QString str = time.toString("hh:mm:ss");

    ui->label->setText(str);

}