How to update the QT Mainwindow at each loop in mainwindow.cpp

My main.cpp look like this:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

An in my mainwindow.cpp I want to show a different image at each loop in "while", so it would look like this:

MainWindow::MainWindow(QWidget *parent) :
        QMainWindow(parent),
        ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    image = load_an_image
    int i=0;
    while (i<15)
    {
        show image in the MainWindow
        waitkey (wait until I press a key or wait some time)
        do something to this image for the next loop
        i++
    }
}

However the Mainwindow does not show up until the "while" is finished and I cannot find how to show the MainWindow at each loop.

Can anyone give me any advice ?

You could delay handling the image by using a Qtimer. Something like this: -

MainWindow::MainWindow(QWidget *parent) :
        QMainWindow(parent),
        ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QTimer::singleShot(5, this, SLOT(timeout());
}

// create as a slot in the MainWindow derived class
void MainWindow::timeout()
{
    image = load_an_image();
    int i=0;
    while (i<15)
    {
        // show image in the MainWindow
        // waitkey (wait until I press a key or wait some time)
        // do something to this image for the next loop
        i++
    } 
}

However, it would be better handled by loading the first image and then reacting to key events, rather than waiting directly in the main thread...

void MainWindow::keyReleaseEvent(QKeyEvent* keyEvent)
{
    if(keyEvent->key() == Qt::Key_Space) // use the space bar, for example
    {
        if(m_imageFrame < 15)
        {
             // update the image
        }
    }
    else
    {
        QMainWindow::keyReleaseEvent(keyEvent);
    }        
}