how to change GUI while processing

I am new to Qt Programming, but I have basic on C++.

I want to update my GUI while it is processing, example:

while (....)
{

        do some calculation...

        if (condition fulfill)

            change the color of label.
}

However, I realise that I failed to get the result I want (update the GUI while processing). The GUI will only update after the while loop. Why is it so? A开发者_如何学运维nyone can help?

In addition, I wish to "slower" the color change since the processing is too fast and I can't see the animation. Any idea to do it?

Thank you very much!

Clarification: Actually I wish to update the GUI while I am processing...Meaning that, if I have 100 iteration, after each iteration I wish to update the GUI immediately.

Use a QTimer. This will allow you to control the speed of your animation and keep your UI responsive.

You have to place your processing code to another thread and update the gui, because like this GUI will be waiting for your process to end and will refresh after its end

read more here:
http://www.qtcentre.org/threads/41545-How-to-refresh-GUI-while-heavy-processing-is-ongoing
http://www.qtcentre.org/threads/32416-Update-GUI-from-another-thread
Forcing the Qt GUI to update

You don't necessarily need a thread.
Calling QApplication::processEvents() will process pending events, including any redraws you may have caused during your processing.

If you wish to animate the color to indicate that the system is currently working, you might want to use QApplication::setOverrideCursor to show a waitCursor, or a QProgressDialog instead.