To get the program execution back to main gui ?

[Krish]

Thanks Sir,

Yes you can, qApp is a global pointer to the application instance.

I have tried this i mean with qapp->processEvents(); but it showed me error that qapp is not declared in this scope.

It won't work that way. processEvents() has to be called inside your do_something function inside the loop at each (well... not each as in every but as in sometimes) iteration.
There is no magic here. processEvents() performs a one time scan over pending events and processes them. You have to call it every time you want pending events to be processed.

Thanks now i came to know what actually happens when this function gets called. It checks for any pending event during the execution in do_something(); so that if user clicks any button or does something it will also be executed as:-

Void Square::do_something()
{
  for(i=o;i<100000000;i++) {
  qapp->processEvents();
  ...
  ....}
}

Void Square::do_something()
{
  for(i=o;i<100000000;i++) {
  qapp->processEvents();
  ...
  ....}
}

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But sir how can i use qapp created in main.cpp in the outer .cpp class? Those are separate files. I have only included its header in sample.cpp where all slots are implemented. qapp is not even detected in Sample.cpp, giving same error. Or do i have to include any file in Square.cpp?

////main.cpp////
#include <QApplication>
#include <QtGui>
#include "sample.h"
 
int main(int argc, char *argv[])
{
    QApplication *qapp(argc, argv);
    sample *dialog = new sample;
    dialog->show();
    qapp->connect( &app, SIGNAL( lastWindowClosed() ), &app, SLOT( quit() ) );
    return app.exec();
}

////main.cpp////
#include <QApplication>
#include <QtGui>
#include "sample.h"

int main(int argc, char *argv[])
{
    QApplication *qapp(argc, argv);
    sample *dialog = new sample;
    dialog->show();
    qapp->connect( &app, SIGNAL( lastWindowClosed() ), &app, SLOT( quit() ) );
    return app.exec();
}

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Thanks again & sorry for disturbing you so much.