bash$ qmake -o Makefile myproj.pro
bash$ make

    QDialog *foo=(QDialog *)QWidgetFactory::create("foo.ui");
    foo->show();

    QLabel *l1=(QLabel *)foo->child("mylabel","QLabel");

// goodbye.cpp - trivial QT example
#include<qapplication.h>
#include<qpushbutton.h>

int main(int argc,char **argv) {
	QApplication app(argc,argv);
	QPushButton *btn= new PushButton("Goodbye, world!!",0);
	// quit when btn is clicked
	QObject::connect(btn,SIGNAL(clicked()),&app,SLOT(quit()));
	app.setMainWidget(btn);     // quit main loop when distruct btn
	btn->show();
	return app.exec();          // QT main loop
}

QObject::connect(btn,SIGNAL(clicked()),&app,SLOT(quit()));

// age.cpp - a slider and a spinbox having the same value
// based on C++ GUI Programming with QT 3 by Bruce Perens
#include <qapplication.h>
#include <qhbox.h>
#include <qslider.h>
#include <qspinbox.h>
int main (int argc, char *argv[]) {
  QApplication app (argc, argv);
  QHBox *hbox = new QHBox (0);
  hbox->setCaption ("Enter Your Age");	//  set title bar
  hbox->setMargin (6);
  hbox->setSpacing (6);
  QSpinBox *spinBox = new QSpinBox (hbox);
  QSlider *slider = new QSlider (Qt::Horizontal, hbox);
  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);
  app.setMainWidget (hbox);
  hbox->show ();
  return app.exec ();
}

/*
 * sum.h: the header file for sum.cpp
 *
 * by Moayyad Al-Sadi<alsadi[at]gmail.com>
 * released under the terms of the GNU General Public License
 * visit www.gnu.org/copyleft
 *
 */
#ifndef SUMDIALOG_H
#define SUMDDIALOG_H
#include <qlabel.h>
#include <qlayout.h>
#include <qlineedit.h>
#include <qpushbutton.h>
#include <qdialog.h>
class SumDialog:public QDialog {
Q_OBJECT public:
  SumDialog (QWidget * parent = 0, const char *name = 0);
    signals:
	void calc (const float a,const float b);
    private slots:
	void okClicked ();
private:
  QLabel * label1,*label2,*label3;
  QLineEdit *num1,*num2,*num3;
  QPushButton *ok;
};
#endif

/*
 * sum.cpp: A sample QT application to add two numbers.
 *
 * by Moayyad Al-Sadi<alsadi[at]gmail.com>
 * released under the terms of the GNU General Public License
 * visit www.gnu.org/copyleft
 *
 */
#include "sum.h"
SumDialog::SumDialog (QWidget * parent, const char *name):
QDialog (parent, name)
{
  setCaption (tr ("Find Summation"));
  label1 = new QLabel (tr ("&First number:"), this);
  label2 = new QLabel (tr ("&Second number:"), this);
  label3 = new QLabel (tr ("Su&mmation:"), this);
  num1 = new QLineEdit (this);
  num2 = new QLineEdit (this);
  num3 = new QLineEdit (this);
  label1->setBuddy (num1);  label2->setBuddy (num2);
  ok = new QPushButton (tr ("OK."), this);
  ok->setDefault (true);
  // num3->setEnabled (false);
  connect (ok, SIGNAL (clicked ()), this, SLOT (okClicked ()));
  QHBoxLayout *hbox1 = new QHBoxLayout;
  hbox1->addWidget (label1);
  hbox1->addWidget (num1);
  QHBoxLayout *hbox2 = new QHBoxLayout;
  hbox2->addWidget (label2);
  hbox2->addWidget (num2);
  QHBoxLayout *hbox3 = new QHBoxLayout;
  hbox3->addWidget (label3);
  hbox3->addWidget (num3);
  QVBoxLayout *vbox = new QVBoxLayout;
  vbox->addLayout (hbox1);
  vbox->addLayout (hbox2);
  vbox->addLayout (hbox3);
  vbox->addWidget (ok);
}
void SumDialog::okClicked () {
  float a = a2f( num1->text () );
  float b = a2f( num2->text () );
  emit calc (a,b);
}
void SumDialog::calc(const float a, const float b) {
  char str[40];
  float c=a+b;
  sprintf(str,"%g",c);
  num3->setText (c);
}
int main(int argc, char *argv[]) {

    QApplication app(argc,argv);
    SumDialog *dialog=new SumDialog;
    app.setMainWidget(dialog);
    dialog->show();
    app.exec();

}

bash$ qmake -project
bash$ qmake -makefile sum.pro
bash$ make && ./sum