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Compiling Qt4 programs is a real pain if you do not know qmake. I ended up with the compile statement

g++ -I/home/kde-devel/kde/include -I/home/kde-devel/qt-copy/include  -I/home/kde-devel/qt-copy/include/Qt -I/home/kde-devel/qt-copy/include/QtGui -L/home/kde-devel/qt-copy/lib -lQtCore -lQtGui main.cpp

Anyway, this was before I got to know qmake. So, here is our hello world project for QT 4:

hello world

Create a directory qttest, proceed in it.

main.cpp

#include <QApplication>
#include <QPushButton>
int main(int argc, char ** argv)
{
  QApplication qa(argc,argv);
  QPushButton* qp=new QPushButton("hello world");
  qp->show();
  return qa.exec();
}

Build and run it:

qmake -project && qmake && make && ./qttest

There is no explanation whatsoever why you need to call

qmake -project && qmake

in order to get a Makefile that can be used by the command

make

to finally build something. But it works :)