main.cpp is simple, like in most Qt applications. We create a QApplication object and a BounceWidget object. We set the window caption, and that's about it.
int main( int argc, char **argv )
{
QApplication a( argc, argv );
BounceWidget bw( 0, "BounceWidget" );
a.setMainWidget( &bw );
bw.setCaption( "Astrophysics for beginners!" );
bw.show();
return a.exec();
}