This first program is a simple hello-world example. ... Qt tutorial 1 ** ****************************************************************/ #include < qapplication.h > #include < qpushbutton.h > int main( int argc, char **argv ) { QApplication a( argc, argv ); QPushButton hello( "Hello world!" ); hello. resize ( 100, 30 ); a. setMainWidget ( &hello ); hello. show (); return a. exec (); } . ... You don't have to have a main widget, but most programs have one. hello. show (); . ... Press the button. ...