QT starting

I won't use QT if I can avoid it, because it does have some compatibility problem.

Good point is that it is free and not difficult to implement.

QT compilation and making uses,

qmake -project
qmake
make

In every GUI application there is one QApplication object, which manages various application-wide resources, such as the default font and cursor etc.

Header file <QApplication> and class name QApplication. For each class which is part of the public QT API, it has a header file with the same name, like QPushButton class has the same name header <QPushButton>.

The QApplication object must be created before any GUI-related features of Qt are used.

QApplication features:

QCoreApplication is QApplication's base class. It can be used when developing non-GUI applications.

In QCoreApplication::exec(), Qt receives and processes user and system events and passes these on to the appropriate widgets.

To change the default font,
QApplication::setFont()