Qt 4.x -> Qt5

http://wiki.qt.io/Transition_from_Qt_4.x_to_Qt5

/*============================================================================*/

error: C1083: Caot open include file: 'QApplication': No such file or directory

*.pro

QT += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

Delete the debug folder!

/*============================================================================*/