---qtcreator installation under Ubuntu 18.04
sudo apt install build-essential
sudo apt install qtcreator
sudo apt install qt5-default
sudo apt install qt5-doc
sudo apt install qt5-doc-html qtbase5-doc-html
sudo apt install qtbase5-examples
sudo apt install build-essential
sudo apt install qtcreator
sudo apt install qt5-default
sudo apt install qt5-doc
sudo apt install qt5-doc-html qtbase5-doc-html
sudo apt install qtbase5-examples