Adding Qt version on Qt Creator - Ubuntu

Step-by-step:

1. Find the version and location of qmake

   $ qmake -version

   QMake version 2.01a
   Using Qt version 4.8.1 in /usr/lib/x86_64-linux-gnu

2. On Qt Creator, Tools --> Option --> Build & Run --> Qt Versions --> Manual --> Add
Add the location as shown by command qmake -version, for example: /usr/lib/x86_64-linux-gnu/qt4/bin/qmake
3. Do the step No. 2 also in Tools --> Option --> Build & Run --> Kits --> Qt Version
4. Finish, debug and run your program