Question: i want to use Qt with Visual Studio 2010 and 2012 parallel. For Visual Studio 2010, i've already installed it and it's running. How do i install it for Visual Studio 2012? In what do i change the environmental variables?

Windows 8.1 64bit

Answer: 
You can install into another path, if you need to you can also compile yourself there, it is not that hard. Then in your respective Solution files change the path of the Qt libraries accordingly.

<http://qt-project.org/doc/qt-5/windows-building.html>
You could install two different Qt versions onto your PC. You can get the versions from here:

[Download Qt](http://qt-project.org/downloads)

Watch out for VS 2012 in brackets. You will need to put the desired version into the `PATH` with priority. For instance, if you are currently developing with VS 2010, you will need to prefer the VS 2010 installation in your PATH, but if it is 2012, then the VS 2012 Qt version, respectively.