How can I detect if I'm running a Windows Phone or a regular Windows in C# ? (for Windows 8, 8.1, 10)
C# can be run on those two kind of platforms.
You can use precompilation directives such as WINDOWS_APP and WINDOWS_PHONE_APP to detect regular windows or mobile devices.
You can see more information on this MSDN blog post here: http://blogs.msdn.com/b/cdndevs/archive/2015/03/06/universal-applications-be-ready-for-windows-10-part-1.aspx
Hope that helps! :)
Shahed