Hi
snewcomer, welcome to GeeksToGo!
When you talk about visual C, I assume you mean the Visual C development environment made by Microsoft? The language itself is simply called "C". To open these files, you need to download Microsoft Visual C++. There is a free version available online called "Microsoft Visual C++ Express Edition".
As far as
multi threading goes, I know it is possible in all the languages you listed above: C, C++, and C#.
The languages you listed are all very similar.
C# and
C++ were both influenced by
C, but
C# is more different because it incorporates the ".NET Framework". You can find more information about the .NET Framework
here.
If you have done programming in the past, then I recommend that you give
C++ a shot. It is basically just a language that was built on
C, and has some added features.
If you haven't programmed at all in the past, you may find it hard to jump into
C++. If this is the case, maybe start by learning a language such as
Python or
Ruby, and work your way up to
C++.
Hope that helps, let me know if you have any other questions