Are you looking for something that's easy to learn? C# is realy to learn and use. It can also do a lot that C++ can. The cool thing about downloading C++ is that you can use C++ with the .Net Framework and thus use similar syntax to C#, which means it can also be easy to learn. If, though, you want make Win32 applications (apps that don't use the .Net Framework) you might have a harder time learning it.
As for the range of mathematical functions, both provide a large range of functions. C# is just a lot easier.
