What's the difference between c# and Unity3D engine c#

Question

What's the difference between c# and Unity3D engine c# and how can I learn it?

Answer 1

c# is the programming language
there is no difference between these two
but the IDE (Unity3D) disabled some features
e.g. the System.Windows.Forms library
the way you write the code in Unity-C# is exactly the same as in Visual Studio or any other c# based IDE

Answer 2

thanks