Notepad++ is just a text editor that supports syntax highlighting for 44 programming, scripting, and markup languages.Also allowing us to define our own language, using the built-in User Language Define System.
why dont you use MS Visual Studio or some other IDE for writing your C# code than doing it in a text editor.
also
SharpDevelop is a free ide for C# and
VB.NET projects on Microsoft's .NET platform.