.NET InterOp
[quote user="saravana kumar"]C# example for microstation[/quote]
Maury and Jan recommend that you study the VBA API. The reason they provide that advice is that, for MicroStation V8i, any C# code you write will be calling the VBA COM server via a .NET InterOp. Therefore, for MicroStation V8i, to write C# code you must understand MicroStation VBA.
Efficiency and Performance
You write that you want to migrate existing MDL (C) code to C#. Jan asks the question: Why? I ask the same question. If you have a working MDL application, what advantage will you gain by rewriting it in C#?
One thing you'll definitely lose is performance. MDL code is reasonably fast; C# code will be comparatively slow because it's calling VBA through an InterOp. VBA is not a high-performance language (it does a lot of marshalling), and consequently neither will your C# application be high-performance.
Of course, if your app. is not CPU intensive then a small loss of performance is not an issue. Perhaps there are benefits of moving to C# that you have not mentioned?