Secure Code?

Sir, then what's your suggestion! In case of protection I should use C++ not C# .
And how I start it (unmanaged)... ?

Thanks for all replay.

Even using a Dotfuscator, if you have written dll's in c# and dotfuscated them then the app that  you want to call the dll from will have a very difficult time, this is because you won't know what the functions / methods in the dll have been changed to.

Sam is right on this, C++ produces machine code which is harder to reverse engineer.

Visual studio comes with a community edition of dotfuscator (check the visual studio tools folder) which will make your code very hard to read. After doing that, the variables, classes, methods, ... will have simple names like a, b, c, ... and you'll get code like
a = b(c[a].f).g(a);
People will still be able to read your code but they'll have to be very motivated to actually understand it.