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Advantages VB.NET:

Has support for optional parameters which makes COM interoperability much easy.

With Option Strict off late binding is supported.Legacy VB functionalities can be used by using Microsoft.VisualBasic namespace.

Has the WITH construct which is not in C#.

The VB.NET part of Visual Studio .NET compiles your code in the background.

While this is considered an advantage for small projects, people creating very large projects have found that the IDE slows down considerably as the project gets larger.

Advantages of C#

XML documentation is generated from source code but this is now been incorporated in Whidbey.

Operator overloading which is not in current VB.NET but is been introduced in Whidbey.

Use of this statement makes unmanaged resource disposal simple.

Access to Unsafe code. This allows pointer arithmetic etc, and can improve performance in some situations. However, it is not to be used lightly, as a lot of the normal safety of C# is lost (as the name implies).This is the major difference that you can access unmanaged code in C# and not in VB.NET.

System exceptions and application exceptions:

All exception derives from Exception Base class. Exceptions can be generated programmatically or can be generated by system. Application Exception serves as the base class for all application specific exception classes. It derives from Exception but does not provide any extended functionality.

You should derive your custom application exceptions from Application Exception. Application exception is used when we want to define user defined exception, while system exception is all which is defined by .NET.

Preventing de compilation of dot net DLL:

By design .NET embeds rich Meta data inside the executable code using MSIL. Any one can easily decompile your DLL back using tools like ILDASM (owned by Microsoft) or Reflector for .NET which is a third party. Secondly there are many third party tools which make this decompiling process a click away.

So any one can easily look in to your assemblies and reverse engineer them back in to actual source code and understand some real good logic which can make it easy to crack your application.

The process by which you can stop this reverse engineering is using "obfuscation". It's a technique which will foil the decompilers. There are many third parties (XenoCode, Demeanor for .NET) which provide .NET obfuscation solution. Microsoft includes one that is Dotfuscator Community Edition with Visual Studio.NET.