why C++ is not called C++.net while C# is called as C#.net?
C# programs require a special VM (called .NET runtime) on top of OS to run.
C++ programs usually run directly on the OS (C++ CLI is *not* C++, it is a different language, although very similar to standard C++)
...and C# is called C# not C#.net. C# is a language created for the .NET Framework initiative and therefore does not need to be distinguished from a prior version (like VB and VB.net).
From c# standard:
Ecma 334 wrote:
This International Standard is based on a submission from Hewlett-Packard, Intel, and Microsoft, that described a language called C#, which was developed within Microsoft. The principal inventors of this language were Anders Hejlsberg, Scott Wiltamuth, and Peter Golde. The first widely distributed implementation of C# was released by Microsoft in July 2000, as part of its .NET Framework initiative.
C++ is not a .net Language however, as has been pointed out above, C++/CLI is.
From C++/CLI standard:
ECMA 372 wrote:
This Standard is based on a submission from Microsoft. It describes a technology, called C++/CLI, which is a binding between the Standard C++ programming language and the Common Language Infrastructure (CLI). That submission evolved from another Microsoft project, Managed Extensions for C++, the first widely distributed implementation of which was released by Microsoft in July 2000, as part of its .NET Framework initiative. The first widely distributed beta implementation of C++/CLI was released by Microsoft in July 2004.
...
C++/CLI is an extension of the C++ programming language as described in ISO/IEC 14882:2003, Programming languages — C++. In addition to the facilities provided by C++, C++/CLI provides additional keywords, classes, exceptions, namespaces, and library facilities, as well as garbage collection.
Edit:
If you are thinking of a .net language to learn, you will have a much easier life with C#. Most books and websites have C# sample code over C++/CLI and C# is very easy to learn. With C++/CLI you will have to learn C++ and the CLI extensions to it (keeping the concepts seperate) along with learning the .net framework and other technologies, I would not recommend that to anyone.
I can confirm what Grey Wolf says. I am a C++ programmer and we transitioned into managed code. Best alternative was C# as working with C++/CLI was a headache.