>i do not have any reason,yet.
>Do you think learning c++.net is a waste of time?

I'd say C++.Net is a narrow niche.

Learning any .Net language is one part learning the language syntax, and one (probably larger) part learning the .Net framework. I get the feeling C++.Net exists so that people who already know C++ but not some other .Net language like C# or VB.Net can start creating .Net apps as quickly as possible. If you are in that group then yes, it could be useful.

If you want to write business apps in .Net, C# or VB.Net are probably better choices if you don't already know C++. C# and VB.Net are higher-level languages than C++; you'll achieve your result with writing less code and finding and fixing fewer bugs. Microsoft seems to be deprecating C++ for general-purpose userland application development, in favour of .Net and its related higher-level languages.

C++ and the related language C are very widely used, on all sorts of computer systems as well as Windows. Arguably, almost all computers and most of the Internet run on C/C++. Knowing C++ is a useful skill but it is aimed more at systems and high-performance computing than general business applications - see the Wikipedia preamble at http://en.wikipedia.org/wiki/C%2B%2B .

If you're looking to learn C++ to be able to write programs on multiple platforms such as Linux, Mac etc. then I'm not sure C++.Net would be a good way to learn C++. MS's version may not be standard (MS often "embraces and extends"), and you may get used to tying your code to the .Net library which may not be available on non-Windows platforms (Mono attempts to address this on some other platforms).

If you'd like to stick with a Microsoft compiler/environment, Visual C++ may be a better choice for learning the pure language ( http://msdn.microsoft.com/en-ca/visualc/default.aspx ) but, for Windows at least, you'll probably get into the Microsoft Foundation Classes (MFC) which probably aren't too portable to other platforms.

For non-MS compilers, you can check out what Bjarne Stroustrup himself has to say: http://www.research.att.com/~bs/compilers.html

One interesting feature of programs written using unmanaged C++ (i.e. compiling to native code) is that those programs are pretty much immune to decompilation. You can't recover the source from the compiled executable. However, this is not true of managed C++.Net, it can be decompiled just like any other .Net executable. So, if protecting your intellectual property in your distributed code is important, native/unmanaged C++ may be worth a look.