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Using c# interface in a c++ project with VS express 1013

I am trying to include a c# interface into a c++ header file which belongs to a clr library.
I add the additional directory and as soon as I include the interface and try to build the c++ project, I get loads of errors leading to the cs file, like:
Do I mess up some VS settings?

It is impossible to #include "IImagesToVideoConverter.cs". The C++ compiler cannot understand c# code. You need to put a c# project and a c++ project in the same solution, reference the c# project from the c++ project, and (i think) #using <the.dll>

including a C# source in a C++ compile makes no sense. They are different languages, why would you ever expect this to work?
Perhaps you want to make a COM interface between them, in which case you use a #import directive.

Calling DLL from Python 3.4

I had a dll written in C. So for a C# application, I wrote a .cs wrapper that worked in calling the dll functions..
Now I have a C# dll and need to call the functions using python 3.4 (LoadLibrary). What would be the preferred route of doing this
1) convert the C# dll code into C and make a new c-style dll (with exports).
2) Create some kind of wrapper in python that allows it to see the C# dll functions as-is? ( if possible)
3) Both Python for .Net and IronPython don't seem to be actively maintained anymore (The windows installer shows python 2.7). Is there a better alternative?

Take a look at this question on stack overflow.It tells how to use ctypes.It describes the ctypes.WinDLL command for including the required dll.You can set up prototype and parameters for the desired function call using ctypes.WINFUNCTYPE.

Call C++ code from C# without creating dll?

I'm noob in C# and I already searched on the web. Anyway I'm still not sure about this and I do not have the total control of the code I have to implement, this is why I would like to be sure I needn't make any dll. I have a C++ file with a method, and I want to call this method from C# code. I just added "extern C" to the function.
When I just add the .h and .cpp files to the C# project they aren't detected. And of course, when I try to add it as reference, it doesn't work.
So do I absolutly have to make a dll ?

Your options for accessing the C++ code from C#:
Compile C++ as unmanaged DLL and access using p/invoke. This requires the C++ code be exposed using a C style API.
Compile C++ as unmanaged DLL and access using COM. This requires that you wrap your C++ in as COM objects.
Compile C++ as mixed/mode C++/CLI assembly and access the assembly as a managed reference. This requires that you wrap the original C++ as managed C++ ref classes.
All of these options, by necessity, involve the creation of another module/assembly. You cannot link the C++ code directly into your C# assembly.

You might like to try using the PInvoke Interop Assistant to generate the C# necessary to interact with the DLL via Platform Invoke. Be aware that this is imperfect though so YMMV.
Another alternative, if you have the knowledge and patience, is to make a COM component out of your native C++ DLL and consume that from C# by using the Type Library Importer to create a managed wrapper.

You won't be able to interact with .cpp/.h files since you need at least a binary object (assembly) for C# to interact with and C# won't generate any binaries from .cpp/.h. That's on the subject about adding these files as references to the project.
As for the argument that you don't have control over the code - well, don't make a DLL out of the actual .cpp/.h, but make your own thin DLL that has a wrapper object that just includes the headers, calls whatever method you would be calling and links to the appropriate .o files or .lib or whatever you have. If the interface changes you would just changed your thing wrapper which should be easy.

Build native c++ for use as .net library

I have the c++ source code of functionality which is appealing to me.
What effort/work is involved/required in order to either reference this from a .net application or build this code as a .net assembly (preferably c#)?
This is my first attempt at porting code, so please breakdown your answer for me step by step.

There are several ways of doing it.
PInvoke
Create C++/CLI wrapper around your C++ native code (make static library out of C++ native code) and C++/CLI generated assembly can be easily utilized in .net application.
COM, i.e using interop (which is difficult among all the options)
In my suggestion easiest way is to use option 2, but you need to take care of proper marshaling.

Solution A:
If you have the source code, then compile the CPP program as a DLL file.
Use P/Invoke
Solution B (if the functionality you want is in a static library):
Create a stub function caller and compile THAT as a DLL
Same as solution A.2

Using C++ code in C#

I had written a code snippet in VC++. However, I cannot continue rest of the application in VC++, so would want to move to C#.
Can I make a dll of the VC++ code and call the functions written in VC++ to work in C#?
I'm quite un-aware if this will work, but I have seen how the native code is called in C# using dll.
Can anyone please help me on this.
Thanks.

You could try compiling your C++ code as managed code using the /clr option and then use it directly or use P/Invoke to call the unmanaged functions from managed code.