this ppt helps you learn and present about Unmanged code InterOperability in C# .net. This has sample code included

1. Rohit Vipin Mathews

2.  Interoperability is the process of communication
between two separate systems.
 In .NET Interop, the first system is always the .NET
Framework; the other system might be any other
technology.
 Unmanaged interoperation is not easy as the managed
interop, and it's also much difficult and much harder
to implement. In unmanaged code interoperation, the
first system is the .NET code; the other system might
be any other technology including Win32
API, COM, ActiveX, etc.

3.  Interoperation with Native Libraries.
 Interoperation with COM components.

4.  This is the most famous form of .NET interop with
unmanaged code. We usually call this
technique, Platform Invocation, or simplyPInvoke.
Platform Invocation or PInvoke refers to the technique
used to call functions of native unmanaged libraries
such as the Windows API.

5. To PInvoke a function, you must declare it in your .NET
code. That declaration is called the Managed Signature.
To complete the managed signature, you need to know
the following information about the function:
1. The library file which the function resides in.
2. Function name.
3. Return type of the function.
4. Input parameters.
5. Other relevant information such as encoding.

6. using System.Runtime.InteropServices;
namespace InterOp_with_API
{
class Program
{
public enum beepType
{
Beep = -1,
OK=0x00,
Question=0x20,
Exclamation=0x30,
Asterix=0x40,
}

7. [DllImport("User32.dll",ExactSpelling=true)]
static extern bool MessageBeep(uint type);
static void Main(string[] args)
{
MessageBeep((uint)beepType.Exclamation);
MessageBeep((uint)beepType.Question);
}
}
}

8.  Marshaling is the process of converting unmanaged
types into managed and vice versa . That conversion
can be done in many ways based on the type to be
converted.
 For example, BOOL can simply be converted to
System.Boolean, and LPCTSTR can be converted to
System.String, System.Text.StringBuilder, or even
System.Char[].
 Compound types (like structures and unions) usually
don't have counterparts in .NET code and thus you
need to create them manually.

10.  COM Interop is very large and much harder than
P/Invoke and it has many ways to implement.
 COM Interop includes all COM-related technologies
such as OLE, COM+, ActiveX, etc.

11.  You can't talk directly to unmanaged code.
 you have to declare your functions and types in your
.NET code.
 To include a COM-component in your .NET
application, you go to the COM tab of the Add
Reference dialog and select the COM component that
you wish to add to your project and use it!

12.  When you add a COM-component to your .NET
application, Visual Studio automatically declares all
functions and types in that library for you.
 It creates a Proxy library (i.e. assembly) that contains
the managed signatures of the unmanaged types and
functions of the COM component and adds it to your
.NET application.
 The proxy acts as an intermediary layer between your
.NET assembly and the COM-component.
Therefore, your code actually calls the managed
signatures in the proxy library that forwards your calls
to the COM-component and returns back the results.
 Proxy libraries also called Primary Interop Assemblies
(PIAs) and Runtime Callable Wrappers (RCWs.)

13.  Now you don't have to ship a proxy/PIA/RCW
assembly along with your executable since the
information in this assembly can now be embedded
into your executable; its called Interop Type
Embedding.

14. //Add a reference to the Microsoft Speech Object Library
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Enter the text to read:");
string txt = Console.ReadLine();
Speak(txt);
}
static void Speak(string text)
{
SpVoice voice = new SpVoiceClass();
voice.Speak(text, SpeechVoiceSpeakFlags.SVSFDefault);
}
}

15.  ActiveX is no more than a COM component that has
an interface.
 To add an ActiveX control to .NET application, right-
click the Toolbox, select Choose Toolbox Items, switch
to the COM Components tab and select the controls to
be used in the application.