Want to know about Interfaces in C# and C++

In C# you can only inherit from a single base class. C++ is different, so I won't talk about that, so as not to confuse.

So you have a class which needs to derive from UserControl. Fine, you inherit UserControl in your class definition and off you go - you have a control you can add other controls to, and display.

class MyClass : UserControl
   {
   }

What if you also want this control to be used in a foreach loop, because it is a list of items in a database? For that, you need to implement a few methods or foreach won't work. But how do you tell the compiler that your class implements the required methods? Simple, you add the IEnumerable interface to your class definition:

class MyClass : UserControl, IEnumerable<string>
   {
   }

Now, in order for your code to compile, you have to add definitions of all the required methods:

public IEnumerator<string> GetEnumerator() { ... }
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { ... }

When you do you have completed your side of the contract, and you can use your class in a foreach:

private void xxx()
    {
    MyClass mine = new MyClass();
    foreach (string s in mine)
        {
        }
    }

And, if you code them as you are supposed to (which is pretty easy most of the time) it will all work.

That is what an Interface is: a contract between you and the interface user. If you follow the rules, you can be a member of the club, and get whatever benefits the club provides.

http://lmgtfy.com/?q=Why+use+Interfaces%3F[^]