We have many books around, anyone can get a definition of interface which is nothing but bookish. In these days we are more interested to know what you know about interfaces rather than what you read for interfaces?
Here, I tried to cover interfaces in my own words:
Interface
An interface is simply a collection of function prototypes. An Interface is a reference type like a class, but interface can contain only abstract members. In other words, Interface is a contract that defines the signature of the functionality.
An interface looks like a class …

A very basic and common questions asked many time to freshers, novoice or intermediate level interviews. I got many emails for the same questions, hereunder I try to answer in a simpler way.
Structures
A structure in C# is simply a composite data type [you are well aware from composite data type, refer to data types for more details], which consists number of members of other types. The structure define simply by using the struct keyword.
eg. struct enroll
{
   public string name, fname, mname;
   public string char sex;
   Public int age;
   public string address;
}
Classes
It is cleared from …