Interface are alternative to multiple inheritance, Interfaces are declared using the interface keyword. It is similar to class declaration. Interface statements are public by default.
see below sample
public interface ITransactions
{
// interface members
void showTransaction();
double getAmount();
}
An interface looks like a class, but has no implementation. The only thing it contains are declarations of events, indexers, methods and/or properties. The reason interfaces only provide declarations is because they are inherited by structs and classes, that must provide an implementation for each interface member declared.
check below links for more detail
http://www.tutorialspoint.com/csharp/csharp_interfaces.htm
http://www.c-sharpcorner.com/UploadFile/sekarbalag/interface-best-example-in-csharp/
Thanks
Koolprasd2003
Editor, DotNetSpider MVM
Microsoft MVP 2014 [ASP.NET/IIS] 
