title: Difference between interface and polymorphism
body: <p>I was reading an online excerpt from a C++ book on polymorphism and interfaces. 
  The book made a distinction between polymorphism and interfaces, and specified how to implement them in C++. However, I was always under the idea that interfaces in C++ (implemented using a base class with pure virtual functions) were nothing more than an application of polymorphism.
  I would like to know the clear distinction between polymorphism and interfaces because the excerpt confused me.</p>