Virtual Functions and Abstract Classes

Question

I read in my book:

An abstract class is a class that is designed specifically for use as a base class. An abstract class contains at least one pure virtual function. You declare a pure virtual function using a pure qualifier (= 0) in the declaration of a virtual member function in the class declaration.

Is it mandatory for an abstract class to have a virtual function? Why?

What is the difference between pure virtual function and virtual function and what is their need?

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class MyAbstractClass
{
    virtual ~MyAbstractClass() = 0;

    virtual void f() 
    {
        IHaveAnImplementation(); 
        SoICannotBePure();
    }
};

// The destructor can unfortunately not be defined inline
MyAbstractClass::~MyAbstractClass() {}

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class AbstractClass {
public:
  virtual void AbstractMemberFunction() = 0; // Pure virtual function makes
                                             // this class Abstract class.
  virtual void NonAbstractMemberFunction1(); // Virtual function.

  void NonAbstractMemberFunction2();
};

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