Solution

The correct answer is A is not correct but R is correct.

Key Points

• A class containing a pure virtual function is referred to as an abstract class.
• An abstract class cannot be instantiated directly. In other words, we cannot create an object of a class that contains at least one pure virtual function.
• The purpose of an abstract class is to serve as a base class for other derived classes that implement the pure virtual functions.
• Assertion A is incorrect because a pure virtual function prevents the instantiation of the class, making it impossible to build an object from such a class.
• Reason R is correct because it accurately defines what an abstract class is, which is a class containing at least one pure virtual function.

Additional Information

• Pure Virtual Functions:
  • A pure virtual function is a virtual function that is declared by assigning it to 0 in its declaration (e.g., virtual void func() = 0;).
  • It serves as a placeholder for derived classes to provide their specific implementation of the function.
  • Classes that contain pure virtual functions are abstract and cannot be instantiated directly.
• Characteristics of Abstract Classes:
  • They can have both pure virtual functions and normal member functions.
  • Derived classes must override all pure virtual functions of the base class to become concrete classes (non-abstract).
  • If a derived class does not override all pure virtual functions, it also becomes an abstract class.
• Example:
  • Consider the following code snippet:

                    class AbstractClass {
                        virtual void pureFunction() = 0; // Pure virtual function
                    };
                    class ConcreteClass : public AbstractClass {
                        void pureFunction() override {
                            // Implementation
                        }
                    };
                    

  • Here, AbstractClass is an abstract class, and ConcreteClass provides an implementation of the pure virtual function, making it a concrete class.
• Important Points:
  • An abstract class can have constructors, destructors, and member variables.
  • Abstract classes are used to define interfaces or base functionality for derived classes.
  • They enable polymorphism, allowing derived classes to provide specific implementations of base class functions.