Question

Fill in the blanks in each of the following statements: a. Treating a base-class object as a(n) ________ can cause errors. b. Polymorphism helps eliminate _________ logic. c. If a class contains at least one pure virtual function, it is a(n) __________ class. d. Classes from which objects can be instantiated are called ________ classes. e. Operator _________ can be used to downcast base-class pointers safely. f. Operator typeid returns a reference to a(n) _________ object. g. _________ involves using a base-class pointer or reference to invoke virtual functions on base-class and derived-class objects. h. Overridable functions are declared using keyword _________ . i. Casting a base-class pointer to a derived-class pointer is called _________ .

Short answer

a. derived-class object b. switch-case c. abstract d. concrete e. dynamic_cast f. type_info g. Dynamic binding h. virtual i. downcasting

Step-by-step solution

Understanding the question

In this exercise, we have a set of statements, each with a blank to fill in with a concept related to object-oriented programming. We will determine the correct term to complete each statement.

Fill in for statement a

a. Treating a base-class object as a(n) **derived-class object** can cause errors. This is because a base-class object does not have the additional features of a derived-class object.

Fill in for statement b

b. Polymorphism helps eliminate **switch-case** logic. Polymorphism allows different methods to be called on different types of objects without explicit decision logic.

Fill in for statement c

c. If a class contains at least one pure virtual function, it is a(n) **abstract** class. An abstract class cannot be instantiated directly.

Fill in for statement d

d. Classes from which objects can be instantiated are called **concrete** classes. These classes do not have any pure virtual functions.

Fill in for statement e

e. Operator **dynamic_cast** can be used to downcast base-class pointers safely. This operator checks the validity of a downcast operation at runtime.

Fill in for statement f

f. Operator typeid returns a reference to a(n) **type_info** object. This object contains information about the type of an expression.

Fill in for statement g

g. **Dynamic binding** involves using a base-class pointer or reference to invoke virtual functions on base-class and derived-class objects. This supports polymorphism.

Fill in for statement h

h. Overridable functions are declared using keyword **virtual**. This indicates that the function can be overridden in derived classes.

Fill in for statement i

i. Casting a base-class pointer to a derived-class pointer is called **downcasting**. This involves converting a pointer to a more specific type.

Key concepts

Polymorphism

In C++ Object-Oriented Programming, polymorphism is a fundamental concept that allows objects of different classes to be treated as objects of a common base class. This is particularly powerful because it enables you to write flexible and reusable code. By utilizing polymorphism, you can call methods defined in a base class and have those methods be overridden in derived classes. One major benefit is that it helps eliminate the need for cumbersome switch-case logic or extensive if-else statements.

When a function expects a parameter of a base class type, it can accept parameters of any derived class, allowing for simple and seamless method switching. This capability makes applications easier to redesign and extend over time.

• Promotes code reusability
• Facilitates maintenance
• Keeps code clean and organized by avoiding complex control flow

Abstract Class

An abstract class in C++ is a class that cannot be instantiated directly and is designed to be a base class for other classes. An abstract class contains at least one pure virtual function. A pure virtual function is a function with no implementation that must be overridden in derived classes. Essentially, abstract classes serve as blueprints for the classes that derive from them.

These classes allow you to define methods that must be created within any child class built off the parent class. They are useful when you want to ensure that a certain method be present in all derived classes, preserving the structure of your application. Abstract classes, therefore, provide a clear protocol for class design.

• Ensures consistency across derived classes
• Provides a conceptual foundation for subclasses
• Cannot be used to create object instances

Dynamic Binding

Dynamic binding, also known as late binding, is a crucial feature in C++ that enables polymorphism. It occurs when a program determines which method to call at runtime, rather than compile time. This is achieved using virtual functions, allowing you to use a base class pointer or reference to invoke methods on derived class objects.

With dynamic binding, the correct method is called according to the type of the object being pointed to, not the type of the pointer. This enables flexibility as it allows for the implementation of extensible and maintainable systems where the specific function version executed is determined on the fly.

• Supports method overriding
• Enhances flexibility and scalability
• Key to effective polymorphism

Downcasting

Downcasting in C++ is the process of converting a base class pointer to a derived class pointer. This technique allows access to methods or properties unique to the derived class. However, downcasting should be handled with care as it can lead to runtime errors if the conversion isn't valid.

To safely perform downcasting, C++ offers the dynamic_cast operator. This operator includes runtime checking to ensure that the conversion is valid before it's performed, thereby avoiding potential errors and crashes that might occur if a simple cast is used.

• Enables access to derived class-specific features
• Requires runtime checks with dynamic_cast for safe operation
• Facilitates enhanced functionality in object hierarchy