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Unit IV
1. Inheritance
Inheritance is based on the concept of code reusability. It saves time of program development. The mechanism of deriving a new derived class (subclass) from an old base class is known as inheritance. Types of Inheritance:
2. Defining Derived Classes
■ A derived class can be defined by specifying its relationship with the base class in addition to its own details. class derived_class : visibility_mode base_class { ………… …………//members of derived class }; ■ Default visibility mode is private ■ Example 1 (Private Derivation): class ABC : private XYZ { members of ABC }; ■ Example 2 (Public Derivation): class ABC : public XYZ { members of ABC }; ■ Example 3 (Default private Derivation): class ABC : XYZ {
members of ABC }; ■ When a base class is privately inherited by a derived class
- Public members of base class become private members of derived class.
- Public members of the base class can only be accessed by member functions of derived class ■ When a base class is publicly inherited by a derived class
- Public members of base class become public members of derived class.
- They are accessible to the objects of the derived class
3. Single Inheritance
In single inheritance a single sub class is derived from the base class. Syntax 1: class A //Base Class { …………… }; class B: public A //Derived Class { ………….. }; Syntax 2: class A //Base Class { …………… }; class B: private A //Derived Class { ………….. }; Example of Single Inheritance: class base { public: int x; void getdata() { cout << "Enter the value of x = "; cin >> x; } }; class derive : public base { private: int y; public: void readdata() { cout << "Enter the value of y = "; cin >> y; } void product() { cout << "Product = " << x * y; } }; void main() { derive a; a.getdata(); a.readdata(); a.product(); } A B
6. Questions
Q.1) Define Inheritance. Q.2) How can you define derived classes from base classes using inheritance? Q.3) What is Single Inheritance? How can it be implemented in C++? Q.4) How can you make a private member inheritable? Q.5) What is Multi-level Inheritance? How can it be implemented in C++?
7. Hierarchical Inheritance
In hierarchical inheritance, the derived classes form a hierarchy. Syntax: class A { …………… }; class B : public A { ………….. }; class C : public A { …………….. };
8. Multiple Inheritance
In multiple inheritance a sub-class is derived from multiple base classes. Syntax: class A { …………… }; class B { ………….. }; class C : public A, public B { …………….. }; Example of Multiple Inheritance: class Vehicle { public: int cost; }; class Manufacturer { public: char m_name[20]; }; class Buyer: public Vehicle,public Manufacturer { public: char b_name[20]; }; void main() {
A
B C
A B
C
Buyer b; clrscr(); cout<<"\nEnter cost:"; cin>>b.cost; cout<<"\nEnter buyer name:"; cin>>b.b_name; cout<<"\nEnter manufacturer name:"; cin>>b.m_name; cout<<"Name of buyer:"<<b.b_name<<endl; cout << "Cost of Car=" << b.cost << endl; cout << "Manufacturer name= " << b.m_name<< endl; getch(); }
9. Hybrid Inheritance
Multiple types of inheritance is combined in a hybrid inheritance. Syntax: class A { …………… }; class B : public A { ………….. }; class C : public A { …………….. }; class D : public B, public C { ………….. };
10. Virtual Base Classes
■ Virtual base class is used in situation where a derived class have multiple copies of base class. ■ Avoids duplication of inherited members A B C D
public: void sound() { cout<<“Meow"<<endl; } }; void main() { Dog obj; obj.sound(); obj.sleeping(); Cat obj1; obj1.sound(); obj1.sleeping(); }
12. Questions
Q.1) What is Hierarchical Inheritance? How can it be implemented in C++? Q.2) What is Multiple Inheritance? How can it be implemented in C++? Q.3) What is Hybrid Inheritance? How can it be implemented in C++? Q.4) What is a Virtual Base Class? Q.5) What are abstract classes? How can it be implemented in C++?
13. Constructor in Derived Classes
■ When a class is derived from another class, it is possible to define a constructor in the derived class, and the data members of both base and derived classes can be initialized. ■ It is not essential to declare a constructor in the base class ■ Example: class A { protected: int x,y; }; class B : private A { public: int z; B() { x=1; y=2;z=3; cout<<“x=“<<x<<“y=“<<y<<“z=“<<z; } }; void main() { B b; }
14. Nesting of Classes
■ Nested class is a class defined inside a class, that can be used within the scope of the class in which it is defined. ■ Example: class Nest { public:
class Display { private: int s; public: void sum( int a, int b) { s =a+b; } void show( ) { cout << "\nSum of a and b is:: " << s;} }; }; void main() { Nest::Display x; x.sum(12, 10); x.show(); } Output: Sum of a and b is:: 22
15. Questions
Q.1) How can you use Constructor in Derived Classes? Q.2) What is nesting of classes? How can it be implemented in C++? Q.3) Write a C++ program to implement a constructor in a derived class. Q.4) What do you mean by a derived class? Q.5) How can a constructor be created for a derived class?
