Inheritance Intro

A class can inherit another. This means that all members of the inherited class (base class) will become members of the inheriting class (derived class). Given a class ClassA, a class ClassB can be defined, inheriting ClassA: 
class ClassA{};

class ClassB: public ClassA {};
The keyword public means that all accessibility levels for ClassA members will be maintained in ClassB, i. e. a public member remains public, so does a protected or a private one. In the program below a class Person is declared, then a class Teacher, derived from Person, is declared. All members of Person become members of Teacher. A Teacher object will contain name, age, setNameAge(). Further, it will contain subject and setSubject(). class Teacher : public Person ensures that: all public members of Person will be public in Teacher, all protected members of Person will be protected in Teacher, all private members of Person will be private in Teacher. Basically it keeps the privacy level of the inherited class members the same as it was in the base class. If the derived class were defined as: 
class Teacher: protected Person
all public base class members would become protected in the derived class. If the derived class were defined as: 
class Teacher: private Person
all public and protected base class members would become private in the derived class.

Example


#include <iostream>
#include <string<
using namespace std;

class Person
{
     string name;   // by default all class members are private
     int age;
public:            // the following members are public
     void setNameAge(string aName, int anAge)
     {
           name = aName;
           age = anAge;
     }

     void printNameAge()
     {
           cout << "name: " << name << " age: " << age << "\n";
     }
};

class Teacher : public Person
{
     string subject;
public:
     void setSubject(string aSubject)
     {
           subject = aSubject;
     }

     void printSubject()
     {
           cout << "subject: " << subject;
     }
};

int main()
{
     Person person1;
     person1.setNameAge("John" , 23);
     Teacher teacher1;
     teacher1.setNameAge("Frank", 78);
     teacher1.setSubject("Math");
     person1.printNameAge();
     teacher1.printNameAge();
     teacher1.printSubject();
}

Output

name: John age: 23
name: Frank age: 78
subject: Math