C++ Inheritance

What is Inheritance?

Inheritance lets a class (child/derived) acquire attributes and methods of another class (parent/base), promoting code reuse.

class DerivedClass : accessSpecifier BaseClass { };

#include <iostream>
using namespace std;

// Base class
class Animal {
  public:
    string name;
    void eat()   { cout << name << " is eating." << endl; }
    void sleep() { cout << name << " is sleeping." << endl; }
};

// Derived class
class Dog : public Animal {
  public:
    void bark() { cout << name << " says: Woof!" << endl; }
};

class Cat : public Animal {
  public:
    void meow() { cout << name << " says: Meow!" << endl; }
};

int main() {
    Dog d; d.name = "Rex";
    d.eat();    // inherited from Animal
    d.bark();   // Dog's own method

    Cat c; c.name = "Whiskers";
    c.sleep();  // inherited
    c.meow();
    return 0;
}

Output:

Rex is eating.
Rex says: Woof!
Whiskers is sleeping.
Whiskers says: Meow!

Constructor Inheritance

The derived constructor calls the base constructor using the initializer list:

class Vehicle {
  public:
    string brand;
    Vehicle(string b) : brand(b) { }
};

class ElectricCar : public Vehicle {
  public:
    int range;
    ElectricCar(string b, int r) : Vehicle(b), range(r) { }
    void info() {
        cout << brand << " — Range: " << range << "km" << endl;
    }
};

ElectricCar tesla("Tesla", 600);
tesla.info();   // Tesla — Range: 600km

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

class Shape {
  public:
    string color;
    Shape(string c) : color(c) { }
    void describe() { cout << "Color: " << color << endl; }
};

class Circle : public Shape {
  public:
    double radius;
    Circle(string c, double r) : Shape(c), radius(r) { }
    double area() { return 3.14159 * radius * radius; }
};

class Square : public Shape {
  public:
    double side;
    Square(string c, double s) : Shape(c), side(s) { }
    double area() { return side * side; }
};

int main() {
    Circle ci("Red", 5);
    ci.describe();
    cout << "Circle area: " << ci.area() << endl;

    Square sq("Blue", 4);
    sq.describe();
    cout << "Square area: " << sq.area() << endl;
    return 0;
}

Summary

• Inheritance enables a derived class to reuse base class members.
• Use class Child : public Parent syntax.
• Derived constructors call base constructors via initializer lists.