Inheritance

Function overriding (preview of polymorphism)

• Derived can redefine a base function with the same signature.
• For runtime polymorphism via base pointers, mark the base function virtual (next lessons).
• Without virtual, calling through a base pointer uses the base version (static binding).

class Shape {
public:
    virtual void draw() const { /* base */ }
    virtual ~Shape() = default;
};
class Circle : public Shape {
public:
    void draw() const override { /* circle */ }
};

Protected members in inheritance

• protected is for “derived may use, outside world may not”.
• Useful for shared hooks; do not overexpose internals as protected.

Real-life inheritance models

• GUI: Widget → Button / TextBox / Label.
• Games: Entity → Player / Enemy / NPC.
• Employees: Employee → Manager / Developer / Intern.
• Devices: Device → Printer / Scanner → AllInOne (multiple/hybrid carefully).

Single inheritance — Animal / Dog

#include <iostream>
using namespace std;

class Animal {
public:
    void eat() { cout << "Eating\n"; }
};
class Dog : public Animal {
public:
    void bark() { cout << "Barking\n"; }
};

int main() {
    Dog d;
    d.eat();
    d.bark();
    return 0;
}

Multilevel — A / B / C

#include <iostream>
using namespace std;

class A {
public:
    void fa() { cout << "A\n"; }
};
class B : public A {
public:
    void fb() { cout << "B\n"; }
};
class C : public B {
public:
    void fc() { cout << "C\n"; }
};

int main() {
    C obj;
    obj.fa(); obj.fb(); obj.fc();
    return 0;
}

Hierarchical — Vehicle family

#include <iostream>
using namespace std;

class Vehicle {
public:
    void start() { cout << "Vehicle start\n"; }
};
class Car : public Vehicle {
public:
    void drive() { cout << "Car drive\n"; }
};
class Bike : public Vehicle {
public:
    void ride() { cout << "Bike ride\n"; }
};

int main() {
    Car c; Bike b;
    c.start(); c.drive();
    b.start(); b.ride();
    return 0;
}

Multiple inheritance — Copier

#include <iostream>
using namespace std;

class Printer {
public:
    void printDoc() { cout << "Printing\n"; }
};
class Scanner {
public:
    void scanDoc() { cout << "Scanning\n"; }
};
class Copier : public Printer, public Scanner {};

int main() {
    Copier m;
    m.printDoc();
    m.scanDoc();
    return 0;
}

Ctor / dtor order

#include <iostream>
using namespace std;

class Base {
public:
    Base() { cout << "Base\n"; }
    ~Base() { cout << "~Base\n"; }
};
class Derived : public Base {
public:
    Derived() { cout << "Derived\n"; }
    ~Derived() { cout << "~Derived\n"; }
};

int main() {
    Derived d;
    return 0;
}

Protected member used by derived

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

class Person {
protected:
    string name;
public:
    Person(string n) : name(n) {}
};
class Student : public Person {
    int roll;
public:
    Student(string n, int r) : Person(n), roll(r) {}
    void show() const { cout << name << " " << roll << "\n"; }
};

int main() {
    Student s("Asha", 10);
    s.show();
    return 0;
}

Ambiguity resolution (qualify)

#include <iostream>
using namespace std;

class A {
public:
    void show() { cout << "A\n"; }
};
class B {
public:
    void show() { cout << "B\n"; }
};
class C : public A, public B {};

int main() {
    C obj;
    obj.A::show();
    obj.B::show();
    return 0;
}