#include <iostream>
using namespace std;

// Base class
class A1 {
public:
    void showA1() {
        cout << "This is class A1" << endl;
    }
};

// Derived class from A1
class A2 : public A1 {
public:
    void showA2() {
        cout << "This is class A2" << endl;
    }
};

// Derived class from A2 (Multilevel Inheritance)
class A3 : public A2 {
public:
    void showA3() {
        cout << "This is class A3" << endl;
    }
};

int main() {
    A3 obj;

    // Accessing members of all classes
    obj.showA1();
    obj.showA2();
    obj.showA3();

    return 0;
}

Documentation

Output

This is class A1
This is class A2
This is class A3

Explanation

Multilevel inheritance occurs when a class is derived from another derived class.
A3 inherits from A2, and A2 inherits from A1.
Hence, object of A3 can access functions of A1, A2, and A3.