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Multilevel Inheritance with Overriding in C++

This C++ program demonstrates multilevel inheritance with method overriding in classes. The val() methods have been declared virtual, the V-table always keeps track of the latest version of val() method. As the pointer to an object is upcast to a ‘less-derived’ Class, correct version of the method is called when a particular method val() is called as the V-table now keeps track of the latest version of method val().

Here is the source code of the C++ program demonstrates multilevel inheritance without method overriding in classes. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
```

 * C++ Program to Illustrate Multilevel Inheritance

```
 * with Method Overriding
```
```
 */
```
```
#include <iostream>
```
```
 
```
```
class Base {
```
```
    int i;
```
```
    public:
```
```
        Base(int i = 0): i(i) { }
```

        virtual int val() const { return i; }

```
        virtual ~Base() { }
```
```
};
```
```
 
```
```
class Derived : public Base
```
```
{
```
```
    int i;
```
```
    public:
```
```
        Derived(int i = 0): i(i) { }
```

        virtual int val() const { return i; }

```
        virtual ~Derived() { }
```
```
};
```
```
 
```
```
class MostDerived : public Derived 
```
```
{
```
```
    int i;
```
```
    public:
```

        MostDerived(int i = 0): i(i) { }

        virtual int val() const { return i; }

```
        virtual ~MostDerived() { }
```
```
};
```
```
 
```
```
int main()
```
```
{
```
```
    Base * B = new Base(1);
```
```
    Base * D = new Derived(2);
```
```
    Base * MD = new MostDerived(3);
```
```
 
```

    std::cout << "Base.Value() = " << B->val() << std::endl;

    std::cout << "Derived.Value() = " << D->val() << std::endl;

    std::cout << "MostDerived.Value() = " << MD->val() << std::endl;

```
}
```

$ a.out
Base.Value() = 1
Derived.Value() = 2
MostDerived.Value() = 3