1. Explain about virtual destructor?

If the destructor in the base class is not made virtual, then an object that might have been declared of type base class and instance of child class would simply call the base class destructor without calling the derived class destructor.

Hence, by making the destructor in the base class virtual, we ensure that the derived class destructor gets called before the base class destructor.

class a
{
public:
a(){printf("nBase Constructorn");}
~a(){printf("nBase Destructorn");}
};

class b : public a
{
public:
b(){printf("nDerived Constructorn");}
~b(){printf("nDerived Destructorn");}
};
int main()
{
a* obj=new b;
delete obj;
return 0;
}

Output:
Base Constructor
Derived Constructor
Base Destructor

By Changing
~a(){printf("nBase Destructorn");}
to
virtual ~a(){printf("nBase Destructorn");}

Output:
Base Constructor
Derived Constructor
Derived Destructor
Base Destructor

2. Explain what is Private Inheritance?

The Public and protected members of Base class become private members of the derived class.

3. Explain what is Public Inheritance?

All the public members and protected members are inherited as public and protected respectively.

4. List the advantages of inheritance?

Allows the code to be reused as many times as needed. The base class once defined and once it is compiled, it need not be reworked.
Saves time and effort as the main code need not be written again.

5. Explain about Protected Inheritance?

Public and Protected members are derived as protected members.

6. Explain what is protected inheritance?

When a class is being derived from another class, we can make use of access specifiers. This is essentially useful to control the access the derived class members have to the base class. When inheritance is protected:

Private members of base class are not accessible to derived class.
Protected members of base class remain protected in derived class.
Public members of base class become protected in derived class.
#include <iostream>
using namespace std;

class base
{
protected:
int i, j;
public:
void setij(int a, int b)
{
i = a;
j = b;
}
void showij()
{
cout <<"nI:"<<i<<"n J:<<j;
}
};

class derived : protected base
{
int k;
public:
void setk()
{
setij();
k = i + j;
}
void showall()
{
cout <<"nK:"<<k<<show();
}
};

int main()
{
derived ob;
//ob.setij(); // not allowed. Setij() is protected member of derived
ob.setk(); //ok setk() is public member of derived
//ob.showij(); // not allowed. Showij() is protected member of derived
ob.showall(); // ok showall() is public member of derived
return 0;
}

7. Explain about the private inheritance?

When a class is being derived from another class, we can make use of access specifiers. This is essentially useful to control the access the derived class members have to the base class. When inheritance is private:

i. Private members of base class are not accessible to derived class.
ii. Protected members of base class become private members of derived class.
iii. Public members of base class become private members of derived class.
#include <iostream>
using namespace std;

class base
{
int i, j;
public:
void setij(int a, int b)
{
i = a;
j = b;
}

void showij()
{
cout <<"nI:"<<i<<"n J:"<<j;
}
};

class derived : private base
{
int k;
public:
void setk()
{
//setij();
k = i + j;
}
void showall()
{
cout <<"nK:"<<k<<show();
}
};

int main()
{
derived ob;
//ob.setij(); // not allowed. Setij() is private member of derived
ob.setk(); //ok setk() is public member of derived
//ob.showij(); // not allowed. Showij() is private member of derived
ob.showall(); // ok showall() is public member of derived
return 0;
}

8. Give example of pure virtual functions?

A pure virtual function is a function which has no definition in the base class. Its definition lies only in the derived class ie it is compulsory for the derived class to provide definition of a pure virtual function. Since there is no definition in the base class, these functions can be equated to zero.

The general form of pure virtual function is:

virtual type func-name(parameter-list) = 0;

Consider following example of base class Shape and classes derived from it viz Circle, Rectangle, Triangle etc.

class Shape
{
int x, y;
public:
virtual void draw() = 0;
};

class Circle: public Shape
{
public:
draw()
{
//Code for drawing a circle
}
};

class Rectangle: public Shape
{
Public:
void draw()
{
//Code for drawing a rectangle
}
};

class Triangle: public Shape
{
Public:
void draw()
{
//Code for drawing a triangle
}
};

Thus, base class Shape has pure virtual function draw(); which is overridden by all the derived classes.

9. Explain the difference between Overriding vs. overloading?

Overloading helps to create different behaviors of methods with the same name and scope. For instance we can overload a method to return float values and integer values.
Overriding on the other hand changes the behavior of a class to make it behave different than its parent class.

10. Explain about overriding?

Defining a function in the derived class with same name as in the parent class is called overriding. In C++, the base class member can be overridden by the derived class function with the same signature as the base class function. Method overriding is used to provide different implementations of a function so that a more specific behavior can be realized.

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