Question

1 What is a pure virtual function? Why would you define a pure virtual function? Give an example of a pure virtual function.

2 When a function has an object parameter that it doesn't modify,
what is the best way to declare the parameter (in the function
signature), and why?

3 Show an example using a function with a string object parameter.

a) When a class has objects as data members, why should its
constructors use initialization lists (member and initializer
syntax) vs. assignment to the members in the body of the ctor?
  
b) Name two cases where you *must* use initialization lists in
constructors (as opposed to assignment in the ctor body).

4 When a function has an object parameter that it doesn't modify,
what is the best way to declare the parameter (in the function
signature), and why?
Show an example using a function with a string object parameter.

Answer 1

Pure virtual function:

It is a type of virtual function whose initialization is done with zero, a pure virtual function is not defined in the base class as it is redefined in the derived class. A base class is said to be an abstract class.

A virtual keyword is used to define a pure virtual function.  

Syntax:

class Parent

{

public:

virtual void see() = 0;

};

Pure virtual function is basically used to create abstract class. A class with at least one pure virtual function is an abstract class.

Also, an object of an abstract class cannot be created, and the definition of a pure virtual function is given in the derived class. Hence, an object of the derived class is used to call a pure virtual function.

Example:

//header file declared

#include <iostream>

//namespace used

using namespace std;

//base class

class Parent

{

//access modifier   

public:

//declaration of pure virtual function

virtual void see() = 0;

};

//inheritance

class Child : public Parent

{

//access modifier   

public:

//definition of pure virtual function

void see()

{

//displaying message

cout<<"pure virtual function is defined in derived class";

}

};

//main function

int main()

{

//creating object of derived class

Child ob;

//calling of pure virtual function

ob.see();

return 0;

}

Output: