Classes and Objects: Two Marks Important Questions and Answers

Object Oriented Programming- C++

Chapter 2: Classes and Objects

Two Marks Questions with Answers

1. What is dynamic constructor? Give example.

Answer: Dynamic constructor is a kind of constructor which can allocate the memory for the objects using the operator new

For example ‒

TEST::TEST() //dynamic constructor

{

len=0; //initially length is 0

str=new char[len+1];

strcpy(str,""); //initialization by empty string

}

2. Write copy constructor for class date(assume mm,dd,yy as its members).

Answer:

#include<iostream.h>

class CopyCons

{

      int dd,mm,yy;

public:

      CopyCons();

      CopyCons(int d,int m,int y){dd=d;mm=m;yy=y;

}

CopyCons(CopyCons &x)

{

      dd=x.dd;

      mm=x.mm;

      yy=x.yy;

}

void display()

{

      cout<<"\nDate: "<<dd;

      cout<<"\nMonth: "<<mm;

      cout<<"\nYear: "<<yy;

}

};

int main()

{

      CopyCons X(10,10,1999);

      CopyCons Y(X);

      CopyCons Z=X;

      cout<<"\n Date using object X: \n";

      X.display();

      cout<<"\n Date using object Y: \n";

      Y.display();

      cout<<"\n Date using object Z: \n";

      Z.display();

      return 0;

}

3. When will the destructor be called? Is it implicit or explicit ?

 Answer: The destructor will be called only when on wants to deallocate the memory. This can be explicitly created using ~ followed by class name function or when the program reached to end, when is encountered then automatically the implicit destructor is called in order to deallocate the memory. It is a good practice to write the explicit destructor to dealllocate the allocated memory for the object.

4. What are copy constructors ?

Answer: Copy constructor is a special type of constructor in which new object is created as a copy of existing object.

5. What is instantiation ?

 Answer: Instantiation of object is needed to use the object of particular class. The class is a kind of template and by instantiation of the object, we can make use of the data members and member function of class.

6. How is class declared in C++?

Answer: The class is declared using the keyword class. Following example shows how to declare class in C++.

Syntax

class classname

{

access specifier:

     data members;

access specifier

      operations;

};

Example

class Student

{

private:

     int rollno;

     float marks;

public:

     void input_marks();

     void display_marks();

};

7. What is scope resolution operator and how it can be used for global variable ?

 Answer: The scope resolution operator is denoted by ::. It is used to define the scope of the variable or a function. If we write some function inside the class, then that function can be accessed from outside the class using the scope resolution of operator. Thus the scope of the scope resolution operator is global.

8. Highlight the advantages of static data members and static functions in C++.

Answer: When a static data member or a static function is created then that means only one copy of that variable or function is created and all other objects must share that single copy. Thus some amount of memory gets saved. Secondly static members can be accessed without any instantiation of class as an object.

9. What is destructor?

Answer: The destructor is a special function which is called when the object is destroyed. The destructor function name is preceded by the tilde sign(~).

10. Give any two characteristics of constructors

Answer:

1. The name of the constructor and the class name must be same.

2. The constructor must be declared in public mode.

3. The constructors can not be inherited.

11. Can the parameter of copy constructor be passed by value ? Justify your answer.

Answer: No the parameter of copy constructor can not be passed by value. Because the copy constructor is a special type of constructor in which new object is created as a copy of existing object. Hence copy constructor always takes a reference (address) to an object of a same class as an argument.

12.  How do the constructor gets invoked?

Answer: The constructor need not be invoked explicitly, instead, it gets invoked automatically when the object of particular class is created.

13. Define attribute.

Answer:Attributes are the data members of the class. These are meant for representing the characteristics of the class.

14. What effects do the visibility labels private, protected and public have on the members of the class ?

Answer: If the base class has the members possessing the visibility label as private then those members are not accessible to derived class. If the members of the class are labelled as protected then that means these members are public to derived class but are private to rest of the program. If the members of the class are labelled as public then that indicates the members can be accessible by any class in the entire program.

15. What is the default access specifier of a class?

Answer: The default access specifier is private.

16.  What is the difference between private, protected and public modes ?

Answer: If the base class have private members then those members are not accessible to derived class. Protected members are public to derived classes but private to reset of the program. And the public members are accessible to all.

17. What are the points to remember about friend function ?

Answer: The friend function is always preceded by the keyword friend. It is not a member of a class but can access the private and protected members of the class.

18. What are merits of using Classes ?

Answer:

1. The data and member function can be encapsulated within one entity.

2. The data hiding property can be achieved.

3. The data can be reused by another class by the OOP feature called inheritance

4. Multiple instances of the same class can be created to handle set of data separately.

19.  What is the use of destructor ?

Answer: When the programmer wants to deallocate the memory being allocated then destructor is called. The destructor uses ~ followed by class name function.