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Question: Question 6 (a) What is the difference between a class and an object in object oriented pro grammi……
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a. What is difference between class and object in object oriented programming language?
Class is a logical entity and group of similar objects. Class doesnt allocated memory when its create.
Object is an instance of class and it is real world entity. Object allocates memory when it is created.
Example: Class Fruit and we have different objects like Apple,Banana, Mango, Guava..etc.
b. Objects model state and exhibit behaviour. Explain how state and behaviour are implemented in c++?
Lamp is an object.
The “state” in lamp:on and off.
The “behavior” in lamp:turn on and turn off.
In c++ programming you declare states in “fields” and behaviors in “methods” etc..
c. What is role of destructor? How is written in c++? Give an example of what you might do in a destructor?
Destructor is a member function which destructs or deletes an object.
Destructors have same name as the class preceded by a tilde (~)
Destructors don’t take any argument and don’t return anything
String(char *); // constructor
~String(); // destructor
size = strlen(c);
s = new char[size+1];
d. When is it necessary to define a default constructor?
A default constructor is a constructor that either has no parameters, or if it has parameters, all the parameters have default values.
If no user-defined constructor exists for a class A and one is needed, the compiler implicitly declares a default parameterless constructor A::A().
e. What is the purpose of static class variable?
A variable declared static within the body of a function maintains its value between invocations of the function.
A variable declared static within a module (but outside the body of a function) is accessible by all functions within that module.
However, it is not accessible by functions from other modules.
static members exist as members of the class rather than as an instance in each object of the class.
There is only a single instance of each static data member for the entire class.
f. Briefly describe the use of encapsulation and abstraction in c++?
Encapsulation: Wrapping data memebers and member function into a single unit called encapsulation i.e class.
Abstraction: Hiding the data and showing the functionality.
In c++ we can use abstraction as
Members declared as public in a class, can be accessed from anywhere in the program.
Members declared as private in a class, can be accessed only from within the class. They are not allowed to be accessed from any part of code outside the class
Within class within subclass Outside class
Public Y Y Y
Private Y N N
Protected Y Y N
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