Classes and Objects in C++

Classes and Objects in C++

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Updated on Jan 16, 2023 17:44 IST

If you are a student then you must have got this question in the exam or practical viva and if you are a job seeker then you must have faced this question about classes in c++ in the interview. So this is a must-know question if you are interested in learning C++. This is the topic that distinguishes C++ from C language. Everything in C++ maps to classes and objects, along with their attributes and methods. Example: In real life, a car is an object. Cars have attributes such as weight and color, and methods such as propulsion and braking. Attributes and methods are basically variables and functions that belong to a class. These are often called “class members”.

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In this blog, I will be explaining classes and objects in C++, and constructors in a simple language. Everything will be explained with examples and explanations.

So let’s get started!!!

What are classes in C++?

A class is like a container containing data variables and functions in it.

A class is a user-defined data type that holds variables and member functions together which can be accessed by using objects. Now, what is an object? That we will discuss in this blog later on. But remember class is a group of objects of the same type. For example, if you have a class name student which has different properties like Name, Roll no., age, then if you want to access them then you need an object.

Declaration and definition of classes

In C+, a class is declared and defined using the class keyword. This should be followed by the class name in case of function declaration and in the case of the class definition, the class body is then added between curly braces { }.

Syntax:

ClassName ObjectName; //class declaration

Syntax:

 
class class_name {
access_specifier_1:
member1;
access_specifier_2:
member2;
...
}
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What are objects?

Objects are the instances of the class

As we see above that we have variables and functions in the class. Can we access them directly? For that, we need to make the object of that class. So objects are the instances of the class. Basically, Objects are created from classes. A Declaration of objects is done in the same way as we do a declaration of variables. The class name is preceded by the object name.

Syntax-

Class_name object_name;

Eg:

NOTE: You have to take the same class name while declaring the objects keeping in mind the uppercase and lowercase.

Understanding Objects with Simple Analogy

Objects are comparable to people. They’re alive, breathing things with knowledge of how to do things and memory so they can recall things. And instead of working with them at a very low level of abstraction you interact with them at a very high degree of abstraction.

Here’s an example: If I’m your laundry object, you can give me your filthy clothing and message me, “Can you have my clothes cleaned, please?” I happen to know where the greatest washing place in San Francisco is. I also speak English and have money in my pockets. So I step outside and grab a taxicab, instructing the driver to take me to this location in San Francisco. I go have your clothing washed, get back in the cab, and return here. “Here are your clean clothes,” I remark as I hand you your clean clothes.

You have no clue how I accomplished it. You have no idea where the laundry is. Perhaps you don’t speak French and can’t even take a taxi. You can’t afford one since you don’t have any money. But I knew how to accomplish it all. And you weren’t required to know any of it. All of that information was contained within me, and we could communicate at a very high degree of abstraction. That’s what an object is. They contain complexity, with high-level interfaces to that complexity.

Accessing Data Members using objects

The public data members of a class that are declared public can be accessed using the direct member access operator i.e dot operator (.). Let us try the following example to make the things clear −

In this, we first declared the variables like Roll no., Name, age, and a member function showage which is being defined in the class only. Then we created an object(std1) of the class student. And then we used this object to assign values to the variables and also to execute showage()

Preparing for a C++ interview? Check out the Top C++ Interview Questions and Answers

Also Read – Understanding Operators in C++

Learn more: Basics of C Programming Language

Related Read – Binary Search in C++

Constructors in C++

Constructors are a special type of member function that are called automatically whenever an object is created. So, in short, constructors initialize objects.

In C++, a constructor has the same name as that of the class, and it does not have a return type. For example,

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Type of constructor

1. Default constructor

This constructor has no argument. Constructor gets invoked at the time of object creation.

Default constructor Invoked is appeared two times in the output because we have two objects of the student class. Whenever objects were created constructor was called. And when the constructor was called whatever was there in the body of the constructor was executed.

2. Parameterized constructor

This is a constructor with parameters. This method is preferred to initialize member data. This constructor is passed with parameters, and the object holds the value of these parameters. So whenever an object is created, this constructor is called. In this, we have a constructor which has parameters. We created an object we pass the values for the member variables as arguments, as shown in the fig below.

Endnotes

In this blog, we understood classes in c++, objects, and constructors with their syntax and examples. If you liked this blog, please do share it with other friends too.

Happy Learning!!!

FAQs

What are classes in C++?

A basic building block of OO software. A class defines a data type much like a struct in C. Classes in C++ are the building blocks that lead to object-oriented programming. This is a user-defined data type containing its own data members and member functions that can be accessed and used by creating an instance of this class. A C++ class is like a blueprint for an object.

What are objects in C++?

Objects are instances of classes. No memory is allocated when a class is defined, but memory is allocated when it is instantiated (that is, when an object is created).

What is the relationship between objects and classes in C++?

Objects are instances of classes. No memory is allocated when a class is defined, but memory is allocated when it is instantiated (that is, when an object is created). If you want to access data members or member function of a class then that can be done with the help of objects.

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