Index
Classes and Objects
In Object-Oriented Programming (OOP), classes and objects are fundamental concepts. To grasp them, let’s explore an analogy and then translate that into C++ code.
Real-Life Analogy: Designing a Car
Imagine you’re a car manufacturer. Before you start building cars, you need a blueprint that defines the features and specifications of the car. This blueprint isn’t a car itself, but it contains all the details necessary to create one. This is analogous to a class in OOP.
Once you have the blueprint, you can create actual cars based on it. Each car you manufacture is a unique instance but follows the same specifications laid out in the blueprint. These cars are analogous to objects.
C++ Class
A class is a blueprint or a template that defines the properties (attributes) and behaviors (methods) of objects. In our analogy, the class would define the characteristics of a car, such as the model, color, and engine type, as well as the actions the car can perform, like accelerating, braking, and honking.
Create a Class
To define a class in C++, use the class keyword followed by the class name. Inside the class, you can define its attributes (data members) and methods (member functions).
class ClassName {
public:
// Public members (attributes and methods)
private:
// Private members (attributes and methods)
};
C++ Object
An object is an instance of a class. Using the car analogy, an object would be a specific car with a particular model, color, and engine type. You can create multiple objects from the same class, each with its own unique set of properties.
Syntax
ClassName object_name;
For Example:
#include <iostream>
#include <string>
using namespace std;
// Define the Student class
class Student {
public:
// Attributes
string name;
int rollNumber;
float marks;
// Method to display student details
void displayDetails() {
cout << "Name: " << name << endl;
cout << "Roll Number: " << rollNumber << endl;
cout << "Marks: " << marks << endl;
}
};
int main() {
// Create an object of the Student class
Student student1;
// Set attributes for student1
student1.name = "Peter";
student1.rollNumber = 23;
student1.marks = 95.5;
// Create another object of the Student class
Student student2;
// Set attributes for student2
student2.name = "John";
student2.rollNumber = 24;
student2.marks = 88.0;
// Display details of student1
cout << "Student 1 Details:" << endl;
student1.displayDetails();
// Display details of student2
cout << "Student 2 Details:" << endl;
student2.displayDetails();
return 0;
}
Output:
Student 1 Details:
Name: Peter
Roll Number: 23
Marks: 93.5
Student 2 Details:
Name: John
Roll Number: 24
Marks: 91
Explanation:
Step 1: Include Necessary Libraries
First, we include the necessary libraries to use standard input-output and string manipulation functionalities.
#include <iostream> // For input and output
#include <string> // For using string data type
using namespace std; // To avoid using std:: prefix repeatedly
Step 2: Define the Student Class
Next, we define a Student class, which serves as a blueprint for creating student objects. The class contains attributes (properties) and a method (function).
// Define the Student class
class Student {
public:
// Attributes
string name; // To store the student's name
int rollNumber; // To store the student's roll number
float marks; // To store the student's marks
// Method to display student details
void displayDetails() {
cout << "Name: " << name << endl;
cout << "Roll Number: " << rollNumber << endl;
cout << "Marks: " << marks << endl;
}
};
Explanation
- Attributes:
string name;— Stores the name of the student.int rollNumber;— Stores the roll number of the student.float marks;— Stores the marks of the student.
- Method:
void displayDetails();— This method displays the student’s details when called.
Step 3: Create and Initialize Objects in main()
In the main() function, we create objects of the Student class, set their attributes, and display their details using the method we defined.
int main() {
// Create an object of the Student class
Student student1;
// Set attributes for student1
student1.name = "Peter";
student1.rollNumber = 23;
student1.marks = 93.5;
// Create another object of the Student class
Student student2;
// Set attributes for student2
student2.name = "John";
student2.rollNumber = 24;
student2.marks = 91;
Explanation:
Creating Objects:
Student student1;— Creates an objectstudent1of theStudentclass.Student student2;— Creates another objectstudent2of theStudentclass.
Setting Attributes:
student1.name = "Peter";— Assigns “Peter” to thenameattribute ofstudent1.student1.rollNumber = 23;— Assigns 23 to therollNumberattribute ofstudent1.student1.marks = 93.5;— Assigns 93.5 to themarksattribute ofstudent1.- The same steps are repeated for
student2, with different values
Step 4: Display the Detail of Each Student
Finally, we call the displayDetails() method on each object to print their details to the console.
// Display details of student1
cout << "Student 1 Details:" << endl;
student1.displayDetails();
// Display details of student2
cout << "Student 2 Details:" << endl;
student2.displayDetails();
return 0;
}
Explanation:
Calling Methods:
student1.displayDetails();— Calls thedisplayDetails()method onstudent1, which prints the name, roll number, and marks ofstudent1.student2.displayDetails();— Calls thedisplayDetails()method onstudent2, which prints the name, roll number, and marks ofstudent2.
Output:
- This will display the details of both students on the console.
Example 2:
#include <iostream>
#include <string>
using namespace std;
// Define the Book class
class Book {
public:
// Attributes (Properties)
string title;
string author;
int pages;
// Method to display book details
void displayDetails() {
cout << "Title: " << title << endl;
cout << "Author: " << author << endl;
cout << "Pages: " << pages << endl;
}
};
int main() {
// Create an object of the Book class
Book book1;
// Set attributes for book1
book1.title = "The Catcher in the Rye";
book1.author = "J.D. Salinger";
book1.pages = 277;
// Create another object of the Book class
Book book2;
// Set attributes for book2
book2.title = "To Kill a Mockingbird";
book2.author = "Harper Lee";
book2.pages = 281;
// Display details of book1
cout << "Book 1 Details:" << endl;
book1.displayDetails();
// Display details of book2
cout << "Book 2 Details:" << endl;
book2.displayDetails();
return 0;
}
Output:
Book 1 Details:
Title: The Catcher in the Rye
Author: J.D. Salinger
Pages: 277
Book 2 Details:
Title: To Kill a Mockingbird
Author: Harper Lee
Pages: 281
Explanation:
Step 1: Include Necessary Libraries
First, we include the necessary libraries for input-output operations and string handling.
#include <iostream> // For input and output operations
#include <string> // For using the string data type
using namespace std; // To avoid using the std:: prefix before standard library functions
Step 2: Define the Book Class
Next, we define the Book class, which serves as a blueprint for creating book objects. The class contains attributes (properties) and a method (function).
// Define the Book class
class Book {
public:
// Attributes (Properties)
string title; // To store the title of the book
string author; // To store the author of the book
int pages; // To store the number of pages in the book
// Method to display book details
void displayDetails() {
cout << "Title: " << title << endl;
cout << "Author: " << author << endl;
cout << "Pages: " << pages << endl;
}
};
Explanation:
- Class Definition:
class Book { ... };defines a class namedBook.
- Attributes:
string title;— Stores the title of the book.string author;— Stores the author of the book.int pages;— Stores the number of pages in the book.
- Method:
void displayDetails();— This method displays the book’s details.
Step 3: Create and Initialize Objects in main()
In the main() function, we create objects of the Book class, set their attributes, and display their details using the method we defined.
int main() {
// Create an object of the Book class
Book book1;
// Set attributes for book1
book1.title = "The Catcher in the Rye";
book1.author = "J.D. Salinger";
book1.pages = 277;
Explanation:
- Creating an Object:
Book book1;creates an object namedbook1of theBookclass.
- Setting Attributes:
book1.title = "The Catcher in the Rye";sets thetitleattribute ofbook1.book1.author = "J.D. Salinger";sets theauthorattribute ofbook1.book1.pages = 277;sets thepagesattribute ofbook1.
Step 4: . Create Another Object and Initialize It
We can create another object of the Book class and assign it different attribute values.
// Create another object of the Book class
Book book2;
// Set attributes for book2
book2.title = "To Kill a Mockingbird";
book2.author = "Harper Lee";
book2.pages = 281;
Explanation:
- Creating Another Object:
Book book2;creates another object namedbook2of theBookclass.
- Setting Attributes:
book2.title = "To Kill a Mockingbird";sets thetitleattribute ofbook2.book2.author = "Harper Lee";sets theauthorattribute ofbook2.book2.pages = 281;sets thepagesattribute ofbook2.
Step 5: Display the Details of Each Book
Finally, we use the displayDetails() method to print the details of each book.
// Display details of book1
cout << "Book 1 Details:" << endl;
book1.displayDetails();
// Display details of book2
cout << "Book 2 Details:" << endl;
book2.displayDetails();
return 0;
}
Explanation:
- Calling Methods:
book1.displayDetails();calls thedisplayDetails()method onbook1, which prints the title, author, and pages ofbook1.book2.displayDetails();calls thedisplayDetails()method onbook2, which prints the title, author, and pages ofbook2.
- Output:
- This will display the details of both books on the console.