Classes and Objects in C++

Welcome to the course “Data Structures and Algorithms with C++”. In this course, we will be covering the fundamentals of classes and objects in C++. Classes and objects are a fundamental concept in object-oriented programming (OOP). These concepts are used to create and manipulate data structures and algorithms in C++.

In this article, we will be discussing the fundamentals of classes and objects in C++. We will explain how they are used and how they can be used to create and manipulate data structures and algorithms. We will also look at some examples of how classes and objects in C++ can be used to create complex data structures and algorithms.

What are Classes and Objects?

To understand classes and objects in C++, we must first understand the concept of object-oriented programming (OOP). OOP is a programming paradigm that is based on the concept of objects. An object is a self-contained unit which contains both data and methods. The data contained in an object is known as its attributes, while the methods are known as its behaviours.

Classes are the blueprints for objects. A class defines the attributes and behaviours of an object. An object is then created based on the class definition. This object will have the same attributes and behaviours as defined by the class.

In C++, classes are defined using the class keyword. The class definition consists of a list of attributes and methods. The attributes are declared using the private keyword and the methods are declared using the public keyword.

Class Example

Let’s now look at an example of a class in C++. We will be creating a class called Point which represents a point in two-dimensional space.

// Point.h 
class Point { 
private: 
	int x; 
	int y; 
public: 
	Point(); 
	Point(int x, int y); 
	int getX(); 
	int getY(); 
	void setX(int x); 
	void setY(int y); 
};

In this class, we have declared two attributes (x and y) and six methods (Point(), Point(int x, int y), getX(), getY(), setX(), and setY()). The attributes are declared using the private keyword and the methods are declared using the public keyword.

Object Example

Now that we have defined our Point class, we can create an object based on this class. We will create an object called myPoint which represents the point (2, 3).

// main.cpp 
#include "Point.h" 
 
int main() { 
	Point myPoint(2, 3); 
	return 0; 
}

In this example, we have created an object called myPoint based on the Point class. This object has the attributes x and y with the values 2 and 3 respectively.

Using Classes and Objects

Now that we have looked at how to define classes and objects in C++, let’s now look at how they can be used to create and manipulate data structures and algorithms. Classes and objects are commonly used to create abstract data types (ADTs), which are user-defined data types that can be used to represent data in a program.

For example, we can use our Point class to create an abstract data type called Vector. A Vector is a mathematical object which represents a directed line segment in two-dimensional space.

// Vector.h 
class Vector { 
private: 
	Point start; 
	Point end; 
public: 
	Vector(); 
	Vector(Point start, Point end); 
	Point getStart(); 
	Point getEnd(); 
	void setStart(Point start); 
	void setEnd(Point end); 
	double length(); 
};

In this class, we have declared two attributes (start and end) and seven methods (Vector(), Vector(Point start, Point end), getStart(), getEnd(), setStart(), setEnd(), and length()). The attributes are both Point objects, and the methods are used to manipulate and calculate the length of the Vector.

Classes and objects are also used to create data structures and algorithms. For example, we can use our Vector class to create an algorithm for calculating the length of a Vector.

// Vector.cpp 
#include "Vector.h" 
 
Vector::Vector() { 
	start = Point(); 
	end = Point(); 
} 
 
Vector::Vector(Point start, Point end) { 
	this->start = start; 
	this->end = end; 
} 
 
Point Vector::getStart() { 
	return start; 
} 
 
Point Vector::getEnd() { 
	return end; 
} 
 
void Vector::setStart(Point start) { 
	this->start = start; 
} 
 
void Vector::setEnd(Point end) { 
	this->end = end; 
} 
 
double Vector::length() { 
	int xDiff = end.getX() - start.getX(); 
	int yDiff = end.getY() - start.getY(); 
	return sqrt(xDiff*xDiff + yDiff*yDiff); 
}

In this example, we have implemented the length() method of the Vector class. This method calculates the length of the Vector by calculating the difference in the x and y coordinates of start and end, and then computing the square root of the sum of these differences.

Conclusion

In this article, we have looked at the fundamentals of classes and objects in C++. We have discussed how they can be used to create and manipulate data structures and algorithms. We have also looked at some examples of how classes and objects can be used to create abstract data types and algorithms.

Exercises

// Rectangle.h 
class Rectangle { 
private: 
	int width; 
	int height; 
public: 
	Rectangle(); 
	Rectangle(int width, int height); 
	int getWidth(); 
	int getHeight(); 
	void setWidth(int width); 
	void setHeight(int height); 
};

// Rectangle.cpp 
#include "Rectangle.h" 
 
Rectangle::Rectangle() { 
	width = 0; 
	height = 0; 
} 
 
Rectangle::Rectangle(int width, int height) { 
	this->width = width; 
	this->height = height; 
} 
 
int Rectangle::getWidth() { 
	return width; 
} 
 
int Rectangle::getHeight() { 
	return height; 
} 
 
void Rectangle::setWidth(int width) { 
	this->width = width; 
} 
 
void Rectangle::setHeight(int height) { 
	this->height = height; 
} 
 
double Rectangle::area() { 
	return width * height; 
}

// Student.h 
class Student { 
private: 
	string name; 
	int age; 
	int grade; 
public: 
	Student(); 
	Student(string name, int age, int grade); 
	string getName(); 
	int getAge(); 
	int getGrade(); 
	void setGrade(int grade); 
};

// Student.cpp 
#include "Student.h" 
 
Student::Student() { 
	name = ""; 
	age = 0; 
	grade = 0; 
} 
 
Student::Student(string name, int age, int grade) { 
	this->name = name; 
	this->age = age; 
	this->grade = grade; 
} 
 
string Student::getName() { 
	return name; 
} 
 
int Student::getAge() { 
	return age; 
} 
 
int Student::getGrade() { 
	return grade; 
} 
 
void Student::setGrade(int grade) { 
	this->grade = grade; 
} 
 
double Student::getAverageGrade() { 
	return grade / age; 
}

// Circle.h 
class Circle { 
private: 
	int radius; 
	Point center; 
public: 
	Circle(); 
	Circle(int radius, Point center); 
	int getRadius(); 
	Point getCenter(); 
	void setRadius(int radius); 
};