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Classes and Objects in C++
Classes are the prime features of C++ as they support OOPS concepts and are user defined data types. Classes provide the specification for an object and contain data variables as well as functions to manipulate the data in a single package.
Class Definitions
A class definition starts with the keyword class and then the class name. After that the class body is defined. It is enclosed by curly braces. A class definition should either contain a semicolon or a list of definitions after it.
An example of a class definition in C++ is as follows.
class student { int rollno; char name[50]; float marks; };
The above class contains the details of a student, namely its roll number, name and marks.
Object Definitions
When a class is defined, it is only a specification. There is no memory or storage allocated at that time. So the object is created from the class to access the data and functions defined in the class. A class can also be called the blueprint for an object.
The declaration of an object of class student is given as follows.
Student stu1;
A program that demonstrates classes and objects in C++ is given as follows.
Example
#include <iostream> using namespace std; class Student { public: int rollno; char name[50]; float marks; void display() { cout<<"Roll Number: "<< rollno <<endl; cout<<"Name: "<< name <<endl; cout<<"Marks: "<< marks <<endl; } }; int main() { Student stu1 = {1, "Harry", 91.5}; stu1.display(); return 0; }
Output
Roll Number: 1 Name: Harry Marks: 91.5
In the above program, first the class student is defined. It contains the details about the student such as roll number, name and marks. It also contains a member function display() that displays all the student details. The code snippet that demonstrates this is as follows.
class student { public: int rollno; char name[50]; float marks; void display() { cout<<"Roll Number: "<< rollno <<endl; cout<<"Name: "<< name <<endl; cout<<"Marks: "<< marks <<endl; } };
In the function main(), the object of the class student is defined with the student details. Then these details are displayed with a function call to display(). This can be seen as follows.
student stu1 = {1, "Harry", 91.5}; stu1.display();