🟣 OOP · Lesson 39

Constructors in C++

What is Constructors in C++?

Constructors in C++
A constructor is a special member function that initializes an object automatically when it is created. It has the same name as the class and no return type.

Level
🟣 Object-Oriented Programming

Example File
constructors.cpp

Main Focus
Concept + syntax + practical C++ program

Why should you learn this?

It helps you write correct and readable C++ programs.
It is used repeatedly in school practicals, projects and competitive programming.
It builds the base for advanced topics such as OOP, STL and data structures.

Important Terms

Term	Meaning / Use
constructor	Constructor used in Constructors in C++ programming.
default constructor	Default constructor used in Constructors in C++ programming.
parameterized constructor	Parameterized constructor used in Constructors in C++ programming.
initialization	Initialization used in Constructors in C++ programming.

Syntax / Pattern

ClassName(parameters) { initialization; }

Example Program

#include <iostream>
using namespace std;
class Student{
    int roll;
public:
    Student(int r){ roll = r; }
    void show(){ cout << roll; }
};
int main(){
    Student s(12);
    s.show();
    return 0;
}

Expected Output

Program Explanation

Student(int r) runs automatically when s is created.
roll is initialized with 12.

Exam Tip: In C++ practical answers, write the logic first, then the program, then expected output. For theory, always include one suitable example.

Where will you use it?

initializing records
setting default values
resource setup

Common Mistakes

Writing return type for constructor.
Forgetting to initialize all data members.

Practice Tasks

Create constructor for Employee.
Write default and parameterized constructor.

Summary

Constructors in C++ is an important C++ topic. Learn the definition, understand the syntax, run the example program and then solve the practice tasks to make the concept strong.