Introduction to constructors

🧱 Introduction to Constructors

A constructor is a special member function of a class that is automatically called when an object is created.

Its main purpose is to initialize objects.

---

✅ Key Features of Constructors

• Same name as the class name.
• No return type, not even void.
• Automatically invoked when an object is created.
• Can be overloaded (multiple constructors with different parameters).

---

🧪 Example:

#include <iostream>
using namespace std;

class Student {
public:
    int rollNo;

    // Constructor
    Student() {
        rollNo = 101;
        cout << "Constructor called!" << endl;
    }

    void display() {
        cout << "Roll No: " << rollNo << endl;
    }
};

int main() {
    Student s1;  // Constructor is called automatically
    s1.display();
    return 0;
}

🔍 Output:

Constructor called!
Roll No: 101

---

🔷 Types of Constructors

Type	Description
Default Constructor	Takes no parameters.
Parameterized Constructor	Takes arguments to initialize data.
Copy Constructor	Creates a copy of another object.

---

1. Default Constructor

cppCopyEditclass A {
public:
    A() {
        cout << "Default constructor called!" << endl;
    }
};

---

2. Parameterized Constructor

class Student {
public:
    int roll;

    Student(int r) {  // Constructor with parameter
        roll = r;
    }

    void display() {
        cout << "Roll No: " << roll << endl;
    }
};

---

3. Copy Constructor

class Student {
public:
    int roll;

    Student(int r) {
        roll = r;
    }

    // Copy constructor
    Student(const Student &s) {
        roll = s.roll;
    }

    void display() {
        cout << "Roll: " << roll << endl;
    }
};

---

📌 Why Use Constructors?

• Ensures automatic initialization of objects.
• Helps avoid writing extra code to initialize variables.
• Makes code cleaner and safer.

---

🛑 Constructor vs. Member Function

Feature	Constructor	Member Function
Name	Same as class	Any valid identifier
Return Type	No return type	Can have return type
Call Time	Called automatically	Called manually
Purpose	Initialization	Perform specific task

---

🧠 Real-Life Analogy

Think of a constructor like the initial setup process when you open a new smartphone:

• Language, time zone, and Wi-Fi setup.
• It happens automatically, once.
• After setup, you can manually use different apps (like member functions).

---

🧾 Summary

• A constructor initializes class objects.
• It runs automatically when an object is created.
• There are three main types: default, parameterized, and copy constructors.
• Constructors help make code modular, reusable, and clean.