How many types of constructors in C++?

There are 3 types of Constructors.
1. Default Constructor

A constructor with no arguments (or parameters) in the definition is a default constructor. Usually, these constructors use to initialize data members (variables) with real values.

Note: If no constructor is explicitly declared, the compiler automatically creates a default constructor with no data member (variables) or initialization.

Syntax of Default Constructor –

class CLASS_NAME
{
   ………
public :
CLASS_NAME()  //Default constructor
{
                            . . . . . .  
}
 
//other member functions
};

Example:

#include 
using namespace std;
 
//Class Name: Default_construct
class Default_construct
{
public:
	int a, b;
 
	// Default Constructor
	Default_construct()
	{
		a = 100;
		b = 200;
	}
};
 
int main()
{
	Default_construct con;  //Object created
	cout << "Value of a: " << con.a;
        cout<< "Value of b: " << con.b;
	return 0;
}

2. Parameterized Constructor

Unlike, Default constructor, It contains parameters (or arguments) in the constructor definition and declaration. More than one argument can also pass through a parameterized constructor.

Moreover, these types of constructors use for overloading to differentiate between multiple constructors.

Syntax –

class class_Name
{
public:
  class_Name(datatype variable) //Parameterized constructor
  {
   ………………..
  }
};

Example:

#include 
using namespace std;
 
// class name: Rectangle
class Rectangle {
  private:
    double length;
    double breadth;
 
  public:
    // parameterized constructor 
    Rectangle(double l, double b) {
      length = l;
      breadth = b;
    }
 
    double calculateArea() {
      return length * breadth;
    }
};
 
int main() {
 	 // create objects to call constructors
Rectangle obj1(10,6);
Rectangle obj2(13,8);
 
 
  cout << "Area of Rectangle 1: " << obj1.calculateArea();
  cout << "Area of Rectangle 2: " << obj2.calculateArea();
 
  return 0;
}

3. Copy Constructor

A copy constructor is a member function that initializes an object using another object of the same class. It helps to copy data from one object to another.

Example –

#include 
using namespace std;
 
// class name: Rectangle
class Rectangle {
  private:
    double length;
    double breadth;
 
  public:
    // parameterized constructor 
    Rectangle(double l, double b) {
      length = l;
      breadth = b;
    }
 
  // copy constructor with a Rectangle object as parameter copies data of the obj parameter
    Rectangle(Rectangle &obj) {
      length = obj.length;
      breadth = obj.breadth;
    }
 
 
    double calculateArea() {
      return length * breadth;
    }
};
 
int main() {
 	 // create objects to call constructors
Rectangle obj1(10,6);
Rectangle obj2 = obj1;   //copy the content using object
 
//print areas of rectangles
  cout << "Area of Rectangle 1: " << obj1.calculateArea();
  cout << "Area of Rectangle 2: " << obj2.calculateArea();
 
  return 0;
}