C++ - Constructor Overloading

Like functions, a constructors can also be overloaded in C++. With constructor overloading feature in C++, two or more constructors can be created in the same class with different definitions like different number and types of parameters. The compiler automatically calls the constructor which matches the argument passed while creating the object.

Example:

In this example two constructors are created. The first constructor (default constructor) takes no parameters and the second constructor takes one parameter to initialize an object of the class Circle.

In the main function, two objects of class Circle are created: Cir1 and Cir2. Cir1 uses default constructor to initialize the object while the Cir2 uses the constructor that takes one parameter to initialize the object.

#include <iostream>
using namespace std;
 
class Circle {
  public:
    int radius;
    float area() {
      return 22/7.0*radius*radius;
    }
    Circle();
    Circle(int);
 };
//constructor without parameter
Circle::Circle() {
  radius = 1;
}
//constructor with one parameter
Circle::Circle(int x) {
  radius = x;
}

int main (){
  //syntax for calling default constructor
  Circle Cir1;
  Circle Cir2(10);

  cout<<Cir1.area()<<"\n";
  cout<<Cir2.area()<<"\n"; 
  return 0;
}

The output of the above code will be:

3.143
314.3

A constructor is called default constructor, if it takes no arguments to initialize the object. Please note down the syntax to initialize an object using default constructor in the above example.