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C++: 6. Constructors

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

In C++, a constructor has the same name as that of the class and it does not have a return type.

C++ Default Constructor
A constructor which has no argument is known as default constructor. It is invoked at the time of creating object.

Example:- 
#include <iostream>  
using namespace std;  
class Employee  
 {  
   public:  
        Employee()    
        {    
            cout<<"Default Constructor Invoked"<<endl;    
        }    
};  
int main(void)   
{  
    Employee e1; //creating an object of Employee   
    Employee e2;   
    return 0;  
}  
Output:- 
Default Constructor Invoked 
Default Constructor Invoked 


C++ Parameterized Constructor
A constructor which has parameters is called the parameterized constructor. It is used to provide different values to distinct objects.

Example:- 
#include <iostream>
using namespace std;
class Employee {
   public:
       int id;//data member (also instance variable)    
       string name;//data member(also instance variable)
       float salary;
       Employee(int i, string n, float s)  
        {  
            id = i;  
            name = n;  
            salary = s;
        }  
       void display()  
        {  
            cout<<id<<"  "<<name<<"  "<<salary<<endl;  
        }  
};
int main(void) {
    Employee e1 =Employee(101, "Sonoo", 890000); //creating an object of Employee 
    Employee e2=Employee(102, "Nakul", 59000); 
    e1.display();  
    e2.display();  
    return 0;
}
Output:- 
101  Sonoo  890000
102  Nakul  59000

Copy Constructor in C++
The copy constructor in C++ is used to copy data of one object to another.

Example:- 
#include<iostream>
using namespace std;
class Demo {
   private:
   int num1, num2;
   public:
   Demo(int n1, int n2) {
      num1 = n1;
      num2 = n2;
   }
   Demo(const Demo &n) {
      num1 = n.num1;
      num2 = n.num2;
   }
   void display() {
      cout<<"num1 = "<< num1 <<endl;
      cout<<"num2 = "<< num2 <<endl;
   }
};
int main() {
   Demo obj1(10, 20);
   Demo obj2 = obj1;
   obj1.display();
   obj2.display();
   return 0;
}
Output:- 
num1 = 10
num2 = 20

num1 = 10
num2 = 20

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