Parameterized constructor in C++ with example

Learn: What is the parameterized constructor in C++ programming language? How to create parameterized constructor to initialize data members of a class?

In our last two posts, we have covered following two topics, if you didn't read them, I would recommend to read them first, the covered topics are:

In this post, we are going to learn parameterized constructor in C++ programming. As the name suggests it's a constructor with arguments/parameters, it follows all properties of the constructor and takes parameters to initialize the data.

For Example: If we want to initialize an object with some values while declaring it, we can do it creating parameterized constructors.

Let suppose there is a class named Person with two data members name and age, we can initialize the data members while creating the objects like this:

Person per1("Manikanth",21);
Person per2("Abhisekh", 19);

Consider this example: Here Demo is a class with three private data members A, B and C

#include <iostream>
using namespace std;

class Demo
{
	private:
		int A;
		int B;
		int C;
	public:
		//parameterized constructor
		Demo(int A, int B, int C);
		void set(int A, int B, int C);
		void print();
};

Demo::Demo(int A, int B, int C)
{
	this->A  = A;
	this->B  = B;
	this->C  = C;
}

void Demo::set(int A, int B, int C)
{
	this->A  = A;
	this->B  = B;
	this->C  = C;
}

void Demo::print()
{
	cout<<"Value of A :  "<<A<<endl;
	cout<<"Value of B :  "<<B<<endl;
	cout<<"Value of C :  "<<C<<endl;
}

int main()
{
	//Parameterized Constructor called when object created
	Demo obj = Demo(1,1,1); 
	//here, 1,1,1 will be assigned to A,B and C
	//printing the value
	obj.print();
	//changing the value using set function
	obj.set(10,20,30);
	//printing the values
	obj.print();

	return 0;
}

Output

Value of A :  1
Value of B :  1
Value of C :  1
Value of A :  10
Value of B :  20
Value of C :  30