When ever an object of class is created the constructor of that class gets called and the required memory get allocated. While creating the object of a class we are explicitly calling the constructor as following

  ConDemo cd = new ConDemo();  (Calling the constructor)

Constructors are of two types

• Parameter-less  (zero argument) Constructor.
•  Parametrized Constructor.

•   Parameter-less  (zero argument) Constructor:   A constructor without any parameter is a parameter-less constructor which can be either defined implicitly provided there is no explicit constructor or else can be defined explicitly.
•  Parametrized Constructor: A constructor with parameters is a Parametrized Constructor and can be defined only explicitly. if the constructor of a class is  Parametrized values to the parameter are sent while calling the constructor.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApps
{
    class ConParam
    {
        int a;   // a is a class variable
        public ConParam(int a)   // a is a block variable
        {
            this.a = a;
        }
        public void display()
        {
            Console.WriteLine("Values of a is{0}", a);
        }
        static void Main()
        {
            ConParam p1 = new ConParam(10);
            ConParam p2 = new ConParam(20);
            ConParam p3 = new ConParam(30);
            p1.display();
            p2.display();
            p3.display(); 
            Console.ReadLine();
        }
     }
}