using System;

public class Program

{

    public static void Main()

    {

        readonly int b=100;//you can not declare an readonly variable at method level it only declare at class level.

        b=200;

        Console.WriteLine(a);

        const int a=20;

        a=30;

        Console.WriteLine(a);

    }

}

//const value can not be change after declaration. Also you need to initilized it in compile time.

//but for readonly you are not force to change to initilized it in compile time.