Constant Vs Readonly In C#

Difference between constant and readonly in C#

1. constant:

•  It is used to store the constant value.
•  It is compiled time constant.
•  We can not modify/change the constant value.
•  The Constant variable can by access by using the class name.
•  We must assign the value to the constant variable at the declaration time.
•  We can not provide the static keyword to the constant variable.
•  We can not access the constant variable by using object of the class.

2. Readonly keyword:

•  It is used to store the constant value.
•  It is run time constant.
•  We can modify/change the readonly variable value in the constructor of the class.
•  The readonly variable can be accessed by using object of the class or class name.
•  we can provide the static keyword to the readonly variable.
•  We can access the readonly variable by using object of the class or class name.

Example: 

using System;

namespace CSharpProject

{

    class Program

    {

        public const string strConnection = "Test Connection";

        //public static readonly double Pi = 3.1; // we can define static keyword to the readonly variables

        public  readonly double Pi = 3.1;

        public Program()

        {

            Pi = 3.14;

        }               

        static void Main(string[] args)

        {

            Program pro = new Program();

            Console.WriteLine(pro.Pi); // Calling not static readonly variable by using object of class.

           // Console.WriteLine(Program.Pi);// calling static readonly keyword by using class name.

            Console.WriteLine(Program.strConnection);

            Console.ReadLine();

        }

    }

}

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