Const Vs Readonly Vs Static in C#

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace ConstVsReadonlyVsStatic

{

    class Program

    {

        public const double PI = 3.14159;

        public readonly string strReadonlyHello = "Readonly Hello";

        public static string strStaticHello = "Static Hello";

        public Program() // Constructor

        {

            strReadonlyHello = "Constructor Readonly Hello";

        }

        public void Display()

        {

            //Error: The left-hand side of an assignment must be a variable, property or indexer

            //PI = 3.125;

            //Error: A readonly field cannot be assigned to (except in a constructor or a variable initializer)

            //strReadonlyHello = "Hello";

            Console.WriteLine("Readonly value change in Constructor - {0}", strReadonlyHello);

            Console.WriteLine("Static value before change - {0}", Program.strStaticHello);

            Console.WriteLine("Enter the value to change the static variable value");

            strStaticHello = Convert.ToString(Console.ReadLine());

            Console.WriteLine("Static value after change - {0}", Program.strStaticHello);

        }

        static void Main(string[] args)

        {

            Program p = new Program();

            p.Display();

            Console.ReadLine();

        }

    }

}

Output:

 

Conclusion:

        

Constant (const):

1. A const field requires a value to be provided at compile-time.

2. Const field value cannot be change once assigned.

         

Readonly:

1. A readonly field cannot be assigned to (except in a constructor or a variable initializer)

        

Static:

1. A static variable is a variable that has been allocated statically—whose lifetime

   or"extent" extends across the entire run of the program.

        

         

For More info about variable initializer refer below link

        

https://msdn.microsoft.com/en-us/library/aa645757%28v=vs.71%29.aspx