Const and ReadOnly in c#. Difference between const and readonly keyword?

const:-

const is a keyword which is used as a modifier.

Constants (const) are immutable values which are known at compile time and do not change for the life of program.

C# does not support const method, property and events.

Example:-

public const int num=10;

public const string strTest="Welcome";

If you didn’t initialized a constant at the time of declaration then it will show an error.

Ex:-

public const int num;

ReadOnly :-

ReadOnly keyword is a modifier that you can use on fields. When a field declaration includes a readonly modifier, assignments to the fields introduced by the declaration can only occur as part of the declaration or in a constructor in the same class.

Example:-

public readonly int num;

you can assign a value to a readonly field only in the following context:-

1.)  At the time of declaration, we can initialized the value

public readonly int num=20;

2.)  In a constructor

public class TestClass1

    {

      

        public readonly int num;

        public TestClass1()

        {

            num = 20;

        }

    }

If you initialized the readonly field value other than over two context then it will give error.

Ex:-

public class TestClass1

    {

      

        public readonly int num;

        public void TestMethod()

        {

            num=20;

        }

    }

 

Note:- Article details referenced by MSDN.