Readonly Vs Const Keywords In C#

In this article, we are going to learn about what is readonly, const keywords, and their difference.

What is Readonly keyword?

A readonly keyword is used to define a variable that can be assigned once after declaration either during declaration or in the constructor.

Example

using System;
 
class Test
 {
    // readonly variables
    public readonly int var1;
    public readonly int var2;
 
    // Using constructor
    public Test(int a, int b)
    {
        var1 = a;
        var2 = b;
        Console.WriteLine("Display value of var1 {0}, "+"and var2 {1}", var1, var2);
    }
 
    // Main method
    static public void Main()
    {
        Test obj1 = new Test(90, 80);
    }
}

Output

Display value of var1 90, and var2 80

What is Const keyword?

Once the variable is defined as const, then the value assigned to that variable cannot be changed throughout the program.

Example

using System;
 
class Test {
 
    // const variables
    public const int var1 = 96;
    public const string var2 = "Riya";
 
    // Main method
    static public void Main()
    {
        Console.WriteLine(var2 + " got " + var1 + " marks in english");
    }
}

Output

Riya got 96 marks in english

Difference between ReadOnly and Const keywords.

That’s it.

Also check, Introduction Of OOP Concept In C#