Services
Technology Web App Development Mobile App Development Windows App Development Database Development UI/UX Development Cloud Development SEO Digital Marketing Guest Posting Content Writing Artificial Intelligence Data Science ERP Development CRM Development CMS Development LMS Development Business Listing Blockchain Technology Startup Promotion
Products
Data Converter Cleaner TUC - Unit Converter Import Export Survey Manager Tweet Controller
Developer
Article Blog Forum Interview Beginner News Startup Quiz
Users
Career
Apply Job Internship
Pricing
Login Sign Up Get a Quote

forum

home / developersection / forums / what is the difference between readonly, const, and static?
Ask Question

What is the difference between readonly, const, and static?

Anubhav Sharma 301 19 Jun 2025

What is the difference between readonly, const, and static?

c# c#
Updated 24 Jun 2025
Anubhav Sharma
Anubhav Sharma

Student

The Anubhav portal was launched in March 2015 at the behest of the Hon'ble Prime Minister for retiring government officials to leave a record of their experiences while in Govt service .

Message

1 Answers

Ponu Maurya
Ponu Maurya 24 Jun 2025
Report Abuse

const

  • Compile-time constant.
  • Must be assigned at the time of declaration.
  • Implicitly static.
  • Cannot be changed after compilation.
  • Value is inlined wherever it's used — changing it requires recompilation of all dependent assemblies.
public class Example
{
    public const double Pi = 3.14159;  // Compile-time constant
}

Use when: Value is truly constant and known at compile time (like Pi, conversion factors, etc.)

readonly

  • Run-time constant.
  • Can be assigned in the declaration or constructor.
  • Value can differ between instances.
  • Ideal for values that should not change after the object is created.
public class Example
{
    public readonly int Id;

    public Example(int id)
    {
        Id = id;  // Allowed in constructor
    }
}

Use when: Value should be set once at runtime (e.g., ID, creation timestamp).

static

  • Belongs to the type itself, not to any instance.
  • Shared across all instances.
  • Can be used with fields, methods, constructors, classes, etc.
public class Example
{
    public static int Counter = 0;

    public Example()
    {
        Counter++;  // Shared by all instances
    }
}

Use when: You want a member that is shared across all instances (like configuration, counters, etc.)

Combined Usage

You can combine static with readonly:

public static readonly string AppName = "MyApp";

Means: shared across all instances, value set at runtime, but not modifiable afterward.

Summary Table

Keyword Assigned When Modifiable? Scope Use For
const Compile-time No Static only Hardcoded values
readonly Runtime (in ctor) After assigned Per-instance or static Init-once values
static Any time Yes (if not readonly) Type-wide Shared data/methods across class
MindStick Training