Constant and Read only in C# full Explanation

In C#, both constants and readonly fields are used to represent values that cannot be changed during the execution of a program. However, there are some differences between them. Let's explore the concept of constants and readonly fields in C# in detail:

 

Constants:

v  Constants are used to represent fixed values that do not change during the execution of a program.

v  They are declared using the `const` keyword.

v  Constant values are implicitly static and are resolved at compile-time.

v  Constants must be initialized with a value at the time of declaration and cannot be changed afterward.

v  Constants are typically used for values that are known and will never change, such as mathematical or physical constants.

v  Constants are defined at the class level and are accessible throughout the class or in other classes where they are visible.

v  Example:

 

  class MathUtils

  {

      public const double Pi = 3.14159;

      public const int MaxValue = 100;

  }

 

  In this example, `Pi` and `MaxValue` are constant fields in the `MathUtils` class.

 

Readonly Fields:

v  Readonly fields are used to represent values that are initialized at runtime and cannot be modified afterward.

v  They are declared using the `readonly` keyword.

v  Readonly fields are evaluated and assigned at runtime, typically within a constructor or an initializer.

v  Unlike constants, readonly fields can have Different values for Different instances of a class.

v  Readonly fields provide more flexibility as they can be assigned Different values based on conditions or calculations.

v  Readonly fields are defined at the class level and are accessible throughout the class or in other classes where they are visible.

v  Example:

 

  class Person

  {

      public readonly string Name;

 

      public Person(string name)

      {

          Name = name;

      }

  }

 

  In this example, the `Name` field is a readonly field that can have Different values for Different instances of the `Person` class.

 

Key Differences:

v  Constants are implicitly static, while readonly fields are instance-specific.

v  Constants are resolved at compile-time, while readonly fields are evaluated and assigned at runtime.

v  Constants must be initialized with a value at the time of declaration, while readonly fields can be assigned a value within a constructor or an initializer.

v  Constants are typically used for fixed values known at compile-time, while readonly fields are used for values that can vary based on runtime conditions.

 

In general, use constants when you have fixed, known values that won't change, and use readonly fields when you have values that can vary at runtime but need to be assigned only once. By using constants and readonly fields, you can enforce immutability and ensure that certain values remain constant or unchangeable throughout your C# programs.