Constant

Constants – immutable values known at compile time which do not change.

• Only built-in types may be declared const.
• Constants cannot be declared static (this would be redundant).

Use

Constants are used instead of magic numbers to provide meaningful names for special values.

Constant Integrals

Instead of a constant int, byte, etc, use an enum.

Best Practice

Constants can be grouped in a single, static class named Constants. This helps ensure those who use the constant understand it is constant and cannot be modified:

public static class Constants 
{
    public const double Pi = 3.141592653589793;
    public const int SpeedOfLight = 3000000; // km per second.
}

Constant vs. Readonly

A const value is declared once at compile time and never changed. A readonly value is declared once at runtime by a constructor and never changed.