Declaring constants in C#

 Constants are fields whose values are set at compile time and can never be changed. Use constants to provide meaningful names instead of numeric literals for special values.

Note
    In C# the #define preprocessor directive cannot be used to define constants in the way that is typically used in C and C++.

    To define constant values of integral types (int, byte, and so on) use an enumerated type. For more information, see enum.

    To define non-integral constants, one approach is to group them in a single static class named Constants. This will require that all references to the constants be prefaced with the class name, as shown in the following example.

Example
static class Constants
{
    public const double Pi = 3.14159;
    public const int SpeedOfLight = 300000; // km per sec.
}
class Program
{
    static void Main()
    {
        double radius = 5.3;
        double area = Constants.Pi * (radius * radius);
        int secsFromSun = 149476000 / Constants.SpeedOfLight; // in km
    }
}
    The use of the class name qualifier helps ensure that you and others who use the constant understand that it is constant and cannot be modified.

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