All About Constants

What are constants?

 

Constants are immutable values whose values are known at runtime and cannot be changed in the whole lifetime of a program.

 

Features of constants

1. Only C# primitive can be declared as const. Shown below is how a constant is declared.
2. User-defined Types such as class, struct and arrays cannot be declared as const.
3. A constant can only be initialized when it is declared and cannot be changed.

   // Value assigned during compile time
   class A {
       public
       const int month = 12; //Legal
   }
   // Value assingement during runtime
   class B {
       public
       const int month;
       public B() {
           this.month = 12; // illegal
       }
   }

   When the compiler encounters a constant identifier in C# code, it substitutes the literal value directly into the IL code that produces it because there is no variable address associated with the constant at runtime.