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

Only C# primitive can be declared as const. Shown below is how a constant is declared.
User-defined Types such as class, struct and arrays cannot be declared as const.
A constant can only be initialized when it is declared and cannot be changed.
1. // Value assigned during compile time
2. class A {
3. public
4. const int month = 12; //Legal
5. }
6. // Value assingement during runtime
7. class B {
8. public
9. const int month;
10. public B() {
11. this.month = 12; // illegal
12. }
13. }
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.