There are 5 access modifiers. Access modifiers define scope for members.
- Private: Accessible only with in the class.
- Protected: -Accessible with in the class and in derived classes.
- Friend (internal in C#):-Accessible anywhere within the current project.
- Protected friend (protected internal in C#):- Accessible with current project and derived classes.
- Public: -Accessible everywhere.
Also see following .NET interview questions video on difference between Constant & Readonly: -