C# - Identifiers and Keywords


In C#, an identifier is a name assigned to a method, a variable, or any other user-defined item. Identifiers can be one or more characters long. Variable names may start with any letter of the alphabet or an underscore. Next may be a letter, a digit, or an underscore.

Remember, you can’t start an identifier with a digit

Although you cannot use any of the reserved C# keywords as identifiers, C# does allow you to precede a keyword with an @, allowing it to be a legal identifier. For example, @for is a valid identifier.In this case, the identifier is actually for and the @ is ignored.

The C# Reserved Keywords

Keywords are predefined, reserved identifiers that have special meanings to the compiler. They cannot be used as identifiers in your program unless they include @ as a prefix. For example, @if is a valid identifier but if is not because if is a keyword.

The first table in this topic lists keywords that are reserved identifiers in any part of a C# program. The second table in this topic lists the contextual keywords in C#. Contextual keywords have special meaning only in a limited program context and can be used as identifiers outside that context. Generally, as new keywords are added to the C# language, they are added as contextual keywords in order to avoid breaking programs written in earlier versions.

Here is the full list of C# keywords:

abstract as base bool break
byte case catch char checked
class const continue decimal default
delegate do double else enum
event explicit extern false finally
fixed float for foreach goto
if implicit in int interface
internal is lock long namespace
new null object operator out
override params private protected public
readonly ref return sbyte sealed
short sizeof stackalloc static string
struct switch this throw true
try typeof uint ulong unchecked
unsafe ushort using virtual volatile
void while

The C# Contextual Keywords

A contextual keyword is used to provide a specific meaning in the code, but it is not a reserved word in C#. Some contextual keywords, such as partial and where, have special meanings in two or more contexts.

from get group into join
let orderby partial select set
value where yield