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C# Keywords

　C# contains reserved words that have special meaning to the compiler. These reserved words are called 'keywords'. Keywords cannot be used as identifiers (variable names, classes, interfaces, etc.).

　C# keywords are distributed in the following categories:

Modifiers

Modifier keywords are specific keywords that indicate who can modify types and type members. Modifiers allow or prevent certain parts of the program from being modified by other parts.

Modifier Keywords
abstract	async	const	event	extern	new	override	partial	readonly
sealed	static	unsafe	virtual	volatile

Access Modifier Keywords:

Access modifiers are applied to declarations of classes, methods, properties, fields, and other members. They define the accessibility of the class and its members.

Access Modifiers	Usage
public	The 'public' modifier allows any part of the program within the same assembly or another assembly to access the type and its members.
private	The 'private' modifier restricts access to the type and its members to other parts of the program. Only code within the same class or structure can access it.
internal	The 'internal' modifier allows other code within the same assembly to access the type or its members. If no modifier is specified, this is the default access modifier.
protected	The 'protected' modifier allows code within the same class or derived classes to access the type or its members.

Statement keywords

Statement keywords are related to program flow.

Statement keywords
if	else	switch	case	do	for	foreach	in	while	break	continue	default	goto	return
yield	throw	try	catch	finally	checked	unchecked	fixed	lock

Method parameter keywords

　 These keywords are applied to method parameters.

Method parameter keywords
params	ref	out

Namespace keywords

These keywords are applied with namespaces and related operators.

Namespace keywords
using	.operator	::operator	extern alias

Operator keywords

Operator keywords perform other operations.

Operator keywords
as	await	is	new	sizeof
typeof	stackalloc	checked	unchecked

Access keywords

Access keywords are used to access the containing class or base class of an object or class.

Access keywords
base	this

Literal keywords

Literal keywords are used for the current instance or value of an object.

Literal keywords
null	false	true	value	void

Type keywords

Type keywords are used for data types.

Input keywords
bool	byte	char	class	decimal	double	enum	float	int	long
sbyte	short	string	struct	uint	ulong	ushort

Content-related keywords

Context keywords are only considered keywords when used in specific contexts. They are not reserved, so they can be used as names or identifiers.

Content-related keywords
add	var	dynamic	global	set	value

When context keywords are used as identifiers in Visual Studio, they will not be converted to blue (the default color of keywords in Visual Studio).

Query keywords

Query keywords are context keywords used in LINQ queries.

Query keywords
from	where	select	group	into	orderby	join
let	in	on	equals	by	ascending	descending

As mentioned above, keywords cannot be used as identifiers (variable names, classes, interfaces, etc.). However, they can be used with the prefix “@”. For example, the keyword “class” is a reserved keyword, so it cannot be used as an identifier, but it can be used as @class as shown below.

Example: Using keywords as identifiers

public　class　@class
{
　　　　public　static　int　MyProperty　{　get;　set;　}
}
@class.MyProperty　=　100;

　Points to Remember:　

Keywords are reserved words and cannot be used as names or identifiers.
If you want to use keywords as identifiers, please add '@' before the keyword.
C# includes various categories of keywords, such as modifier keywords, access modifier keywords, statement keywords, method parameter keywords, and so on.
Contextual keywords can be used as identifiers.

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