C# Keywords

Last Updated : 21 Apr, 2025

Keywords or Reserved words are the words in a language that are used for some internal process or represent some predefined actions. These words are therefore not allowed to be used as variable names or objects. Doing this will result in a compile-time error.

Example:

// C# Program to illustrate the keywords  using System;     class Geeks {         // Here static, public, void       // are keywords          static public void Main () {                     // here int is keyword          // a is identifier          int a = 10;                     Console.WriteLine("The value of a is: {0}",a);                     // this is not a valid identifier             // removing comment will give compile time error          // double int = 10;                }  }

Output

The value of a is: 10

Keywords in C#

There are total 78 keywords in C# as follows:

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

Keywords in C# is mainly divided into 10 categories as follows:

1. Value Type Keywords: There are 15 keywords in value types which are used to define various data types.

bool	byte	char	decimal
double	enum	float	int
long	sbyte	short	struct
uint	ulong	ushort

Example:

// C# Program to illustrate the  // value type keywords  using System;      class Geeks {          // Here static, public, void       // are keywords          static public void Main () {                      // here byte is keyword          // a is identifier          byte a = 47;          Console.WriteLine("The value of a is: {0}",a);                                  // here bool is keyword          // b is identifier          // true is a keyword          bool b = true;                      Console.WriteLine("The value of b is: {0}",b);                 }  }

Output

The value of a is: 47 The value of b is: True

2. Reference Type Keywords: There are 6 keywords in reference types which are used to store references of the data or objects. The keywords in this category are: class, delegate, interface, object, string, void.

3. Modifiers Keywords: There are 17 keywords in modifiers which are used to modify the declarations of type member.

public	private	internal	protected	abstract
const	event	extern	new	override
partial	readonly	sealed	static	unsafe
virtual	volatile

Example:

// C# Program to illustrate the  // modifiers keywords  using System;     class Geeks {         class Mod      {          // using public modifier          // keyword          public int n1;         }      // Main Method      static void Main(string[] args) {             Mod obj1 = new Mod();             // access to public members          obj1.n1 = 77;             Console.WriteLine("Value of n1: {0}", obj1.n1);         }     }

Output

Value of n1: 77

4. Statements Keywords: There are total 18 keywords which are used in program instructions.

if	else	switch	do	for
foreach	in	while	break	continue
goto	return	throw	try	catch
finally	checked	unchecked

Example:

// C# program to illustrate the statement keywords  using System;      class Geeks   {       public static void Main()       {               // using for as statement keyword          // GeeksforGeeks is printed only 2 times           // because of continue statement           for(int i = 1; i < 3; i++)           {                              // here if and continue are keywords              if(i == 2)               continue;                              Console.WriteLine("GeeksforGeeks");           }       }   }

Output

GeeksforGeeks

5. Method Parameters Keywords: There are total 4 keywords which are used to change the behavior of the parameters that passed to a method. The keyword includes in this category are: params, in, ref, out.

6. Namespace Keywords: There are total 3 keywords in this category which are used in namespaces. The keywords are: namespace, using, extern.

7. Operator Keywords: There are total 8 keywords which are used for different purposes like creating objects, getting a size of object etc. The keywords are: as, is, new, sizeof, typeof, true, false, stackalloc.

8. Conversion Keywords: There are 3 keywords which are used in type conversions. The keywords are: explicit, implicit, operator.

9. Access Keywords: There are 2 keywords which are used in accessing and referencing the class or instance of the class. The keywords are base, this.

10. Literal Keywords: There are 2 keywords which are used as literal or constant. The keywords are null, default.

Important Points:

Keywords are not used as an identifier or name of a class, variable, etc.
If you want to use a keyword as an identifier then you must use @ as a prefix. For example, @abstract is valid identifier but not abstract because it is a keyword.

Example:

int a = 10; // Here int is a valid keyword

double int = 10.67; // invalid because int is a keyword

double @int = 10.67; // valid identifier, prefixed with @

int @null = 0; // valid

Illustration:

// C# Program to illustrate the use of   // prefixing @ in keywords  using System;     class Geeks {         // Here static, public, void       // are keywords          static public void Main () {                     // here int is keyword          // a is identifier          int a = 10;                     Console.WriteLine("The value of a is: {0}",a);                     // prefix @ in keyword int which           // makes it a valid identifier          int @int = 11;                     Console.WriteLine("The value of a is: {0}",@int);                }  }

Output

The value of a is: 10 The value of a is: 11

Contextual Keywords

These are used to give a specific meaning in the program. Whenever a new keyword comes in C#, it is added to the contextual keywords, not in the keyword category. This helps to avoid the crashing of programs which are written in earlier versions.

Important Points:

These are not reserved words.
It can be used as identifiers outside the context that’s why it named contextual keywords.
These can have different meanings in two or more contexts.
There are total 30 contextual keywords in C#.

add	equals	nameof	value
alias	from	on	var
ascending	get	orderby	when
async	global	partial(type)	where
await	group	partial(method)	yield
by	into	remove
descending	join	select
dynamic	let	set

Example:

// C# program to illustrate contextual keywords  using System;  public class Student {     // Declare name field       private string name = "GeeksforGeeks";      // Declare Name property       public string Name     {         // 'get' is a contextual keyword          get         {             return name;         }                  // 'set' is a contextual keyword          set         {             name = value;         }     } }  class TestStudent {     // Main Method       public static void Main(string[] args)     {         Student s = new Student();          // Calls set accessor of the property Name           s.Name = "GFG";          // Calls get accessor of the property Name           Console.WriteLine("Name: " + s.Name);          // Using 'get' and 'set' as identifiers (contextual usage)         int get = 50;         int set = 70;          Console.WriteLine("Value of get is: {0}", get);         Console.WriteLine("Value of set is: {0}", set);     } }

Output

Name: GFG Value of get is: 50 Value of set is: 70

Reference: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/

C# Decision Making (if, if-else, if-else-if ladder, nested if, switch, nested switch)

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C# Keywords

Keywords in C#

Contextual Keywords

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