C# | Keywords

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 use as variable names or objects. Doing this will result in a compile-time error.

Example:

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// C# Program to illustrate the keywords
using System;
  
class GFG {
  
    // 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;
         
    }
}

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Output:



The value of a is: 10

There are total 78 keywords in C# as follows:

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
unit
ulong
unchecked
unsafe
ushort
using
using static
virtual
void
volatile
while

 
 

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
    unit ulong ushort

    Example:



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    // C# Program to illustrate the
    // value type keywords
    using System;
       
    class GFG {
       
        // 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);
               
              
              
        }
    }

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    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.  

  4. 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:

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    // 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);
      
        }
      
    }

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    Output:

    Value of n1: 77
  5. 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:

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    // C# program to illustrate the statement keywords
    using System; 
      
    class demoContinue 
        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"); 
            
        

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    Output:

    GeeksforGeeks
  6. 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.
  7.  

  8. Namespace Keywords: There are total 3 keywords in this category which are used in namespaces. The keywords are: namespace, using, extern.
  9.  

  10. 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.
  11.  

  12. Conversion Keywords: There are 3 keywords which are used in type conversions. The keywords are: explicit, implicit, operator.
  13.  



  14. 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.
  15.  

  16. 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
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// C# Program to illustrate the use of 
// prefixing @ in keywords
using System;
  
class GFG {
  
    // 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);
         
    }
}

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

 
 
 
 

Example:

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// 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 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, 
        // and pass "GFG" as value of the 
        // standard field 'value'. 
        s.Name = "GFG"
  
        // displays GFG, Calls the get accessor 
        // of the property Name. 
        Console.WriteLine("Name: " + s.Name); 
          
        // using get and set as identifier
        int get = 50;
        int set = 70;
          
        Console.WriteLine("Value of get is: {0}",get);
        Console.WriteLine("Value of set is: {0}",set);
    

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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/



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