C# | Identifiers

Difficulty Level : Easy
Last Updated : 07 Jul, 2021

In programming languages, identifiers are used for identification purposes. Or in other words, identifiers are the user-defined name of the program components. In C#, an identifier can be a class name, method name, variable name or label.
Example:

public class GFG {
    static public void Main () 
    {
          int x;
    }
}

Here the total number of identifiers present in the above example is 3 and the names of these identifiers are:

GFG: Name of the class
Main: Method name
x: Variable name

Rules for defining identifiers in C#:
There are certain valid rules for defining a valid C# identifier. These rules should be followed, otherwise, we will get a compile-time error.

The only allowed characters for identifiers are all alphanumeric characters([A-Z], [a-z], [0-9]), ‘_‘ (underscore). For example “geek@” is not a valid C# identifier as it contain ‘@’ – special character.
Identifiers should not start with digits([0-9]). For example “123geeks” is a not a valid in C# identifier.
Identifiers should not contain white spaces.
Identifiers are not allowed to use as keyword unless they include @ as a prefix. For example, @as is a valid identifier, but “as” is not because it is a keyword.
C# identifiers allow Unicode Characters.
C# identifiers are case-sensitive.
C# identifiers cannot contain more than 512 characters.
Identifiers does not contain two consecutive underscores in its name because such types of identifiers are used for the implementation.

Example:

CSharp

// Simple C# program to illustrate identifiers
using System;
 
class GFG {
 
    // Main Method
    static public void Main()
    {
 
        // variable
        int a = 10;
        int b = 39;
        int c;
 
        // simple addition
        c = a + b;
        Console.WriteLine("The sum of two number is: {0}", c);
    }
}