C# Identifiers

Last Updated : 11 Jan, 2025

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

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

Aspect	Description
Allowed Characters	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.
Starting Character	Identifiers should not start with digits([0-9]). For example, "123geeks" is not valid in the C# identifier.
No Whitespaces	Identifiers must not contain whitespace characters.
Keywords	Identifiers are not allowed to use as keywords unless they include @ as a prefix. For example, @as is a valid identifier, but "as" is not because it is a keyword.
Unicode Support	C# identifiers allow Unicode Characters.
Case - Sensitivity	C# identifiers are case-sensitive.
Length Restriction	C# identifiers cannot contain more than 512 characters.
No Double Underscores	Identifiers do not contain two consecutive underscores in their name because such types of identifiers are used for the implementation.

Example:

// Simple C# program to illustrate identifiers
using System;

class Geeks 
{
    // Main Method
    static public void Main()
    {
        // variable
        int a = 10;
        int b = 39;
        int c;

        // basic operation
        c = a + b;
      
        Console.WriteLine("The sum of two number is: {0}", c);
    }
}

Output

The sum of two number is: 49

Below data shows the identifiers and keywords present in the above example:

Keywords: using, public, static, void, int.
Identifiers: Geeks, Main , a, b, c.

C# Data Types

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