C# Identifiers (original) (raw)

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:

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:

C# `

// 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: