C# Identifiers

Last Updated : 6 Oct, 2026

An identifier in C# is a name given to programming elements such as variables, classes, methods, namespaces, properties, interfaces, and objects. It is used to uniquely identify these elements in a program.

  • Identifiers help in naming and accessing different elements in a C# program.
  • Each identifier must follow C# naming rules to avoid compilation errors.
C# 
class Geeks
{
    static void Main(string[] args)
    {
        int x = 9;
    }
}

In the above program:

  • Geeks -> identifier (class name)
  • Main -> identifier (method name)
  • args -> identifier (parameter name)
  • x-> identifier (variable name)
image1

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.  

  • The allowed characters for C# identifiers include letters (A-Z, a-z), digits (0-9), underscore (_), and Unicode characters. For example, geek@ is not a valid C# identifier because it contains @.
  • Identifiers should not start with digits (0-9). For example, 123geeks is not a valid C# identifier.
  • C# identifiers are case-sensitive. For example, student, Student, and STUDENT are treated as different identifiers.
  • There is no fixed limit on the length of a C# identifier, but it is advisable to use meaningful and readable names.
  • Spaces are not allowed in identifiers. For example, student name is invalid. Use studentName or student_name instead.
  • C# keywords cannot normally be used as identifiers. For example, int class = 20; is invalid because class is a keyword.
  • Keywords can be used as identifiers by prefixing them with @. For example, int @class = 20; is valid.

Note: C# has a set of reserved keywords and contextual keywords. Reserved keywords such as class, int, public, static, and void cannot normally be used as identifiers. The @ prefix can be used to escape a keyword and use it as an identifier.

Types of Identifiers

Identifiers in C# can represent different program elements:

  • Class Identifiers: Names of classes (e.g., GFG)
  • Method Identifiers: Names of methods (e.g., Main)
  • Variable Identifiers: Names of variables (e.g., x)
  • Object Identifiers: Names of objects created from classes
C# 
using System;

class Greeks
{
    static void Main()
    {
        string name = "GFG";
        Console.WriteLine(name);
    }
}

Output

GFG

In the above example:

  • Keywords: using, public, static, void.
  • Identifiers: System, Main, Program.

Examples of Valid Identifiers

MyVariable
MYVARIABLE
myvariable
x
i
x1
i1
_myvariable
sum_of_array
student123
StudentName
totalMarks

Examples of Invalid Identifiers

My Variable          // contains a space
123student           // begins with a digit
a+c                  // contains +
variable-2           // contains -
sum&difference       // contains &
class                // keyword
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