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    Keywords and Identifiers in C#: Understanding the Basics

    Rumman Ansari October 01, 2024 6,484 views
    Keywords and Identifiers in C#: Understanding the Basics

    C# Keywords

    Keywords are predefined sets of reserved words that have special meaning in a program. The meaning of keywords can not be changed, neither can they be directly used as identifiers in a program.

    For example,

    long mobileNum;

    Here, long is a keyword and mobileNum is a variable (identifier). long has a special meaning in C# i.e. it is used to declare variables of type long and this function cannot be changed.

    Also, keywords like long, int, char, etc can not be used as identifiers. So, we cannot have something like:

    long long;

    C# has a total of 79 keywords. All these keywords are in lowercase. Here is a complete list of all C# keywords.

    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 in (generic modifier) int interface
    internal is lock long
    namespace new null object
    operator out out (generic modifier) override
    params private protected public
    readonly ref return sbyte
    sealed short sizeof stackalloc
    static string struct switch
    this throw true try
    typeof uint ulong unchecked
    unsafe ushort using using static
    void volatile while  

    Although keywords are reserved words, they can be used as identifiers if @ is added as prefix. For example,

    int @void;

    The above statement will create a variable @void of type int.

    Contextual Keywords

    Besides regular keywords, C# has 25 contextual keywords. Contextual keywords have specific meaning in a limited program context and can be used as identifiers outside that context. They are not reserved words in C#.

    add alias ascending
    async await descending
    dynamic from get
    global group into
    join let orderby
    partial (type) partial (method) remove
    select set value
    var when (filter condition) where (generic type constraint)
    yield    

    C# Identifiers

     Identifiers are the name given to entities such as variables, methods, classes, etc. They are tokens in a program which uniquely identify an element. For example,

    int value;

    Here, value is the name of variable. Hence it is an identifier. Reserved keywords can not be used as identifiers unless @ is added as prefix. For example,

    int break;

    This statement will generate an error in compile time.

    Rules for Naming an Identifier

    • An identifier can not be a C# keyword.
    • An identifier must begin with a letter, an underscore or @ symbol. The remaining part of identifier can contain letters, digits and underscore symbol.
    • Whitespaces are not allowed. Neither it can have symbols other than letter, digits and underscore.
    • Identifiers are case-sensitive. So, getName, GetName and getname represents 3 different identifiers.

    Here are some of the valid and invalid identifiers:

    Identifiers Remarks
    number Valid
    calculateMarks Valid
    hello$ Invalid (Contains $)
    name1 Valid
    @if Valid (Keyword with prefix @)
    if Invalid (C# Keyword)
    My name Invalid (Contains whitespace)
    _hello_hi Valid

    Example: Find list of keywords and identifiers in a program

    Just to clear the concept, let's find the list of keywords and identifiers in the program we wrote in C# Hello World.using System;

    namespace HelloWorld{ class Hello{  static void Main(string[] args) { Console.WriteLine("Hello World!"); } }}
    Keywords Identifiers
    using System
    namespace HelloWorld (namespace)
    class Hello (class)
    static Main (method)
    void args
    string Console
      WriteLine

    The "Hello World!" inside WriteLine method is a string literal.