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Posted 13 Oct 2001


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Enums and Structs in C#

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13 Oct 2001CPL4 min read
Two oft-overlooked value types that C# offers and where they can be used


Just about everything is a heap object when you are using C#. Only elementary native types like int are treated as value types. But there are two value types in C# that are pretty much more useful that first glances would tell you. They are the enum and struct types. Very few tutorials even cover these topics, but they have their own uses. And both of them are a lot more efficient than classes and you can use them in place of classes when they meet your requirements to improve performance.


Enums are basically a set of named constants. They are declared in C# using the enum keyword. Every enum type automatically derives from System.Enum and thus we can use

methods on our Enums. Enums are value types and are created on the stack and not on the heap. You don't have to use new to create an enum type. Declaring an enum is a little like setting the members of an array as shown below.

enum Rating {Poor, Average, Okay, Good, Excellent}

You can pass enums to member functions just as if they were normal objects. And you can perform arithmetic on enums too. For example we can write two functions, one to increment our  enum and the other to decrement our enum.

Rating IncrementRating(Rating r)
    if(r == Rating.Excellent)
        return r;
        return r+1;
Rating DecrementRating(Rating r)
    if(r == Rating.Poor)
        return r;
        return r-1;

Both functions take a Rating object as argument and return back a Rating object. Now we can simply call these functions from elsewhere.

for (Rating r1 = Rating.Poor; 
    r1 < Rating.Excellent ; 
    r1 = IncrementRating(r1))


for (Rating r2 = Rating.Excellent; 
    r2 > Rating.Poor; 
    r2 = DecrementRating(r2))

And here is a sample code snippet showing how you can call

methods on our Enum object. We call the
method which retrieves an array of the names of the constants in the enumeration.

foreach(string s in Rating.GetNames(typeof(Rating)))

Where to use enums

Quite often we have situations where a class method takes as an argument a custom option. Let's say we have some kind of file access class and there is a file open method that has a parameter that might be one of read-mode, write-mode, read-write-mode, create-mode and append-mode. Now you might think of adding five static member fields to your class for these modes. Wrong approach! Declare and use an enumeration which is a whole lot more efficient and is better programming practice in my opinion.


In C++ a struct is just about the same as a class for all purposes except in the default access modifier for methods. In C# a

are a pale puny version of a class. I am not sure why this was done so, but perhaps they decided to have a clear distinction between structs and classes. Here are some of the drastic areas where classes and structs differ in functionality.

  • structs are stack objects and however much you try you cannot create them on the heap
  • structs cannot inherit from other structs though they can derive from interfaces
  • You cannot declare a default constructor for a struct, your constructors must have parameters
  • The constructor is called only if you create your struct using new, if you simply declare the struct just as in  declaring a native type like int, you must explicitly set each member's value before you can use the
struct Student : IGrade
    public int maths;
    public int english;
    public int csharp;

    //public member function
    public int GetTot()
        return maths+english+csharp;

    //We have a constructor that takes an int as argument
    public Student(int y)
        maths = english = csharp = y;

    //This method is implemented because we derive
    //from the IGrade interface
    public string GetGrade()
        if(GetTot() > 240 )
            return "Brilliant";
        if(GetTot() > 140 )
            return "Passed";
        return "Failed";

interface IGrade
    string GetGrade();

Well, now let's take a look at how we can use our struct.

Student s1 = new Student();


Here the default constructor gets called. This is automatically implemented for us and we cannot have our own default parameter-less constructor. The default parameter-less constructor simply initializes all values to their zero-equivalents. This is why we get a 0 as the total.

Student s2;
s2.maths = s2.english = s2.csharp = 50;


Because we haven't used new, the constructor does not get called. Of all the silly features this one must win the annual contest by a long way. I see no sane reason why this must be so. Anyway you have to initialize all the member fields. If you comment out the line that does the initialization you will get a compiler error :- Use of unassigned local variable 's2'

Student s3 = new Student(90);


This time we use our custom constructor that takes an int as argument.

When to use structs

Because structs are value types they would be easier to handle and more efficient that classes. When you find that you are using a class mostly for storing a set of values, you must replace those classes with structs. When you declare arrays of structs because they are created on the heap, efficiency again improves. Because if they were classes each class object would need to have memory allocated on the heap and their references would be stored. In fact lots of classes within the .NET framework are actually structs. For example

is actually a struct and not a


This article, along with any associated source code and files, is licensed under The Common Public License Version 1.0 (CPL)


About the Author

Nish Nishant
United States United States
Nish Nishant is a Principal Software Architect based out of Columbus, Ohio. He has over 17 years of software industry experience in various roles including Lead Software Architect, Principal Software Engineer, and Product Manager. Nish was a Microsoft Visual C++ MVP between 2002 and 2015.

Nish is an industry acknowledged expert in the Microsoft technology stack. He authored C++/CLI in Action for Manning Publications in 2005, and had previously co-authored Extending MFC Applications with the .NET Framework for Addison Wesley in 2003. In addition, he has over 140 published technology articles on and another 250+ blog articles on his WordPress blog. Nish is vastly experienced in team management, mentoring teams, and directing all stages of software development.

Contact Nish : If you are interested in hiring Nish as a consultant, you can reach him via his google email id voidnish.

Company Website :

Comments and Discussions

Questionc#: conversion of string variable to struct variable Pin
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GeneralMy vote of 5 Pin
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SuggestionUnions Pin
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AnswerRe: Unions Pin
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QuestionImport WIN32 DLL Pin
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GeneralMy vote of 5 Pin
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mvaSergey Alexandrovich Kryukov17-Feb-11 12:21 
GeneralRe: My vote of 5 Pin
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QuestionProblem of Event and Delegate Pin
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GeneralNewbie Question Pin
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AnswerRe: Newbie Question Pin
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QuestionHow to load a lot of data into structs? Pin
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GeneralProblems with structs in C# Pin
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GeneralRe: Problems with structs in C# Pin
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GeneralRe: Problems with structs in C# Pin
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GeneralUsing typedef structs in C# ,C++ Pin
arssa202017-Jun-04 9:26
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QuestionDoes know anybody how to extend a enum? Pin
srlopez25-Feb-03 4:21
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AnswerRe: Does know anybody how to extend a enum? Pin
Daniel Turini25-Feb-03 4:32
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GeneralRe: Does know anybody how to extend a enum? Pin
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GeneralRe: Does know anybody how to extend a enum? Pin
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GeneralRe: Does know anybody how to extend a enum? Pin
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AnswerRe: Does know anybody how to extend a enum? Pin
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QuestionLanguage bug or language feature? Pin
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GeneralGuess: why no overloading default struct ctor Pin
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GeneralYou rock Nish Pin
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