When should I use a struct rather than a class in C#?

Question

When should you use struct and not class in C#? My conceptual model is that structs are used in times when the item is merely a collection of value types. A way to

Answer 1

A struct is a value type. If you assign a struct to a new variable, the new variable will contain a copy of the original.

public struct IntStruct {
    public int Value {get; set;}
}

Excecution of the following results in 5 instances of the struct stored in memory:

var struct1 = new IntStruct() { Value = 0 }; // original
var struct2 = struct1;  // A copy is made
var struct3 = struct2;  // A copy is made
var struct4 = struct3;  // A copy is made
var struct5 = struct4;  // A copy is made

// NOTE: A "copy" will occur when you pass a struct into a method parameter.
// To avoid the "copy", use the ref keyword.

// Although structs are designed to use less system resources
// than classes.  If used incorrectly, they could use significantly more.

A class is a reference type. When you assign a class to a new variable, the variable contains a reference to the original class object.

public class IntClass {
    public int Value {get; set;}
}

Excecution of the following results in only one instance of the class object in memory.

var class1 = new IntClass() { Value = 0 };
var class2 = class1;  // A reference is made to class1
var class3 = class2;  // A reference is made to class1
var class4 = class3;  // A reference is made to class1
var class5 = class4;  // A reference is made to class1  

Structs may increase the likelihood of a code mistake. If a value object is treated like a mutable reference object, a developer may be surprised when changes made are unexpectedly lost.

var struct1 = new IntStruct() { Value = 0 };
var struct2 = struct1;
struct2.Value = 1;
// At this point, a developer may be surprised when 
// struct1.Value is 0 and not 1