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C++ Academy · Lesson

struct vs class When to Use Each

Understand the only real difference between struct and class and apply conventions.

struct vs class When to Use Each is a free C++ Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C++ Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Same Mechanism, Different Defaults

In C++, struct and class are nearly identical. The only language-level difference is the default access specifier.

struct: Public by Default

In a struct, members are public unless marked otherwise.

struct Point {
    int x;
    int y;
};  // x and y are public

class: Private by Default

In a class, members are private unless marked public.

class Counter {
    int n_ = 0;       // private
public:
    void increment() { n_++; }
    int  value() const { return n_; }
};

Convention, Not Just Syntax

The C++ community uses the two keywords to communicate intent:

  • struct — passive data (POD-like, all public)
  • class — encapsulated behavior (private state with public interface)

When to Use struct

Use struct for plain data aggregates: coordinates, RGB colors, simple records.

struct Point { int x; int y; };
struct Color { unsigned char r, g, b, a; };
struct Person { std::string name; int age; };

When to Use class

Use class when you have invariants to protect, when state changes through methods, or when you need encapsulation.

class BankAccount {
    double balance_ = 0.0;   // protected invariant
public:
    void deposit(double amount);
    bool withdraw(double amount);
    double balance() const;
};

Aggregate Initialization

Structs with only public members can be initialized with brace syntax — listing values in declaration order.

struct Point { int x; int y; };
Point p1{3, 4};      // aggregate init
Point p2{.x = 3, .y = 4};   // designated init (C++20)

Inheritance Differs Too

Inheritance is public by default for struct and private by default for class. Be explicit when in doubt.

class B {};
struct D1 : B {};         // public inheritance
class D2 : B {};          // private inheritance

Mixed Members

Even though defaults differ, both keywords can use public, private, and protected sections.

struct Config {
private:
    int internalCount = 0;
public:
    std::string name;
    void incrementCount() { ++internalCount; }
};

Reading Code by Keyword

When you see struct, expect data fields. When you see class, expect encapsulated logic. Treat the keyword as a hint about the author s intent.

Style Guides

Most style guides (Google, LLVM, ISO C++ Core) recommend struct only for passive aggregates without invariants. Anything with non-trivial methods becomes a class.

Quick Check

What is the only language-level difference between struct and class in C++?

Recap

Use struct for plain data aggregates and class for types with invariants and behavior. The only language difference is the default access — but convention treats them very differently.

Frequently asked questions

Is the “struct vs class When to Use Each” lesson free?

Yes — the full text of “struct vs class When to Use Each” is free to read here on the web, and the C++ Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C++ Academy course, upgrade to CoddyKit PRO.

What will I learn in “struct vs class When to Use Each”?

Understand the only real difference between struct and class and apply conventions. You practise C++ Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C++ Academy?

No prior experience is required. C++ Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “struct vs class When to Use Each” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C++ Academy lesson?

Yes. Every C++ Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. struct vs class When to Use Each
  2. Member Variables and Methods
  3. Constructors and Member Initializer Lists
  4. The this Pointer and Encapsulation
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