C++ Academy · Lesson

Member Variables and Methods

Declare member variables, write member methods, and reference them through instances.

Lesson 2 of 413 steps

Member Variables and Methods is a free C++ Academy lesson on CoddyKit. This is lesson 2 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the C++ Academy learning path, and your progress syncs across the web and the CoddyKit app. The C++ Academy course includes 4 lessons in total.

Members of a Class

A class can contain:

Member variables (data, sometimes called fields)
Member functions (methods)
Nested types (typedefs, enums, classes)
Static members (shared across all instances)

Declaring Member Variables

Declare them in the class body. Use C++11 in-class default initializers for cleanliness.

class Person {
    std::string name_ = "unknown";
    int age_ = 0;
public:
    // ...
};

Naming Conventions

Common conventions for private members:

Trailing underscore: name_
Leading m_: m_name
Plain names with implicit this->

Pick one and stay consistent.

Defining Methods Inside the Class

Short methods can be defined inline in the class body — and are implicitly inline.

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

Defining Methods Outside the Class

Longer methods are usually defined outside, often in a .cpp file. Use the scope resolution operator ::.

// header
class Logger {
public:
    void log(const std::string& msg);
};

// implementation
void Logger::log(const std::string& msg) {
    std::cout << "[LOG] " << msg << "\n";
}

Calling Methods

Use dot syntax on objects and arrow syntax on pointers.

Counter c;
c.increment();

Counter* p = &c;
p->increment();

Const Methods

Methods that do not modify the object should be marked const. They can be called on const instances.

class Counter {
    int n_ = 0;
public:
    int value() const { return n_; }   // does not modify *this
};

Static Members

Static members belong to the class, not to instances. Declare with static; define in a source file.

class Logger {
public:
    static int messageCount;
    static void log(const std::string& msg);
};
int Logger::messageCount = 0;

Access Specifiers

Three access levels:

public — accessible from anywhere
private — accessible only inside the class
protected — accessible inside the class and derived classes

Encapsulation in Practice

Make data members private. Expose them through methods that enforce invariants.

class Temperature {
    double celsius_ = 0.0;
public:
    void setCelsius(double c);     // validates range
    double celsius() const { return celsius_; }
    double fahrenheit() const { return celsius_ * 9.0/5.0 + 32; }
};

Methods and Free Functions

Not everything must be a method. If a function uses only the public interface, prefer a free function — it reduces coupling.

Quick Check

What keyword marks a member function as not modifying the object?

Answer it in the interactive lesson

Recap

Member variables hold per-instance state; methods operate on that state. Mark non-modifying methods const. Make data private and expose behavior through a small, intentional public interface.

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Frequently Asked Questions

Is the “Member Variables and Methods” lesson free?

Yes — any 3 lessons of the C++ Academy learning path, including “Member Variables and Methods”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The C++ Academy course includes 4 lessons in total.

What will I learn in “Member Variables and Methods”?

Declare member variables, write member methods, and reference them through instances. 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, so you can start here or from the beginning and move at your own pace. This is lesson 2 of 4.

How long does the “Member Variables and Methods” 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

struct vs class When to Use Each
Member Variables and Methods
Constructors and Member Initializer Lists
The this Pointer and Encapsulation

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