C++ Classes and Objects

So far you have used built-in types like int, double, and string. A class lets you invent brand-new types that model things from the real world, such as a car, a bank account, or a student. You describe the type once, then create as many objects from it as you like.

Defining a Class

You create a class with the class keyword followed by a name and a pair of curly braces. Inside the braces you list the members: variables that hold data (called attributes) and functions that describe behavior (called methods). Class names usually start with a capital letter to make them easy to spot.

#include <iostream>
#include <string>
using namespace std;

class Car {
  public:
    string brand;   // attribute
    string model;   // attribute
    int year;       // attribute
};

int main() {
  Car myCar;                // create an object
  myCar.brand = "Toyota";   // set attribute values
  myCar.model = "Corolla";
  myCar.year = 2024;

  cout << myCar.brand << " " << myCar.model << " (" << myCar.year << ")";
  return 0;
}

The public keyword means the members can be reached from outside the class. Once the object myCar exists, you use the dot operator (.) to read or change each attribute.

Creating Multiple Objects

One class can produce many independent objects. Each object keeps its own copy of the attributes, so changing one object never affects another.

#include <iostream>
#include <string>
using namespace std;

class Student {
  public:
    string name;
    int score;
};

int main() {
  Student a;
  a.name = "Maya";
  a.score = 92;

  Student b;
  b.name = "Leo";
  b.score = 78;

  cout << a.name << ": " << a.score << endl;
  cout << b.name << ": " << b.score << endl;
  return 0;
}