Classes

by Eddie Huang

A class is to a car factory as an object is to a car. Classes define the behavior of a type of object. They contain variables and functions that are inherent to the class.

A Simple Rectangle Example

rectangle.h

class Rectangle {
    int width, height;
  public:
    Rectangle();
    Rectangle(int a, int b);
    int area() {
      return width * height;
    }
    int circumference();
};

rectangle.cpp

Rectangle::Rectangle() {
  width = 5;
  height = 5;
}

Rectangle::Rectangle(int a, int b) {
  this->width = a;
  this->height = b;
}

int Rectangle::circumference() {
  return (width + height) * 2;
}

main.cpp

#include <iostream>
using namespace std;

int main() {
  Rectangle rect(3,4);
  Rectangle rect_default;
  cout << "rect area: " << rect.area() << endl;
  cout << "rect_default area: " << rect_default.area() << endl;
  return 0;
}

Output

rect area: 12
rect_default area: 25