Classes

Class Intro

A class groups related data and behavior into one type.

class A class definition describes the fields and functions that objects of that type can use.

Class Intro

example
class_intro.cpp
Replay: real traced execution (multi-file project)
#include <iostream>

class Rectangle {
public:
    int width;
    int height;

    int area() {
        return width * height;
    }
};

int main() {
    int width = 4;
    int height = 3;

    Rectangle card;
    card.width = width;
    card.height = height;

    std::cout << "width=" << card.width << std::endl;
    std::cout << "height=" << card.height << std::endl;
    std::cout << "area=" << card.area() << std::endl;
    return 0;
}

#include <iostream>

class Rectangle {
public:
    int width;
    int height;

    int area() {
        return width * height;
    }
};

int main() {
    int width = 2;
    int height = 3;

    Rectangle card;
    card.width = width;
    card.height = height;

    std::cout << "width=" << card.width << std::endl;
    std::cout << "height=" << card.height << std::endl;
    std::cout << "area=" << card.area() << std::endl;
    return 0;
}

#include <iostream>

class Rectangle {
public:
    int width;
    int height;

    int area() {
        return width * height;
    }
};

int main() {
    int width = 6;
    int height = 3;

    Rectangle card;
    card.width = width;
    card.height = height;

    std::cout << "width=" << card.width << std::endl;
    std::cout << "height=" << card.height << std::endl;
    std::cout << "area=" << card.area() << std::endl;
    return 0;
}

#include <iostream>

class Rectangle {
public:
    int width;
    int height;

    int area() {
        return width * height;
    }
};

int main() {
    int width = 4;
    int height = 5;

    Rectangle card;
    card.width = width;
    card.height = height;

    std::cout << "width=" << card.width << std::endl;
    std::cout << "height=" << card.height << std::endl;
    std::cout << "area=" << card.area() << std::endl;
    return 0;
}

#include <iostream>

class Rectangle {
public:
    int width;
    int height;

    int area() {
        return width * height;
    }
};

int main() {
    int width = 4;
    int height = 7;

    Rectangle card;
    card.width = width;
    card.height = height;

    std::cout << "width=" << card.width << std::endl;
    std::cout << "height=" << card.height << std::endl;
    std::cout << "area=" << card.area() << std::endl;
    return 0;
}

  1. width ← 4, height ← 3, card ← (empty), card.width ← 4, card.height ← 3

    13int main() {14    int width→ 4 = 4; //@width=2, 615    int height→ 3 = 3; //@height=5, 71617    Rectangle card→ (empty);18    card.width→ 4 = width4;19    card.height→ 3 = height3;2021    std::cout << "width=" << card(empty).width << std::endl;22    std::cout << "height=" << card(empty).height << std::endl;23    std::cout << "area=" << card(empty).area() << std::endl;24    return 0;
    outputwidth=4
height=3

  2. int area()

    8int area() {9    return width4 * height3;10}

  3. std::cout << "area=" << card.area() << std::endl;

    22    std::cout << "height=" << card.height << std::endl;23    std::cout << "area=" << card(empty).area() << std::endl;24    return 0;25}
    outputarea=12

  1. width ← 2, height ← 3, card ← (empty), card.width ← 2, card.height ← 3

    13int main() {14    int width→ 2 = 2;15    int height→ 3 = 3;1617    Rectangle card→ (empty);18    card.width→ 2 = width2;19    card.height→ 3 = height3;2021    std::cout << "width=" << card(empty).width << std::endl;22    std::cout << "height=" << card(empty).height << std::endl;23    std::cout << "area=" << card(empty).area() << std::endl;24    return 0;
    outputwidth=2
height=3

  2. int area()

    8int area() {9    return width2 * height3;10}

  3. std::cout << "area=" << card.area() << std::endl;

    22    std::cout << "height=" << card.height << std::endl;23    std::cout << "area=" << card(empty).area() << std::endl;24    return 0;25}
    outputarea=6

  1. width ← 6, height ← 3, card ← (empty), card.width ← 6, card.height ← 3

    13int main() {14    int width→ 6 = 6;15    int height→ 3 = 3;1617    Rectangle card→ (empty);18    card.width→ 6 = width6;19    card.height→ 3 = height3;2021    std::cout << "width=" << card(empty).width << std::endl;22    std::cout << "height=" << card(empty).height << std::endl;23    std::cout << "area=" << card(empty).area() << std::endl;24    return 0;
    outputwidth=6
height=3

  2. int area()

    8int area() {9    return width6 * height3;10}

  3. std::cout << "area=" << card.area() << std::endl;

    22    std::cout << "height=" << card.height << std::endl;23    std::cout << "area=" << card(empty).area() << std::endl;24    return 0;25}
    outputarea=18

  1. width ← 4, height ← 5, card ← (empty), card.width ← 4, card.height ← 5

    13int main() {14    int width→ 4 = 4;15    int height→ 5 = 5;1617    Rectangle card→ (empty);18    card.width→ 4 = width4;19    card.height→ 5 = height5;2021    std::cout << "width=" << card(empty).width << std::endl;22    std::cout << "height=" << card(empty).height << std::endl;23    std::cout << "area=" << card(empty).area() << std::endl;24    return 0;
    outputwidth=4
height=5

  2. int area()

    8int area() {9    return width4 * height5;10}

  3. std::cout << "area=" << card.area() << std::endl;

    22    std::cout << "height=" << card.height << std::endl;23    std::cout << "area=" << card(empty).area() << std::endl;24    return 0;25}
    outputarea=20

  1. width ← 4, height ← 7, card ← (empty), card.width ← 4, card.height ← 7

    13int main() {14    int width→ 4 = 4;15    int height→ 7 = 7;1617    Rectangle card→ (empty);18    card.width→ 4 = width4;19    card.height→ 7 = height7;2021    std::cout << "width=" << card(empty).width << std::endl;22    std::cout << "height=" << card(empty).height << std::endl;23    std::cout << "area=" << card(empty).area() << std::endl;24    return 0;
    outputwidth=4
height=7

  2. int area()

    8int area() {9    return width4 * height7;10}

  3. std::cout << "area=" << card.area() << std::endl;

    22    std::cout << "height=" << card.height << std::endl;23    std::cout << "area=" << card(empty).area() << std::endl;24    return 0;25}
    outputarea=28