Enumerations and State

Enum Basics

An enum gives names to a small set of related choices.

unscoped enum An unscoped enum creates named constants that can be used instead of plain numbers.

Enum Basics

light
enum_basics.cpp
Replay: real traced execution (multi-file project)
#include <iostream>
#include <string>

enum TrafficLight {
    Red,
    Yellow,
    Green
};

std::string describe(TrafficLight light) {
    if (light == Red) {
        return "stop";
    }
    if (light == Yellow) {
        return "slow";
    }
    return "go";
}

int main() {
    TrafficLight light = Green;

    std::string action = describe(light);

    std::cout << "light=" << light << std::endl;
    std::cout << "action=" << action << std::endl;
    return 0;
}

#include <iostream>
#include <string>

enum TrafficLight {
    Red,
    Yellow,
    Green
};

std::string describe(TrafficLight light) {
    if (light == Red) {
        return "stop";
    }
    if (light == Yellow) {
        return "slow";
    }
    return "go";
}

int main() {
    TrafficLight light = Red;

    std::string action = describe(light);

    std::cout << "light=" << light << std::endl;
    std::cout << "action=" << action << std::endl;
    return 0;
}

#include <iostream>
#include <string>

enum TrafficLight {
    Red,
    Yellow,
    Green
};

std::string describe(TrafficLight light) {
    if (light == Red) {
        return "stop";
    }
    if (light == Yellow) {
        return "slow";
    }
    return "go";
}

int main() {
    TrafficLight light = Yellow;

    std::string action = describe(light);

    std::cout << "light=" << light << std::endl;
    std::cout << "action=" << action << std::endl;
    return 0;
}

  1. light ← 2

    20int main() {21    TrafficLight light→ 2 = Green; //@light=Red, Yellow2223    std::string action = describe(light2);

  2. std::string describe(TrafficLight light)

    10std::string describe(TrafficLight light2) {11    if (light == Red) {12        return "stop";13    }14    if (light == Yellow) {15        return "slow";16    }17    return "go";18}

  3. action ← go

    23    std::string action→ go = describe(light2);2425    std::cout << "light=" << light2 << std::endl;26    std::cout << "action=" << actiongo << std::endl;27    return 0;28}
    outputlight=2
action=go

  1. light ← 0

    20int main() {21    TrafficLight light→ 0 = Red;2223    std::string action = describe(light0);

  2. std::string describe(TrafficLight light)

    10std::string describe(TrafficLight light0) {11    if (light == Red) {

  3. if (light == Red)

    10std::string describe(TrafficLight light) {11    if (light0 == Red) {12        return "stop";13    }

  4. action ← stop

    23    std::string action→ stop = describe(light0);2425    std::cout << "light=" << light0 << std::endl;26    std::cout << "action=" << actionstop << std::endl;27    return 0;28}
    outputlight=0
action=stop

  1. light ← 1

    20int main() {21    TrafficLight light→ 1 = Yellow;2223    std::string action = describe(light1);

  2. std::string describe(TrafficLight light)

    10std::string describe(TrafficLight light1) {11    if (light == Red) {

  3. if (light == Yellow)

    13}14if (light1 == Yellow) {15    return "slow";16}

  4. action ← slow

    23    std::string action→ slow = describe(light1);2425    std::cout << "light=" << light1 << std::endl;26    std::cout << "action=" << actionslow << std::endl;27    return 0;28}
    outputlight=1
action=slow