C++ Enumration 列舉

C++ Enumration 列舉

• 介紹

以enum為宣告字眼，給予列舉名稱，後面大括號寫入列舉元

enum 列舉名{列舉元1, 2, 3....};

給予列舉元指定常數，不選擇用常數而用列舉元來表示狀態，讓程式更加清楚

• 使用規則

#include <iostream>

using namespace std;

int main(){

    // 沒有特別指定數字給列舉元會從0往上遞加

    enum status {sit, stand, walk, run};

    status checkStatus = sit;

    cout << "status number: " << checkStatus << endl; // 0

    checkStatus = stand;

    cout << "status number: " << checkStatus << endl; // 1

    checkStatus = walk;

    cout << "status number: " << checkStatus << endl; // 2

    checkStatus = run;

    cout << "status number: " << checkStatus << endl; // 3



    // 有指定數字給列舉元，且指定數字可以重複

    enum menu {pork = 1, beef, noodles = 4, rice};

    menu order = pork;

    cout << "order number: " << order << endl; // 1

    order = beef;

    cout << "order number: " << order << endl; // 2

    order = noodles;

    cout << "order number: " << order << endl; // 4

    order = rice;

    cout << "order number: " << order << endl; // 5



    // 不能直接指定數字給列舉元

    // order = 5; error

    // 可以拿列舉元來做運算    

    cout << order + 8 << endl; // 13

    order = rice;

    // 以下兩個if statement 是正確可行的

    if (order == 5) {

        cout << "you have ordered the rice." << endl;

    }

    if (order == rice) {

        cout << "you have ordered the rice." << endl;

    }

    // 不能使用postfix increment or decrement

    // cout << order++ << endl;

    // 不能使用prefix increment or decrement

    // cout << ++order << endl;    

    int i = 1;

    cout << menu(i) << endl;    

    // 代替常數來作為判別狀態 or 作為傳入函式的參數



}

• 應用
  • 代替常數作為傳入函式的參數
  • 代替常數來代表狀態，更容易給撰寫者表明用意

#include <iostream>

using namespace std;

enum status {sit, stand, walk, run};

void getStatus(status);

int main(){

    int i = 4;

    getStatus(status(i));

    status s = sit;

    getStatus(s);    

}

void getStatus(status s) {

    cout << "s : " << s << endl;

    switch(s){

        case 0:

            cout << "You are sitting now, you can choose stand as next step."<< endl;

            break;

        case 1:

            cout << "You are standing now, you can choose either sit or walk." << s << endl;

            break;

        case 2:

            cout << "You are walking now, you can choose either stand still or run. " << s << endl;

            break;

        case 3:

            cout << "You are running now, you can choose to walk." << s << endl;

            break;

        default:

            cout << "You are not in the right status" << endl;    

    }

}

• 參考資料

列舉 / OpenHome.cc

tags: C++

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