[C#] 列挙型(enum)の使い方を初心者向けに解説

enum DayOfWeek
{
    Sunday,
    Monday,
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday
}

enum ErrorCode
{
    None = 0,
    NotFound = 404,
    ServerError = 500
}

DayOfWeek today; // デフォルト値は DayOfWeek.Sunday

public enum Color
{
    Red,
    Green,
    Blue
}
private enum Status
{
    Active,
    Inactive
}

enum DayOfWeek
{
    Sunday,
    Monday,
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday
}
class Program
{
    static void Main(string[] args)
    {
        DayOfWeek today = DayOfWeek.Monday; // 列挙型の値を変数に代入
        Console.WriteLine(today);
    }
}

Monday

class Program
{
    static void Main(string[] args)
    {
        DayOfWeek today = DayOfWeek.Monday;
        if (today == DayOfWeek.Monday)
        {
            Console.WriteLine("今日は月曜日です。");
        }
    }
}

今日は月曜日です。

class Program
{
    static void Main(string[] args)
    {
        DayOfWeek today = DayOfWeek.Wednesday;
        string todayString = today.ToString(); // 列挙型の値を文字列に変換
        Console.WriteLine(todayString);
    }
}

Wednesday

class Program
{
    static void Main(string[] args)
    {
        DayOfWeek today = DayOfWeek.Friday;
        int todayValue = (int)today; // 列挙型の値を整数に変換
        Console.WriteLine(todayValue);
    }
}

5

[Flags]
enum Permissions
{
    None = 0,
    Read = 1,      // 0001
    Write = 2,     // 0010
    Execute = 4,   // 0100
    Admin = 8      // 1000
}
class Program
{
    static void Main(string[] args)
    {
        Permissions userPermissions = Permissions.Read | Permissions.Write; // 複数の権限を組み合わせる
        Console.WriteLine(userPermissions);
    }
}

Read, Write

class Program
{
    static void Main(string[] args)
    {
        DayOfWeek today = DayOfWeek.Saturday;
        switch (today)
        {
            case DayOfWeek.Sunday:
                Console.WriteLine("今日は日曜日です。");
                break;
            case DayOfWeek.Saturday:
                Console.WriteLine("今日は土曜日です。");
                break;
            default:
                Console.WriteLine("平日です。");
                break;
        }
    }
}

今日は土曜日です。

class Program
{
    static void Main(string[] args)
    {
        foreach (DayOfWeek day in Enum.GetValues(typeof(DayOfWeek)))
        {
            Console.WriteLine(day);
        }
    }
}

Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday

class Program
{
    static void Main(string[] args)
    {
        string input = "Friday";
        DayOfWeek day = (DayOfWeek)Enum.Parse(typeof(DayOfWeek), input); // 文字列から列挙型の値を取得
        Console.WriteLine(day);
    }
}

Friday

enum ErrorCode
{
    None = 0,
    NotFound = 404,
    Deleted = 404, // 同じ値を持つメンバー
    ServerError = 500
}
class Program
{
    static void Main(string[] args)
    {
        ErrorCode error = ErrorCode.NotFound;
        if (error == ErrorCode.Deleted)
        {
            Console.WriteLine("エラーは削除されました。");
        }
        else
        {
            Console.WriteLine("エラーは見つかりませんでした。");
        }
    }
}

エラーは削除されました。

class Program
{
    static void Main(string[] args)
    {
        DayOfWeek day = (DayOfWeek)10; // 範囲外の値を代入
        Console.WriteLine(day); // 出力は "10"
    }
}

10

public static class EnumExtensions
{
    public static DayOfWeek NextDay(this DayOfWeek day)
    {
        return (DayOfWeek)(((int)day + 1) % 7); // 次の曜日を計算
    }
}
class Program
{
    static void Main(string[] args)
    {
        DayOfWeek today = DayOfWeek.Friday;
        DayOfWeek tomorrow = today.NextDay(); // 拡張メソッドを使用
        Console.WriteLine(tomorrow);
    }
}

Saturday

enum TaskStatus
{
    NotStarted,
    InProgress,
    Completed,
    OnHold
}
class Program
{
    static void Main(string[] args)
    {
        TaskStatus status = TaskStatus.NotStarted;
        // 状態を変更
        status = TaskStatus.InProgress;
        Console.WriteLine($"タスクの状態: {status}");
    }
}

タスクの状態: InProgress

enum ErrorCode
{
    None,
    NotFound,
    InvalidInput,
    ServerError
}
class Program
{
    static void Main(string[] args)
    {
        ErrorCode error = ProcessData();
        if (error != ErrorCode.None)
        {
            Console.WriteLine($"エラーが発生しました: {error}");
        }
    }
    static ErrorCode ProcessData()
    {
        // 処理中にエラーが発生した場合
        return ErrorCode.NotFound;
    }
}

エラーが発生しました: NotFound

enum Theme
{
    Light,
    Dark,
    Blue,
    Green
}
class Program
{
    static void Main(string[] args)
    {
        Theme currentTheme = Theme.Dark;
        Console.WriteLine($"現在のテーマ: {currentTheme}");
    }
}

現在のテーマ: Dark

enum CharacterState
{
    Idle,
    Running,
    Jumping,
    Attacking
}
class Program
{
    static void Main(string[] args)
    {
        CharacterState state = CharacterState.Idle;
        // 状態を変更
        state = CharacterState.Running;
        Console.WriteLine($"キャラクターの状態: {state}");
    }
}

キャラクターの状態: Running