C# 取得中文星期名稱的簡易方法

方法一：Switch 表達式 (C# 8.0+)

public static string GetChineseWeekName() {
    return DateTime.Now.DayOfWeek switch {
        DayOfWeek.Monday    => "星期一",
        DayOfWeek.Tuesday   => "星期二",
        DayOfWeek.Wednesday => "星期三",
        DayOfWeek.Thursday  => "星期四",
        DayOfWeek.Friday    => "星期五",
        DayOfWeek.Saturday  => "星期六",
        DayOfWeek.Sunday    => "星期日",
        _ => throw new ArgumentOutOfRangeException()
    };
}

方法二：陣列查表 (效能最佳、相容所有版本)

private static readonly string[] ChineseWeekNames = 
    { "星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六" };

public static string GetChineseWeekName() {
    return ChineseWeekNames[(int)DateTime.Now.DayOfWeek];
}

方法三：傳統 Switch (舊版 C# 相容)

public static string GetChineseWeekName() {
    switch (DateTime.Now.DayOfWeek) {
        case DayOfWeek.Monday:    return "星期一";
        case DayOfWeek.Tuesday:   return "星期二";
        case DayOfWeek.Wednesday: return "星期三";
        case DayOfWeek.Thursday:  return "星期四";
        case DayOfWeek.Friday:    return "星期五";
        case DayOfWeek.Saturday:  return "星期六";
        case DayOfWeek.Sunday:    return "星期日";
        default: throw new InvalidOperationException();
    }
}

使用範例

Console.WriteLine($"今天是 {GetChineseWeekName()}"); // 輸出：今天是 星期三

補充：取得指定日期的星期

public static string GetChineseWeekName(DateTime date) {
    return ChineseWeekNames[(int)date.DayOfWeek];
}