MyWeek myWeek = new MyWeek();
for (int i = 1; i <= myWeek.Length; i++)
{
    Console.WriteLine(myWeek[i]);
}

/// <summary>
/// 索引指示器的实质是含参属性，
///     参数并不只限于 int, string 也可以。
/// </summary>
public class MyWeek
{
    public int Length
    {
        get { return 7; }
    }

/// <summary>
    /// 使用 int 作为参数的索引指示器
    /// </summary>
    /// <param name="Index"></param>
    /// <returns></returns>
    public string this[int Index]
    {
        get
        {
            string dayName;
            switch (Index)
            {
                case 1:
                    dayName = "Monday";
                    break;
                case 2:
                    dayName = "Tuesday";
                    break;
                case 3:
                    dayName = "Wednesday";
                    break;
                case 4:
                    dayName = "Thursday";
                    break;
                case 5:
                    dayName = "Friday";
                    break;
                case 6:
                    dayName = "Saturday";
                    break;
                case 7:
                    dayName = "Sunday";
                    break;
                default:
                    dayName = "";
                    break;
            }
            return dayName;
        }
    }

/// <summary>
    /// 使用 string 作为参数的索引指示器
    /// </summary>
    /// <param name="dayName"></param>
    /// <returns></returns>
    public int this[string dayName]
    {
        get
        {
            dayName = dayName.ToLower();
            switch (dayName)
            {
                case "monday":
                    return 1;
                case "tuesday":
                    return 2;
                case "wednesday":
                    return 3;
                case "thursday":
                    return 4;
                case "friday":
                    return 5;
                case "saturday":
                    return 6;
                case "sunday":
                    return 7;
                default:
                    return -1;
            }
        }
    }
}

MyWeek myWeek = new MyWeek();
for (int i = 1; i <= myWeek.Length; i++)
{
    Console.WriteLine(myWeek[i]);
}
string dayName;
for (int i = 1; i <= myWeek.Length; i++)
{
    dayName = myWeek[i];
    Console.WriteLine(myWeek[dayName].ToString()); 
}