using System;

public class Program

{

    public static void Main()

    {

        // less work, but not reliable

        var lazy = (WeekDays)(int)TrueDaysOfWeek.Monday;

        Console.WriteLine($"Lazy Casting: {lazy}");

        var safe = Translate(WeekDays.Monday);

        Console.WriteLine($"Explicit Conversion: {safe}");

    }

    public static TrueDaysOfWeek Translate(WeekDays day) => day switch

    {

      WeekDays.Sunday => TrueDaysOfWeek.Sunday,

      WeekDays.Monday => TrueDaysOfWeek.Monday,

      WeekDays.Tuesday => TrueDaysOfWeek.Tuesday,

      WeekDays.Wednesday => TrueDaysOfWeek.Wednesday,

      WeekDays.Thursday => TrueDaysOfWeek.Thursday,

      WeekDays.Friday => TrueDaysOfWeek.Friday,

      WeekDays.Saturday => TrueDaysOfWeek.Saturday,

      // Throwing an exception (perhaps not the base excption class) will let the developer know when they've added something and not accounted for it.

      _ => throw new Exception("UnhandledType")

    };

}

​

public enum WeekDays

{

  Monday = 0,

  Tuesday = 1,

  Wednesday = 2,

  Thursday = 3,

  Friday = 4,

  Saturday = 5,

  Sunday = 6

}

​

public enum TrueDaysOfWeek

{

  Sunday = 1,

  Monday = 2,

  Tuesday = 3,

  Wednesday = 4,

  Thursday = 5,

  Friday = 6,

  Saturday = 7,

}