using System;

public class Program

{

    public static void Main()

    {       

        DaysOfWeek selectedDaysOfWeek = DaysOfWeek.Monday | DaysOfWeek.Wednesday | DaysOfWeek.Friday;

        selectedDaysOfWeek |= DaysOfWeek.Saturday;

        Console.WriteLine(selectedDaysOfWeek);

        Console.WriteLine(selectedDaysOfWeek.IsDayOfWeekSelected(DayOfWeek.Monday));

        Console.WriteLine(selectedDaysOfWeek.IsDayOfWeekSelected(DayOfWeek.Tuesday));       

        Console.WriteLine(selectedDaysOfWeek.IsDaysOfWeekSelected(DaysOfWeek.Monday | DaysOfWeek.Wednesday));

        Console.WriteLine(selectedDaysOfWeek.IsDaysOfWeekSelected(DaysOfWeek.Monday | DaysOfWeek.Tuesday));

    }

}

[Flags]

public enum DaysOfWeek

{

    Monday = 1 << DayOfWeek.Monday,

    Tuesday = 1 << DayOfWeek.Tuesday,

    Wednesday = 1 << DayOfWeek.Wednesday,

    Thursday = 1 << DayOfWeek.Thursday,

    Friday = 1 << DayOfWeek.Friday,

    Saturday = 1 << DayOfWeek.Saturday,

    Sunday = 1 << DayOfWeek.Sunday

}

​

public static class DaysOfWeekExtensions

{

    public static bool IsDayOfWeekSelected(this DaysOfWeek selection, DayOfWeek which)

    {

        var d = (DaysOfWeek)(1 << (int)which);

        return (selection & d) == d;

    }

    public static bool IsDaysOfWeekSelected(this DaysOfWeek selection, DaysOfWeek which)

    {

        return (selection & which) == which;

    }

}