using System;               

​

public class Program

{

    public static void Main()

    {

        var flagVal = 7;

        DateTime startVal = DateTime.Today;

        for (int i = 0; i < 100; ++i) {

            var newDay = startVal.AddDays(i);

            var flag = newDay.Subtract(startVal).Days % flagVal == 0;

            Console.WriteLine((flag ? " Yep  : " : " Nope : ") + newDay.ToString("dddd"));

        }

    }

}