using System;

using System.Collections.Generic;

using System.Linq;

using static System.Console;

​

//C# 7 is coming soon in VS 2017

//Try out some of the new features without having to install VS 2017 RC

​

//Source 1: http://www.c-sharpcorner.com/article/top-10-new-features-of-c-sharp-7-with-visual-studio-2017/

//Source 2: https://docs.microsoft.com/en-us/dotnet/articles/csharp/csharp-7

​

public class Program

{

    public interface IPeriodo

    {

        void Fechas(String FechaI, String FechaF);

    }

    public  class frmAsistencia : IPeriodo

    {

        private String incioF;

        private String finF;

​

        void IPeriodo.Fechas(string FechaI, string FechaF)

        {

            this.incioF = FechaI;

            this.finF = FechaF;

            Console.WriteLine("Desde hijo, fecha es: " + FechaI + " & " + FechaF);

        }

    }

    public class Padre

    {

        IPeriodo date {get; set;}

        public void Anterior()

        {

            DateTime[] Per = new DateTime[2] { DateTime.Now, DateTime.Now};

            if(Per[0] > Convert.ToDateTime("2020/01/30"))

            {

                date = new frmAsistencia();

                Per[0] = Per[0].AddDays(-7);

                Per[1] = Per[1].AddDays(-7);

                date.Fechas(Per[0].ToShortDateString(), Per[1].ToShortDateString());//error

            }

        }

    }

    public static void Main()

    {

        Padre padre = new Padre();

        padre.Anterior();

    }

}