using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var dateList = new List<DateTime>();

        dateList.Add(new DateTime(2019,2,28));

        dateList.Add(new DateTime(2019,3,1));

        dateList.Add(new DateTime(2020,1,1));

        dateList.Add(new DateTime(2020,2,28));

        dateList.Add(new DateTime(2020,2,29));

        dateList.Add(new DateTime(2020,3,1));

        foreach(var date in dateList)

        {

            var m = date.Month;

            var d = date.Day;

            Console.WriteLine("受診日：" + date.ToString("yyyy/MM/dd"));

            var date_screen = date;

            if(m == 2 && d == 29)

            {

                Console.WriteLine("！！！うるう年！！！");

                date_screen = date.AddYears(1); // 1年後（うるう年の場合・・・だけどちゃんと2/28になっている）

            }

            else

            {

                date_screen = date.AddYears(1); // 1年後

            }

            Console.WriteLine("有効期限：" + date_screen.ToString("yyyy/MM/dd"));

            Console.WriteLine("期限切れ間近：" + date_screen.AddMonths(-2).ToString("yyyy/MM/dd") + " ～ " + date_screen.ToString("yyyy/MM/dd")); // 2ヶ月前 ～ 有効期限

            Console.WriteLine("期限切れ：" + date_screen.AddDays(1).ToString("yyyy/MM/dd"));

​

            Console.WriteLine();

        }

    }

}