using System;

using System.Globalization;

public class Program {

    public static void Main() {

        string[] dateStrings = { "20161205", "12052016", "111312", "00012333", "06152014", "NotADate" };

        Console.WriteLine("Hello World. What will we hallucinate about today?");

        bool ismonth = true;

​

        foreach (string dateString in dateStrings) {

            //ismonth = !ismonth;

            Console.WriteLine(getYear(dateString, ismonth));

        }

    }

    private static string getYear(string dateStr, bool hasMonth) {

            string strYear = String.Empty;

​

            DateTime dateVal;

​

            if (DateTime.TryParseExact(dateStr, "yyyyMMdd", CultureInfo.InvariantCulture, DateTimeStyles.None, out dateVal)) {

                if (isValidYear(dateVal.Year)) strYear = String.Format("{0:d}{1}", dateVal.Year, hasMonth ? dateVal.Month.ToString("00") : "");

            } else if (DateTime.TryParseExact(dateStr, "MMddyyyy", CultureInfo.InvariantCulture, DateTimeStyles.None, out dateVal)) {

                if (isValidYear(dateVal.Year)) strYear = String.Format("{0:d}{1}", dateVal.Year, hasMonth ? dateVal.Month.ToString("00") : "");

            } else if (DateTime.TryParseExact(dateStr, "MMddyy", CultureInfo.InvariantCulture, DateTimeStyles.None, out dateVal)) {

                if (isValidYear(dateVal.Year)) strYear = String.Format("{0:d}{1}", dateVal.Year, hasMonth ? dateVal.Month.ToString("00") : "");

            } else if (DateTime.TryParseExact(dateStr, "yyMMdd", CultureInfo.InvariantCulture, DateTimeStyles.None, out dateVal)) {

                if (isValidYear(dateVal.Year)) strYear = String.Format("{0:d}{1}", dateVal.Year, hasMonth ? dateVal.Month.ToString("00") : "");

            } else {

                Console.WriteLine(String.Format("Unable to Convert '{0}' to a valid date.", dateStr));

                strYear = String.Empty;

            }

​

        return String.Format("{2} = {0}{1}",strYear,"",dateStr);    

    }

    private static bool isValidYear(int year) { return (year > 2007 && year < 2023); }

}