Finding if a string contains a date and time

Update 2: Found out using DateTime.TryParseExact is a much better way that using Regex Expressions

DateTime myDate;
if (DateTime.TryParseExact(inputString, "dd-MM-yyyy hh:mm:ss", 
    CultureInfo.InvariantCulture, DateTimeStyles.None, out myDate))
{
    //String has Date and Time
}
else
{
    //String has only Date Portion    
}

If the format of the date has been defined, you can use Regex to solve it.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace RegTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string testDate = "3214312402-17-2013143214214";
            Regex rgx = new Regex(@"\d{2}-\d{2}-\d{4}");
            Match mat = rgx.Match(testDate);
            Console.WriteLine(mat.ToString());
            Console.ReadLine();
        }
    }
}

   string s = " Subject: Current account balances for 21st December 2017 and 2nd January 2019 mnmnm ";//here is u r sample string

   s = s.ToLower();
   string newStrstr = Regex.Replace(s, " {2,}", " ");//remove more than whitespace
   string newst = Regex.Replace(newStrstr, @"([\s+][-/./_///://|/$/\s+]|[-/./_///://|/$/\s+][\s+])", "/");// remove unwanted whitespace eg 21 -dec- 2017 to 21-07-2017
   newStrstr = newst.Trim();
   Regex rx = new Regex(@"(st|nd|th|rd)");//21st-01-2017 to 21-01-2017
   string sp = rx.Replace(newStrstr, "");
   rx = new Regex(@"(([0-2][0-9]|[3][0-1]|[0-9])[-/./_///://|/$/\s+]([0][0-9]|[0-9]|[1][0-2]|jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec|january|february|march|april|may|june|july|augu|september|october|november|december)[-/./_///:/|/$/\s+][0-9]{2,4})");//a pattern for regex to check date format. For August we check Augu since we replaced the st earlier
   MatchCollection mc = rx.Matches(sp);//look for strings that satisfy the above pattern regex

   List<DateTime> dates=new List<DateTime>(); //Create a list to store the detected dates

   foreach(Match m in mc)
   {
        string s2=Regex.Replace(m.ToString(), "augu", "august");
        dates.Add(DateTime.Parse(s2);
   }