CalculateDays

using System;
using System.Text;
using System.Text.RegularExpressions;

class CalculateDaysAlg
{
    static void Main()
    {
        Console.Write("Please enter the first date in the format dd.mm.yyyy:");//27.02.2006
        string first = Console.ReadLine();
        Console.Write("Please enter the second date in the format dd.mm.yyyy:");//03.03.2006
        string second = Console.ReadLine();
        Console.WriteLine("{0} day/s", CalculateDays(first, second));
    }
    static int CalculateDays(string first, string second)
    {
        DateTime firstDate = DateTime.Now;
        if (ValidDate(first))
        {
            firstDate = DateTime.Parse(first);
        }
        else
        {
            Console.WriteLine("Please enter the data in the specified format!");

        }

        DateTime secondDate = DateTime.Now;
        if (ValidDate(second))
        {
            secondDate = DateTime.Parse(second);
        }
        else
        {
            Console.WriteLine("Please enter the data in the specified format!");
        }

        int days = (int)((secondDate - firstDate).TotalDays);
        return days;
    }
    static bool ValidDate(string data)
    {
        if (Regex.IsMatch(data, "[0-9]{1,2}[.][0-9]{2,}[.][0-9]{4,}"))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}