using System;

​

public class Program

{

    static DateTime mExpiryDate = DateTime.Parse("09/29/2015");

    public static void Main()

    {

        var result = string.Empty;

        var noticeDate = DateTime.Parse("09/05/2015");

        mExpiration_Compute(ref result, noticeDate);

        Console.WriteLine(result);

    }

​

    public static void mExpiration_Compute(ref string result, DateTime noticeDate)

    {

        DateTime a = noticeDate;

        DateTime b = mExpiryDate;

        TimeSpan ts = b.Subtract(a);

        result = string.Format("You have {0} days to expiry date.", ts.Days);

    }

}