public static class DateExprieHelper
{
  /// <summary>
  /// 根据签约时间和签约时长来判断是否到期
  /// </summary>
  /// <param name="joinDate">签约时间</param>
  /// <param name="duration">签约时长</param>
  /// <returns></returns>
  public static bool IsExpriredByDay(DateTime joinDate, double duration)
  {
    return DateTime.Now - joinDate > TimeSpan.FromDays(duration); 
  }
}

class Program
{
  static void Main(string[] args)
  {
    var result = DateExprieHelper.IsExpriredByDay(new DateTime(2014, 1, 1), 365);
    if (result)
    {
      Console.WriteLine("已经到期了~~");
    }
    else
    {
      Console.WriteLine("还没到期~~");
    }
    Console.ReadKey();
  }
}