计算某月的第一天和最后一天

int Month = 9;
//第一天
DateTime TheFirstDay = Convert.ToDateTime(DateTime.Now.Year + "/" + Month + "/1 00:00:00");
//最后一天
DateTime TheLastDay = TheFirstDay.AddMonths(1).AddDays(-TheFirstDay.Day).AddHours(23).AddMinutes(59).AddSeconds(58);

string first = "第一天：" + TheFirstDay;
string end = "最后一天：" + TheLastDay;

Console.WriteLine(first);
Console.WriteLine(end);

计算某月的第一天和最后一天

原文：http://www.cnblogs.com/huyueping/p/4110504.html