.net 获取本周、本月第一天和最后一天

DateTime dt = DateTime.Now;
//本月第一天时间
DateTime dt_First = dt.AddDays(-(dt.Day) + 1);
Label1.Text = dt_First.ToString("yyyy-MM-dd");
//将本月月数+1
DateTime dt2 = dt.AddMonths(1);
//本月最后一天时间
DateTime dt_Last = dt2.AddDays(-(dt.Day));
Label2.Text = dt_Last.ToString("yyyy-MM-dd");

int weeknow = Convert.ToInt32(System.DateTime.Now.DayOfWeek);
//星期日 获取weeknow为0
weeknow=weeknow==0?7:weeknow;
int daydiff = (-1) * weeknow + 1;
int dayadd = 7 - weeknow;

//本周第一天
string datebegin = System.DateTime.Now.AddDays(daydiff).ToString("yyyy-MM-dd");

//本周最后一天
string dateend = System.DateTime.Now.AddDays(dayadd).ToString("yyyy-MM-dd");
Label3.Text = datebegin;
Label4.Text = dateend;