asp.Net 中获取一周第一天,一月第一天等实现代码

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);
int daydiff = (-1) * weeknow + 1;
int dayadd = 7 - weeknow; 
//本周第一天
lblbegin.text = system.datetime.now.adddays(daydiff).tostring("yyyy-mm-dd");
//本周最后一天
lblend.text = system.datetime.now.adddays(dayadd).tostring("yyyy-mm-dd");