C#-日期計算之今天的n天前

[轉貼]http://www.wretch.cc/blog/sean9148/29664215

private void Form1_Load(object sender, EventArgs e)

{

int day = 20;//天數

this.Text = Convert.ToDateTime(DateTime.Today.AddDays(- (int)DateTime.Today.DayOfWeek - day) +

(DateTime.Today.Date - DateTime.Today.AddDays(- (int)DateTime.Today.DayOfWeek - day)) -

(DateTime.Today.AddDays(-(int)DateTime.Today.DayOfWeek) - DateTime.Today.AddDays(-(int)DateTime.Today.DayOfWeek - day))).ToString("yyyyMMdd");

}