string dateTime1 = DateTime.Now.ToString("D");
Console.WriteLine(dateTime1);//2022年2月24日
string dateTime2 = DateTime.Now.ToString("d");
Console.WriteLine(dateTime2);//2022/2/24
string dateTime3 = DateTime.Now.ToString("F");
Console.WriteLine(dateTime3);//2022年2月24日 14:50:07
string dateTime4 = DateTime.Now.ToString("f");
Console.WriteLine(dateTime4);//2022年2月24日 14:50
string dateTime5 = DateTime.Now.ToString("G");
Console.WriteLine(dateTime5);//2022/2/24 14:50:07
string dateTime6 = DateTime.Now.ToString("g");
Console.WriteLine(dateTime6);//2022/2/24 14:50
string dateTime7 = DateTime.Now.ToString("T");
Console.WriteLine(dateTime7);//14:50:07
string dateTime8 = DateTime.Now.ToString("t");
Console.WriteLine(dateTime8);//14:50
string dateTime9 = DateTime.Now.ToString("U");
Console.WriteLine(dateTime9);//2022年2月24日 6:50:07
string dateTime10 = DateTime.Now.ToString("u");
Console.WriteLine(dateTime10);//2022-02-24 14:50:07Z
string dateTime11 = DateTime.Now.ToString("m");
Console.WriteLine(dateTime11);//2月24日
string dateTime12 = DateTime.Now.ToString("M");
Console.WriteLine(dateTime12);//2月24日
string dateTime13 = DateTime.Now.ToString("r");
Console.WriteLine(dateTime13);//Thu, 24 Feb 2022 14:50:07 GMT
string dateTime14 = DateTime.Now.ToString("R");
Console.WriteLine(dateTime14);//Thu, 24 Feb 2022 14:50:07 GMT
string dateTime15 = DateTime.Now.ToString("y");
Console.WriteLine(dateTime15);//2022年2月
string dateTime16 = DateTime.Now.ToString("Y");
Console.WriteLine(dateTime16);//2022年2月
string dateTime17 = DateTime.Now.ToString("o");
Console.WriteLine(dateTime17);//2022-02-24T14:50:07.6460955+08:00
string dateTime18 = DateTime.Now.ToString("O");
Console.WriteLine(dateTime18);//2022-02-24T14:50:07.6460955+08:00
string dateTime19 = DateTime.Now.ToString("s");
Console.WriteLine(dateTime19);//2022-02-24T14:50:07
string dateTime20 = DateTime.Now.ToString("yyyy-MM-dd HH：mm：ss：ffff");
Console.WriteLine(dateTime20);//022-02-24 14：50：07：6471
string dateTime21 = DateTime.Now.ToString("yyyy年MM月dd HH时mm分ss秒");
Console.WriteLine(dateTime21);//2022年02月24 14时50分07秒
string dateTime22 = DateTime.Now.ToString("dddd, MMMM dd yyyy");
Console.WriteLine(dateTime22);//星期四, 二月 24 2022
string dateTime23 = DateTime.Now.ToString("ddd, MMM d \"'\"yy");
Console.WriteLine(dateTime23);//周四, 2月 24 '22
string dateTime24 = DateTime.Now.ToString("dddd, MMMM dd");
Console.WriteLine(dateTime24);//星期四, 二月 24
string dateTime25 = DateTime.Now.ToString("M/yy");
Console.WriteLine(dateTime25);//2/22
string dateTime26 = DateTime.Now.ToString("dd-MM-yy");
Console.WriteLine(dateTime26);//24-02-22
string[] Day = new string[] { "星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六" };
// 昨天
string dateTime27 = DateTime.Now.AddDays(-1).ToShortDateString();
Console.WriteLine(dateTime27);//2022/2/23
// 明天
string dateTime28 = DateTime.Now.AddDays(1).ToShortDateString();
Console.WriteLine(dateTime28);//2022/2/25
//本周星期天
string dateTime29 = DateTime.Now.AddDays(Convert.ToDouble((0 - Convert.ToInt16(DateTime.Now.DayOfWeek)))).ToShortDateString();
Console.WriteLine(dateTime29);//2022/2/20
//本周星期六
string dateTime30 = DateTime.Now.AddDays(Convert.ToDouble((6 - Convert.ToInt16(DateTime.Now.DayOfWeek)))).ToShortDateString();
Console.WriteLine(dateTime30);//2022/2/26
//今天周几
string dateTime31 = Day[Convert.ToInt16(DateTime.Now.DayOfWeek)];
Console.WriteLine(dateTime31);//星期四
//上周日
string dateTime32 = DateTime.Now.AddDays(Convert.ToDouble((0 - Convert.ToInt16(DateTime.Now.DayOfWeek))) - 7).ToShortDateString();
Console.WriteLine(dateTime32);//2022/2/13
//上周六
string dateTime33 = DateTime.Now.AddDays(Convert.ToDouble((6 - Convert.ToInt16(DateTime.Now.DayOfWeek))) - 7).ToShortDateString();
Console.WriteLine(dateTime33);//2022/2/19
// 下周日
string dateTime34 = DateTime.Now.AddDays(Convert.ToDouble((0 - Convert.ToInt16(DateTime.Now.DayOfWeek))) + 7).ToShortDateString();
Console.WriteLine(dateTime34);//2022/2/27
// 下周六
string dateTime35 = DateTime.Now.AddDays(Convert.ToDouble((6 - Convert.ToInt16(DateTime.Now.DayOfWeek))) + 7).ToShortDateString();
Console.WriteLine(dateTime35);//2022/3/5
// 本月一号
string dateTime36 = DateTime.Now.ToString("yyyy-MM-01");
Console.WriteLine(dateTime36);//2022-02-01
// 本月最后一天
string dateTime37 = DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(1).AddDays(-1).ToShortDateString();
Console.WriteLine(dateTime37);//2022/2/28
// 上个月一号
string dateTime38 = DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(-1).ToShortDateString();
Console.WriteLine(dateTime38);//2022/1/1
//下个月一号
string dateTime39 = DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(1).ToShortDateString();
Console.WriteLine(dateTime39);//2022/3/1
Console.ReadKey();

@CSDN