The built-in DateTime in C # can basically implement these functions.

1. // Some optional date ranges (for example) are preset for users when making reports or queries)
2. // Such as annual sales, quarterly profit, and new customers this month
3. // The built-in datetime in C # can basically implement these functions. The clever use of datetime will make it much easier for you to handle these tasks.
5. // Today
6. Datetime. Now. Date. tow.datestring ();
7. // Yesterday, that is, one minus today's date
8. Datetime. Now. adddays (-1). tow.datestring ();
9. // Tomorrow, similarly, add one
10. Datetime. Now. adddays (1). tow.datestring ();
12. // This Week (to know the first day of this week, you must first know the day of the week, so that the first day of this week is the day of the day a few days ago, note that every week starts from Sunday to Saturday.
13. Datetime. Now. adddays (convert. todouble (0-convert. toint16 (datetime. Now. dayofweek). toshortdatestring ();
14. Datetime. Now. adddays (convert. todouble (6-convert. toint16 (datetime. Now. dayofweek). toshortdatestring ();
15. // If you still don't understand it, you should understand how to display the day of the week in Chinese.
16. // Because DayOfWeek returns the day of the week of the number, we need to convert it into Chinese characters to facilitate reading. Some people may use the switch to compare them one by one. In fact, this is not so troublesome.
17. String [] Day = new string [] {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday "};
18. String DayName = Day [Convert. ToInt16 (DateTime. Now. DayOfWeek)];
19. // Last week. Similarly, a week is 7 days. Last week is the week minus 7 days. The same is true for next week.
20. DateTime. Now. AddDays (Convert. ToDouble (0-Convert. ToInt16 (DateTime. Now. DayOfWeek)-7). ToShortDateString ();
21. DateTime. Now. AddDays (Convert. ToDouble (6-Convert. ToInt16 (DateTime. Now. DayOfWeek)-7). ToShortDateString ();
22. // Next week
23. DateTime. Now. AddDays (Convert. ToDouble (0-Convert. ToInt16 (DateTime. Now. DayOfWeek) + 7). ToShortDateString ();
24. DateTime. Now. AddDays (Convert. ToDouble (6-Convert. ToInt16 (DateTime. Now. DayOfWeek) + 7). ToShortDateString ();
25. // This month, many people will say that the first day of this month must be the first day of the month, and the last day is the second day of the month. Of course this is correct
26. // Easy to format with the ToString character in C #
27. DateTime. Now. ToString ("yyyy-MM-01 ");
28. DateTime. Parse (DateTime. Now. ToString ("yyyy-MM-01"). AddMonths (1). AddDays (-1). to1_datestring ();
30. // Last month, minus a month
31. DateTime. Parse (DateTime. Now. ToString ("yyyy-MM-01"). AddMonths (-1). to1_datestring ();
32. DateTime. Parse (DateTime. Now. ToString ("yyyy-MM-01"). AddDays (-1). to1_datestring ();
33. // Add a month to the next month
34. DateTime. Parse (DateTime. Now. ToString ("yyyy-MM-01"). AddMonths (1). to1_datestring ();
35. DateTime. Parse (DateTime. Now. ToString ("yyyy-MM-01"). AddMonths (2). AddDays (-1). to1_datestring ();
36. // 7 days later
37. DateTime. Now. Date. tow.datestring ();
38. DateTime. Now. AddDays (7). tow.datestring ();
39. // Seven days ago
40. DateTime. Now. AddDays (-7). tow.datestring ();
41. DateTime. Now. Date. tow.datestring ();
43. // During the current year, it is easy for us to format with ToString characters to calculate the first and last days of the year.
44. DateTime. Parse (DateTime. Now. ToString ("yyyy-01-01"). to1_datestring ();
45. DateTime. Parse (DateTime. Now. ToString ("yyyy-01-01"). AddYears (1). AddDays (-1). to1_datestring ();
46. // For the previous year, do not explain it again
47. DateTime. Parse (DateTime. Now. ToString ("yyyy-01-01"). AddYears (-1). to1_datestring ();
48. DateTime. Parse (DateTime. Now. ToString ("yyyy-01-01"). AddDays (-1). to1_datestring ();
49. // Next year
50. DateTime. Parse (DateTime. Now. ToString ("yyyy-01-01"). AddYears (1). to1_datestring ();
51. DateTime. Parse (DateTime. Now. ToString ("yyyy-01-01"). AddYears (2). AddDays (-1). to1_datestring ();
53. // This quarter, many people will find it difficult and need to write a long process to judge. In fact, we don't need to. We all know that a year, four quarters, one quarter, three months.
54. // First, we will push the date to the first month of the quarter, and then the first day of the month will be the first day of the quarter.
55. DateTime. Now. AddMonths (0-(DateTime. Now. Month-1) % 3). ToString ("yyyy-MM-01 ");
56. // Similarly, the last day of this quarter is the first day of the next quarter minus one
57. Datetime. parse (datetime. now. addmonths (3-(datetime. now. month-1) % 3 )). tostring ("yyyy-MM-01 ")). adddays (-1 ). toshortdatestring ();
58. // Next quarter, I believe you all know .... Close
59. Datetime. Now. addmonths (3-(datetime. Now. Month-1) % 3). tostring ("yyyy-MM-01 ");
60. Datetime. parse (datetime. now. addmonths (6-(datetime. now. month-1) % 3 )). tostring ("yyyy-MM-01 ")). adddays (-1 ). toshortdatestring ();
61. // Last quarter
62. Datetime. Now. addmonths (-3-(datetime. Now. Month-1) % 3). tostring ("yyyy-MM-01 ");
63. Datetime. parse (datetime. now. addmonths (0-(datetime. now. month-1) % 3 )). tostring ("yyyy-MM-01 ")). adddays (-1 ). toshortdatestring ();