c# 根据当前时间获取,本周,本月,本季度,月初,月末,各个时间段

1. DateTime dt = DateTime.Now;  //当前时间  
2. DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") //24小时制 
3. DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss")  //12小时制    
4. DateTime startWeek = dt.AddDays(1 - Convert.ToInt32(dt.DayOfWeek.ToString("d")));  //本周周一  
5. DateTime endWeek = startWeek.AddDays(6);  //本周周日    
6. DateTime startMonth = dt.AddDays(1 - dt.Day);  //本月月初  
7. DateTime endMonth = startMonth.AddMonths(1).AddDays(-1);  //本月月末  //DateTime endMonth = startMonth.AddDays((dt.AddMonths(1) - dt).Days - 1);  //本月月末    
8. DateTime startQuarter = dt.AddMonths(0 - (dt.Month - 1) % 3).AddDays(1 - dt.Day);  //本季度初  
9. DateTime endQuarter = startQuarter.AddMonths(3).AddDays(-1);  //本季度末    
10. DateTime startYear = new DateTime(dt.Year, 1, 1);  //本年年初 
11. DateTime endYear = new DateTime(dt.Year, 12, 31);  //本年年末     至于昨天、明天、上周、上月、上季度、上年度等等，只要AddDays()、AddMonths()、AddYears()这几种方法组合一下就可以了。
13. //C#中datetime的使用                 
14. //如本年度销售额、本季度利润、本月新增客户                  
15. //C#里内置的DateTime基本上都可以实现这些功能，巧用DateTime会使你处理这些事来变轻松多了                                  
16. //今天                  
17. DateTime.Now.Date.ToShortDateString();                   
18. //昨天，就是今天的日期减一                  
19. DateTime.Now.AddDays(-1).ToShortDateString();                   
20. //明天，同理，加一                  
21. DateTime.Now.AddDays(1).ToShortDateString();                    
22. //本周(要知道本周的第一天就得先知道今天是星期几，从而得知本周的第一天就是几天前的那一天，要注意的是这里的每一周是从周日始至周六止                  
23. DateTime.Now.AddDays(Convert.ToDouble((0 -  Convert.ToInt16(DateTime.Now.DayOfWeek)))).ToShortDateString();                   
24. DateTime.Now.AddDays(Convert.ToDouble((6 -  Convert.ToInt16(DateTime.Now.DayOfWeek)))).ToShortDateString();                   
25. //如果你还不明白，再看一下中文显示星期几的方法就应该懂了                  
26. //由于DayOfWeek返回的是数字的星期几，我们要把它转换成汉字方 便我们阅读，有些人可能会用switch来一个一个地对照，其实不用那么麻烦的                               
27. 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" };                    
28. Day[Convert.ToInt16(DateTime.Now.DayOfWeek)];                  //上周，同理，一个周是7天，上周就是本周再减去7天，下周也是一样                 
29. DateTime.Now.AddDays(Convert.ToDouble((0 -  Convert.ToInt16(DateTime.Now.DayOfWeek))) - 7).ToShortDateString();                   
30. DateTime.Now.AddDays(Convert.ToDouble((6 -  Convert.ToInt16(DateTime.Now.DayOfWeek))) - 7).ToShortDateString(); //下周                  
31. DateTime.Now.AddDays(Convert.ToDouble((0 -  Convert.ToInt16(DateTime.Now.DayOfWeek))) + 7).ToShortDateString();                   
32. DateTime.Now.AddDays(Convert.ToDouble((6 -  Convert.ToInt16(DateTime.Now.DayOfWeek))) + 7).ToShortDateString();  //本月,很多人都会说本月的第一天嘛肯定是1号，最后一天就是下个月一号再减一天。当然这是对的                 
33. //一般的写法                 
34. DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString() + "1"; //第一天                 
35. DateTime.Parse(DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString() +  "1").AddMonths(1).AddDays(-1).ToShortDateString();//最后一天                 
36. //巧用C#里ToString的字符格式化更简便                  
37. DateTime.Now.ToString("yyyy-MM-01");                    
38. DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(1).AddDays(-1).ToShortDateString();                                   
39. DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(-1).ToShortDateString();                   //上个月，减去一个月份   
40. DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(1).ToShortDateString();                   //下个月，加去一个月份
41. DateTime.Now.AddDays(7).ToShortDateString();                 //7天前                  
42. DateTime.Now.AddDays(-7).ToShortDateString();//7天后       
43. //本年度，用ToString的字符格式化我们也很容易地算出本年度的第一天和最后一天                   
44. DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).ToShortDateString();                    
45. DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(1).AddDays(-1).ToShortDateString();                                   
46. DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(-1).ToShortDateString();                 //上年度，不用再解释了吧     
47. DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddDays(-1).ToShortDateString();                                
48. DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(1).ToShortDateString();                   //下年度     
49. DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(2).AddDays(-1).ToShortDateString();                  //本季度，很多人都会觉得这里难点，需要写个长长的过程来判断。其实不用的，我们都知道一年四个季度，一个季度三个月                  //首先我们先把日期推到本季度第一个月，然后这个月的第一天就是本季度的第一天了                  
50. DateTime.Now.AddMonths(0 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01");                  //同理，本季度的最后一天就是下季度的第一天减一                 
51. DateTime.Parse(DateTime.Now.AddMonths(3 - ((DateTime.Now.Month - 1) %  3)).ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString();    //下季度，相信你们都知道了。。。。收工                  
52. DateTime.Now.AddMonths(3 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01");                   
53. DateTime.Parse(DateTime.Now.AddMonths(6 - ((DateTime.Now.Month - 1) %  3)).ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString();                 //上季度                 
54. DateTime.Now.AddMonths(-3 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01");                    
55. DateTime.Parse(DateTime.Now.AddMonths(0 - ((DateTime.Now.Month - 1) %  3)).ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString(); 

转自：http://wenku.baidu.com/link?url=Kq2mVGamPH-nC8y8SwACBd9KqXq41FUkTigP6jod0vyptUSw2HiURuwHzalkAwCmUodxj2nK55nRdj2CSqC77DAcyhyybJ8wsMrIT3aUfR3