[C#] DateTime convert String

Using DateTime.ToString(string format) to covert it to string. The following is:
y: represents the year
M: represents the month
d: represents the day
h, H: represents the hour: h with a 12-hour; H with a 24-hour clock.
m: represents the minute
s: represents the second

Format	Output	Samples
year
y	13-04 (if now is 2013-04-28)  6-04 (if now is 2006-04-28)	string str = DateTime.Now.ToString("y-MM");
yy	13-05	string yy = DateTime.Now.ToString("yy-MM");
yyyy	2013	string yy = DateTime.Now.ToString("yyyy");
month
M	2013-5	string mon = DateTime.Parse("2013-05-09").ToString("yyyy-M");
MM	05	string mon = DateTime.Parse("2013-05-09").ToString("MM");
MMM	English OS: Jul Chinese OS: 七月	string mon = DateTime.Parse("2013-07-01").ToString("MMM");
MMMM	English OS: July Chinese OS: 七月	string mon = DateTime.Parse("2013-07-01").ToString("MMMM");
date & week
d	5/9/2013	string dd= DateTime.Parse("2013-05-09").ToString("d");
dd	09	string dd= DateTime.Parse("2013-05-09").ToString("dd");
ddd	English OS：Thu Chinese OS: 星期四	string dd = DateTime.Parse("2013-05-09").ToString("ddd");
dddd	English OS：Thursday Chinese OS: 星期四	string dd = DateTime.Parse("2006-07-01").ToString("dddd")
hour
hh	01	string hh = DateTime.Now.ToString("hh");
H	2013-13	string hh = DateTime.Now.ToString("yyyy-H");
HH	2013-13 2006-18	string hh = DateTime.Now.ToString("yyyy-HH"); string hh = DateTime.Parse("2006-7-4 18:00:00").ToString("yyyy-HH");
minute
m	2013-05-07-15	string mm =  DateTime.Now.ToString("yyyy-MM-dd-m");
mm	2013-05-07-15	string mm =  DateTime.Now.ToString("yyyy-MM-dd-mm");
second
s	2013-05-07-27	string ss =  DateTime.Now.ToString("yyyy-MM-dd-s");
ss	2013-05-07-27	string ss =  DateTime.Now.ToString("yyyy-MM-dd-ss");