DateTime and Number Format in C#

int intNum = 13; 

String.Format("{0:d4}", intNum);          // "0013"

intNum.ToString("D4");                    // "0013"

Decimal

// fixed two decimal part

String.Format("{0:0.00}", 123.4567);      // "123.46"
String.Format("{0:0.00}", 123.4);         // "123.40"

String.Format("{0:0.00}", 123.0);         // "123.00"
// maximum two decimal part
String.Format("{0:0.##}", 123.4567);      // "123.46"
String.Format("{0:0.##}", 123.4);         // "123.4"

String.Format("{0:0.##}", 123.0);         // "123"
// at least two digits at integer part
String.Format("{0:00.0}", 123.4567);      // "123.5"
String.Format("{0:00.0}", 1.4567);        // "01.5"

String.Format("{0:00.0}", -1.4456);       // "-03.4"
// Align numbers with spaces
// To align numbers to the left use negative number of spaces
String.Format("{0,10:0.0}", 123.4567);    // "     123.5"
String.Format("{0,-10:0.0}", 123.4567);   // "123.5     "
String.Format("{0,10:0.0}", -123.4567);   // "    -123.5"

String.Format("{0,-10:0.0}", -123.4567);  // "-123.5    "

Currency
123.456 ("C3", en-US) -> ($123.456)
-123.456 ("C3", fr-FR) -> -123,456 €
-123.456 ("C3", ja-JP) -> -¥123.456

Decimal
1234 ("D") -> 1234
-1234 ("D6") -> -001234

Fixed-point
1234 ("F1", en-US) -> 1234.0
1234 ("F1", en-US) -> 1234.0

General
-123.456 ("G", en-US) -> -123.456
-1.234567890e-25 ("G", sv-SE) -> -1,23456789E-25

Number
1234.567 ("N", en-US) -> 1,234.57
1234 ("N", en-US) -> 1,234.0

Percent
1 ("P", en-US) -> 100.00 %
-0.39678 ("P1", en-US) -> -39.7 %

Round-trip
123456789.12345678 ("R") -> 123456789.12345678
-1234567890.12345678 ("R") -> -1234567890.1234567

Hexadecimal
255 ("X") -> FF
-1 ("x") -> ff
255 ("x4") -> 00ff
-1 ("X4") -> 00FF

DateTime.ToString() Patterns

ddd, dd MMM yyyy HH':'mm':'ss 'GMT'      Tue, 22 Aug 2006 06:30:07 GM

dddd, dd MMMM yyyy HH:mm:ss              Tuesday, 22 August 2006 06:30:07

yyyy'-'MM'-'dd'T'HH':'mm':'ss.fffffffK   2006-08-22T06:30:07.7199222-04:00 

// create date time 2008-03-09 16:05:07.123
DateTime dt = new DateTime(2008, 3, 9, 16, 5, 7, 123);

String.Format("{0:y yy yyy yyyy}", dt);  // "8 08 008 2008"   year
String.Format("{0:M MM MMM MMMM}", dt);  // "3 03 Mar March"  month
String.Format("{0:d dd ddd dddd}", dt);  // "9 09 Sun Sunday" day
String.Format("{0:h hh H HH}",     dt);  // "4 04 16 16"      hour 12/24
String.Format("{0:m mm}",          dt);  // "5 05"            minute
String.Format("{0:s ss}",          dt);  // "7 07"            second
String.Format("{0:f ff fff ffff}", dt);  // "1 12 123 1230"   sec.fraction
String.Format("{0:F FF FFF FFFF}", dt);  // "1 12 123 123"    without zeroes
String.Format("{0:t tt}",          dt);  // "P PM"            A.M. or P.M.
String.Format("{0:z zz zzz}",      dt);  // "-6 -06 -06:00"   time zone

String.Format("{0:d/M/yyyy HH:mm:ss}", dt); // "9/3/2008 16:05:07" - english (en-US)
String.Format("{0:d/M/yyyy HH:mm:ss}", dt); // "9.3.2008 16:05:07" - german (de-DE)

// month/day numbers without/with leading zeroes
String.Format("{0:M/d/yyyy}", dt);            // "3/9/2008"
String.Format("{0:MM/dd/yyyy}", dt);          // "03/09/2008"

// day/month names
String.Format("{0:ddd, MMM d, yyyy}", dt);    // "Sun, Mar 9, 2008"
String.Format("{0:dddd, MMMM d, yyyy}", dt);  // "Sunday, March 9, 2008"

// two/four digit year
String.Format("{0:MM/dd/yy}", dt);            // "03/09/08"
String.Format("{0:MM/dd/yyyy}", dt);          // "03/09/2008" 

String.Format("{0:t}", dt);  // "4:05 PM"                         ShortTime
String.Format("{0:d}", dt);  // "3/9/2008"                        ShortDate
String.Format("{0:T}", dt);  // "4:05:07 PM"                      LongTime
String.Format("{0:D}", dt);  // "Sunday, March 09, 2008"          LongDate
String.Format("{0:f}", dt);  // "Sunday, March 09, 2008 4:05 PM"  LongDate+ShortTime
String.Format("{0:F}", dt);  // "Sunday, March 09, 2008 4:05:07 PM" FullDateTime
String.Format("{0:g}", dt);  // "3/9/2008 4:05 PM"                ShortDate+ShortTime
String.Format("{0:G}", dt);  // "3/9/2008 4:05:07 PM"             ShortDate+LongTime
String.Format("{0:m}", dt);  // "March 09"                        MonthDay
String.Format("{0:y}", dt);  // "March, 2008"                     YearMonth
String.Format("{0:r}", dt);  // "Sun, 09 Mar 2008 16:05:07 GMT"   RFC1123
String.Format("{0:s}", dt);  // "2008-03-09T16:05:07"             SortableDateTime
String.Format("{0:u}", dt);  // "2008-03-09 16:05:07Z"            UniversalSortableDateTime 

d	Represents the day of the month as a number from 1 through 31. A single-digit day is formatted without a leading zero
dd	Represents the day of the month as a number from 01 through 31. A single-digit day is formatted with a leading zero
ddd	Represents the abbreviated name of the day of the week (Mon, Tues, Wed etc)
dddd	Represents the full name of the day of the week (Monday, Tuesday etc)
h	12-hour clock hour (e.g. 7)
hh	12-hour clock, with a leading 0 (e.g. 07)
H	24-hour clock hour (e.g. 19)
HH	24-hour clock hour, with a leading 0 (e.g. 19)
m	Minutes
mm	Minutes with a leading zero
M	Month number
MM	Month number with leading zero
MMM	Abbreviated Month Name (e.g. Dec)
MMMM	Full month name (e.g. December)
s	Seconds
ss	Seconds with leading zero
t	Abbreviated AM / PM (e.g. A or P)
tt	AM / PM (e.g. AM or PM
y	Year, no leading zero (e.g. 2001 would be 1)
yy	Year, leadin zero (e.g. 2001 would be 01)
yyy	Year, (e.g. 2001 would be 2001)
yyyy	Year, (e.g. 2001 would be 2001)
K	Represents the time zone information of a date and time value (e.g. +05:00)
z	With DateTime values, represents the signed offset of the local operating system's time zone from Coordinated Universal Time (UTC), measured in hours. (e.g. +6)
zz	As z but with leadin zero (e.g. +06)
zzz	With DateTime values, represents the signed offset of the local operating system's time zone from UTC, measured in hours and minutes. (e.g. +06:00)
f	Represents the most significant digit of the seconds fraction; that is, it represents the tenths of a second in a date and time value.
ff	Represents the two most significant digits of the seconds fraction; that is, it represents the hundredths of a second in a date and time value.
fff	Represents the three most significant digits of the seconds fraction; that is, it represents the milliseconds in a date and time value.
ffff	Represents the four most significant digits of the seconds fraction; that is, it represents the ten thousandths of a second in a date and time value. While it is possible to display the ten thousandths of a second component of a time value, that value may not be meaningful. The precision of date and time values depends on the resolution of the system clock. On Windows NT 3.5 and later, and Windows Vista operating systems, the clock's resolution is approximately 10-15 milliseconds.
fffff	Represents the five most significant digits of the seconds fraction; that is, it represents the hundred thousandths of a second in a date and time value. While it is possible to display the hundred thousandths of a second component of a time value, that value may not be meaningful. The precision of date and time values depends on the resolution of the system clock. On Windows NT 3.5 and later, and Windows Vista operating systems, the clock's resolution is approximately 10-15 milliseconds.
ffffff	Represents the six most significant digits of the seconds fraction; that is, it represents the millionths of a second in a date and time value. While it is possible to display the millionths of a second component of a time value, that value may not be meaningful. The precision of date and time values depends on the resolution of the system clock. On Windows NT 3.5 and later, and Windows Vista operating systems, the clock's resolution is approximately 10-15 milliseconds.
fffffff	Represents the seven most significant digits of the seconds fraction; that is, it represents the ten millionths of a second in a date and time value. While it is possible to display the ten millionths of a second component of a time value, that value may not be meaningful. The precision of date and time values depends on the resolution of the system clock. On Windows NT 3.5 and later, and Windows Vista operating systems, the clock's resolution is approximately 10-15 milliseconds.
F	Represents the most significant digit of the seconds fraction; that is, it represents the tenths of a second in a date and time value. Nothing is displayed if the digit is zero.
:	Represents the time separator defined in the current DateTimeFormatInfo..::.TimeSeparator property. This separator is used to differentiate hours, minutes, and seconds.
/	Represents the date separator defined in the current DateTimeFormatInfo..::.DateSeparator property. This separator is used to differentiate years, months, and days.
"	Represents a quoted string (quotation mark). Displays the literal value of any string between two quotation marks ("). Your application should precede each quotation mark with an escape character (\).
'	Represents a quoted string (apostrophe). Displays the literal value of any string between two apostrophe (') characters.
%c	Represents the result associated with a c custom format specifier, when the custom date and time format string consists solely of that custom format specifier. That is, to use the d, f, F, h, m, s, t, y, z, H, or M custom format specifier by itself, the application should specify %d, %f, %F, %h, %m, %s, %t, %y, %z, %H, or %M. For more information about using a single format specifier, see Using Single Custom Format Specifiers.

Related Link

http://www.csharp-examples.net/string-format-double/