Referenc type are pass by value or reference?

No, you are wrong, Reference types are passed by Value by default, surprised?
Explanation:
Pass-By-Value

Test(object R2)
{
R2=null;
}
//you call
object R1 = new object();
Test(R1);
WriteLine(R1==null) //result false.

Reference type R1 is created on address y100 and its value is some another address called x100; // as we know refrence type refer to an address
now in method
Reference type R2 is created on a memory address y200,
and it is copied value of R1 ie. x100;
so when you reset R2=null. only value of the r2 set to null. means now its not pointing to address x100. but R1 still pointing to address x100.
NOTE: if value at address x100 is changed, both R2 and R1 will show that, because both pointing to the same address.

Pass-By-Reference ->
Test(ref object R2)
{
R2=null;
}
object R1 = new Object();
Test(ref R1);
WriteLine(R1==null) //result true.

now we are passing variable by Reference. now here address of R1 is passed i.e y100. so R1 & R2 both are pointing to y100. so if you change R2's value, R1's will also changed

Any issue please comment.

csharp(c#) customizing Date time format using toString, for display gridview and database storage

Problem 1: how to display date time in 24 hour format
solution : DateTime.Now.ToString("dd/MM/yyyy HH-mm-ss");
Note:Captial HH is used for 24 hour format.
small for 12 hour format


Problem 2: how to display am/pm in date time or 12 hour format time.
Solution : DateTime.Now.ToString("hh-mm-ss tt");
Key: "tt" for AM or PM

Problem 3: how to display time zone in date time.
Solution : DateTime.Now.ToString("hh-mm-ss tt zzz");
Note: zzz is used to display time zone.

Problem 4: how to show full month name in date.
Solution: DateTime.Now.ToString("dd-MMMM-yy");

Problem 5: how to format full day name in date.
Solution : DateTime.Now.ToString("dddd-MMMM-yy");
note: MMMM

Problem 6: how to format full year name in date.
Solution: DateTime.Now.ToString ("dddd-MMMM-yyyy");
note: yyyy

Problem 7: how to reduce/subtract date or days
solution : DateTime.Now.AddDays(-10)

for converting date retrieved from database, firstly convert the column to dateTime and use above techniques.

for details of the above solution, you can read followings.....

In C# DateTime class is used to represent the date & time. But for the display purpose on the front end either on

1 data Grid View (GridView / DataGrid) (as by default time field is shown or you want to show in particular format)
2. labels,
3 storing in the database

in to a particular format
for all the above scenario we need to change the date & time format.
as some need only examples and others full details, i will firstly give examples.

GridView

In Grid view we have two ways to show colums

1. Bound Column
2. Template fields
in both we show date format differently.
Bound Field:

<:BoundField DataField="BirthDate" DataFormatString="{0:d}" HeaderText="BirthDate" SortExpression="BirthDate" >
                                  <HeaderStyle BackColor="Green" Font-Names="Verdana"  />
                              </asp:BoundField>>

here DataFormatString="{0:d}" is used to format the date.
"d:" is standard format already defined in c# library,( For details standard format read full article)
or

DataFormatString="{0:dd/MM/yyyy}"

here all specifier are case sensitive.

Template fields:
as we know template fields can be bind using Eval and Bind functions.
Difference: The Eval function is used to define one-way (read-only) binding. The Bind function is used for two-way (updatable) binding.

to format a date with any of the above method following syntax is used.
'<asp :Label ID="lblDate" runat="server"
Text=
'<%# Eval("CreationDate", "{0:dd-MM-yyyy}") %>'>
</asp>

<asp :Label ID="lblDate1" runat="server"
Text='<%# Bind("CreationDate", "{0:dd-MM-yyyy}") %>'>
'</asp>
-----------------------------------------------------------------------------------------------------------------------

How it works....
DateField..ToString() is used to convert a datetime object to specific format. Internally gridview call this method.

C-sharp comes with two type of format specifier.

1. Standard
2. Custom

1. Standard date Format Specifier.

format of these are already defined in the libary.

dt.ToString("y") will show "January, 2009"

Caution now if you want only "9" you will have to prefix a % to interpret it as custom specifier e.g dt.ToString("%d");

other specifiers are.

• d 1/1/2009
  
• D Thursday, January 01,2009
  
• t 8:59 PM
  
• T 8:59:59 PM
  
• f Thursday, January 01,2009 8:59 PM
  
• F Thursday, January 01,2009 8:59:59 PM
  
• g 1/1/2009 8:59 PM
  
• 1/1/2009 8:59:59 PM

Custom format specifiers
if standard specifier are not working for your requirement. use custom format specifier.

when you are using single custom format specifier you need to append either '%' or surround the specifier with spaces e.g ' d ' . else it will collide with the Standard date Format Specifier and you will get wrong/different format.
-----------------------------------------------------------------------
for Day %d dd ddd dddd 01 thu thurday
------------------------------------------------------------------------
for Year %y yy yyyy
Result 9 09 2009
------------------------------------------------------------------------
for Month %M MM MMM MMMM
Result: 1 01 Jan January
------------------------------------------------------------------------
for Hour %h hh H HH
result: 8 08 20 20
------------------------------------------------------------------------
for minute %m mm
Result: 59 59
------------------------------------------------------------------------
for Sec %s ss
result: 59 59
------------------------------------------------------------------------
AM PM : tt
Result: PM
--------------------------------------------------------------------------
Time zone: zzz
Result +05:30
--------------------------------------------------------------------------

for e.g changing form 12 hrs format to 24 hours format or some time you want to show full year name, full month name.

DataBase

Different databases have different format for storing the date. so it needs to be change.

e.g: like sqlserver, oracle, mysql and postgresql store the date in following format yyyy-mm-dd.

oracle- mm/dd/yyyy etc.

for these purposes C# has provided many format strings.

----------------------------------------------------------------------------------------------

Example: 1-jan-2009 08-59-59 PM

how to create a DateTime Object. This date object will be used for all the example below.

DateTime dt = new DateTime(2009,01,01,20,59,59);

//Parameters order wise

year

The year (1 through 9999).

month

The month (1 through 12).

day

The day (1 through the number of days in month).

hour

The hours (0 through 23).

minute

The minutes (0 through 59).

second

The seconds (0 through 59).

1. Now to format string date as 20-January-2009
   dt.ToString("dd-MMMM-yyyy");
   Caution: for Month capital M is used.
2. Now to get the short day name of date and short month name
   dt.ToString("ddd-MMM-yyyy"); //Thu-Jan-2009
3. To display data in AM PM format. //08-59-59 PM
   dt.ToString("hh-mm-ss tt"); . //08-59-59 PM
   Caution: small "m", small h and "tt" for AM or PM
   HH capital H is used to display time in 24 hour format.

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Culture also play role while formatting the dates.

by default CLR picks running thread's culture. you can also specify the differnt culture while formatting the string. My system has default culture en-US.