Answer Posted / murugesh

Only a copy of a variable is passed when an argument is
passed by value. If the procedure changes the value, the
change affects only the copy and not the variable itself.
Use the ByVal keyword to indicate an argument passed by
value.
For example:
Sub PostAccounts(ByVal intAcctNum as Integer)
.
. ' Place statements here.
.
End Sub
Passing Arguments By Reference
Passing arguments by reference gives the procedure access
to the actual variable contents in its memory address
location. As
a result, the variable's value can be permanently changed
by the procedure to which it is passed. Passing by
reference is the
default in Visual Basic.
If you specify a data type for an argument passed by
reference, you must pass a value of that type for the
argument. You can
work around this by passing an expression, rather than a
data type, for an argument. Visual Basic evaluates an
expression
and passes it as the required type if it can.
The simplest way to turn a variable into an expression is
to enclose it in parentheses. For example, to pass a
variable
declared as an integer to a procedure expecting a string as
an argument, you would do the following:
Sub CallingProcedure()
Dim intX As Integer
intX = 12 * 3
Foo(intX)
End Sub

Sub Foo(Bar As String)
MsgBox Bar 'The value of Bar is the string "36".
End Sub
Using Optional Arguments
You can specify arguments to a procedure as optional by
placing the Optional keyword in the argument list. If you
specify an
optional argument, all subsequent arguments in the argument
list must also be optional and declared with the Optional
keyword. The two pieces of sample code below assume there
is a form with a command button and list box.
For example, this code provides all optional arguments:
Dim strName As String
Dim strAddress As String

Sub ListText(Optional x As String, Optional y _
As String)
List1.AddItem x
List1.AddItem y
End Sub

Private Sub Command1_Click()
strName = "yourname"
strAddress = 12345 ' Both arguments are provided.
Call ListText(strName, strAddress)
End Sub
This code, however, does not provide all optional
arguments:
Dim strName As String
Dim varAddress As Variant

Sub ListText(x As String, Optional y As Variant)
List1.AddItem x
If Not IsMissing(y) Then
List1.AddItem y
End If
End Sub

Private Sub Command1_Click()
strName = "yourname" ' Second argument is not
' provided.
Call ListText(strName)
End Sub
In the case where an optional argument is not provided, the
argument is actually assigned as a variant with the value
of
Empty. The example above shows how to test for missing
optional arguments using the IsMissing function.
Providing a Default for an Optional Argument
It's also possible to specify a default value for an
optional argument. The following example returns a default
value if the
optional argument isn't passed to the function procedure:
Sub ListText(x As String, Optional y As _
Integer = 12345)
List1.AddItem x
List1.AddItem y
End Sub

Private Sub Command1_Click()
strName = "yourname" ' Second argument is not
' provided.
Call ListText(strName) ' Adds "yourname" and
' "12345".
End Sub
Using an Indefinite Number of Arguments
Generally, the number of arguments in the procedure call
must be the same as in the procedure specification. Using
the
ParamArray keyword allows you to specify that a procedure
will accept an arbitrary number of arguments. This allows
you to
write functions like Sum:
Dim x As Integer
Dim y As Integer
Dim intSum As Integer

Sub Sum(ParamArray intNums())
For Each x In intNums
y = y + x
Next x
intSum = y
End Sub

Private Sub Command1_Click()
Sum 1, 3, 5, 7, 8
List1.AddItem intSum
End Sub
Creating Simpler Statements with Named Arguments
For many built-in functions, statements, and methods,
Visual Basic provides the option of using named arguments
as a
shortcut for typing argument values. With named arguments,
you can provide any or all of the arguments, in any order,
by
assigning a value to the named argument. You do this by
typing the argument name plus a colon followed by an equal
sign
and the value ( MyArgument:= "SomeValue") and placing that
assignment in any sequence delimited by commas. Notice that
the arguments in the following example are in the reverse
order of the expected arguments:
Function ListText(strName As String, Optional strAddress As
String)
List1.AddItem strName
List2.AddItem strAddress
End Sub

Private Sub Command1_Click()
ListText strAddress:=”12345”, strName:="Your Name"
End Sub
This is especially useful if your procedures have several
optional arguments that you do not always need to specify.
Determining Support for Named Arguments
To determine which functions, statements, and methods
support named arguments, use the AutoQuickInfo feature in
the
Code window, check the Object Browser, or see the Language
Reference. Consider the following when working with named
arguments:
· Named arguments are not supported by methods on objects
in the Visual Basic (VB) object library. They are supported
by all language keywords in the Visual Basic for
applications (VBA) object library.
· In syntax, named arguments are shown as bold and italic.
All other arguments are shown in italic only.
Important You cannot use named arguments to avoid entering
required arguments. You can omit only the optional
arguments. For Visual Basic (VB) and Visual Basic for
applications (VBA) object libraries, the Object Browser
encloses optional
arguments with square brackets [ ].
For More Information See "ByVal," "ByRef," "Optional,"
and "ParamArray" in the Language Reference

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