VBScript
Session 7
Dani Vainstein
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What we learn last session?
Interacting in VBScript
VBScript constants groups.
Dani Vainstein
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Subjects for session 7
VBScript procedures.
Sub procedures.
Function Procedures.
Getting data into and out of procedures
Call statement.
Arguments ByVal and ByRef
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VBScript Procedures
In VBScript, there are two kinds of
procedures;
the Sub procedure and the Function
procedure.
Dani Vainstein
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VBScript Procedures
Sub Procedures
A Sub procedure is a series of VBScript statements
(enclosed by Sub and End Sub statements) that
perform actions but don't return a value.
A Sub procedure can take arguments
(constants, variables, or expressions that are
passed by a calling procedure).
If a Sub procedure has no arguments, its Sub
statement must include an empty set of
parentheses ().
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VBScript Procedures
Function Procedures
A Function procedure is a series of VBScript statements
enclosed by the Function and End Function statements.
A Function procedure is similar to a Sub procedure, but
can also return a value.
If a Function procedure has no arguments, the Function
statement must include an empty set of parentheses.
A Function returns a value by assigning a value to its name
in one or more statements of the procedure.
The return type of a Function is always a Variant.
The MsgBox and InputBox, are VBScript functions.
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VBScript Procedures
Sub and Function Procedures
If not explicitly specified using either Public or Private,
Sub procedures are public by default, that is, they are
visible to all other procedures in your script.
The value of local variables in a Sub or a Function
procedure is not preserved between calls to the procedure.
You can't define a Sub procedure inside any other
procedure.
The Exit Sub, Exit Function statement causes an
immediate exit from a Sub or Function procedure.
Any number of Exit Sub or Exit Function statements can
appear anywhere in a Sub or Function procedure.
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VBScript Procedures
Sub Procedures
Like a Function procedure, a Sub procedure is a separate
procedure that can take arguments, perform a series of
statements, and change the value of its arguments.
However, unlike a Function procedure, which returns a
value, a Sub procedure can't be used in an expression
You call a Sub procedure using the procedure name
followed by the argument list.
Caution Sub procedures can be recursive, that is, they
can call themselves to perform a given task. However,
recursion can lead to stack overflow.
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VBScript Procedures
Function Procedures
To return a value from a function, assign the value to the
function name.
If no value is assigned to name, the procedure returns a
default value
a numeric function returns 0
string function returns a zero-length string ("").
A function that returns an object reference returns Nothing
if no object reference is assigned to name.
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VBScript Procedures
Function Procedures
Variables used in Function procedures fall into two
categories: those that are explicitly declared within the
procedure and those that are not.
Variables that are explicitly declared in a procedure
(using Dim or the equivalent) are always local to the
procedure.
Variables that are used but not explicitly declared in a
procedure are also local unless they are explicitly
declared at some higher level outside the procedure.
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VBScript Procedures
Function Procedures
Caution A procedure can use a variable that is not
explicitly declared in the procedure, but a naming
conflict can occur if anything you have defined at the
script level has the same name.
If your procedure refers to an undeclared variable that
has the same name as another procedure, constant, or
variable, it is assumed that your procedure is referring
to that script-level name.
To avoid this kind of conflict, use an Option Explicit
statement to force explicit declaration of variables.
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Function Procedures
Caution VBScript may rearrange arithmetic expressions to
increase internal efficiency.
Avoid using a Function procedure in an arithmetic
expression when the function changes the value of variables
in the same expression.
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Function Procedures
In the following example, the Celsius function calculates degrees
Celsius from degrees Fahrenheit.
Sub ConvertTemp()
Dim Temp
temp = InputBox("Please enter the temperature in degrees F.", 1)
MsgBox "The temperature is " & Celsius(temp) & " degrees C."
End Sub
Function Celsius(fDegrees)
Celsius = (fDegrees - 32) * 5 / 9
End Function
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Getting Data into and out of Procedures
Each piece of data is passed into your procedures using an
argument .
Arguments serve as placeholders for the data you want to pass
into your procedure.
You can name your arguments any valid variable name.
When you create a procedure using either the Sub statement or
the Function statement, parentheses must be included after the
name of the procedure.
Any arguments are placed inside these parentheses, separated by
commas.
To get data out of a procedure, you must use a Function.
Remember, a Function procedure can return a value; a Sub
procedure can't.
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Sub Implementation
Getting an argument
Sub doLoops (iNum)
Dim i
For i = 1 To iNum Step 1
‘ do nothing
Next
End Sub
Sending an argument
doLoops 5
Call doLoops(5)
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Sub Implementation
Getting several arguments
Sub doLoops (iNum,strString)
Dim i
For i = 1 To iNum Step 1
‘ do nothing
Next
End Sub
Sending an argument
doLoops 5,”Hello”
Call doLoops(5,Hello)
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Sub Implementation
Getting an argument
Function ByteMe (sngNum)
ByteMe = CByte(sngNum)
End Function
Sending an argument
X = ByteMe(5.5)
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Sub Implementation
Getting several arguments
Function ByteMe (sngNum,ByRef errNumber)
ByteMe = CByte(sngNum)
errNumber = Err.Number
End Function
Sending an argument
X = ByteMe(5.5,errNumber)
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Call Statement
To call a Sub procedure from another procedure, type the
name of the procedure along with values for any required
arguments, each separated by a comma.
The Call statement is not required, but if you do use it, you
must enclose any arguments in parentheses.
The Call statement Transfers control to a Sub or Function
procedure.
If you omit the Call keyword, you also must omit the
parentheses around argumentlist.
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Call Statement
If you use either Call syntax to call any intrinsic or userdefined function, the function's return value is discarded.
Call MyFunction("Hello World")
Function MyFunction(text)
MsgBox text
End Function
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Arguments ByVal and ByRef
ByVal | ByRef] varname
ByVal
Indicates that the argument is passed by value.
ByRef
Indicates that the argument is passed by reference.
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Excercise
Dani Vainstein
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Lab 7.1
Use the InputBox for retrieve two numbers,representing
the flanks of a rectangle.
Write 2 functions :
First function calculates the area of the rectangle
Second function calculates the perimeter of the rectangle
The results must be displayed in a two lined msg box,
each line for each result + information icon + EX 7.1
title.
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