Scripting Languages

1
Scripting Languages

• VBScript - Recognized mainly by Internet Explorer
  only - Netscape does have a plug-in
• JavaScript - Recognized by Internet Explorer and
  Netscape
• Perl - Used at the server side
• Server v.s. Client programming
• VBScript is similar to VB programming, but uses a
  subset of the language.

2
VBScripting

• To include a control use input tags.
• ltINPUT TYPEBUTTON NAMEcmdButton VALUE"Click
  Here"gt
• To have VBScript recognized by the browser - use
  the following
• ltSCRIPT LANGUAGE"VBScript"gt
• lt!-- Use comment tag so that browsers that do not
  support VBScript will not print the code --gt
• lt/SCRIPTgt

3
VBScripting contd.

• To build the command button for the Input tag
• ltSCRIPT LANGUAGE"VBScript"gt
• lt!--
• Sub cmdButton_OnClick
• Msgbox Please enter a number from 1 to 10."
• End Sub

4
Data - Variables Constants

• Constant is data that will not change - fixed in
  value
• Variable is data that can change during the
  course of the running of a program
• Identifier is a name assigned to a variable or
  constant - memory is reserved for the variable /
  constant
• Declaration statements define the variable /
  constant for the program

5
Declaration Statements

• Const Identifier As Datatype Value
• Const is a reserved word to define a constant in
  the declaration section
• Dim Identifier As Datatype
• A defaulted datatype becomes type variant
• String values are called string literals
• Intrinsic constants are VB built-in constants

6
Data Types

• Boolean - True or False value (0 or 1)
• Byte - A single ASCII character
• Single Currency - Floating Point
• Date - An eight character date
• Double - Double precision floating point
• Long Integer - Whole number
• String - Alphanumeric characters
• Variant - Stores any type

7
Local Declarations

• The Dim statement can be placed anywhere within
  the local procedure
• It is recommended to be placed at the top of the
  procedure
• It must be placed before the variable is used
• Variables and constants can be declared locally

8
Arithmetic Operators

• The order of precedence is as follows
• Exponentiation -
• Multiplication and Division - , /
• Addition and Subtraction - , -
• Use parenthesis to change evaluation order of a
  mathematical expression
• All evaluations occur from left to right
• Parenthesis are performed first then in the order
  of precedence

9
Arrays

• A series of items (Data Types) that are related
  to one another
• They use the same name with an index to each part
  (element) of the array
• They are similar to a control array except they
  are for data storage
• The name tables or subscripted variables is
  sometimes used with them
• The index is the subscript of the array

10
Dimensioning Arrays

• The Dim statement is used similar to all other
  declarations
• Dim Arrayname (lower To Upper) As Datatype
• The lower subscript is not necessary - if left
  out the lower subscript will be zero
• The datatype may be left out and defaults to
  variant
• All data elements are initialized to zero for
  numerics and null string for strings

11
Dynamic Arrays

• Arrays can be dimensioned dynamically
• An array declared as - Dim Name() As Integer
• Will allow redimensioning during program
  execution
• The Redim statement is used to rediminsion an
  array
• All other arrays are static arrays

12
Array Subscripts

• The subscript used to reference into the array
  can be a constant
• A literal number
• A variable
• A numeric expression
• The subscript MUST reference a valid element of
  the array

13
Message Boxes

• Message Boxes are used to notify the user of an
  error or display information
• The message box can contain a message, icon,
  title bar caption or command button
• MsgBox message ,buttons/icon, title bar
• Displays the message centered in box
• Displays title bar caption in the title bar

14
Message Box Buttons

• vbOKOnly - 0 - Shows only the OK button
• vbOkCancel - 1 - Shows the OK and Cancel buttons
• vbAbortRetryIgnore - 2 - Shows the Abort, Retry
  and Ignore buttons
• vbYesNoCancel - 3 - Shows the Yes, No and Cancel
  buttons
• vbYesNo - 4 - Shows the Yes and No buttons
• vbRertyCancel - 5 - Shows the Retry and Cancel
  buttons

15
Message Box Parameters

• vbCritical - 16 - Uses a Critical X as an
  indicator
• vbQuestion - 32 - Uses a Question mark as an
  indicator
• vbExclamation - 48 - Uses a Exclamation point as
  an indicator
• vbInformation - 64 - Uses an I as an indicator

16
Message Box Return Codes

• vbOk -1 - Indicates an OK status
• vbCancel - 2 - Indicates a return of cancel
• vbAbort - 3 - Indicates a return of abort
• vbRetry - 4 - Indicates a return of retry
• vbIgnore - 5 - Indicates a return of Ignore
• vbYes - 6 - Indicates a return of yes
• vbNo - 7 - Indicates a return of No

17
Procedures / Functions

• A sub procedure is code that performs a given
  operation, but does not return anything.
• A function is code that performs a given
  operation and then returns a value to the caller.
  This value can be the result of some operation or
  just an error code.
• The returned value is accomplished by using the
  name of the function and assigning a value.
• To exit a sub procedure prematurely use Exit Sub.

18
Functions

• Functions perform an action and return a value
  associated with that action
• The VAL function will convert data into a numeric
  format
• The Val function converts until the first
  non-numeric character is read

19
System Procedures

• There are two types of system classes.
• Events - a subroutine executed automatically by
  the system when a certain event takes place.
• OnBlur - executed when an object is deselected
• OnChange - executed when a user changes the
  object
• OnClick - executed when an object is clicked
• OnFocus - executed when an object is active (user
  selects)
• Methods - controlled events. Methods normally are
  used to cause something to occur.
• Calling a method is done by using the object name
  and the method name.
• Objectname.Methodname

20
Conditional Statements

• If ( condition) Then
• statements
• ElseIf (condition) Then
• statements
• Else
• statements
• End If
• All data types must be of the same type

21
Relational Operators

• The relational operators are used to compare two
  values - the result of the comparison is either
  True or False
• gt - Greater than
• lt - Less than
• - Equal to
• ltgt - not equal to
• gt - Greater than or equal to
• lt - Less than or equal to

22
Conditional Statements contd.

• ASCII comparisons, handled left to right
• All string literals must be enclosed in double
  quotes
• Be careful using text boxes - their data type is
  variant
• To check uppercase characters - Ucase()
• To check lowercase characters - Lcase()
• Use logical operators to test multiple conditions
  - Or , And , Not, Xor, Equ, Imp

23
Conditional statements contd.

• Nested If Statements can be used, just remember
  to include the End If inside the nested If
• The nesting can be accomplished in the Then
  portion of the condition, or in the Else portion
• The ElseIf statement or an If within an If are
  both valid statements
• It is highly recommended to flowchart conditional
  statements

24
Case Statements

• Multiple If tests (nested or otherwise) can be
  replaced with the Case Statement
• It is easier to read and easier to construct

25
Case Statement contd.

• Select Case expression
• Case Is relational expression
• Statement
• Case Constant To Constant
• Statement
• Case Else
• Statement
• End Select

26
Do Loops

• Do Loops repeat instructions until a condition is
  met
• Do While condition
• statements to be repeated
• Loop
• Do
• statements to be repeated
• Loop Until condition

27
For / Next Loops

• Used to allow repetitive operations in a sequence
  of code.
• For LoopIndex Startvalue To EndValue Step
  Increment
• statements to be repeated
• Next LoopIndex
• The Loop Index must be declared before entering
  the loop and the end value must be attainable.

28
For / Next Loops contd.

• Once the end value has been reached the execution
  will drop out of the loop.
• Negative numbers are allowed for the step value
• Altering the values of the control variables will
  not affect the operation of the loop