Introduction to Programming and VBScript

1
Introduction to Programming and VBScript
2
Data and Information

• Data are raw facts
• Examples of data include transactions, dates,
  amounts, etc.
• Information are data that have been processed
  into a usable form
• Information includes tables, documents, charts,
  etc.
• Goal of computer applications is to process data
  into information

3
Six Basic Computer Operations

• 1. A computer can receive (input) data
• 2. A computer store data in memory
• 3. A computer can perform arithmetic and
  manipulate text strings
• 4. A computer can compare the contents of two
  memory locations and select one of two
  alternatives
• 5. A computer can repeat a group of operations
• 6. A computer can output information (processed
  data)

4
Computer Operations
5
Programs and Programming

• A program is a very specific set of rules that
  tell the computer which switches should be "ON"
  or "OFF".
• The process of creating a program is called
  programming.
• The computer only knows what it is told through
  programs, so they must be accurate and very
  specific.

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What is Programming?

• Deciding if there is a task to be accomplished or
  problem to be solved using a computer, eg, is
  there a need for a program?
• Determining the nature of the task or problem,
  eg, what must the program do?
• Developing a plan that will accomplish the task
  or solve the problem, eg, generating the
  step-by-step process that the program will follow
  (algorithm)
• Converting the plan into a computer language
  program
• Testing the program to ensure it accomplishes
  task or solves problem defined earlier
• Implementing the program to accomplish the task
  or solve the problem

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Types of Computer Languages

• Procedural Monolithic programs that run from
  start to finish with no intervention from user
  other than input
• Basic, QBasic, QuickBasic
• COBOL, FORTRAN, C
• Object Oriented/Event Driven (OOED) Programs
  that use objects which respond to events use
  small segments ot code for each object
• Visual Basic
• Visual C
• Scripting languages Simplified languages that
  must be interpreted by other software (eg,
  browser, server software) gtgtVBScript, Javascipt,
  PerlScript

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Object-Oriented Programming (OOP)

• OOP uses objects, or self contained modules that
  combine data and program code which pass strictly
  defined messages to one another.
• OOED is easier to work with, because it is more
  intuitive than traditional programming methods.
• Visual Basic is almost a OOP language
• Users can combine the objects with relative ease
  to create new systems or extend existing ones.
• Properties of objects are attributes associated
  with an object
• Methods of objects are those activities that the
  object can carry out
• Objects respond to events

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Web Development with Scripting

• Web development creating applications that run
  on either or both the server and browser software
• Web development process
• 1. Define problem (functional definition)
• 2. Determine form of input from browser (html)
• 3. Determine form of output to browser (html)
• 4. Write and debug client-side script to
  pre-process browser input
• 5. Write and debug server-side script to process
  input to generate output to browser in form of
  HTML
• 6. Test entire project (client and server side)
• Final project must solve problem defined in 1st
  step

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Declaring Variables

• Declare ALL variables with the DIM statement
• General form
• Dim Variable1, variable2
• For example,
• Dim MyName, MyValue
• Dim Taxes, Price
• Two or more variables can be declared with same
  Dim statement
• Begin ALL pages with the ltOption Explicitgt
  statement even before the ltHTMLgt statement. This
  forces all variables to be declared--a good thing
  to do
• If you fail to declare a variable after the
  Option Explicit statement has been entered, an
  error occurs at Run time

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Keeping Tags and Code Apart

• In an .asp page, tags and code are separated by
  delimiters
• Tags appear and work in an asp document just like
  they do in a normal HTML page.
• Code is interspersed in page surrounded by lt and
  gt code delimiters, eg,
• lt Dim ftsize, ftcolor gt
• Multiple lines of code can be surrounded by one
  set of code delimiters,eg,
• lt Dim ftsize, ftcolor
• For ftsize 1 to 7 gt

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Using comments

• You can add internal documentation in the form of
  VBScript comments by using apostrophes
• Anything inside code delimiters beginning with an
  apostrophe is ignored by the server when
  interpreting an asp page, eg
• lt
• This code loops 7 times changing the
  ltignored
• font size each time through the loop
  ltignored
• for ftsize 1 to 7 ltexecuted
• You can delete code without removing it by
  preceding it with an apostrophe

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Line Continuation

• VbScript code statements in code delimiters can
  be continued by ending a statement with a space
  and an underline, eg,
• lt if weekday(date) gt 3 and _
• weekday(date) lt 6 then
• gt
• is the same as
• lt if weekday(date) gt 3 and weekday(date) lt 6
  then gt

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Assignment Statements

• Used to assign a value to a variable, eg
• lt Taxes VideoPrice TaxRate gt
• A variable or expression will be on right of
  assignment statement
• An expression is a combination of one or more
  variables and/or constants with operators
• Operators are symbols used for carrying out
  processing

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Arithmetic Operators

• () for grouping for addition
• for exponentiation - for subtraction
• - for negation
• for multiplication
• / for division
• \ for integer division
• mod for modulus

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Hierarchy of Operations

• Operations within parentheses ( )
• Exponentiation ()
• Negation (-)'
• Multiplication and division (,/)
• Integer division (\)
• Modulo arithmetic (Mod)
• Addition and subtraction (,-)
• String concatenation ()

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Arithmetic Example

• ltGross 3 (Salary - Taxes)2 Bonus/Months
  gt
• 3 1 2 5
  4 (order)
• Order
• 1 Subtract Taxes from Salary
• 2 Square the result
• 3 Multiply this result by 3
• 4 Divide Bonus by Months
• 5 Add result to first expression

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Displaying Variable Values

• To output the result of an assignment statement,
  use the following statement in the asp page
• lt variablegt
• For example, to compute taxes and total cost
• lt Option Explicit gt
• ltHTMLgt
• lt Dim TotalCost, Videoprice, TaxRate, Taxes
• VideoPrice 2.99
• TaxRate 0.07
• Taxes TaxRate VideoPrice
• TotalCost VideoPrice Taxes gt
• lt TotalCostgt
• lt/HTMLgt
• Enter this code in Notepad and save as
  Compute.asp and add this line to default.asp lta
  href compute.aspgtCompute Example lt/agt

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More on Delimiters

• If is possible (and often useful) to include code
  delimiters inside an HTML tag, eg,
• ltfont size ltftsizegtgt
• In this case, instead of displaying the value of
  the ftsize variable, the HTML ltfont size gt tag
  takes on the value of ftsize
• If the ftsize variable is equal to, say, 5 then
  the above tag is the same as
• ltfont size 5gt
• But since ftsize is a variable, it can take on
  many different values changing the size of the
  font

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Working with strings

• It is possible to work with strings, that is,
  sequences of characters
• Strings can be concatenated, that is, combined
  with the ampersand operator, eg,
• lt Option Explicit gt
• ltHTMLgt
• lt Dim FirstName, LastName, Name
• FirstName Bill
• LastName Gates
• Name FirstName LastName gt
• lt Namegt
• lt/HTMLgt
• Whats wrong with the assignment statement?
• Correct it and save the file as String.asp and
  add this line to default.asp lta href
  String.aspgtString Example lt/agt

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Symbolic Constants

• We can assign a name to a constant with the Const
  statement
• lt const constant name value gt
• Example
• lt Const TaxRate 0.07gt
• This assigns the constant the same value
  throughout the program

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Using Functions

• Sometimes we carry out a specific operation for
  which aVBScript function already exists to
  compute a single value
• To do this, we use a function that is nothing
  more than an operation that takes a multiple
  arguments and generates a single value
• variable functionName(arg1, arg2, )
• Example functions
• Date to return the current date
• Int to return the integer part of a number
• Len to return the length of a string

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Other Functions

• Other useful functions include
• Abs for absolute value Sqr for square root
• Ucase/Lcase to convert to upper/lower case
• DateValue for the date corresponding to string
  argument
• FormatCurrency to display a number as currency
• Instr to return the location of a substring in a
  string
• Example change the ltTotalcostgt statement in
  compute.asp to lt formatcurrency(Totalcost)gt
  and run it again. Note the difference in the
  output.
• For more information on VBScript functions, go to
  http//msdn.microsoft.com/scripting/VBScript/doc/v
  bstoc.htm and select Functions