Chapter One An Introduction to Programming and Visual Basic

1
Chapter OneAn Introduction to Programming and
Visual Basic
2
What is Visual BASIC

• Visual
• Using GUI (Graphic User Interface) Technologies
• Window Objects Controls (Forms, Buttons,
• BASIC
• Programming Language (Beginners All-purpose
  Symbolic Instruction Code)
• Different versions of BASIC
• MBASIC - Microsoft BASIC
• BASICA - BASIC Advanced
• Quick BASIC, QBASIC

3
Six Basic Computer Operations

• Input data
• Store data
• Process data
• Compare values and select among alternatives
• Repeat a group of actions
• Output the results

4
Types of Computer Languages

• Procedural 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 (OO/ED) Programs
  that use objects which respond to events use
  small segments of code for each object
• Visual Basic
• Visual C

5
Levels of Computer Languages

• Low Level at the level of the computer, i.e., in
  binary (0-1) format (machine code)
• Computer can only execute the binary form of a
  program
• Intermediate level close to the computer but
  uses abbreviated English words e.g., Assembler,
  that is converted directly into binary
• High Level at the level of the programmer using
  English like words and clearly defined syntax
  e.g., Visual Basic must be converted or
  translated into binary for computer to implement
  it,
• Need a software program to handle the conversion
  of high-level into binary

6
Translating from High-level Language to Binary

• Interpreted each statement translated as it is
  executed--slow but easy to use (instant results,
  easy to debug)
• Compiled entire program is converted to
  binary--executes faster, but more difficult to
  use (.exe files are compiled programs)
• VB is interpreted during creation and debug/test
  but can then be compiled into an .exe file

7
(No Transcript)
8
Three Basic Control Structures in a Program

• Sequence control structure
• Decision control structure (Conditions)
• Repetition control structure (Loops)

9
Basic Concepts of Windows Programming

• Windows The primary container of programming.
• Events Operation activities (mouse click,
  keyboard press,...).
• Message Information about the event.
• Objects Identifiable entities (forms, controls,
  data objects,)
• Properties The attributes associated with an
  object (name, caption, size, position, )
• Methods A set of predefined activities that the
  object can carry out

10
Object Oriented Programming

• Procedural Programming Making the entire
  program, from the interface appearance to the
  process codes May be divided into the modules.
• OOP Only make small pieces of codes into
  individual event snippets of objects. Not need to
  code for the interface itself.

11
OOP Programming Process

• A six step process for writing an OOP computer
  program
• 1. Define problem.
• 2. Create interface
• 3. Develop logic for action objects
• 4. Write and test code for action objects
• 5. Test overall project
• 6. Document project in writing

12
IPO Table for Calculate Button
13
Using Pseudocode

• An important part of the developing the logic for
  action objects is generating corresponding
  pseudocode.
• Pseudocode involves actually writing a program
  in English rather than in a computer language.
• When the actual computer program is written, the
  pseudocode is translated into computer language.
• A pseudocode program is useful for two reasons
• The programmer may use it to structure the
  algorithm's logic in writing.
• It provides a relatively direct link between the
  algorithm and the computer program

14
Pseudocode for Calculate Button

• Begin procedure
• Input Video Price
• Taxes 0.07 x Video Price
• Amount Due Video Price Taxes
• Output Taxes and Amount Due
• End procedure

15
Step Six Documentation

• Three levels of documentation
• Comments in the code
• On-line Help
• Users Guide and Programmer Document

16
Chapter Two Creating a First Project in Visual
Basic
17
Getting Started with Visual Basic

• Double-click VB icon on Desktop or use
  StartProgramsVisual Basic to bring up opening
  dialog box

18
Basic Components of VB

• Project (.vbp)
• Forms (.frm)
• Controls
• Event procedures
• Modules (.bas)
• procedures
• Additional components
• Data Environment Designer - DED (.dsr)
• Data Report Designer - DRD (.dsr)

19
VB Development Environment
Form Size
Toolbar
Project Explorer
Initial Form Window
Toolbox
Properties Window
Project Window
Form Layout Window
Sizing Handles
20
The Toolbox
Label Control
Textbox control
Used to select a control to place on form.
21
Project Explorer Window
View code
View Object
Change Folders
Used to select the code or object or to change
folders.
22
The Properties Window
Window Name
Object Box
Properties List Tabs
Scrollable list of properties
Description Pane
Used to change the properties of controls at
design time.
23
Important Properties

• Name identifies the object (the text seen by VB)
• Should start with three letter prefix (see
  recommendation)
• lbl for label
• txt for text box
• frm for form
• Can include letters, numbers, and underscore
• Caption The text (of the object) you see on
  screen

24
Adding a Control (Special Object)

• Double-click to add control to center of form
• Can be moved around from there
• Use sizing handles to change size
• Single Click and draw on form
• Select an exist one and use Copy/Paste methods.

25
Controls to Add to Form

• Label control provides description of other
  controls
• Image control holds a graphic image
• Stretch property should be set to True
• Picture property is set to graphic file
• Command button control can be clicked to provide
  action
• Caption property

26
Adding Code to Project

• Code is organized in Code Window as EVENT
  PROCEDURE
• Event procedure begins with Private Sub and
  ends with End Sub
• Example Use Msgbox command to display dialog box
  with message
• Msgbox Welcome to Vintage Videos

27
Design Time and Run Time

• The project is in Design Time when you are
  designing the project and adding code.
• The project is in Run Time when you run the
  project by clicking the VCR Run icon or Menu Run
  Start.
• You can stop the project and exit Run time by
  clicking the VCR Stop Icon or Menu Run End. The
  project returns to Design Time.
• You can go to Break Mode by clicking the VCR
  Pause Icon or Menu Run Break.

28
Difference between End and Break Mode

• When the project is ended, all the internal
  results are lost. It can only be started from
  beginning.
• When project is break, all the internal results
  are kept in memory. You can check these results
  to see whether your program is in right
  direction. It can be re-started just from the
  break point.

29
The Toolbar and Menu System

• The VB menu system provides access to all
  commands.
• The Toolbar uses icons for more commonly used
  menu commands (benefit? One click through!).

30
Files in Visual Basic

• All projects in VB have a .vbp (project) file and
  at least one .frm (form file) file.
• Always save .frm files first and then save
  project files. Use FileSave or FileSave as
  commands for this purpose or click Disk icon on
  Toolbar.
• Projects with graphics also have .frx (binary
  form) files. They are saved automatically.
• Module files have a .bas extension and are pure
  code files.

31
Visual Basic Help

• There are three types of Help
• Help menu option
• context-sensitive help
• and Auto Help (IntelliSense)
• In VB 6, Help uses the familiar Internet Explorer
  browser interface for the first two types of
  help.
• You can seek help by selecting Contents, Index,
  or Search from the Help menu item
• Pay attention to the selected Active Subset

32
Context-Sensitive and Auto Help

• With context-sensitive help, pressing the F1 key
  provides help on whatever item the cursor is
  located.
• With Auto Help, VB tries to help you with a code
  statement by providing
• A list of items to complete the statement
• Info on the statement you have started
• Tips on the type of data you are working with

33
Chapter 3Variables, Assignment Statements, and
Arithmetic
34
Variables

• Variables are named locations in memory (memory
  cells) in which we store data that will change at
  run time
• Variable names in VB
• Must begin with letter
• cant include period
• cant be over 255 characters
• are not case-sensitive
• Example variable names
• VideoPrice for Video Rental Price
• Taxes for taxes on this price
• AmountDue for sum of price and taxes
• YTDEarnings for year to date earnings
• EmpLastName for employees last name

35
Name Convention

• Use capital letters to distinguish parts in a
  name.
• LastName, StudentID, StreetNum
• Use standard prefix for certain type object
• txt Text box, txtName
• but( or cmd) Command button, butOK
• lst List box, lstPrices
• frm Form, frmInput
• str String variable, strName
• (see the recommendation list)

36
Data Types I

• Two primary types of data numeric and string
• Numeric data
• 3.154 2300 -34 .0000354 0.97E-5
• are all numeric constants
• String data must use or as the delimiters
• Dogs 123-45-6789 Dr. Brown
• are all string constants
• Numeric data types can be subdivided into
  specific types
• currency 55,567.78 integer 255
• single 567.78 long (integer) 35,455
• double 567.78129086 Boolean True or False

37
Data Types II

• Numeric data types can be subdivided into
  following specific types

38
Variant Type

• A special data type in VB that can be used to
  store (reference) any previous data type and even
  image data.

39
Declaring Variables

• Declare ALL variables with the Dim statement
• Syntax
• Dim Variable1 as type1, variable2 as type2
• For example,
• Dim MyName as string, MyValue as single
• Dim Taxes as Currency, Price as Currency
• Dim AmountDue as Currency
• Dim mVar
• Dim mVar, AmountDue as Currency
• Two or more variables can be declared with same
  Dim statement but you must include the variable
  type
• Use variables rather than objects in processing
  since all text boxes are strings

40
The Option Explicit Statement

• Begin ALL Forms with the Option Explicit
  command in the declarations procedure of the
  general object. This forces all variables to be
  declared
• To automatically include Option Explicit, go to
  the ToolsOptionsEditor menu selection and check
  the box for Require variable declaration
• If you fail to declare a variable after the
  Option Explicit statement has been entered, an
  error occurs at Run time

41
Variable vs Constant

• Variable is a memory unit with a named ID
• Constant is a prefixed value in program codes.
• Variable can be changed in run time. Constant
  never changes.
• Variable is referenced quicker than constant.
  Because constant needs to to translated/extracted
  from codes.
• To improve performance, use variable instead of
  constant if that constant is used frequently in a
  program.

42
Assignment Statements

• Must convert strings in text boxes to numeric
  with Val function, eg,
• Price val(txtPrice)
• Convert numeric variables to strings before
  assigning to text box, e.g.,
• txtAmountDue str(AmountDue)
• Carry out calculations with assignment
  statements, eg,
• Taxes 0.07Price
• AmountDue Price Taxes

43
Using Functions

• Sometimes we want to convert a string to a number
  or vice versa or 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 for converting data
• Val to convert a string to a number
• Str to convert a number to a string
• Ccur to convert a string to a currency data type

44
Using Assignment Statements for Calculations

• Sometimes, an 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

45
Arithmetic Operators

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

46
Hierarchy of Operations

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

47
Arithmetic Example

• 3 (Salary - Taxes)2 Bonus/Months
• 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 Subtract result from first expression

48
Symbolic Constants

• We can assign a name to a constant with the Const
  statement
• const constant name as variable type value
• Example
• Const IntRate as single 0.07

49
Comments

• To explain the purpose of a statement, a comment
  statement is added
• Any statement beginning with an apostrophe or REM
  is a comment
• Comments can be added to end of statements using
  apostrophe

50
Formatting Data

• To display information in a well designed form,
  we can use the Format function
• variable Format(variable, format expression)
• Where the format expressions are in quotes and
  include
• Currency
• Fixed
• Standard
• Percent
• Scientific
• Example
• txtTaxes.text Format(Taxes, currency)

51
Print Form, Clearing Entries and Setting Focus

• To print the form, use the PrintForm command
• To clear a text box, set it equal to the null
  string
• To set the focus to a text box, use the Setfocus
  method
• For example,
• txtCustName.SetFocus sets focus to this textbox

52
Using Other Arithmetic Functions

• Other useful functions include
• Abs for absolute value Sqr for square root
• FV for future value PV for present value
• IRR for internal rate of return Pmt for payment
• Ucase/Lcase to convert to upper/lower case
• Len for length of a string
• Date for the system date
• DateValue for the date corresponding to string
  argument
• We will use Pmt to compute the monthly payment
• MonPay Pmt(rate, Nper,-LoanAmt)
• ?Pmt(.08/12,60,-10000) (The result is 256.03 )

53
Creating a Monthly Payment Calculator

• Assume you wanted to determine the monthly
  payment necessary to pay off a loan at a given
  interest rate in some number of months
• Use PMT function
• PMT(rate, nper, pv) where
• rate monthly interest rate
• nper number of months
• pv negative value of loan amount

54
The Monthly Payment Form
55
Compute Button Click event
Dim Amount as currency, Months as integer, Rate
as single Dim Payment as currency Amount
Ccur(txtAmount) Months Cint(txtMonths) Rate
Csng(txtRate) Payment Pmt(Rate, Months,
-Amount) txtPayment Format(Payment,
Currency) txtAmount Format(Amount,
Currency) txtRate Format(Rate, Percent)
56
Visual Basic Errors

• Syntax errors (Design Time) caused by incorrect
  grammar, vocabulary, or spelling . Also caused by
  using a keyword. Usually caught as you enter the
  statement. These are pointed out by VB and are
  usually easy to find and correct.
• Run time errors errors not caught at entry but
  which involve an incorrect statement or bad data,
  e.g, dividing by zero. The presence of an error
  is detected by VB when you run the program, but
  you still have to find the source of the error.
  More difficult to correct than syntax errors.
• Logic errors those that are VB does not catch as
  being wrong, but which involve erroneous
  logic, say, only having a program include 11
  months of data instead of 12. These are the
  hardest to find!
• Debugging is the art and science of finding
  errors. VB has debugging tools to be discussed
  later.

57
Chapter 4 The Selection Process in Visual Basic
58
The Selection Process

• One of the key operations of a computer is to
  select between two or more alternatives to make a
  decision
• Every decision involves a comparison between a
  variable and a constant, variable, or expression
  using comparison operators and logical operators
• Decisions can involve two-alternatives or
  multiple alternatives

59
The If-Then-Else-End If Decision Structure

• For two alternative decisions, the
  If-Then-Else-End If decision structure should be
  used
• In pseudocode, this is
• If condition is true then
• implement true alternative
• Else
• implement false alternative
• End Decision

60
Multiple Alternatives

• For multiple alternatives, the general form in
  pseudocode is
• Select one
• Condition 1 is true implement alternative 1
• Condition 2 is true implement alternative 2
• Condition 3 is true implement alternative 3
• End Selection.

61
The Two Alternative Decision Structure

• The If-Then-Else statement is
• If condition is true Then
• statements for true alternative
• Else
• statements for false alternative
• End if
• The If-Then condition
• expression1 ComparisonOperator expression2
• where comparison operator is one of these six
  operators
• Equal to Less then lt
• Greater than gt Less than or equal to lt
• Greater than or equal to gt Not equal to ltgt

62
The If-Then-Else Decision Structure (cont.)
63
Example of If-Then-Else Decision to Compute
Payroll
sngPayrate Csng(txtPayRate.text) intHours
Cint(txtHours.text) If intHours gt 40 then
sngPay sngPayRate 40 1.5 sngPayRate
(intHours - 40) Else sngPay intHours
sngPayRate Endif txtPay.text Format(sngPay,curr
ency)
64
One-Alternative Decision

• If there is only a true alternative, then this is
  a special case of the two-alternative decision
  structure
• If condition is true Then
• true alternative is implemented
• End If
• One-alternative decision can be combined with
  InputBox used to validate user input, e.g., to
  test that Customer Name textbox has something in
  it
• If TxtCustName.Text then
• txtCustName.Text InputBox(Enter Name and try
  again)
• Exit Sub
• End if
• Where the Exit Sub statement exits the event
  procedure

65
If-Then-ElseIf Decision Structure

• One way to implement a multiple alter-native
  decision structure is through the If-Then-ElseIf
  decision structure
• If condition1 true then
• first set of statements
• ElseIf condition2 true then
• second set of statements
• ElseIf condition3 true then
• third set of statements
• Else
• last set of statements
• End if

66
If-Then-ElseIf Decision StructureAssume
condition3 is True
67
Example of If-Then-ElseIf for Letter Grade
Determination

• Dim intAverage as Integer, strLetterGrade as
  string
• intAverage Cint(txtAverage.text)
• If intAverage gt 90 then
• strLetterGrade A
• ElseIf intAverage gt 80 then
• strLetterGrade B
• ElseIf intAverage gt 70 then
• strLetterGrade C
• ElseIf intAverage gt 60 then
• strLetterGrade D
• Else
• strLetterGrade F
• End if.
• txtLetter.Text strLetterGrade

68
Using the Select Case Decision Structure for
Multiple Alternatives

• General form
• Select Case expression
• Case Condition1 is true
• First set of statements
• Case Condition2 is true
• Second set of statements
• Case Condition3 is true
• Third set of statements
• Case Else
• Last set of statements
• End Select

69
Case Conditions

• Conditions for Case statement can be in 3 forms
• Test Condition Example
• Exact Value Case 91, 92, 93
• Range of values Case 90 to 100
• Comparison condition Case Is gt 89

70
Example of Select Case to Determine LetterGrade
Dim intAverage as Integer, strLetterGrade as
String intAverage CInt(txtAverage.text) Select
Case intAverage Case Is gt 90 strLetterGrade
A Case Is gt 80 strLetterGrade B
Case Is gt 70 strLetterGrade C Case Is gt
60 strLetterGrade D Case
Else strLetterGrade F End Select
71
Using the List Box and Combo Box

• The List box enables the user to select from a
  list of items.
• lst is prefix for name and the List property of
  the list box can be set at design time or run
  time.
• The Text property of the list box is equal to the
  selected item.
• We can test the Text property to determine which
  item was selected.

72
Important Properties and Methods of ListBox
ComboBox

• Property
• List()
• ListCount
• ListIndex
• Method
• AddItem
• RemoveItem
• Clear
• Examples of using ListBox Add/Remove Items, Show
  List(),ListCount,ListIndex

73
More Complex Decisions

• Decisions within decisions are know as nested
  decisions
• Interior decision must be an alternative of outer
  decision
• Decisions that combine two or more test
  conditions using logical operators are known as
  compound decisions
• And, Or, Not, and Xor are logical operators
  (Hierarchy Not - And - Or, Xor)
• Both conditions must be able to stand alone

74
Example of Nested Decisions

• Need to check if employee is hourly paid before
  checking for overtime
• if PayType Hourly then Hourly, Can make
  overtime
• If hours gt 40 then
• Pay 40 PayRate 1.5 (Hours-40) PayRate
• Else
• Pay Hours PayRate
• End if
• Else Salaried employee cannot be paid overtime
• Pay 40 PayRate
• End if

75
Example of Compound Decisions

• Using compound condition to test for average AND
  number of absences
• If Average gt 90 AND Absences lt 3 then
• LetterGrade A
• ElseIf Averager gt 80 AND Absences lt 5 then
• LetterGrade B
• etc.
• In this case, if a student has an average of 93
  and 4 absences, he/she will receive a grade of
  B because he/she has more than 3 absences.

76
Example of Using List Box

• Dim VideoType as String, Price as Currency
• VideoType lstTypes.Text lstTypes is list box
• Select Case VideoType
• Case Kids
• Price 0.99
• Case Regular
• Price 1.99
• Case Classic
• Price 2.99
• End Select
• txtVideoType.text Format(Price,currency)
• End Sub

77
Using the Form_Load Event

• The Form_Load event occurs when the project is
  started and the form is loaded.
• Code from a command button can be cut (or copied)
  and then pasted into the form_load event

78
Using the Debug ToolBar

• To view the Debug Toolbar, Select ViewToolbars
  and click the Debug checkbox
• The Debug Toolbar

Run Stop Step Into Step Out
Immediate Window Quick Watch
Break Toggle Step Over
Locals Watch Window Call Stack
Breakpoint
Window
79
Debugging With the Immediate Window

• By clicking the Immediate Window icon on the
  debug toolbar, you can then print the current
  value of a textbox or variable
• Use the Print variable or textbox command to
  display its current value
• This can enable you to find errors in the code

80
Chapter 5 The Repetition Process in Visual Basic
81
The Repetition Process

• The capability to repeat one or more statements
  as many times as necessary is what really sets a
  computer apart from other devices
• All loops have two parts
• the body of the loops (the statements being
  repeated)
• a termination condition that terminates the loop
• Failure to have a valid termination condition can
  lead to an endless loop

82
Types of Loops

• There are three types of loops
• event-driven
• determinate
• indeterminate
• Event-driven loops are repeated by the user
  causing an event to occur
• Determinate loops repeat a known number of times
• Indeterminate loops repeat an unknown number of
  times
• Variables should be initialized before being used
  in a loop

83
Event-Driven Loops

• Event-driven loops are repeated by user causing
  an event to occur--clicking a button
• Variable scope is important for loops Variables
  in event procedures are local and are reset to
  zero when procedure terminates
• Variables defined at form level are known to all
  procedures and retain their value between events
• Form-level variables are declared in the
  Declarations procedure of the General object
• Static variables retain their value between
  events but are local to event procedure
• Declared with Static keyword

84
Form-level Variables
85
Use of AddItem and Clear Methods

• The AddItem method is used to add items to a list
  box at run time
• Form of AddItem method
• list1.Additem string
• Always add a string to list box since it contains
  text
• The Clear method clears a list box
• list1.Clear

86
Code to Sum a Series of Numbers

• Private Sub cmdCalc_Click()
• Dim TheValue As Integer
• TheValue CInt(txtTheValue.text)
• Sum Sum TheValue Sum declared at form
  level
• NumValues NumValues 1 NumValues declared
  as form level
• txtSum.Text Str(Sum)
• txtNumValues.text Str(NumValues)
• lstEntries.AddItem str(TheValue)Add value to
  list box
• txtTheValue.text "
• txtTheValue.SetFocus Set focus back to
  txtTheValue
• End Sub

87
Determinate Loops Using For-next Loop

• Best way to create a determinate loop is to use a
  For-Next Loop
• Form of For-Next Loop
• For variable start value to end value Step
  change value
• statements that compose body of loop
• Next variable
• where variable the counter variable in the
  loop
• start value the beginning value of the
  counter variable
• end value the ending value of the counter
  variable
• change value the amount the counter
  variable changes each time through the loop
• Next variable the end of the For loop

88
Example of For-Next Loop
89
Code To Sum using For-Next Loop

• Private Sub cmdCalc_Click()
• Dim TheValue as Integer, Sum as Integer
• Dim NumValues as Integer, Counter as Integer
• Sum 0 Initialize Sum to Zero
• If txtNumValues.Text "" then Number not
  entered
• Msgbox "Please enter number of values to be
  summed"
• Exit Sub Do not go into loop
• End if
• NumValues CInt(txtNumValues.Text)
• For Counter 1 to NumValues
• TheValue CInt(InputBox("Enter next value"))
• Sum Sum TheValue
• lstEntries.AddItem Str(TheValue) Add value to
  list
• Next
• txtSum.Text Str(Sum)
• lstEntries.AddItem "Sum is " str(Sum)
• End sub

90
Printing a List

• To print the contents of listbox, use the
  Listcount and List() properties of the list box
• Listcount is the number of items in list box but
  list() property runs from 0 to Listcount -1
• List(Counter) is equal to the contents of the
  corresponding list box
• Code to print contents of list box to Immediate
  Window
• For Counter 0 to lstEntries.ListCount - 1
  Debug.Print lstEntries.List(Counter)
• Next

91
Indeterminate Loops

• Indeterminate loops run for an unknown number of
  repetitions until a condition is true or while a
  condition is true
• Four types of indeterminate loops
• Until loop with termination condition before body
  of loop
• While loop with termination condition before body
  of loop
• Until loop with termination condition after body
  of loop
• While loop with termination condition after body
  of loop
• Pre-Test loops have termination condition before
  loop body
• Post-test loops have termination condition after
  loop body

92
Form of Pre- and Post-Test Loops

• The form of the pre-test loops is
• Do Until (or While) condition
• body of loop
• Loop
• The form of the post-test loops is
• Do
• body of loop
• Loop Until (or While) condition

93
Pre and Post-Test Loops
94
Processing an Unknown Number of Values from a
File

• A data file is a collection of data stored on
  magnetic or optical secondary storage in the form
  of records.
• A record is a collection of one or more data
  items that are treated as a unit.
• Files are identified by the computers operating
  system with filenames assigned by the user.
• Files are important to processing data into
  information because they provide a permanent
  method of storing large amounts of data that can
  be input whenever needed for processing into
  information
• Three types of files sequential access, database,
  and direct access files
• We will use sequential access files as input.

95
Using Sequential Access Files

• Sequential access files must be read in same
  order as they are created so they replicate the
  action of entering data from a keyboard.
• The number of records on a sequential access file
  is often unknown, but there is an invisible
  binary marker at the end of the file called the
  EOF (end of file) marker.
• Use a Do While loop or a Do Until loop to input
  data from sequential access file.
• Loops can input data until the EOF marker is
  encountered (or while it has not been
  encountered).
• Create sequential access files by using the
  Notepad text editor

96
Opening and Inputting Data from a File

• Files must be opened with the Open statement
• Open filename" for Input as n
• To input data from a file, use the Input n,
  statement
• Input n, list of variables
• Files must be closed at end of procedure
• Close n
• Using an Until loop to input data from file
• Do Until EOF(n)
• Input n, list of variables
• Loop

97
Code to Input and Sum values from File

• Private Sub cmdCalc_Click()
• Dim TheValue As Integer, Sum As Integer
• Dim NumValues As Integer
• Open "a\SumData.txt" For Input As 10
• Sum 0
• NumValues 0
• Do Until EOF(10) Input to end of file
• Input 10, TheValue
• Sum Sum TheValue
• NumValues NumValues 1
• lstEntries.AddItem str(TheValue)
• Loop
• txtNumValues.text Str(NumValues)
• txtSum.Text Str(Sum)
• lstEntries.AddItem "Sum is " str(Sum)
• Close 10
• End Sub

98
The Combo Box

• A combo box is a combination of a text box and a
  list box. It typically a drop-down list box
• It has a text box portion that is displayed at
  all times and a drop-down list of items that can
  be displayed by clicking on the down arrow.
• One property of note for the combo box is the
  Style property, which can be set at design time
  to Drop Down combo (the default), Simple Combo,
  or Drop Down list. Its prefix is cbo .
• The combo box has all the properties and methods
  of the list box including the AddItem, Listcount,
  and list properties.

99
More on Combo Boxes

• The default event for the Combo box is the Change
  event--to use the Click event, you must change to
  it.
• The Sorted property is a useful property for the
  combo and list boxes that arranges the items in
  the box.
• Items can be removed from a combo or list box
  with the RemoveItem method which requires that
  number of the item to be remove be given.
  However, to remove a selected item, use the
  ListIndex property, e.g,
• cboMembers.RemoveItem cboMembers.ListIndex

100
Nested Loops

• A Nested loop is a loop within a loop. Must
  complete the inner loop within the outer loop.
• Nested For-Next loops have a For-Next loop within
  a For-Next loop in which the inner loop will go
  through all its values for each value of the
  outer loop.
• Three key programming rules to remember about
  using nested For-Next loops
• Always use different counter variables for the
  outer and inner For-Next loops.
• Always have the Next statement for the inner
  For-Next loop before the Next statement for the
  outer For-Next loop.
• Always include the counter variable in the Next
  statements to distinguish between the loops.

101
Creating an Executable File

• An executable file is one that can be executed on
  any computer on which it is installed.
• Creating an executable file in VB is accomplished
  with the FileMake filename.exe menu selection.
• Once an executable file is created, a shortcut to
  it can be created by right-clicking the file name
  in Windows Explorer and selecting Create
  Shortcut.
• Drag the shortcut to the desktop.

102
Debugging Loops

• Debug a loop by inserting a debug.print command
  in the loop to print to the Immediate Window.
• Add a Quick Watch by locating the pointer on a
  variable and clicking the eyeglass icon on the
  Debug Toolbar. The values for this variable will
  be shown in the Watch Window.
• Use the Locals window to display the values of
  variables local to a procedure.
• Use the Toggle Breakpoint icon to pause execution
  at a designated line in the code and then use the
  various windows to view the values for variables.

103
Chapter 6 Using Arrays
104
Using Control Arrays
1. A control array is group of the same type
control which is assigned a single name. 2. The
individual controls are identified by the control
array name and an index value. 3. The Case
decision structure can be useful in working with
a control array. 4. To create a control array,
just enter the same name for more than one
control and replay yes to the query. 5. The
order in which the controls are entered
determines the index values for the controls in
the control array.
105
Using List Arrays

• Arrays are lists or tables of data which have
  single name. Individual array elements are
  identified by the array name and one or more
  subscripts or index values.
• To be use in Visual Basic, an array must be
  declared arrays can be fixed size or dynamic
  size (we use only fixed arrays.)
• The default lower limit on an array index is zero
  but this can be changed to one or any other
  value..
• It is not possible to exceed the upper limit or
  go below the lower limit on the array index
  values
• To declare an array
• Dim arrPrice(25) As Currency
• or Dim arrPrice() As Currency
• Redim arrPrice(25)

106
Comparing Listboxes and Arrays
107
Entering Array Data
1. Arrays can be input with any of the three
types of loops discussed earlier--Event-driven,
For-Next, or While/Until loops. 2. Event-driven
loops and For-Next loops are good for keyboard
input While or Until loops are good for input
from a file. 3. In any case, each array element
must be input using its subscript value. 4. With
an event driven loop, each click of a button
increments a counter and inputs the corresponding
array element. 5. With a For-Next loop, you must
input the number of arrays elements. The array
values must be input with an InputBox with the
For-Next counter variable matching the array
index. 6. With an Until loop, you can input from
a file. You must increment a counter that matches
the index for the array element.
108
Code to Input from For-Next and Until Loops
For-Next Loop Dim counter As Integer NumPrices
ccint(InputBox("How many prices?")) For counter
0 To NumPrices - 1 Prices(counter)
CCur(InputBox("Next price")) Next Until
Loop Open "a\prices.txt" For Input As 1 Do
Until EOF(1) Input 1, Prices(NumPrices)
NumPrices NumPrices 1 Loop
109
Processing Arrays
1. Typical array operations include summing and
averaging the array values and finding the
largest or smallest value in the array. 2.
Working with arrays usually involves a For-Next
loop. 3. Summing Prices array elements involves
using a statement of the form Sum Sum
Prices(Counter) 4. Averaging Prices array
elements involves dividing the Sum by the number
of elements 5. Finding the largest or smallest
value involves multiple comparisons of array
elements. 6. To find the maximum Price, you must
compare each array value to the current highest
price if it is higher, it becomes the highest
price. Do this using For-Next loop and If-then
If Max lt Price(Counter) then Max
Price(counter) end if
110
Code to Find Maximum Value in List
Private Sub cmdFindMax_Click() Dim Counter As
Integer, Largest As Currency Largest
Prices(0) For Counter 1 To NumPrices - 1
If Prices(Counter) gt Largest Then Largest
Prices(Counter) End If Next txtMaxPrice
Format(Largest, "currency") End Sub
111
Finding items and working with multiple lists
1. It is possible to work with multiple list
arrays by matching the index values for the
arrays. 2. Finding a specific array value
involves comparing each array element to the
desired value. A flag is often used to indicate
whether a match was found. 3. The Msgbox can be
used as a function by including multiple
parameters within parentheses. These parameters
can be internal constants and the Msgbox function
returns a value which can be checked to determine
which button was clicked. varMsgBox(message,butt
ons,title)
112
Pseudocode to Find Price for Part Identifier
Begin procedure to find part identifier Input
part identifier Set Flag to false Repeat for
each part in parts list If part identifier
identifier on parts list then Flag True Save
index of part identifier on parts list End
decision End repeat If Flag true Use saved
index to display part identifier and price
Else Display message that part not on parts
list End decision End procedure
113
Code to Find Price for a Part Identifier
Private Sub cmdFind_Click() Dim Counter As
Integer, Results As Integer, FindID as string Dim
Found As Boolean, PriceIndex as
Integer FindPartID InputBox("Input part
identifier to find") Found False For Counter
0 To NumPrices - 1 If FindPartID
PartId(Counter) Then Found True PriceIndex
Counter Exit For End If Next If Found
Then txtFound PartId(PriceIndex) " "
_ Format(Prices(PriceIndex), "Currency") Else Resu
lts MsgBox("Part not found", VbExclamation,
"Price Search") End If End Sub
114
Code to Save Index of Part with Highest Price
Private Sub cmdFindMax_Click() Dim Counter As
Integer, Largest As Currency, MaxIndex as
Integer Largest Prices(0) For Counter 1
To NumPrices - 1 If Prices(Counter) gt Largest
Then Largest Prices(Counter)
MaxIndex Counter End If Next
txtMaxPrice PartId(MaxIndex) " " _
Format(Prices(MaxIndex), "Currency") End Sub
115
Working with Multiple Forms
1. It is possible to have multiple forms in a
project. To display a form, use Object.Show To
hide the form, use Object.Hide 2. A new form can
be added using the ProjectNew Form menu option
or the New Form icon on the toolbar. 3. If a
control on one form is referred to on another
form, the form name must be included as a part of
the control reference.
116
Searching in Strings
Searching for strings using a loop requires
that you use Ucase or Lcase to convert all
strings to the same case. To search for a
substring within a string, you use the
(Instr(string to search, search string)
function. For example, Instr(Go Dogs, D )
returns 4 because D is in the 4th position. If
the character does not exist, Instr returns a
zero. NOTE Instr is case sensitive!!!
117
Code to Search for a Partial Video Name
Private Sub cmdSearch_Click() Dim VideoName As
String, Counter As Integer, NumMatches As
Integer VideoName txtSearch lstVideos.Clear
lstVideos.AddItem "Video Name" For Counter 0
To NumVideos If InStr(UCase(Videos(Counter)),
UCase(VideoName)) gt 0 Then NumMatches
NumMatches 1 lstVideos.AddItem
Videos(Counter) End If Next If NumMatches
0 Then MsgBox ("No matching videos found!
Try again.") ElseIf NumMatches lt 5 Then
lstVideos.AddItem Str(NumMatches) " videos
found" Else lstVideos.Clear MsgBox
("Too many matching videos!") End If End Sub
118
Code to Display Video Information
Private Sub lstVideos_Click() Dim VideoName As
String, Counter As Integer VideoName
lstVideos lstVideos.Clear For Counter 0 To
NumVideos If VideoName Videos(Counter)
Then lstVideos.AddItem VideoName " "
_ Format(VideoPrice(Counter), "currency")
_ " " VideoLoc(Counter) Exit For
End If Next End Sub
119
Two-dimensional Arrays

• When you are working with a table instead of a
  list, you have a 2-dimensional array
• 2-D arrays two subscripts with the first
  subscript referring to the row value and the
  second subscript referring to the column value
• Nest For-next loops are often used to work with
  2-D arrays with the inner loop matching the
  columns and the outer loop matching the rows.

120
Using the Step Commands for Debugging
Stepout of
Step into
The Step Commands
Step Over
If you select Step Into, you can step through
the code, line by line and note the result of the
code in the various windows--Watch, Locals, or
Immediate.
121
Chapter 7Using Functions, Subs, and Modules
122
Design for Expanded Vintage Videos project
123
Membership Management Form
124
Modified Videos Form
125
Using General Procedures

• Event procedures are associated with a particular
  event and are not usually available to other
  forms
• General procedures are used for specific tasks
  that are not associated with an event.
• General procedures are defined in the General
  object of form and then invoked (called)
  elsewhere in the project.
• Two types of general procedures
• subs (subroutines)
• functions

126
Advantages of General Procedures

• Share the abilities.
• Reduce the complexity and redundancy.
• Enhance the adaptability easy to change. Similar
  to the concept of symbolic constants.

127
Relationship between general and event procedures
128
Subs and Functions

• A sub is a unit of code that performs a specific
  tasks but returns no value
• A function is similar to the built in functions
  in that arguments are passed to it and processed
  to compute a single value returned by its name.
• In both case, the arguments (variables passed to
  the sub) will be changed.

129
Primary purposes of subs and functions
130
Working with General Procedures

• General procedures must be created and then
  invoked
• Invoking a function
• variable functionname(arg1, arg2, , argn)
• Invoking a sub
• subname arg1, arg2, , argn

131
Creating Subs and Functions

• To create a sub or function you can
• Use the ToolsAdd Procedure menu command and
  select the type of procedure to add
• or
• simply type the word Sub or Function and press
  Enter after any existing event or general
  procedure
• In either case, then add the parameters

132
Creating a Function

• The definition statement is
• Function FuncName(parameter1 as type, parameter2
  as type, ) as type
• FuncNameltexpressiongt
• End Function
• For example
• Function FindMax(Num1 as Integer, Num2 as
  Integer) as Integer
• An important rule is that the name of the
  function must be assigned a value in the function

133
Creating a Sub

• The general form of the sub definition statement
  is
• Sub SubName (parameter1 as type, parameter2 as
  type, )
• Note that the sub name is not assigned a type
• Example
• Sub Reverse(First as Currency, Second as Currency)

134
Relationship between Sub definition statement and
statement invoking the sub
135
Relationship between Function definition
statement and the statement invoking the function
136
Matching Arguments and Parameters

• For both sub and functions, the number and type
  of arguments in invoking statement must match the
  number and type of parameters in the procedure
  definition statement
• In both the argument and parameter list,
  fixed-size arrays are referenced by the name of
  the array followed by parentheses

137
Function to Compute Income Taxes

• Public Function ComputeTaxes(NumExm As Integer, _
• GrossIncome As Currency) as Currency
• Dim TaxIncome As Currency
• TaxIncome GrossIncome - 4150 - NumDep 2650
• Select Case TaxIncome
• Case Is lt 24650
• ComputeTaxes 0.15 TaxIncome
• Case Is lt 59750
• ComputeTaxes 3697.50 0.28 (TaxIncome -
  24650)
• Case Is lt 124650
• ComputeTaxes 13525.50 0.31 (TaxIncome -
  59750)
• Case Is lt 271050
• ComputeTaxes 33644.50 0.36 (TaxIncome -
  124650)
• Case Else
• ComputeTaxes 86348.5 0.396 (TaxIncome -
  271050)
• End Select
• End Function

138
Sub to Reverse two values
Sub Reverse(First as Currency, Second as
Currency) Dim Temp as Currency Temp First First
Second Second Temp End sub
139
Sort the Items in a List Bubble Sort

• Bubble sort is the simplest, although not the
  fastest, sorting method.
• Pseudocode of Bubble Sort
• Repeat until not reversals made
• Repeat for each pair of the items
• If the two items are not in the order
• Reverse the items
• End if
• End inner repeat
• End outer repeat

140
Sub to Sort arrays

• Public Sub Sort(FirstList() As Currency,
  SecondList() _
• As String, NumList As Integer)
• Dim NoReversal As Boolean, Counter As Integer
• NoReversal False
• Do Until NoReversal
• NoReversal True
• For Counter 0 To NumList - 2
• If FirstList(Counter) gt FirstList(Counter
  1) Then
• Reverse FirstList(Counter),FirstList(Counter
  1)
• Reverse SecondList(Counter),SecondList(Counter1)
  
• NoReversal False
• End If
• Next
• Loop
• End Sub
• To call the sub, enter Sort Prices(),PartID(),Num
  Prices

141
Global Declarations and the Code Module

• In a global declaration, the scope of global
  variables covers all parts of the project. They
  must be defined in a code module.
• Use Public statement to declare variables
• Public varName1 as type, varName2 as type,
• Global variables cant be defined again in
  procedures.
• The Code Module is the section of pure code that
  is known to all parts of the project.

142
Scope of Global Variables
143
Use of String Functions

• Len(string)--returns number of characters in
  string
• Left(string, N) or Right(string, N)--returns the
  leftmost or rightmost N characters in a string
• Mid(String,P,N)--returns N characters in a string
  starting at Pth character
• Trim(String), Ltrim(string) or Rtrim(String) --
  trims blank characters from left (right) end of
  string

144
Passing by Value in Subs

• If there is a two-way communication between
  arguments and parameters, then you have passing
  by reference
• If there is a one-way communication between (you
  dont want the variables in mail procedure being
  affected), then you have passing by value
• To pass by value, add the keyword ByVal prior to
  a variable in the procedure definition statement
• E.g. Sub Reverse(ByVal First As Currency, Second
  As Currency)

145
Global Variable vs Pass Variable

• To exchange the data among variables in different
  procedures, both methods can be used.
• Global variables will be changed anywhere they
  are used. Difficult to debug.
• Using the variable pass method can keep the
  privacy of variables.

146
Chapter 8Security, Menus, and Files
147
Security

• Passwords are often used to control access to a
  computer or software program
• Passwords should be at least 6 characters in
  length and something that cannot be easily
  guessed
• It should not be possible to move, resize, or
  bypass the password form in VB and it should be
  the Startup object.
• The Tag property for a textbox can be used for
  the password and the PasswordChar property can be
  used to hide the password as it is entered.
• A user should be given a set number of chances
  to enter the correct password.

148
Menu Systems in VB

• A menu system for a form can be created using the
  Menu Editor.
• Menu bar options as well as submenus can be
  created with this editor
• Menu and submenu items have caption and name
  properties (the prefix is mnu)
• Code is written for menu items just like for
  other event procedures (Click the menu item to
  enter)
• Menu options are always click events
• Most menus contain File and Help menu bar options
  in addition others specific to the application

149
Access Key and Shortcut Key

• Assign before one of the letters of a controls
  CAPTION to make the control accessible by key
  combination ALTletter (available to Buttons or
  Menu items)
• Assign Ctrl or Shift or Function Key plus a
  letter or a Function Key to create a shortcut key
  and make to control be accessible by keyboard.
  (available to Menu items)

150
Custom Controls

• Beyond the standard controls, there are some
  custom controls to be added.
• To add custom controls, select menu
  ProjectComponents and then make ticks.
• Useful controls
• Masked Edit Control
• Common Dialog Control

151
Important Properties of Masked Edit Box

• Format Decide the display format of the box.
• Mask Decide the input format of the box.
• In Microsoft Library, choose help index MaskEDBox
  to see how to use this control.

152
Important Properties Methods of Common Dialog
Control

• Filter sets the filters that are displayed in
  the Type list.
• FilterIndexSets a default filter for dialog box.
• ShowOpen Displays the CommonDialog control's
  Open dialog box.
• ShowSave Displays the CommonDialog control's
  Save As dialog box.

153
Use Common Dialog Control

• The Filter property of the common dialog control
  is used to display a list of files
• It has the form
• dlgName.Filter description1filter1descr
  iption2filter2etc
• The FilterIndex property determines the default
  file type
• When a file is selected or a filename entered,
  this becomes the Filename property for the dialog
  box
• The FreeFile function returns an unused file
  number and the On Error Goto statement causes
  control to jump to a label when an error is
  encountered. Both ar useful in working with
  files.

154
Other File Operations

• A file can be opened from a common dialog box
  with the ShowOpen method
• The contents of the file can be input using the
  Input function
• Input(number, filenumber) where number
  number of characters in file that is identified
  by filenumber
• The LOF(FileNumber) function can be used to
  determine the number of characters in a file
• A memo can be saved by printing its contents to a
  file--its common to query the user to save the
  file if it has been changed.

155
Error Handling

• As a mature software, it shouldnt be terminated
  by any errors.
• To direct the error handling, use On Error
  statement
• On Error Goto ltlinegt Go to the handling block
  started by the line
• On Error Resume Next Go to next statement after
  the error position
• On Error Goto 0 Disable the error handling

156
Error Handling Block

• Begins with the line code with a colon ().
• Should use Exit Sub at the places needed.
• Use Err object to detect the error. Useful
  properties are
• .Number The error code number.
• .Source Name of the current Visual Basic
  project.
• Description Error description.

157
Some Useful Functions

• Input(NumChar, FileNum) Returns a string from
  a file opened with the FileNum. The length is
  decided by NumChar.
• LOF(FileNum) Returns the length of the file
  opened with FileNum

158
Creating a Memo Editor

• Creating a memo editor in VB involves using a
  textbox as the location of the text and a menu
  system for the various editor commands
• The textbox should have its Multiline property
  set to true and its Scrollbars property set to
  vertical.
• The Form_Resize event occurs when the user
  changes forms size--it can be used to cause the
  memo text box to fill its form by setting the
  Height and Width properties to ScaleHeight and
  ScaleWidth

159
The Memo Editor File Menu

• The File Menu should have options to begin a new
  memo, open an existing memo, save a memo under
  the current name or a new one, close the memo,
  print it, or exit the memo editor.
• Key to the File Menu is the use of the common
  dialog control which must be added to the Toolbar
  with the ProjectComponents VB menu option before
  being added to the form
• The common dialog control (with dlg prefix) can
  be used to open or save files with the ShowOpen
  and ShowSave methods