Fundamentals of Programming in Visual Basic

1
Chapter 3

• Fundamentals of Programming in Visual Basic

2
Outline and Objectives

• Visual Basic Objects
• Visual Basic Events

• Numbers
• Strings
• Input/Output
• Built-In Functions

3
The Initial Visual Basic Screen
Menu bar
Project Explorer window
Toolbar
Toolbox
Properties window
Description pane
Form
Form Layout window
Project Container window
4
Steps to Create a Visual Basic Program

• 1. Create the interface by placing controls on
  the form
• 2. Set properties for the controls and the form
• 3. Write code for event procedures associated
  with the controls and the form

5
Four Useful Visual Basic Controls

• Text Boxes
• Labels
• Command Buttons
• Picture Boxes

6
Placing a Text Box on a Form

• Double-click on the text box icon in the toolbox
  to add a text box to your form
• Activate the properties window (Press F4)
• Set values of properties for text box

7
Placing a Text Box on a Form
Text box
8
Some Useful Properties of Objects

• Name
• Caption
• Text (for Text Boxes)

• BorderStyle
• Visible
• BackColor
• Alignment
• Font

9
Example
10
Naming Objects

• Use the Property window to change the Name
  property of an object
• Good programming practice dictates that each
  object name begins with a three letter prefix
  that identifies the type of object.

11
Naming Objects
12
Naming Objects

• An Object Name
• Must Start with a letter
• Can include numbers and underscore (_)
• Cannot include punctuation or spaces
• Can be a maximum of 40 characters

13
Visual Basic Events

• Code is a set of statements that instruct the
  computer to carry out a task.
• Code can be associated with events
• When an event occurs, the code associated with
  that event (called an Event Procedure) is
  executed.

14
Creating An Event Procedure

• Double-click on an object to open a Code window.
  (The empty default event procedure will appear.
  Click on the Procedure box if you want to display
  a different event procedure.)
• Write the code for that event procedure.

15
Example of An Event Procedure

• Private Sub objectName_event ( )
• statements
• End Sub
• Private Sub txtOne_GotFocus( )
• txtOne.Font.Size 12
• txtOne.Font.Bold False
• End Sub

16
More Examples

• Private Sub cmdButton_Click( )
• txtBox.ForeColor vbRed
• txtBox.Font.Size 24
• txtBox.Text Hello
• End Sub

17
Exercises
11. Private Sub cmdButton_Click( ) frmHi
Hello End Sub 12. Private Sub
cmdButton_Click( ) txtOne.ForeColor red
End Sub
18
Exercises
13. Private Sub cmdButton_Click( )
txtBox.Caption Hello End Sub 16.
Private Sub cmdButton_Click( )
txtOne.MultiLine True End Sub

19
Tips

• Most Properties can be set or altered at run time
  with code.
• cmdButton.visible False
• The BorderStyle and MultiLine properties of a
  text box can only be set from the properties
  window
• surrounds Caption, Name, Font.Name or strings
  not True, vars or numeric constants

20
Color Constants

• At design time colors are selected from a palette
• At run time the eight most common colors can be
  assigned with the color constants

21
Components of Visual Basic Statements

• Constants
• Variables
• Keywords (reserved words)

22
Constant

• Can NOT change during the execution of a program.
• Types of Constants
• numeric constants
• string constants

23
Valid Numeric Constants

• Integer Real
  number
• -2987
  -1900.05
• 16
  0.0185
• 5
  10.56

24
Invalid Numeric Constants

• 14,005.5
  6.8
• 33-
  190.04
• 15 78
  3.5

25
Arithmetic Operations

• Operator Operation Basic expression
• Exponentiation A
  B
• Multiplication A
  B
• / Division
  A / B
• Addition
  A B
• - Subtraction
  A - B

26
Scientific Notation

• Largest/Smallest number a Single can handle

27
Variables

• A storage location in main memory whose value can
  be changed during program execution.
• These storage locations can be referred to by
  their names.
• Every variable has three properties a Name, a
  Value, and a Data Type.
• Types of variables Numeric and String

28
Rules for Naming Variables

• Must begin with a letter
• Must contain only letters, numeric digits, and
  underscores ( _ )
• Can have up to 255 characters
• Cannot be a Visual Basic language keyword (for
  example, Sub, End, False)

29
Keywords

• Words that have predefined meaning to Visual
  Basic .
• Can Not be used as variable names.
• Examples
• End - Print
• Sub - Let
• If -Select
• While -Call

30
Numeric Variables

• Used to store numbers
• Value is assigned by a statement of the form
  numVar expression
• The variable must be on the left and the
  expression on the right.

31
Assignment Statement

• The statement var expr assigns the value of the
  expression to the variable
• tax 0.02 (income - 500 dependents)
• sum 2 x 4.6 y

32
Valid Numeric Variable Names

• timeElapsed
• taxRate
• speed
• n
• celsius

33
Invalid Numeric Variable Names

• maximum/average
• 1stChoice
• square yard

34
Valid Assignment Statements

• count count 1
• num 5
• count count num /2

35
Invalid Assignment Statements

• 10 count
• count 1 count

36
Visual Basic Print Statement

• Print is a method used to display data on the
  screen or printer.
• Can be used to display values of variables or
  expressions

37
Examples of Print Statements

• Private Sub cmdCompute_Click()
• picResults.Print 3 2
• picResults.Print 3 - 2
• picResults.Print 3 2
• picResults.Print 3 / 2
• picResults.Print 3 2
• picResults.Print 2 (3 4)
• End Sub

38
Examples of Print Statements

• picOutput.Print speed
• picOutput.Print taxRate
• picOutput.Print Class average is total / 3

39
Examples of Print Statements

• x 15
• y 5
• picOutput.Print (x y) / 2, x / y
• Output
• 10 3

40
String Constants

• A sequence of characters treated as a single item
• The characters in a string must be surrounded by
  double quotes ( )

41
Valid String Constants

• A rose by any other name
• 9W
• 134.23
• She said, stop , thief!

42
Invalid String Constants

• Down by the Seashore
• 134.24
• She said, Stop, thief!

43
String Variables

• A string variable stores a string.
• The rules for naming string variables are
  identical to those for naming numeric variables.
• When a string variable is first declared, its
  value is the empty string.

44
String Variable Example

• Private Sub cmdShow_Click()
• picOutput.Cls
• phrase "win or lose that counts."
• picOutput.Print "It's not whether you "
  phrase
• picOutput.Print "It's whether I " phrase
• End Sub

45
Concatenation

• Two strings can be combined by using the
  concatenation operation.
• The concatenation operator is the ampersand ()
  sign.

46
Examples of Concatenation

• strVar1 HellostrVar2 WorldpicOutput.Prin
  t strVar1 strVar2
• txtBox.Text 32 Chr(176) Fahrenheit

47
Declaring Variable Types

• Use the Dim statement to declare the type of a
  variable.
• Examples
• Dim number As Integer
• Dim flower As String
• Dim interestRate As Single

48
Data Types

• Single a numeric variable that stores real
  numbers
• Integer a numeric variable that stores integer
  numbers (from -32768 to 32767)
• String a variable that stores a sequence of
  characters

49
Using Text Boxes for Input/Output

• The contents of a text box are always a string.
• Numbers can be stored in text boxes as strings.

50
Using Text Boxes for Input/Output

• The contents of a text box should be converted
  to a number before being assigned to a numeric
  variable.
• Val(txtBox.Text) gives the value of a numeric
  string as a number
• Example Dim numVar as Single numVar
  Val(txtBox.Text)

51
Example (convert miles to furlongs and vice versa)

• Example 1
• xString528
• xValueVal(xString) ? xValue528
• Example 2
• yValue428
• yStringStr(yValue) ? yString428

52
Example (convert miles to furlongs and vice versa)

• Private Sub txtFurlong_LostFocus()
• txtMile.Text Str(Val(txtFurlong.Text / 8))
• End Sub
• Private Sub txtMile_LostFocus()
• txtFurlong.Text Str(8 Val(txtMile.Text))
• End Sub

53
Program Documentation

• An apostrophe (') is used to indicate that the
  remainder of the line is a comment. (Comments are
  ignored by Visual Basic.)
• Remarks can appear on a separate line or
  following a Visual Basic statement.

54
The KeyPress Event Procedure

• Private Sub txtCharacter_KeyPress(KeyAscii As
  Integer)
• txtCharacter.Text ""
• picOutput.Cls
• picOutput.Print Chr(KeyAscii) " has ANSI
  value" KeyAscii
• End Sub

55
Reading Data from Files

• 1. Choose a number to be the reference number for
  the file
• 2. Execute an Open statement
• 3. Read the data sequentially using Input
  statements
• 4. Close the file

56
Example of Reading from a File
Open the file

• Open DATA.TXT For Input As 1
• Input 1, num1
• Input 1, num2
• picOutput.Print num1num2
• Close 1

Reference number
Read the data and assign it to num1
Close the file
57
Example of Reading from a File

• Open DATA.TXT For Input As 1
• Input 1, num1, num2
• picOutput.Print num1num2
• Close 1

58
Reading Data from Files

• Files can be also used for output rather than
  input. More about files will be discussed in
  chapter 8 and 9.

59
Input Dialog Box

• An input dialog box can be used to obtain a
  single item of input from the user
• Presents a window (dialog box) requesting input
• Syntax stringVar InputBox(prompt, title)

60
Example of an Input Dialog Box

• Private Sub cmdDisplay_Click()
• Dim fileName As String, prompt As String,
  title As String
• Dim houseNumber As Single, street As String
• prompt "Enter the name of the file
  containing the information."
• title "Name of File"
• fileName InputBox(prompt, title)
• Open fileName For Input As 1
• Input 1, houseNumber
• Input 1, street
• picAddress.Print "The White House is at"
  houseNumber street
• Close 1
• End Sub

After executing, an input dialog box will pop up
61
Using Message Dialog Box for Output

• The message dialog box is used to present a
  pop-up window containing information for the user
• Syntax MsgBox prompt, , title

62
Example of a Message Dialog Box

• MsgBox Nice try, but no cigar, , Consolation

Stays on the screen until the user presses OK
63
Formatting the Output

• Create easily readable output
• In the Print method, the spacing of the output is
  controlled by the following devices
• semicolon
• comma
• Tab function

64
Semicolons

• The next value output is placed in the next
  column position.
• Example
• picOutput.Print Patrick Jon
• Output
• PatrickJon

65
Example of Semicolon

• picOutput.Print Patrick Jon
• Output Screen
• Patrick Jon

Space here
Space here
66
Example of Semicolon

• picOutput.Print 100 -200 300
• Output Screen
• 100 -200 300

Two spaces
One space
67
Commas

• A comma in a Print method causes the next value
  output to be placed in the next available print
  zone.
• Each print zone is 14 positions wide.

68
Using Commas

• Example
• picOutput.Print SEE, YOU, SOON
• Output Screen
• SEE YOU SOON

Column 29
Column 15
Column 1
69
Using Commas

• Example
• picOutput.Print abc123def456ghi, whatever
• Output Screen
• abc123def456ghi whatever

Column 29
Column 15
Column 1
70
Using Commas

• A print zone can be skipped by typing consecutive
  commas
• Example
• picOutput.Print HOURLY, , PAY
• Output Screen
• HOURLY PAY

Column 29
71
Tab Function

• Specifies the column where output will start
• Use only semicolons with the Tab function
• Can only be used to advance the print position
  (cannot move backwards)

72
Example of Tab Function

• Example
• picOutput.Print Tab(3) Hi there! Tab(25)
  Bye!
• Output Screen
• Hi there! Bye!

Column 25
Column 3
73
Example of Tab Function

• Example
• picOutput.Print Tab(3) Hi there! Tab(5)
  Bye!
• Because column 5 is already occupied by the
  previous string, the output will be at the next
  line
• Output Screen
• Hi there!
• Bye!

Column 3
Column 5
74
Built-In Functions

• Take one or more input values and return an
  output value
• A means provided by Visual Basic for carrying out
  small, common tasks
• Types of Built-In functions
• Numeric functions (manipulate numbers)
• String functions (manipulate strings)

75
Numeric Functions
76
Example of Numeric Functions

• Private Sub cmdEvaluate_Click()
• Dim n As Single, root As Single
• n 6.76
• root Sqr(n)
• picResults.Print root Int(n) Round(n,1)
• End Sub
• Output 2.6 6 6.8

77
Commonly-Used String Functions

• Function Left(Penguin, 4)
• Purpose Returns the number of characters
  specified, starting at the beginning of the
  string

78
Commonly-Used String Functions

• Function Right(Gotham City, 4)
• Purpose Returns the number of characters
  specified from the end of the string

79
Commonly-Used String Functions

• Function Mid(Commissioner, 4, 3)
• Purpose Returns the substring starting at the
  position indicated by the first number and
  continuing for the length specified by the second
  number

80
Commonly-Used String Functions

• Function UCase(Yes)
• Purpose Converts any lowercase letters in a
  string to uppercase

81
String-Related Numeric Functions

• Function InStr(John Smith, m)
• Purpose Searches for the first occurrence of
  one string in another and gives the position at
  which the string is found

82
String-Related Numeric Function

• Function Len(John Smith)
• Purpose Returns the number of characters in the
  string.

83
Strings and string Functions examples

• picBoard.print len(left(welcome,3))
• picBoard.print UCase(left(welcome,3))

84
Format Functions

• The format functions provide detailed control of
  how numbers, dates, and strings are displayed.
• Examples
• FormatNumber (12345.678, 1)
  12,345.7
• FormatCurrency (12345.678, 2) 12,345.68
• FormatPercent (.185, 2)
  18.50
• FormatNumber (1 Sqr(2), 3)
  2.414

85
Format Function

• Format (expr, _at_.._at_)
• Purpose The value of this function is the value
  of expr right justified in a field of n spaces,
  where n is the number of _at_ symbols.

86
Format Examples

• Format(12345, _at__at__at__at__at_) 12345
• Format(123, _at__at__at__at__at_) 123
• Format(123.4, _at__at__at__at__at_) 123.4

87
Examples
88
Examples
89
Examples
90
FormatDateTime Example

• FormatDateTime (9-15-04, vbLongDate)
• Output Monday, September 15, 2004

91
Rnd Function

• Returns a random number from 0 to 1.
• (excluding 1).
• Example
• picBox.Print Rnd
• Output Displays a random number from 0 to 1 (0
  included and 1 excluded).
• Example
• picBox.Print Rnd 5
• Output Displays a random number from 5 to 6 (5
  included and 6 excluded).

92
Rnd Function

• Example
• picBox.Print Int(Rnd)
• Output Displays 0.
• Example
• picBox.Print Int(Rnd 5)
• Output Displays 5.
• Example
• picBox.Print Int(Rnd) 5
• Output Displays 5.

93
Rnd Function

• Example
• picBox.Print Int(5Rnd)
• Output Displays a random Integer from 0 to 4 (0
  and 4 included).
• OR
• Output Displays a random Integer from 0 to 5 (0
  included and 5 excluded)
• Example
• picBox.Print Int(5Rnd) 2
• Output Displays a random Integer from 2 to 6 (2
  and 6 included).