Introduction to Programming

1
Introduction to Programming

• Fundamentals of Programming in Visual Basic

2
Outline and Objective

• Visual Basic Objects
• Visual Basic Events

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

3
The Initial Visual Basic screen
Toolbar
Menu bar
Project Explorer window
Toolbox
Properties window
Form
4
Steps to Create a Visual Basic Program

• 1. Create the Objects
• 2. Set Properties
• 3. Write the Code for each Event

5
Four most useful Visual Basic Controls

• Text Boxes
• Labels
• Command Buttons
• Picture Boxes

6
A Text Box Walkthrough

• Double-click on Text Box to add a Text Box to
  your form
• Activate the Properties window (Press F4)
• Set values of Properties for Text Box

7
A Text Box Walkthrough
Text box
8
Some Useful Properties

• Name
• Caption

• Border style
• Visible
• Back Color
• Alignment
• Font

9
Naming Objects

• Use the Property window to change the Name
  property of an object
• Good Programming habit is that each name begins
  with three letter prefix that identifies the type
  of control.

10
Naming Objects
11
Visual Basic Events

• Code is a set of statements that will be executed
  when you run a program.
• Write Code for each Event.
• Most Events are associated with Objects.
• The code for each event is called an Event
  Procedure.

12
The steps for creating a VB program

• Create the Interface.
• Set Properties for the objects.
• Write the code that executes when event occur.

13
An Event Procedure Walkthrough

• Create the interface.
• Set Properties.
• Double click on the object to open the Code
  window.
• Click on the Procedure box to find the event
• Write the code for that event.

14
Example of An Event

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

15
More Example

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

16
Components of Visual BASIC Statements

• Variables
• Keywords (reserved words)
• Constants

17
Variables

• A storage location in main memory whose value can
  change 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

18
Rules for Creating Variable Names

• Must begin with a letter.
• Can contain letters, numeric digits.
• Can have up to 255 characters.
• Can Not be restricted keyword.

19
Numeric Variables

• Used to store Numbers .
• The value is assigned either by the programmer or
  by calculation.

20
Valid Numeric Variable Names

• timeElapsed
• taxRate
• speed
• n
• celsius

21
Invalid Numeric Variable Names

• maximum/average
• 1stChoice
• square yard

22
Constant

• Similar to a variable, but 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
Numeric Constants in a Statement

• tax 0.02 (income - 500 dependence)
• sum 2 x 4.6 y

26
String Constants

• A group of alphanumeric data consisting of any
  type of symbols.

27
Valid String Constants

• A rose by any other name
• Down By the Sea Shore
• 134.23
• She said, stop , thief!

28
Invalid String Constants

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

29
Arithmetic Operations Hierarchy of Operations

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

30
Examples

• Evaluate the following expressions
• x 3 6 - 12 / 3
• x 4 (8 / 4)
• y 12 6 / (3 (10 - 9))
• z 5 4 2
• m 6 / 3 3

31
Keywords

• Words that have predefined meaning to Visual
  Basic .
• Can Not be used as variable names.
• Example Print
• Cls
• If
• While

32
Visual Basic Print Statement

• Print Is a method used to display data on the
  screen or printer.
• Can be used to print value of variables.
• Can be used to print value of arithmetic
  expressions .

33
Example 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 2 (3 4)
• End Sub

34
Example of Print Statement

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

35
Example

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

36
Output

• 10 3

37
Internal Documentation

• An apostrophe () can be used to indicate
  comments comments are ignored by Visual Basic.
• The keyword Rem can also be used instead of an
  apostrophe for comments.
• Remarks can also be placed after program
  statement too.

38
Visual Basic Assignment Statement

• The statement var expr assigns the value of the
  expression to the variable.
• Assigns the value of the expression on the right
  to the variable on the left.

39
Example

• Private Sub cmdCompute_Click( )
• picResults.Cls
• a 5
• b 4
• c a (2 b)
• picResults.Print c
• End Sub

40
Valid Assignment Statement

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

41
Invalid Assignments

• 10 count
• count 1 count

42
String Variables

• A String variable stores character strings.
• The rules for naming string variables are
  identical to those of numeric variables.
• When a String variable is first declared, its
  value is the null string. (that is, the empty
  string).

43
Example of String Variable

• 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

44
Concatenation

• Two string can be combined with the concatenation
  operation.
• Concatenation is represented with the ampersand (
  ) sign.

45
Example of Concatenation

• strVar1 Hello
• strVar2 World
• picOutput.Print strVar1 strVar2

46
Example of Concatenation

• txtBox.Text 32 CHR(176) Fahrenheit

47
Data Types

• Each variable in the program is assigned to a
  data type.

48
Declaring Variable Types

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

49
Data Types

• Single-precision numeric variable Stores real
  numbers
• Double-precision numeric variable Stores real
  numbers with many digits
• Integer Stores integers
• Long integer Stores integers with many digits

50
Using Text Boxes for Input/Output

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

51
Using Text Boxes for Input/Output

• Therefore, the contents of a text box should be
  changed to a number before being assigned to a
  numeric variable.
• Val (txtBox.Text) changes the input string into a
  number.
• Example
• numVar Val (txtBox.Text)

52
Example (convert miles to furlong 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
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

54
Reading Data from Files

• 1. Choose a number to be the reference number to
  the file.
• 2. Set the mode in which the file is to be used
• Input
• Output
• Append
• 3. Read the data sequentially using Input
  statement.
• 4. Close the file .

55
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 from the file
Read the data and assign it to num1
Close the file
56
Example of Reading from a File

• Open Data.txt for Input As 1
• Input 1,num1, num2
• picOutput.Print num1num2
• Close 1

57
Input from an Input Box

• Use Text Box to obtain input.
• For one piece of input use input box instead of
  a text box
• Input Box is a predefined dialog box.

58
Syntax for an Input Box

• stringVar InputBox (prompt, title)

59
Example of Input 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 box would pop up
60
Using Message Box for Output

• Use message box to get the users attention.
• Message box is a predefined dialog box too.

61
Syntax for Message Box

• MsgBox prompt, , title

62
Example of Message Box

• MsgBox Nice try, but no cigar, , Consolation

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

• Create user friendly output.
• In the Print method, control of the spacing of
  the output is controlled by the following devices.

64
Formatting the Output

• Semicolon
• Comma
• Tab Function

65
Semicolons

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

66
Example of Semicolon

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

Space here
Space here
67
Example of Semicolon

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

Two spaces
One space
68
Commas

• The next value output is placed in the next
  available print zone.

69
Print Zones

• Each print zone is 14 positions wide.

70
Example of Print Zone

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

Column 29
Column 15
Column 1
71
Example of Commas

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

Column 29
72
Tab Function

• Starts output in the specified column.
• It provides more flexibility in formatting.
• Only use Semicolons with the Tab function.
• Only can be used to advance the print position.

73
Example of Tab Function

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

Column 25
Column 3
74
Example of Tab

• Example
• picOutput.Print TAB(25) 5 TAB(15) 4 TAB(5) 3
• Output Screen
• 5
• 4
• 3

Column 25
Column 15
Column 5
75
Functions

• What is a function?
• What are advantages of using functions?
• How do you use a function?

76
What is a function

• A sub program designed to perform a specific
  task.
• A sub program designed to return a single value
  to the calling program.

77
Types of Functions

• Built-In functions (library)
• User-defined functions

78
Example

• x Sqr(225)
• y Int (2.7)
• str1 Left (John Smith, 4)
• number Rnd

79
Types of Standard Functions

• Numeric Functions (manipulate numbers)
• String Functions (manipulate strings)

80
Numeric Functions
81
Example of Numeric Functions

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

82
Commonly-Used String Functions

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

83
Commonly-Used String Functions

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

84
Commonly-Used String Functions

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

85
Commonly-Used String Functions

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

86
String-Related Numeric Functions

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

87
String-Related Numeric Function

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

88
Format Function

• The format functions provide detailed control of
  how numbers, dates, and strings are displayed.

89
Examples of Format Functions

• FormatNumber (12345.678, 1) 12,345.6
• FormatCurrency (12345.678, 2) 12,345.68
• FormatPercent (.185, 2)
  18.50
• FormatNumber (1 Sqr(2), 3) 2.414

90
Format Function

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

91
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

92
Example

• FormatDateTime (9-15-99, vbLongDate)
• Output Wednesday, September 15, 1999

93
Rnd Function

• Returns a random number from 0 up to 1.
• (excluding 1).
• Example Displays a random integer from 1 through
  6.
• picBox.Print Int(6 Rnd) 1

94
Examples of Using Rnd Function

• An integer from 1 through 100?
• A number from 2 through 4 (excluding 4)?
• An even integer from 2 through 100 ?
• Either 0 or 1?