1. Tony Gaddis Kip Irvine STARTING OUT WITH Visual Basic 2008
FOURTH EDITION
Tony Gaddis
Haywood Community College
Kip Irvine
Florida International University

2. 8 Chapter Arrays, Timers, and More
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

3. Introduction
Arrays are like groups of variables that allow you to store sets of similar data
A single dimension array is useful for storing and working with a single set of data
A multidimensional array can be used to store and work with multiple sets of data
Array programming techniques covered
Summing and averaging all the elements in an array
Summing all the columns in a two-dimensional array
Searching an array for a specific value
Using parallel arrays

4. 8.1 Arrays An Array Is Like a Group of Variables With One Name
You Store and Work Values in an Array by Using a Subscript
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

5. Array Characteristics
An array stores multiple values of same type
Like a group of variables with a single name
For example, the days of the week might be:
a set of 7 string variables
with a maximum length of 9 characters
All variables within an array are called elements and must be of the same data type
You access the elements in an array through a subscript

6. Subscript Characteristics
A subscript, also called an index, is a number that identifies a specific element within an array
Subscript numbering works like a list box index:
Subscript numbering begins at 0
1st element in an array is always subscript 0
Last element is total number of elements – 1
An array with 7 elements refers to the 1st element as subscript 0 and the last element as subscript 6

7. Declaring an Array ArrayName is the variable name of the array
Dim ArrayName(UpperSubscript) As DataType
ArrayName is the variable name of the array
UpperSubscript is the value of the array's highest subscript
Must be a positive whole number
DataType may be any Visual Basic data type
VB knows an array is declared when name is followed by parentheses with number of elements

8. Array Declaration Example
Dim intHours(5) As Integer
intHours(0) intHours(1) intHours(2) intHours(3) intHours(4) intHours(5)
Note that 6 elements are available when an array with an upper subscript of 5 is declared
Each element is an integer type

9. Default Initialization
All elements of an Integer array are initialized to zero
Same initialization as an integer variable
Each array element is initialized exactly the same as a simple variable of that data type
A Single is initialized to zero (0.0)
A String is initialized to nothing (empty string)

10. Implicit Array Sizing & Initialization
An array can be initialized when declared
Example:
This array is implicitly sized
Upper subscript value is left blank
Number of elements implied from initialization
Upper subscript of 5 implied by this example
This results in a 6 element array
Elements are assigned the values shown
Dim intNumbers() As Integer = {2, 4, 5, 7, 9, 12}

11. Named Constant as Upper Subscript
A named constant may be used as an array's highest subscript instead of a number
This is a common use for named constants
Highest subscript is often used multiple times
If highest subscript changes, use of a named constant allows it to be changed in one place
Const UPPER_SUB As Integer = 100
Dim array(UPPER_SUB) As Integer

12. Working With Array Elements
Simply include the subscript to use an array element like an ordinary variable
intNumbers(2) refers to 3rd element of array
intNumbers(0) = 100
intNumbers(1) = 200
intNumbers(2) = 300
intNumbers(3) = 400
intNumbers(4) = 500
intNumbers(5) = 600
decPay = intHours(3) * decRate
intTallies(0) += 1
MessageBox.Show(decPay(5).ToString())

13. Arrays and Loops Loops are frequently used to process arrays
Use a loop to prompt for 10 values
Use a loop to reset values in the strNames array to an empty string
Dim intNbrs(9) as Integers
Dim intCount As Integer
For intCount = 0 To 9
intNbrs(intCount) = CInt(InputBox("Enter number"))
Next intCount
Dim strNames(999) as String
Dim intCount As Integer
For intCount = 0 To 999
strNames(intCount) = ""
Next intCount

14. Array Bounds Checking
Visual Basic checks each subscript value of each array reference used at run time
A subscript is invalid if it is
Negative
Greater than the UpperSubscript declared
An invalid subscript causes VB to throw a run-time exception
Bounds checking is not done at design time

15. For Each Loop Array Processing
A For…Each loop is similar to a For…Next
Iterates for each element in the array
strName is assigned the value of the next array element at each iteration
Tutorial 8-1 demonstrates array processing
Dim strEmployees As String() = {"Jim", "Sally", _
"Henry", "Jean", "Renee"}
Dim strName As String
For Each strName In strEmployees
MessageBox.Show(strName)
Next strName

16. Use For Each To Sum an Array
Private intArray() as Integer = {10, 20, 90, -20)
Dim intSum as Integer = 0
For Each intVal as Integer in intArray
intSum = intSum + intVal
Next
Start of iteration 1 intVal = 10 intSum = 0
End of iteration 1 intVal = 10 intSum = 10
Start of iteration 2 intVal = 20 intSum = 10
End of iteration 2 intVal = 20 intSum = 30
Start of iteration 3 intVal = 90 intSum = 30
End of iteration 3 intVal = 90 intSum = 120
End of iteration 4 intVal = -20 intSum = 120
Start of iteration 4 intVal = -20 intSum = 100

17. Use For Each To Find Largest Value
Dim intArray() as Integer = {10, 20, 90, -20)
Dim intLargest as Integer = intArray(0)
For Each intVal as Integer in intArray
If intVal > intLargest Then intLargest = intVal
Next
Start of iteration 1 intVal = 10 intLargest = 10
End of iteration 1 intVal = 10 intLargest = 10
Start of iteration 2 intVal = 20 intLargest = 10
End of iteration 2 intVal = 20 intLargest = 20
Start of iteration 3 intVal = 90 intLargest = 30
End of iteration 3 intVal = 90 intLargest = 90
End of iteration 4 intVal = -20 intLargest = 90
Start of iteration 4 intVal = -20 intLargest = 90

18. More About Array Processing
8.2
Arrays Have Many Uses & Many Programming Techniques Can Be Applied to
For Example, Arrays Are Used to Total Values or Search for Data
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

19. Determining Number of Elements
Arrays have a Length property that holds the number of elements in the array
Note that length is number of array elements, not the upper subscript of the array
Length property always 1 greater than the upper subscript
Dim intValues(25) As Integer
For intCount = 0 to (intValues.Length – 1)
MessageBox.Show(intValues(intCount).ToString)
Next intCount

20. Total the Values in an Array
Variable to hold sum (intTotal)is initialized to zero prior to loop
Iterate over all elements, adding each element to intTotal
Dim intUnits(24) as Integer ‘Declare array
Dim intTotal As Integer = 0 'Initialize accumulator
Dim intCount as Integer ‘Declare loop counter
‘Find total of all values held in array
For intCount = 0 To (intUnits.Length – 1)
intTotal += intUnits(intCount)
Next intCount

21. Average the Values in an Array
Similar to previous example but then divides total by number of elements to get average
Dim intUnits(24) as Integer ‘Declare array
Dim intTotal As Integer = 0 'Initialize accumulator
Dim dblAverage as Double ‘Declare average var
Dim intCount as Integer ‘Declare loop counter
‘Find total of all values held in array
For intCount = 0 To (intUnits.Length – 1)
intTotal += intUnits(intCount)
Next intCount
‘Use floating-point division to compute average
dblAverage = intTotal / intUnits.Length

22. Find Highest & Lowest Array Values
Pick first element as the highest
Search rest of array for higher values
If a higher value is located, save the value
Use similar logic to find lowest value
Dim intNumbers(24) as Integer
Dim intCount as Integer
Dim intHighest as Integer = intNumbers(0)
For intCount = 1 To (intNumbers.Length - 1)
If intNumbers(intCount) > intHighest Then
intHighest = intNumbers(intCount)
End If
Next intCount

23. Copy Values in One Array to Another
Must copy each element one at a time
Note that this cannot be done by a simple assignment intNewValues = intOldValues
Causes intNewValues array to reference the same memory location as intOldValues
Thus any change to intOldValues will affect intNewValues and vice versa
This is because arrays are object variables
For intCount = 0 To intOldValues.Length -1
intNewValues(intCount) = intOldValues(intCount)
Next intCount

24. Parallel Arrays
Sometimes it’s useful to store related data in two or more arrays called parallel arrays
Causes the nth element of one array to be related to the nth element of another
Allows related data to be accessed using the same subscript on both arrays

25. Parallel Arrays Example
Assume the following array declarations
Element 1 refers to the same person with name in one array and address in the other
Dim strNames(4) As String
Dim strAddresses(4) As String
strNames(0) strNames(1) strNames(2) strNames(3) strNames(4)
Person #1 Person #2 Person #3 Person #4 Person #5
strAddresses(0) strAddresses(1) strAddresses(2) strAddresses(3) strAddresses(4)

26. Parallel Arrays Processing
Use parallel array processing to add name and address of each person to a list box
Tutorial 8-2 has an example of parallel arrays
Dim strNames(4) As String
Dim strAddresses(4) As String
For intCount = 0 To 4
lstPeople.Items.Add("Name: " & strNames(intCount) _
& " Address: " & strAddresses(intCount))
Next intCount

27. Array & List Box Parallel Processing
A list box selection used as an array index
' Initialize a List Box with names
lstPeople.Items.Add("Jean James") ' Subscript 0
lstPeople.Items.Add("Kevin Smith") ' Subscript 1
lstPeople.Items.Add("Joe Harrison") ' Subscript 2
' Initialize an Array with corresponding phone numbers
phoneNumbers(0) = " "
phoneNumbers(1) = " "
phoneNumbers(2) = " "
' Process a selection
If lstPeople.SelectedIndex > -1 And _
lstPeople.SelectedIndex < phoneNumbers.Length Then
MessageBox.Show(phoneNumbers(lstPeople.SelectedIndex))
Else
MessageBox.Show("That is not a valid selection.")
End If

28. Searching Arrays, The Search
Find 1st instance of value 100 in array intScores
intPosition gives position of this value
Dim blnFound as Boolean = False
Dim intCount as Integer = 0
Dim intPosition as Integer = -1
‘ Search for a 100 in the array
Do While Not blnFound And intCount < scores.Length
If intScores(intCount) = 100 Then
blnFound = True
intPosition = intCount
End If
intCount += 1
Loop

29. Searching Arrays, The Result
Indicates whether the value was found
If found, position is given as a test number
' Was 100 found in the array?
If blnFound Then
MessageBox.Show( _
"Congratulations! You made a 100 on test " & _
(intPosition + 1).ToString, "Test Results")
Else
"You didn’t score a 100, but keep trying!", _
"Test Results")
End If

30. Sorting an Array Arrays have a Sort method
Arranges elements in ascending order (lowest to highest)
Sort so intNumbers order is {1, 3, 6, 7, 12}
Sort so strNames order is {Alan, Bill, Kim, Sue}
Dim intNumbers() As Integer = { 7, 12, 1, 6, 3 }
Array.Sort(intNumbers)
Dim strNames() As String = { "Sue", "Kim", _
"Alan", "Bill" }
Array.Sort(strNames)

31. Dynamically Sizing an Array
ReDim [Preserve] Arrayname(UpperSubscript)
ReDim is a new keyword
Used to change nbr of elements at run time
If Preserve is specified, the existing contents of the array are preserved
Arrayname names the existing array
UpperSubscript specifies the new highest subscript value
Can declare an array with no subscript and state number of elements later with ReDim

32. Resizing Example Array sngScores declared with no elements
User prompted for number of elements
ReDim resizes array based on user input
Dim sngScores() As Single ' Declared with no elements
Dim intNumScores as Integer
' Obtain number of elements from the user
intNumScores = CInt(InputBox("Enter number of test scores"))
If intNumScores > 0 Then
ReDim sngScores(intNumScores - 1)
Else
MessageBox.Show("You must enter 1 or greater.")
End If

33. Procedures and Functions That Work With Arrays
8.3
Procedures and Functions That Work With Arrays
You Can Pass Arrays As Arguments to Sub Procedures and Functions
You Can Also Return an Array From a Function
This Allows You to Write Sub Procedures and Functions That Perform General Operations With Arrays
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

34. Passing Arrays as Arguments
Array intNumbers passed to DisplaySum sub
Sub computes & shows sum of array elements
Can pass any integer array to DisplaySum
Dim intNumbers() As Integer = { 2, 4, 7, 9, 8, 12 }
DisplaySum(intNumbers)
Sub DisplaySum(ByVal intArray() As Integer)
Dim intTotal As Integer = 0 ' Accumulator
Dim intCount As Integer ' Loop counter
For intCount = 0 To (intArray.Length - 1)
intTotal += intArray(intCount)
Next
MessageBox.Show(“Total is " & intTotal.ToString)
End Sub

35. Passing Arrays: ByVal and ByRef
When passing an array ByVal
Calling procedure “sees” sub procedure changes to element values
Simple variables don’t work this way
If sub assigns array argument to another array, no effect on array in calling procedure
When passing an array ByRef
If sub assigns array argument to another array, calling procedure array values affected

36. Passing Arrays Example
After ResetValues procedure executes, intNumbers array still contains { 1, 2, 3, 4, 5 }
If array passed ByRef, intNumbers array will contain { 0, 0, 0, 0, 0 } after procedure runs
Dim intNumbers() As Integer = { 1, 2, 3, 4, 5 }
ResetValues(intNumbers)
Sub ResetValues(ByVal intArray() As Integer)
Dim newArray() As Integer = {0, 0, 0, 0, 0}
intArray = newArray
End Sub

37. An Array Returned From a Function
Return type String() indicates array of strings returned
Thus the function result must be assigned to an array of strings
Function GetNames() As String()
' Get four names from user
' Return them as an array of strings.
Dim strNames(3) As String
Dim strInput As String
Dim intCount As Integer
For intCount = 0 To 3
strInput = InputBox("Enter name " & _
(intCount + 1).ToString)
strNames(intCount) = strInput
Next
Return strNames
End Function

38. Multidimensional Arrays
8.4
Multidimensional Arrays
You May Create Arrays With More Than Two Dimensions to Hold Complex Sets of Data
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

39. A Two Dimensional Array Picture
Thus far, arrays have been one-dimensional
Arrays can also be two-dimensional
A two-dimensional array looks like a spreadsheet with rows and columns
Column 0 Column 1 Column 2 Column 3
Row 0
Row 1
Row 2

40. Two Dimensional Array Syntax
Dim ArrayName(UpperRow, UpperColumn) As DataType
UpperRow and UpperColumn give the highest subscript for the row and column indices of the array
The array on the previous slide could be:
Defines three rows; 0, 1, and 2
And four columns; 0, 1, 2, and 3
Dim array(2,3) As Single

41. Two Dimensional Array Subscripts
Dim array(2,3) As Single
Column 0 Column 1 Column 2 Column 3
Row 0 sngScores(0,0) sngScores(0,1) sngScores(0,2) sngScores(0,3)
Row 1 sngScores(1,0) sngScores(1,1) sngScores(1,2) sngScores(1,3)
Row 2 sngScores(2,0) sngScores(2,1) sngScores(2,2) sngScores(2,3)

42. Nested Loops And Two Dimensions
Must use two subscripts to indicate a single element in a two dimensional array
Nested loops are often used to specify subscripts for two-dimensional array processing
For example, a nested loop below is used to insert a value into every element of array scores
For intRow = 0 To 2
For intCol = 0 To 3
intNum = Val(InputBox("Enter a score."))
sngScores(intRow, intCol) = intNum
Next intCol
Next intRow

43. Implicit Sizing and Initialization
Can be used with multi-dimensional arrays:
Row 0 values
Row 1 values
Row 2 values
Initializes array intNumbers with the following values
Dim intNumbers(,) As Integer = _
{ {1, 2, 3}, {4, 5, 6}, {7, 8, 9} }
Col 0
Col 1
Col 2
Row 0 1 2 3
Row 1 4 5 6
Row 2 7 8 9

44. Sum Columns, 2 Dimensional Array
Code below uses nested loops to compute sum of elements in each column of a 2 dimensional array
Outer loop controls column subscript
Dim intValues(,) As Integer = {{1, 2, 3, 4}, _
{5, 6, 7, 8}, _
{9, 10, 11, 12}}
For intCol = 0 to 3
intTotal = 0 ‘Initialize accumulator
For intRow = 0 to 2 ‘Sum rows in this column
intTotal += intValues(intRow, intCol)
next intRow
‘Display the sum of the column
MessageBox.Show(“Column “ & intCol.ToString() _
& “ sum is “ & intTotal.ToString)
Next intCol

45. Three-Dimensional Arrays & Beyond
VB allows arrays of up to 32 dimensions
Can think of a 3 dimensional array as having multiple pages of two dimensional arrays
Arrays beyond three dimensions are difficult to visualize
But, all one needs to do is to be consistent in the use of the different indices

46. Enabled Property, Timer Control, and Splash Screens
8.5
Enabled Property, Timer Control, and Splash Screens
You Disable Controls by Setting Their Enabled Property to False
The Timer Control Allows Your Application to Execute a Procedure at Regular Time Intervals
Splash Screens Are Forms That Appear As an Application Begins Executing
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

47. Enabled Property Most controls have an Enabled property
If this Boolean property is set to false the control is disabled meaning the control:
Cannot receive the focus
Cannot respond to user generated events
Will appear dimmed, or grayed out
Default value for this property is true
May be set in code when needed as shown:
btnExample.Enabled = False

48. Timer Control A Timer control generates Tick events
Double-click on Timer tool in Toolbox to add
Appears in component tray
Standard prefix is tmr
Can perform a process at regular intervals by coding the process in a Tick event procedure
Two important properties
Enabled must be true to generate Tick events
Interval (milliseconds) decides tick frequency
Interval of 1000 causes 1 timer tick per second
Tutorial 8-5 demonstrates the Timer control

49. Splash Screens
A form, often with an application logo, that is displayed while an application is loading
A splash screen usually:
Has Topmost property set to True so it is displayed over the forms of other applications
Disappears shortly by using a Timer
Is modeless so the application continues to load while the splash screen is displayed
Tutorial 8-6 demonstrates a splash screen

50. Anchoring and Docking Controls
8.6
Anchoring and Docking Controls
Controls Have Two Properties, Anchor and Dock, That Allow You to Determine the Control’s Position on the Form When the Form Is Resized at Run Time
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

51. Anchor Property Anchor - a property of various form controls
A control anchored to a form edge keeps the same distance to the form edge
Controls may be anchored to any, all, or none of the right, left, top, or bottom edges
Default is to anchor to top and left edges
Can just as easily anchor to bottom right
If anchoring to opposing sides, control is resized when form is resized
Anchoring to all 4 sides causes control to be resized proportionally to form

52. Dock Property
Dock - a property of various form controls
A control docked to a form edge is placed directly against the form edge
Controls may be docked to
Any one form edge but not more than one
No edge or not docked (the default)
Length or width of docked control changes to match length or width of the form edge

53. Visual Basic Provides the Tools to Generate Random Numbers
8.7
Random Numbers
Visual Basic Provides the Tools to Generate Random Numbers
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

54. Initial Random Number Generation
Often used for games and simulations
Must create an instance of the Random class to use random number methods and properties
May supply a seed number as below so the same set of random numbers are generated every time
If no seed number is supplied when instantiated:
VB uses its default random number seed
Causes each sequence to be unique
Private rand as New Random
Private rand as New Random(25)

55. Generating More Random Numbers
The Next method returns the next integer in a random number sequence
Returns integer between 0 and 2,147,483,647
Repeatedly use a statement such as the following to generate additional random numbers
Dim intNum as Integer = rand.Next()
intNum = rand.Next()

56. Random Numbers in a Range
Can set an upper limit for the number generated by specifying the limit as an argument
Following example generates a random number between 0 and 99
Lower limit of a random number is always 0
Can add or subtract to change this lower limit
Following example generates a random number between -50 and +49
intNum = rand.Next(100)
intNum = rand.Next(100) - 50

57. Random Numbers of Type Double
Use NextDouble method to generate random numbers of type double
Returns floating point number from 0.0 to 1.0
For a random double between 0.0 and 500.0
For a random double between and 600.0
Tutorial 8-7 shows an interesting use of random numbers
Dim dblNum as Double = rand.NextDouble()
dblNum = rand.NextDouble() * 500
dblNum = (rand.NextDouble() * 500) + 100

58. Building the Demetris Leadership Center Application
8.8
Building the Demetris Leadership Center Application
Build an application making use of arrays and a splash screen
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

59. Demetris Leadership Center Form

60. Demetris Leadership Center Form
Splash
Screen
Publisher of books, audiocassettes, and videos
Product info stored in parallel arrays
Input boxes used to prompt for sales, product, & quantity
Sales displayed as shown on right