1. Chapter 8
Arrays, Timers, and More

2. Chapter 8 Introduction

3. Chapter 8 Topics
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. Section 8.1 Arrays An Array Is Like a Group of Variables With One Name
You Store and Work With Values in an Array by Using a Subscript

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 would be:
a set of 7 string variables
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 known as an index, is a number that identifies a specific element within an array
Subscript numbering works like the index for a list box:
Subscript numbering begins at 0
1st element in an array is always subscript 0
Last element is total number of elements - 1

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 valid Visual Basic data type
VB knows an array is declared when name is followed by number of elements in parens

8. Array Declaration Example
Dim hours(5) As Integer
hours(0) hours(1) hours(2) hours(3) hours(4) hours(5)
Note that 6 elements are available when an array with an uppersubscript 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 initializled 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
A 6 element array is declared
Elements are assigned the values shown
Dim numbers() 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
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
numbers(2) refers to 3rd element of array
numbers(0) = 100
numbers(1) = 200
numbers(2) = 300
numbers(3) = 400
numbers(4) = 500
numbers(5) = 600
pay = hours(3) * rate
tallies(0) += 1
MessageBox.Show(grossPay(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 names array to an empty string
Dim count As Integer
For count = 0 To 9
series(count) = CInt(InputBox("Enter a number"))
Next count
Dim count As Integer
For count = 0 To 999
names(count) = ""
Next count

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 an exception
Bounds checking is not done at design time

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

16. Section 8.2 More About Array Processing
There Are Many Uses of Arrays and Many Programming Techniques That Involve Them
For Example, Arrays Are Used to Total Values or Search for Data

17. 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 values(25) As Integer
For count = 0 to (values.Length – 1)
MessageBox.Show(values(count).ToString)
Next count

18. 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

19. 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

20. 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

21. Copy Values in One Array to Another
Done by copying elements one at a time
Note that this cannot be done by a simple assignment newValues = oldValues
Causes newValues variable to reference the same memory location as oldValues
Thus any change to oldValues will affect newValues and vice versa
For intCount = 0 To 100
newValues(intCount) = oldValues(intCount)
Next intCount

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

23. 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 names(4) As String
Dim addresses(4) As String
Names(0) Names(1) Names(2) Names(3) Names(4)
Person #1 Person #2 Person #3 Person #4 Person #5
Addresses(0) Addresses(1) Addresses(2) Addresses(3) Addresses(4)

24. 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 names(4) As String
Dim addresses(4) As String
For intCount = 0 To 4
lstPeople.Items.Add("Name: " & names(intCount) & _
" Address: " & addresses(intCount))
Next intCount

25. 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

26. Searching Arrays, The Search
Find 1st instance of value 100 in array scores
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 scores(intCount) = 100 Then
blnFound = True
intPosition = intCount
End If
intCount += 1
Loop

27. 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

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

29. Resizing an Array ReDim is a new keyword
ReDim [Preserve] Arrayname(UpperSubscript)
ReDim is a new keyword
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

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

31. Section 8.3 Sub Procedures and Functions That Work With Arrays
You May Pass Arrays As Arguments to Sub Procedures and Functions
You May Also Return an Array From a Function
This Allows You to Write Sub Procedures and Functions That Perform General Operations With Arrays

32. Passing Arrays as Arguments
Array numbers passed to DisplaySum sub
Sub computes/shows sum of array elements
Can pass any integer array to DisplaySum
Dim numbers() As Integer = { 2, 4, 7, 9, 8, 12, 10 }
DisplaySum(numbers)
Sub DisplaySum(ByVal intArray() As Integer)
Dim total As Integer = 0 ' Accumulator
Dim count As Integer ' Loop counter
For count = 0 To (intArray.Length - 1)
total += intArray(count)
Next
MessageBox.Show(“Total is " & total.ToString)
End Sub

33. 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

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

35. An Array Returned From a Function
Return type String() indicates an array of strings
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 count As Integer
For count = 0 To 3
strInput = InputBox("Enter name " & _
(count + 1).ToString)
strNames(count) = strInput
Next
Return strNames
End Function

36. Section 8.4 Multidimensional Arrays
You May Create Arrays With More Than Two Subscripts to Hold Complex Sets of Data

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

38. 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

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

40. Nested Loops And Two Dimensions
Nested loops are often used in processing two-dimensional arrays
In the example, a nested loop is used to insert a value into every element of array scores
For row = 0 To 2
For col = 0 To 3
num = Val(InputBox("Enter a score."))
scores(row, col) = num
Next col
Next row

41. Implicit Sizing and Initialization
Can be used with multi-dimensional arrays:
Row 0 values
Row 1 values
Row 2 values
Initializes array numbers with the following values
Dim numbers(,) 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

42. For Each Loop With Two Dimensions
A For Each Loop will process all elements of an array without requiring nested loops
The example below computes the sum of all elements
Total has the value 45 when loop is complete
Dim numbers(,) As Integer = {{1, 2, 3}, _
{4, 5, 6}, _
{7, 8, 9}}
For Each element In numbers
total += element
Next element

43. Sum Two-Dimensional Array Columns
Outer loop controls column subscript
Inner loop controls row subscript
' Process each column in turn
For col = 0 To 2
' Initialize column accumulator
total = 0
' Sum the column values from each row
For row = 0 To 4
total += values(row, col)
Next row
' Display the sum of the column.
MessageBox.Show("Sum of column " & _
col.ToString & " is " & total.ToString)
Next col

44. Three-Dimensional Arrays & Beyond
VB allows arrays of up to 32 dimensions
Beyond three dimensions, they are difficult to visualize
But, all one needs to do is to be consistent in the use of the different indices

45. Section 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

46. 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

47. 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

48. 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

49. Section 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

50. 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

51. 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

52. Section 8.7 Random Numbers
Visual Basic Provides the Tools to Generate Random Numbers

53. Initial Random Number Generation
Often used for games and simulations
A Random class provides methods and properties to work with random numbers
May supply a seed number as below causing same sequence of numbers to be generated
Leave the argument blank to omit the seed
VB then uses its default random number seed
Sequence not repeated if seed omitted
Randomize [Number]

54. Generating More Random Numbers
To get next random number in sequence
Repeatedly use a statement like the above to generate additional random numbers
randomNumber = Rnd

55. Random Numbers in a Range
Rnd creates random numbers in the range of 0.0 to 1.0
Can scale these to a selected range of integer numbers needed in your program:
Where LowerNumber and UpperNumber are the lowest and highest numbers permitted
Tutorial 8-7 shows an interesting use of random numbers
randomNumber = Int(LowerNumber + Rnd * _
(UpperNumber - LowerNumber))

56. Section 8.8 Building the Demetris Leadership Center Application
Build an application making use of arrays and a splash screen