Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Slide 8- 1 STARTING...

Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Slide 8- 1

STARTING OUT WITH

Visual Basic 2008FOURTH EDITION

Tony GaddisHaywood Community College

Kip IrvineFlorida International University

Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Chapter

Arrays, Timers, and More8


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


Arrays8.1

An Array Is Like a Group of Variables With One Name

You Store and Work Values in an Array by Using a Subscript


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


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


Declaring an Array

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

Dim ArrayName(UpperSubscript) As DataType


Array Declaration Example

intHours(0) intHours(1) intHours(2) intHours(3) intHours(4) intHours(5)

Dim intHours(5) As Integer

Note that 6 elements are available when an array with an upper subscript of 5 is declared

Each element is an integer type


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)


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}


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 = 100Dim array(UPPER_SUB) As Integer


Working With Array Elements Simply include the subscript to use an array

element like an ordinary variable intNumbers(2) refers to 3rd element of arrayintNumbers(0) = 100intNumbers(1) = 200intNumbers(2) = 300intNumbers(3) = 400intNumbers(4) = 500intNumbers(5) = 600

decPay = intHours(3) * decRate

intTallies(0) += 1

MessageBox.Show(decPay(5).ToString())


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 IntegersDim intCount As IntegerFor intCount = 0 To 9 intNbrs(intCount) = CInt(InputBox("Enter number"))Next intCount

Dim strNames(999) as StringDim intCount As IntegerFor intCount = 0 To 999

strNames(intCount) = ""Next intCount


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


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 StringFor Each strName In strEmployees

MessageBox.Show(strName)Next strName


Use For Each To Sum an Array

Start of iteration 1 intVal = 10 intSum = 0 End of iteration 1 intVal = 10 intSum = 10



End of iteration 4 intVal = -20 intSum = 120 Start of iteration 4 intVal = -20 intSum = 100

Private intArray() as Integer = {10, 20, 90, -20)Dim intSum as Integer = 0For Each intVal as Integer in intArray intSum = intSum + intValNext


Use For Each To Find Largest Value

Start of iteration 1 intVal = 10 intLargest = 10 End of iteration 1 intVal = 10 intLargest = 10



End of iteration 4 intVal = -20 intLargest = 90 Start of iteration 4 intVal = -20 intLargest = 90

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 = intValNext


More About Array Processing8.2

Arrays Have Many Uses & Many Programming Techniques Can Be Applied to

For Example, Arrays Are Used to Total Values or Search for Data


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


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 arrayDim intTotal As Integer = 0 'Initialize accumulatorDim intCount as Integer ‘Declare loop counter

‘Find total of all values held in arrayFor intCount = 0 To (intUnits.Length – 1)

intTotal += intUnits(intCount)Next intCount


Average the Values in an Array Similar to previous example but then divides total

by number of elements to get averageDim intUnits(24) as Integer ‘Declare arrayDim intTotal As Integer = 0 'Initialize accumulatorDim dblAverage as Double ‘Declare average varDim intCount as Integer ‘Declare loop counter

‘Find total of all values held in arrayFor intCount = 0 To (intUnits.Length – 1)

intTotal += intUnits(intCount)Next intCount

‘Use floating-point division to compute averagedblAverage = intTotal / intUnits.Length


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 IntegerDim intCount as IntegerDim intHighest as Integer = intNumbers(0)

For intCount = 1 To (intNumbers.Length - 1)If intNumbers(intCount) > intHighest Then

intHighest = intNumbers(intCount)End If

Next intCount


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


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


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 StringDim strAddresses(4) As String

strNames(0) strNames(1) strNames(2) strNames(3) strNames(4)

strAddresses(0) strAddresses(1) strAddresses(2) strAddresses(3) strAddresses(4)

Person #1 Person #2 Person #3 Person #4 Person #5


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

Slide 8- 26

Parallel Arrays Processing

Dim strNames(4) As StringDim strAddresses(4) As String

For intCount = 0 To 4lstPeople.Items.Add("Name: " & strNames(intCount) _

& " Address: " & strAddresses(intCount))Next intCount


Array & List Box Parallel Processing

' Initialize a List Box with nameslstPeople.Items.Add("Jean James") ' Subscript 0lstPeople.Items.Add("Kevin Smith") ' Subscript 1lstPeople.Items.Add("Joe Harrison") ' Subscript 2' Initialize an Array with corresponding phone numbersphoneNumbers(0) = "555-2987"phoneNumbers(1) = "555-5656"phoneNumbers(2) = "555-8897"

' Process a selectionIf lstPeople.SelectedIndex > -1 And _

lstPeople.SelectedIndex < phoneNumbers.Length ThenMessageBox.Show(phoneNumbers(lstPeople.SelectedIndex))

ElseMessageBox.Show("That is not a valid selection.")

End If

A list box selection used as an array index


Searching Arrays, The Search Find 1st instance of value 100 in array intScores intPosition gives position of this valueDim blnFound as Boolean = FalseDim intCount as Integer = 0Dim intPosition as Integer = -1

‘ Search for a 100 in the arrayDo While Not blnFound And intCount < scores.Length

If intScores(intCount) = 100 ThenblnFound = TrueintPosition = intCount

End IfintCount += 1Loop


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")

ElseMessageBox.Show( _

"You didn’t score a 100, but keep trying!", _"Test Results")

End If


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)


Dynamically Sizing an Array

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

ReDim [Preserve] Arrayname(UpperSubscript)


Resizing Example

Dim sngScores() As Single ' Declared with no elementsDim intNumScores as Integer

' Obtain number of elements from the userintNumScores = 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

Array sngScores declared with no elements User prompted for number of elements ReDim resizes array based on user input


Procedures and Functions That Work With Arrays8.3

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


Passing Arrays as Arguments

Dim intNumbers() As Integer = { 2, 4, 7, 9, 8, 12 }DisplaySum(intNumbers)

Sub DisplaySum(ByVal intArray() As Integer)Dim intTotal As Integer = 0 ' AccumulatorDim intCount As Integer ' Loop counterFor intCount = 0 To (intArray.Length - 1)

intTotal += intArray(intCount)NextMessageBox.Show(“Total is " & intTotal.ToString)

End Sub

Array intNumbers passed to DisplaySum sub

Sub computes & shows sum of array elements Can pass any integer array to DisplaySum


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

Calling procedure “sees” sub procedure changes to element values

If sub assigns array argument to another array, calling procedure array values affected


Passing Arrays Example

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 = newArrayEnd Sub

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


An Array Returned From a Function

Function GetNames() As String()' Get four names from user' Return them as an array of strings.Dim strNames(3) As StringDim strInput As StringDim intCount As IntegerFor intCount = 0 To 3 strInput = InputBox("Enter name " & _

(intCount + 1).ToString) strNames(intCount) = strInputNextReturn strNames

End Function

Return type String() indicates array of strings returned Thus the function result must be assigned to an array

of strings


Multidimensional Arrays8.4

You May Create Arrays With More Than Two Dimensions to Hold

Complex Sets of Data


A Two Dimensional Array Picture

Column 0 Column 1 Column 2 Column 3

Row 0

Row 1

Row 2

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


Two Dimensional Array Syntax

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 ArrayName(UpperRow, UpperColumn) As DataType

Dim array(2,3) As Single


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)




Nested Loops And Two Dimensions

For intRow = 0 To 2For intCol = 0 To 3

intNum = Val(InputBox("Enter a score."))sngScores(intRow, intCol) = intNum

Next intColNext intRow

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


Implicit Sizing and Initialization

Can be used with multi-dimensional arrays:

Row 0 values Row 1 values Row 2 values

Initializes array intNumberswith 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


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 subscriptDim intValues(,) As Integer = {{1, 2, 3, 4}, _

{5, 6, 7, 8}, _{9, 10, 11, 12}}

For intCol = 0 to 3intTotal = 0 ‘Initialize accumulatorFor intRow = 0 to 2 ‘Sum rows in this column

intTotal += intValues(intRow, intCol)next intRow‘Display the sum of the columnMessageBox.Show(“Column “ & intCol.ToString() _

& “ sum is “ & intTotal.ToString)Next intCol


Three-Dimensional Arrays & Beyond

VB allows arrays of up to 32 dimensions Can think of a 3

dimensional arrayas 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


Enabled Property, Timer Control, and Splash Screens

8.5You 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


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


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


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


Anchoring and Docking Controls8.6

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


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


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


Random Numbers8.7

Visual Basic Provides the Tools to Generate Random Numbers


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(25)

Private rand as New Random


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()


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


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 100.0 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


Building the Demetris Leadership Center Application

8.8

Build an application making use of arrays and a splash screen


Demetris Leadership Center Form

Slide 8- 59


Demetris Leadership Center Form

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

Slide 8- 60

SplashScreen

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