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# Arrays, Timers, and More - PowerPoint PPT Presentation

Chapter 8. Arrays, Timers, and More. 8.1 Introduction. Chapter 8 Topics. Arrays are like groups of variables that allow you to store sets of data A one dimensional array is useful for storing and working with a single set of data

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### Chapter 8

Arrays, Timers, and More

### 8.1Introduction

• Arrays are like groups of variables that allow you to store sets of data

• A one dimensional 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

### 8.2Arrays

An Array Is Like a Group of Variables With One Name

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

• An array is a like group of variables with a single name

• All of the variables within an array are called elements and are of the same data type

• You access the individual variables in an array through a subscript

• A subscript, also known as an index, is a number that identifies a specific element within an array

• Subscript numbering begins at 0, so the subscript of the first element in an array is 0

• The subscript of the last element in an array is one less than the total number of elements

• ArrayName is the name of the array

• UpperSubscript is the value of the array's highest subscript

• It must be a positive whole number

• DataType is a Visual Basic .NET data type

Dim ArrayName(UpperSubscript) As DataType

Dim hours(5) As Integer

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

• All of the elements of an Integer array are initialized with the same value as a normal integer, zero (0)

• Same for other types of arrays

• Float, zero (0.0)

• String, Nothing

• Example:

• No upper subscript value is given

• Visual Basic .NET will automatically make the array long enough to hold the values

Dim numbers() As Integer = {2, 4, 5, 7, 9, 12}

Named Constant As Array's Highest Subscript Value

• In place of a whole number, a named constant may be used as an array's highest subscript:

Const upperSub As Integer = 100

Dim array(upperSub) As Integer

• An Array element (e.g., numbers(2)) is used just like an ordinary variable:

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)

• Frequently, arrays will be processed in loops

Dim series(9) As Double

Dim count As Integer

For count = 0 To 9

series(count) = Val(InputBox("Enter a number."))

Next count

Dim names(999) As String

Dim count As Integer

For count = 0 To 999

names(count) = ""

Next count

• Visual Basic .NET will check each subscript value of each array reference used at run time

• If a subscript is used that is either negative or greater than the highest allowed, a dialog box will appear giving the option of Debugging or Stopping the application

• (Note that no bounds checking is done at design time)

Dim employees As String() = {"Jim", "Sally", _

"Henry", "Jean", "Renee" }

Dim name As String

For Each name In employees

MessageBox.Show(name)

Next name

'above is an alternative to:

Dim i As Integer

For i = 0 To 4

MessageBox.Show(employees(i))

Next i

• This statement is similar to a For…Next

There Are Many Uses of Arrays and Many Programming Techniques That Involve Them

Arrays May Be Used to Total Values and Search for Data

Related Information May Be Stored in Multiple Parallel Arrays

In Addition, Arrays May Be Resized at Run Time

Determining the Number ofElements in an Array

• Arrays have a Length property that holds the number of elements in the array

• Note that the length is the number of elements in the array, not the largest subscript

Dim values(25) As Integer

For count = 0 to (values.Length – 1)

MessageBox.Show(values(count).ToString)

Next count

• The values are summed up in a variable that is initialized to zero beforehand:

Dim units() As Integer = {2, 4, 5, 10}

Dim total As Integer = 0 ' Initialize accumulator

For count = 0 To (units.Length – 1)

total += units(count)

Next count

' Total now equals 21

Getting the Average of theValues in a Numeric Array

• This algorithm first totals the values, then calculates the average:

Dim total As Integer = 0 ' Initialize accumulator

Dim average As Single

For count = 0 To (units.Length – 1)

total += units(count)

Next count

average = total / units.Length

Finding the Highest and LowestValues in a Numeric Array

• Pick the first element as the highest, then look through the rest of the array for even higher ones, always saving the highest value

• Proceed analogously to find the lowest value

Dim numbers() As Integer = {2, 4, 5, 7, 9, 12}

Dim highest As Integer = numbers(0)

For count = 1 To (numbers.Length - 1)

If numbers(count) > highest Then

highest = numbers(count)

End If

Next count

Copying One Array'sContents to Another

• This is done by copying the elements one at a time, thusly

• Note that newvalues = oldvalues will not work for this use because oldvalues stores a reference to the array (stores the location of the elements contained inside)

Dim newValues(99), oldValues(99) As Double

For count = 0 To 99

newValues(count) = oldValues(count)

Next count

• Sometimes it is useful to store related data in two or more arrays

• Hence the ith element of one array is related to the ith element of another

• Then the program can access this related information by using the same subscript on both arrays

Dim names(4) As String

Dim names(4) As String

For count = 0 To 4

lstPeople.Items.Add( "Name: " & names(count) & _

Next count

Parallelism Between Arrays andList Boxes and Combo Boxes

Dim names(4) As String

' Initialize a List Box with names from previous slide

Dim name as String

For Each name in names

Next name

' Process a selection

If lstPeople.SelectedIndex > -1 And _

Else

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

End If

• This code hunts for the value 100 in the array scores (one student’s scores)

Dim scores(4) As Integer 'initialization not shown

' Search for a 100 in the array.

Dim found As Boolean = False

Dim count As Integer = 0

If scores(count) = 100 Then

found = True

position = count

End If

count += 1

Loop

• This code indicates whether or not the value was found

' Was 100 found in the array?

If found Then

MessageBox.Show( _

"Congratulations! You made a 100 on test " & _

(position + 1).ToString, "Test Results")

Else

MessageBox.Show( _

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

"Test Results")

End If

• There is an Array.Sort method that sorts arrays in ascending order, examples:

Dim numbers() As Integer = { 7, 12, 1, 6, 3 }

Array.Sort(numbers)

' OR

Dim names() As String = { "Sue", "Kim", "Alan", "Bill" }

Array.Sort(names)

• 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

ReDim [Preserve] Arrayname(UpperSubscript)

Dim scores() As Single ' Start array as having "Nothing"

' Now obtain a size from the user

numScores = Val(InputBox("Enter the number of test scores."))

If numScores > 0 Then

ReDim scores(numScores - 1)

Else

MessageBox.Show("You must enter 1 or greater.")

End If

### 8.4Sub 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

These Capabilities Allow You to Write Sub Procedures and Functions That Perform General Operations With Arrays

' In the calling program

Dim numbers() As Integer = { 2, 4, 7, 9, 8, 12, 10 }

DisplaySum(numbers)

' The sub procedure

Sub DisplaySum(ByVal a() As Integer)

' Displays the sum of the elements

Dim total As Integer = 0 ' Accumulator

Dim count As Integer ' Loop counter

For count = 0 To (a.Length - 1) ' << Length obtained

total += a(count)

Next

MessageBox.Show("The total is " & total.ToString)

End Sub

• ByRef when used with an array, allows unrestricted changes to the array

• ByVal with an array

• Does not restrict its values from being changed from within the sub procedure

• It does prevent an array argument from be assigned to another array (see next slide)

ByRef Allows This Sort of ModificationByVal Does Not

Dim numbers() As Integer = { 1, 2, 3, 4, 5 }

ResetValues(numbers)

Sub ResetValues(ByVal a() As Integer)

' Assign the array argument to a

' new array. Does this work?

' NOT when using ByVal

' It would if ByRef was used instead

Dim newArray() As Integer = {0, 0, 0, 0, 0}

a = newArray

End Sub

Function GetNames() As String()

' Get four names from the user

' and return them as an array

' of strings.

Dim names(3) As String

Dim input As String

Dim count As Integer

For count = 0 To 3

input = InputBox("Enter name " & _

(count + 1).ToString)

names(count) = input

Next

Return names

End Function

### 8.5Multidimensional Arrays

You May Create Arrays With More Than Two Subscripts to Hold Complex Sets of Data

Column 0 Column 1 Column 2 Column 3

Row 0

Row 1

Row 2

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:

Dim array(2,3) As Single

A Two Dimensional Array Showing the 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)

Two Dimensional Arrays AreOften Processed With Nested Loops

For row = 0 To 2

For col = 0 To 3

num = Val(InputBox("Enter a score."))

scores(row, col) = num

Next col

Next row

Implicit Sizing and Initializationof Two-Dimensional Arrays

• This works for multi-dimensional arrays as well as singly dimensioned ones:

Dim numbers(,) As Integer = {{1, 2, 3}, _

{4, 5, 6}, _

{7, 8, 9}}

For Each Loops andMulti-dimensional Arrays

• A For Each Loop will process all of the elements in an array (without having to have nested loops):

Dim numbers(,) As Integer = {{1, 2, 3}, _

{4, 5, 6}, _

{7, 8, 9}}

For Each element In numbers

total += element

Next element

Summing the Columns of aTwo-dimensional Array

' Sum the columns.

For col = 0 To 2

' Initialize the accumulator.

total = 0

' Sum a column.

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

Three-dimensional Arraysand Beyond

• Visual Basic .NET allows arrays with 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

### 8.6Enabled Property,Timer Control,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

• Most controls have a Boolean property named Enabled

• When a control’s Enabled property is set to false, it is considered disabled, which means:

• It cannot receive the focus and cannot respond to events generated by the user

• In addition, it will appear dimmed, or grayed out

• This property defaults to true (Enabled)

• Under program control this property can be set to whatever the application logic dictates

• This control, when placed on a form, generates Tick events on a regular interval

• If there is a corresponding Tick event procedure, it executes at these intervals

• Hence, your form can perform needed operations on a regular interval

• The timer control has two important properties:

• Enabled - if set to True, it generates the Tick events, otherwise not

• Interval - holds the interval between Ticks in milliseconds (thousandths of a second)

• This is a form, typically with the application's logo, that is often displayed while an application is loading, it should:

• Have its Topmost property set to True so that it will be seen in preference to the applications other forms

• Disappear shortly (using a Timer)

• Be modeless

### 8.6Anchoring 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

• A control may be Anchored to two adjacent sides of the form

• This situation will maintain the same distances from those edges whenever the form is resized by the user (control does not change size)

• A control may be anchored to opposite sides of a form

• This situation will again maintain those distances, but by changing the size of the control

• A control can be docked against any side of a form

• Whenever the form is resized, the control will change in size also to fill up the edge that it is docked to

### 8.7Random Numbers

Visual Basic .NET Provides the Tools to Generate Random Numbers and Initialize the Sequence of Random Numbers With a Seed Value

• Random number generation is initiated with the selection of a "seed" number

• If you wish to repeat the same sequence of random numbers, then use the above statement with the same argument Number

• If you do not want to repeat a sequence, omit the argument (it will use system time as seed)

Randomize (Number)

• Obtain the next random number in the sequence

• Repeatedly use a statement like the above to generate additional random numbers

randomNumber = Rnd()

• Rnd creates random numbers in the range of 0.0 to 0.9999 (from 0 to just less than 1)

• To scale these to a range between two integers that may be needed in your program:

randomNumber= CInt(Int((upperbound - lowerbound + 1)

* Rnd + lowerbound)