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Chapter 7 - Arrays
Outline
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.10
7.11
Introduction
Arrays
Declaring and Allocating Arrays
Examples Using Arrays
7.4.1
Allocating an Array
7.4.2
Initializing the Values in an Array
7.4.3
Summing the Elements of an Array
7.4.4
Using Arrays to Analyze Survey Results
7.4.5
Using Histograms to Display Array Data Graphically
Passing Arrays to Procedures
Passing Arrays: ByVal vs. ByRef
Sorting Arrays
Searching Arrays: Linear Search and Binary Search
7.8.1
Searching an Array with Linear Search
7.8.2
Searching a Sorted Array with Binary Search
Multidimensional Rectangular and Jagged Arrays
Variable-Length Parameter Lists
For Each/Next Repetition Structure
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7.1 Introduction
• Arrays
– Arrays are data structures consisting of data items of the
same type
– “Static” entities
• They remain the same size once they are created
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7.2 Arrays
• Array
– Group of contiguous memory locations that have the same
name and the me type
• Position number
– Values that indicate specific locations within arrays
– The first element in every array is the zeroth element
• Length property
– Every array in Visual Basic “knows” its own length through
the Length property
• GetUpperBound method
– Returns the index of the last element in the array
– The value returned by this GetUpperBound is one less
than the value of the array’s Length property
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7.2 Arrays
Name of array (note that
all elements of this array
have the same name,
numberArray)
Position number (index or
subscript) of the element
within array numberArray
Fig. 7.1
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numberArray(0)
-45
numberArray(1)
6
numberArray(2)
0
numberArray(3)
72
numberArray(4)
1543
numberArray(5)
-89
numberArray(6)
0
numberArray(7)
62
numberArray(8)
-3
numberArray(9)
1
numberArray(10)
6453
numberArray(11)
78
Array consisting of 12 elements.
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7.3 Declaring and Allocating Arrays
• Memory
– The amount of memory required by an array depends on the length
of the array and the size of the data type of the elements in the
array
• Keyword New
– It is used to specify the size of the array and allocate memory for
the array
• Array bounds
– Determine what indices can be used to access an element in the
array
• Initializer list
– Specify the initial values of the elements in the array
• Keyword Nothing
– Denotes an empty reference
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7.4 Examples Using Arrays
• Several examples that demonstrate
– Declaration
– Allocation
– Initialization of arrays
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' Fig. 7.2: CreateArray.vb
' Declaring and allocating an array.
Imports System.Windows.Forms
Outline
CreateArray.vb
Module modCreateArray
Sub Main()A variable capable of storing a reference to
Allocateelements
an array of 10 elements
an array
of Integer
Dim output
As String
Dim i As Integer
using New and assigns it to array
Appends to output the headings for
As the
Integer()
' declare
array
variable
columns For
displayed
by the
program
structure
is used
to append
Dim array
array = New Integer(9) {} ' allocate memory for array
output &= "Subscript "
the index number and value of
&each
vbTab
& "Value"
array
element &to vbCrLf
output
' display values in array
For i = 0 To array.GetUpperBound(0)
The length property returns the
output &= i & vbTab
array(i)
vbCrLf
number& of
elements& in
the array
Next
output &= vbCrLf & "The array contains " & _
array.Length & " elements."
MessageBox.Show(output, "Array of Integer Values", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main
End Module ' modCreateArray
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7.4 Examples Using Arrays
Outline
CreateArray.vb
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Outline
' Fig. 7.3: InitArray.vb
' Initializing arrays.
Imports System.Windows.Forms
InitArray.vb
Module
modInitArray
One statement
is used
to
declare
the two arrays
Sub
Main()
Dim output As String
Dim i As Integer
array1 with
Allocates array2, whose size is determined
New andbyinitialize the values in the array,
'
initializer
list
specifies
number
of elements
arry1.GetUpperBound(0), so that
array1
using an initializer list
' and value of each element
andarray1
array2
have
the same {32,
upper27,
bound
= New
Integer()
64, 18, 95, _
Allocates
the 10two
elements
of
Dim array1, array2 As Integer()
' declare
arrays
14, 90, 70, 60, 37}
Initializes each element in
array2
to the even
integers
based
on length
of array1
' allocate array2
array2 = New Integer(array1.GetUpperBound(0)) {}
' set values in array2 by a calculation
For i = 0 To array2.GetUpperBound(0)
array2(i)
2 + 2in*the
i arrays to
Uses the =values
Next
build String output, which
is &=
displayed
in a MessageBox
output
"Subscript
" & vbTab & "Array1"
& vbTab & _
"Array2" & vbCrLf
' display values for both arrays
For i = 0 To array1.GetUpperBound(0)
output &= i & vbTab & array1(i) & vbTab & array2(i) & _
vbCrLf
Next
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MessageBox.Show(output, "Array of Integer Values", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main
End Module ' modInitArray
Outline
InitArray.vb
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' Fig. 7.4: SumArray.vb
' Computing sum of elements in array.
Declares, allocates and initializes
the 10-element array, array
Imports System.Windows.Forms
Outline
SumArray.vb
Module modSumArray
Sub Main()
Dim array As Integer() = New Integer() _
{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
Performs the addition
Dim total As Integer = 0, i As Integer = 0
' sum array element values
For i = 0 To array.GetUpperBound(0)
total += array(i)
Next
MessageBox.Show("Total of array elements: " & total, _
"Sum the elements of an Array", MessageBoxButtons.OK, _
MessageBoxIcon.Information)
End Sub ' Main
End Module ' modSumArray
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' Fig. 7.5: StudentPoll.vb
' Using arrays to display poll results.
Imports System.Windows.Forms
Outline
StudentPoll.vb
Module modStudentPoll
Array responses is a 40-element
Sub Main()
integer
array containing the student’s
Dim answer, rating As Integer
responses
theString
survey
Dim
outputto As
' student response array (typically input at run time)
Dim responses As Integer()
Reads
the responses
the8,
array
responses = New
Integer()
{1, 2,from
6, 4,
5, responses
9, 7, _
8, 10, 1, 6, 3,
10, and
3, increments
8, 2, 7, 6,
5,of7,the
6,10_
one8,at 6,
a time
one
8, 6, 7, 5, 6, 6, 5, 6, 7, 5, 6, 4, 8, 6, 8, 10}
counters in the frequency array
' response frequency array (indices 0 through 10)
Dim frequency As Integer() = New Integer(10) {}
' count frequencies
For answer = 0 To responses.GetUpperBound(0)
frequency(responses(answer)) += 1
Next
output &= "Rating " & vbTab & "Frequency " & vbCrLf
For rating = 1 To frequency.GetUpperBound(0)
output &= rating & vbTab & frequency(rating) & vbCrLf
Next
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MessageBox.Show(output, "Student Poll Program", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main
End Module ' modStudentPoll
Outline
StudentPoll.vb
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' Fig. 7.6: Histogram.vb
' Using data to create histograms.
Imports System.Windows.Forms
Outline
Histogram.vb
Module modHistogram
Sub Main()
Dim output As String
Dim i, j As Integer
' output string
' counters
' create data array
Nested For loops append the bars to
Dim array1 As Integer() = New Integer() _
the String
that
is displayed
{19, 3, 15,
7, 11, 9,
13,
5, 17, 1}in the
MessageBox
output &= "Element " & vbTab & "Value " & vbTab & _
"Histogram" Inner For structure counts from
1 to array(i), which is the value
For i = 0 To array1.GetUpperBound(0)
ithvbTab
index &ofarray1(i)
array1 & vbTab
output &= vbCrLfin&the
i &
For j = 1 To array1(i)
output &= "*" ' add one asterisk
Next
Next
MessageBox.show(output, "Histogram Printing Program", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main
End Module ' modHistogram
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Outline
Histogram.vb
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7.5 Passing Arrays to Procedures
• Passing the Array
– Specify the name of the array without using parentheses
– Every array object “knows” its own upper bound
• Do not need to pass the upper bound of the array as a separate
argument
– In Visual Basic, arrays always are passed by reference
• Receiving the array
– The procedure’s parameter list must specify that an array
will be received
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' Fig. 7.8: PassArray.vb
' Passing arrays and individual array elements to procedures.
Imports System.Windows.Forms
Outline
PassArray.vb
Module modPassArray
Dim output As String
Sub Main()
Dim array1 As Integer() = New Integer() {1, 2, 3, 4, 5}
Dim i As Integer
Appends
five elements
of
output the
= "EFFECTS
OF PASSING
ENTIRE ARRAY
array1
String output
"BYtoREFERENCE:"
& vbCrLf & vbCrLf & _
" & _
"The values of the original array are:" & vbCrLf
' display original elements of array1
Passes array1 to procedure
For i = 0 To array1.GetUpperBound(0)
ModifyArray
output &= " " & array1(i)
Next
ModifyArray(array1) ' array is passed by reference
output &= vbCrLf & _ Appends the elements of
"The values of the modified
are:" & vbCrLf
array1 array
to output
' display modified elements of array1
For i = 0 To array1.GetUpperBound(0)
output &= " " & array1(i)
Next
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output &= vbCrLf & vbCrLf & _
"EFFECTS OF PASSING ARRAY ELEMENT " & _
"BY VALUE:" & vbCrLf & vbCrLf & "array1(3) " & _
"before ModifyElementByVal: " & array1(3)
Outline
PassArray.vb
' array element passed by value
ModifyElementByVal(array1(3))
output &= vbCrLf & "array1(3) after " & _
"ModifyElementByVal: " & array1(3)
output &= vbCrLf & vbCrLf & "EFFECTS OF PASSING " & _
"ARRAY ELEMENT BY REFERENCE: " & vbCrLf & vbCrLf & _
"array1(3) before ModifyElementByRef: " & array1(3)
' array element passed by reference
ModifyElementByRef(array1(3))
output &= vbCrLf & "array1(3) after " & _
"ModifyElementByRef: " & array1(3)
Multiplies the elements of
MessageBox.Show(output, "Passing Arrays", _
arrayParameter
by 2 MessageBoxIcon.Information)
MessageBoxButtons.OK,
End Sub ' Main
' procedure modifies array it receives (note ByVal)
Sub ModifyArray(ByVal arrayParameter As Integer())
Dim j As Integer
For j = 0 To arrayParameter.GetUpperBound(0)
arrayParameter(j) *= 2
Next
End Sub ' ModifyArray
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' procedure modifies integer passed to it
' original is not be modified (note ByVal)
Sub ModifyElementByVal(ByVal element As Integer)
output &= vbCrLf & "Value
"ModifyElementByVal: "
element *= 2
output &= vbCrLf & "Value
"ModifyElementByVal: "
End Sub ' ModifyElementByVal
received in " & _
& element
Outline
PassArray.vb
calculated in " & _
& element
' procedure modifies integer passed to it
' original is be modified (note ByRef)
Sub ModifyElementByRef(ByRef element As Integer)
output &= vbCrLf & "Value
"ModifyElementByRef: "
element *= 2
output &= vbCrLf & "Value
"ModifyElementByRef: "
End Sub ' ModifyElementByRef
received in " & _
& element
calculated in " & _
& element
End Module ' modPassArray
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Outline
PassArray.vb
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7.6 Passing Arrays: ByVal vs. ByRef
• Visual Basic.NET
– A variable that “stores” an object, such as an array, does not
actually store the object itself
– The variable stores a reference to the object
• Location in memory where the object is already stored
• ByVal
– Causes the value of the argument to be copied to a local
variable in the procedure
– Changes to the local variable are reflected in the local copy
of that variable, not in the original variable in the calling
program
– But if the argument is of a reference type, like an array,
passing it ByVal actually passes it by reference, so changes
to the object affect the original objects in the callers
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7.6 Passing Arrays: ByVal vs. ByRef
• ByRef
– When an array is passed with ByRef the called procedure
gains control over the passed reference itself
• This allows the called procedure to replace the original
reference in the object with another object or even Nothing
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' Fig. 7.9: ArrayReferenceTest.vb
' Testing the effects of passing array references using
' ByVal and ByRef.
Module modArrayReferenceTest
Outline
ArrayReferenceTe
st.vb
Sub Main()
Dim i As Integer
Copies reference firstArray to
' declare array references
variable firstArrayCopy, now
Dim firstArray As Integer()
they reference
the same object
Dim firstArrayCopy
As Integer()
' allocate firstArray and copy its reference
firstArray = New Integer() {1, 2, 3}
firstArrayCopy = firstArray
Console.WriteLine("Test passing array reference " & _
"using ByVal.") Prints contents first to verify that FirstDouble
Console.Write("Contents of indeed
firstArray
before
" & _ contents
changes
the array’s
"calling FirstDouble: ")
' print contents of firstArray
For i = 0 To firstArray.GetUpperBound(0)
Console.Write(firstArray(i)
& " ")
firstArray
is passed to
Next
FirstDouble
' pass firstArray using ByVal
FirstDouble(firstArray)
Console.Write(vbCrLf & "Contents of firstArray after " & _
"calling FirstDouble: ")
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' references
print contents
of firstArray
Compares
firstArray
For i = 0 To firstArray.GetUpperBound(0)
and firstArrayCopy
Console.Write(firstArray(i) & " ")
Next
' test whether reference was changed by FirstDouble
If firstArray Is firstArrayCopy Then
Console.WriteLine(vbCrLf & "The references are " & _
"equal.")
Else
Console.WriteLine(vbCrLf & "The references are " & _
"not equal.")
End If
Outline
ArrayReferenceTe
st.vb
' declare array references
Dim secondArray As Integer()
Dim secondArrayCopy As Integer()
' allocate secondArray and copy its reference
secondArray = New Integer() {1, 2, 3}
secondArrayCopy = secondArray
Console.WriteLine(vbCrLf & "Test passing array " & _
"reference using ByRef.")
Console.Write("Contents of secondArray before " & _
"calling SecondDouble: ")
' print contents of secondArray before procedure call
For i = 0 To secondArray.GetUpperBound(0)
Console.Write(secondArray(i) & " ")
Next
' pass secondArray using ByRef
SecondDouble(secondArray)
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Outline
Console.Write(vbCrLf & "Contents of secondArray " & _
"after calling SecondDouble: ")
' print contents of secondArray after procedure call
For i = 0 To secondArray.GetUpperBound(0)
Console.Write(secondArray(i) & " ")
Next
ArrayReferenceTe
st.vb
' test whether the reference was changed by SecondDouble
If secondArray Is secondArrayCopy Then
Console.WriteLine(vbCrLf & "The references are " & _
"equal.")
Else
Console.WriteLine(vbCrLf & "The references are " & _
"not equal.")
End If
End Sub ' Main
Reference is passed ByVal
' procedure modifies elements of array and assigns
' new reference (note ByVal)
Sub FirstDouble(ByVal array As Integer())
Dim i As Integer
Multiplies all the elements of the array by 2
' double each element value
new array, and attempts to assign it’s reference to parameter
For Allocates
i = 0 To aarray.GetUpperBound(0)
array(i)
*= 2
array, attempting
to overwrite reference firstArray in memory, but
Next
will fail because the reference was passed ByVal
' create new reference and assign it to array
array = New Integer() {11, 12, 13}
End Sub ' FirstDouble
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Reference is passed ByRef
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' procedure modifies elements of array and assigns
' new reference (note ByRef)
Sub SecondDouble(ByRef array As Integer())
Dim i As Integer
Because
the reference
was passed with ByRef, the called
' double
contents
of array
For i =procedure
0 To array.GetUpperBound(0)
has the ability to modify what the reference
array(i) *= 2
actually points to
Next
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Outline
ArrayReferenceTe
st.vb
' create new reference and assign it to array
array = New Integer() {11, 12, 13}
End Sub ' SecondDouble
End Module ' modPassArray
Test passing array reference using ByVal.
Contents of firstArray before calling FirstDouble: 1 2 3
Contents of firstArray after calling FirstDouble: 2 4 6
The references are equal.
Test passing array reference using ByRef.
Contents of secondArray before calling SecondDouble: 1 2 3
Contents of secondArray after calling SecondDouble: 11 12 13
The references are not equal.
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7.7 Sorting Arrays
• Sorting
– Sorting data is one of the most popular computing
applications
– Sometimes, the simplest algorithms perform poorly
• Bubble Sort (a.k.a. sinking sort)
– Smaller values “bubble” their way to the top of the array,
(i.e. toward the first element)
– Larger values “sink” to the bottom of the array, (i.e. toward
the end)
– In general only n-1 passes are needed to sort an n-element
array
– The bubble sort is easy to program, but runs slowly
• Becomes apparent when sorting large arrays
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Outline
' Fig. 7.10: BubbleSort.vb
' Procedures for sorting an integer array.
Sorts the elements of it’s parameter sortArray
Module modBubbleSort
' sort array using bubble sort algorithm
The nested
performs
sortArraystructure
As Integer())
This Sub
innerBubbleSort(ByVal
loop controls
the For/Next
comparisons
Dim pass, i As Integer
BubbleSort.vb
the sort
and swapping, if necessary, of the elements
For during
pass =each
1 Topass
sortArray.GetUpperBound(0)
For i = 0 To sortArray.GetUpperBound(0) - 1
If sortArray(i) > sortArray(i + 1) Then
Swap(sortArray, i)
End If
Next
Next
Gets called by BubbleSort to
End Subtwo
' BubbleSort
transpose
of the array elements
' swap two array elements
Sub Swap(ByVal swapArray As Integer(), _
ByVal first As Integer)
Dim hold As Integer
hold = swapArray(first)
swapArray(first) = swapArray(first + 1)
swapArray(first + 1) = hold
End Sub ' Swap
End Module ' modBubbleSort
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' Fig. 7.11: BubbleSortTest.vb
' Program creates random numbers and sorts them.
Imports System.Windows.Forms
Public Class FrmBubbleSort
Inherits System.Windows.Forms.Form
Outline
BubbleSortTest.v
b
' buttons
Friend WithEvents cmdCreate As Button
Friend WithEvents cmdSort As Button
' labels
Friend WithEvents lblOriginal As Label
Friend WithEvents lblSorted As Label
' textboxes
Friend WithEvents txtOriginal As TextBox
Friend WithEvents txtSorted As TextBox
' Visual Studio .NET generated code
Dim array As Integer() = New Integer(9) {}
' creates random generated numbers
Private Sub cmdCreate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles cmdCreate.Click
Dim output As String
Dim randomNumber As Random = New Random()
Dim i As Integer
txtSorted.Text = ""
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' create 10 random numbers and append to output
For i = 0 To array.GetUpperBound(0)
array(i) = randomNumber.Next(100)
output &= array(i) & vbCrLf
Next
Outline
BubbleSortTest.v
b
txtOriginal.Text = output ' display numbers
cmdSort.Enabled = True
' enables cmdSort button
End Sub ' cmdCreate_Click
' sorts randomly generated numbers
Private Sub cmdSort_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles cmdSort.Click
Dim output As String
Dim i As Integer
' sort array
modBubbleSort.BubbleSort(array)
' creates string with sorted numbers
For i = 0 To array.GetUpperBound(0)
output &= array(i) & vbCrLf
Next
txtSorted.Text = output ' display numbers
cmdSort.Enabled = False
End Sub ' cmdSort_Click
End Class ' FrmBubbleSort
 2002 Prentice Hall.
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Outline
BubbleSortTest.v
b
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32
7.8 Searching Arrays: Linear Search and
Binary Search
• Searching
– The process of locating a particular element value in an array
• Linear Search
– Simple searching technique
– Works well for small or unsorted arrays
– On average half the elements of the array will be compared
• Binary Search
– If array is sorted, binary search is more efficient, but also a
more complex technique
– After each comparison, the binary search algorithm
eliminates half of the elements in the array
– The maximum number of comparisons in a binary search is
the exponent of the first power of 2 that is greater than the
number of elements being searched
 2002 Prentice Hall. All rights reserved.
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' Fig. 7.12: LinearSearch.vb
' Linear search of an array.
Module modLinearSearch
Outline
LinearSearch.vb
' iterates through array
Function LinearSearch(ByVal key As Integer, _
ByVal
Compares
eachnumbers
elementAs
of Integer())
the array As Integer
with a search key
Dim n As Integer
' structure iterates linearly through array
For n = 0 To numbers.GetUpperBound(0)
If numbers(n) = key Then
If the search key
is notnfound, the procedure
Return
End aIf
returns –1,
non-valid index number
Next
Return -1
End Function ' LinearSearch
End Module ' modLinearSearch
 2002 Prentice Hall.
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' Fig. 7.13: LinearSearchTest.vb
' Linear search of an array.
Imports System.Windows.Forms
Public Class FrmLinearSearchTest
Inherits System.Windows.Forms.Form
Outline
LinearSearchTest
.vb
' buttons
Friend WithEvents cmdSearch As Button
Friend WithEvents cmdCreate As Button
' text boxes
Friend WithEvents txtInput As TextBox
Friend WithEvents txtData As TextBox
' labels
Friend WithEvents lblEnter As Label
Friend WithEvents lblResult As Label
' Visual Studio .NET generated code
Dim array1 As Integer() = New Integer(19) {}
' creates random data
Private Sub cmdCreate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles cmdCreate.Click
Dim output As String
Dim randomNumber As Random = New Random()
Dim i As Integer
output = "Index" & vbTab & "Value" & vbCrLf
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' creates string containing 11 random numbers
For i = 0 To array1.GetUpperBound(0)
array1(i) = randomNumber.Next(1000)
output &= i & vbTab & array1(i) & vbCrLf
Next
Outline
LinearSearchTest
.vb
txtData.Text = output
' displays numbers
txtInput.Text = ""
' clear search key text box
cmdSearch.Enabled = True ' enable search button
End Sub ' cmdCreate_Click
' searches key of element
Private Sub cmdSearch_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles cmdSearch.Click
' if search key text box is empty, display
' message and exit procedure
If txtInput.Text = "" Then
MessageBox.Show("You must enter a search key.")
Exit Sub
End If
Dim searchKey As Integer = Convert.ToInt32(txtInput.Text)
Dim element As Integer = LinearSearch(searchKey, array1)
If element <> -1 Then
lblResult.Text = "Found Value in index " & element
Else
lblResult.Text = "Value Not Found"
End If
End Sub ' cmdSearch_Click
End Class ' FrmLinearSearch
 2002 Prentice Hall.
All rights reserved.
36
Outline
LinearSearchTest
.vb
 2002 Prentice Hall.
All rights reserved.
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' Fig. 7.14: BinarySearchTest.vb
' Demonstrating binary search of an array.
Imports System.Windows.Forms
Public Class FrmBinarySearch
Inherits System.Windows.Forms.Form
' labels
Friend WithEvents
Friend WithEvents
Friend WithEvents
Friend WithEvents
Friend WithEvents
Friend WithEvents
Outline
BinarySearchTest
.vb
lblEnterKey As Label
lblResult As Label
lblResultOutput As Label
lblDisplay As Label
lblIndex As Label
lblIndexes As Label
' button
Friend WithEvents cmdFindKey As Button
' text box
Friend WithEvents txtInput As TextBox
' Visual Studio .NET generated code
Dim array1 As Integer() = New Integer(14) {}
' FrmBinarySearch initializes array1 to ascending values
' 0, 2, 4, 6, ..., 28 when first loaded
Private Sub FrmBinarySearch_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles MyBase.Load
Dim i As Integer
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For i = 0 To array1.GetUpperBound(0)
array1(i) = 2 * i
Next
End Sub ' FrmBinarySearch_Load
Outline
BinarySearchTest
.vb
' event handler for cmdFindKey button
Private Sub cmdFindKey_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles cmdFindKey.Click
Dim searchKey As Integer = Convert.ToInt32(txtInput.Text)
lblDisplay.Text = ""
' perform binary search
Dim element As Integer = BinarySearch(array1, searchKey)
If element <> -1 Then
lblResultOutput.Text = "Found value in element " & element
Else
lblResultOutput.Text = "Value not found"
Receives
End Iftwo arguments, the array to
search, and the search key
End Sub ' cmdFindKey_Click
' performs binary search
Function BinarySearch(ByVal array As Integer(), _
ByVal key As Integer) As Integer
Dim low As Integer = 0
' low index
Dim high As Integer = array.GetUpperBound(0) ' high index
Dim middle As Integer
' middle index
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While low <= high
middle = (low + high) \ 2
' the following line displays part
' of
array
being of
manipulated
during
Calculates
thethe
middle
element
thekey,
array
If
middle
matches
then
' each iteration of loop
middle
is returned
BuildOutput(low,
middle,
high)
Outline
BinarySearchTest
.vb
If key = array(middle) Then
' match
Return middle
ElseIf key < array(middle) Then ' search low end
high = middle - 1
' of array
Else
low = middle + 1
End If
If key
does
End
While
not match middle, then the low or high index
is adjusted so that a smaller subarray can be searched
Return -1 ' search key not found
End Function ' BinarySearch
Sub BuildOutput(ByVal low As Integer, _
ByVal middle As Integer, ByVal high As Integer)
Dim i As Integer
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For i = 0 To array1.GetUpperBound(0)
If i < low OrElse i > high Then
lblDisplay.Text &= "
"
ElseIf i = middle Then ' mark middle element in output
lblDisplay.Text &= String.Format("{0:D2}", _
array1(i)) & "* "
Else
lblDisplay.Text &= String.Format("{0:D2}", _
array1(i)) & " "
End If
Outline
BinarySearchTest
.vb
Next i
lblDisplay.Text &= vbCrLf
End Sub ' BuildOutput
End Class ' FrmBinarySearch
 2002 Prentice Hall.
All rights reserved.
41
Outline
BinarySearchTest
.vb
 2002 Prentice Hall.
All rights reserved.
42
7.9 Multidimensional Rectangular and
Jagged Arrays
• Multidimensional arrays (multiple-subscripted)
– Require two or more indices to identify particular elements
• Rectangular arrays
– Two indices, first identifies the element’s row, the second
the elements column
– A rectangular two-dimensional array with m rows and n
columns is called an m-by-n array
• Jagged arrays
– Jagged arrays are maintained as arrays of arrays
– Rows in jagged arrays can be of different lengths
 2002 Prentice Hall. All rights reserved.
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7.9 Multidimensional Rectangular and
Jagged Arrays
Column 0
Column 1
Column 2
Column 3
Row 0
a(0, 0)
a(0, 1)
a(0, 2)
a(0, 3)
Row 1
a(1, 0)
a(1, 1)
a(1, 2)
a(1, 3)
Row 2
a(2, 0)
a(2, 1)
a(2, 2)
a(2, 3)
Column index
Row index (or subscript)
Array name
Fig. 7.15 Two-dimensional array with three rows and four columns.
 2002 Prentice Hall. All rights reserved.
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' Fig. 7.16: MultidimensionalArrays.vb
' Initializing multi-dimensional arrays.
Imports System.Windows.Forms
Module modMultidimensionalArrays
Outline
Multidimensional
Arrays.vb
Sub Main()
Dim output As String
Dim i, j As Integer
Allocates array1 with six initializers in two sublists
' create rectangular
two-dimensional
array
The declaration
and allocation of
array2
Dim array1 As Integer(,)
creates a jagged array of 3 arrays
array1 = New Integer(,) {{1, 2, 3}, {4, 5, 6}}
' create jagged two-dimensional array
Dim array2 As Integer()() = New Integer(2)() {}
array2(0) = New Integer() {1, 2}
array2(1)
New in
Integer()
{3}
Traverses
the=array
two dimensions
array2(2) = New Integer() {4, 5, 6}
output = "Values in array1 by row are " & vbCrLf
For i = 0 To array1.GetUpperBound(0)
For j = 0 To array1.GetUpperBound(1)
output &= array1(i, j) & " "
Next
output &= vbCrLf
Next
 2002 Prentice Hall.
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In a jagged two-dimensional array, the second dimension is
output &= vbCrLf & "Values in array2 by row are " &
actually the first dimension of a separate array
vbCrLf
For i = 0 To array2.GetUpperBound(0)
For j = 0 To array2(i).GetUpperBound(0)
output &= array2(i)(j) & " "
Next
45
_
Outline
Multidimensional
Arrays.vb
output &= vbCrLf
Next
MessageBox.Show(output, _
"Initializing Multi-Dimensional Arrays", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main
End Module ' modMultidimensionalArrays
 2002 Prentice Hall.
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Outline
' Fig 7.17: JaggedArray.vb
' Jagged two-dimensional array example.
Imports System.Windows.Forms
JaggedArray.vb
Module modJaggedArray
Dim lastStudent, lastExam As Integer
Dim output As String
Sub Main()
Dim i As Integer
' jagged array with 3 rows of exam scores
Dim gradeArray As Integer()() = New Integer(2)() {}
' allocate each
gradeArray(0) =
gradeArray(1) =
gradeArray(2) =
row
New
New
New
with 4 student
Integer() {77,
Integer() {98,
Integer() {70,
grades
68, 86, 73}
87, 89, 81}
90, 86, 81}
' upper bounds for array manipulations
lastStudent = gradeArray.GetUpperBound(0)
lastExam = gradeArray(0).GetUpperBound(0)
output = "Students
\
Exams" & vbCrLf
' build output string
BuildString(gradeArray)
output &= vbCrLf & vbCrLf & "Lowest grade: " & _
Minimum(gradeArray) & vbCrLf & "Highest grade: " & _
Maximum(gradeArray) & vbCrLf
 2002 Prentice Hall.
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' calculate each student's average
For i = 0 To lastStudent
output &= vbCrLf & "Average for student " & _
i & " is " & Average(gradeArray(i))
Next
Outline
JaggedArray.vb
MessageBox.Show(output, "Jagged two-dimensional array", _
MessageBoxIcon.Information)
Determines MessageBoxButtons.OK,
the lowest grade of any student
for the semester
End Sub ' Main
' find minimum grade
Function Minimum(ByVal grades As Integer()()) _
As Integer
Dim lowGrade As Integer = 100
Dim i, j As Integer
For i = 0 To lastStudent
For j = 0 To lastExam
If grades(i)(j) < lowGrade Then
lowGrade = grades(i)(j)
End If
Next
Next
Return lowGrade
End Function ' Minimum
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' find the maximum grade
Function Maximum(ByVal grades As Integer()()) _
As Integer
Dim highGrade As Integer = 0
Dim i, j As Integer
48
Outline
JaggedArray.vb
Determines the highest grade of any student for the semester
For i = 0 To lastStudent
For j = 0 To lastExam
If grades(i)(j) > highGrade Then
highGrade = grades(i)(j)
End If
Next
Next
Determines
a particular student’s semester average
Return highGrade
End Function ' Maximum
' determine the average grade for student
' (or set of grades)
Function Average(ByVal setOfGrades As Integer()) _
As Double
Dim i As Integer, total As Integer = 0
' find sum of student's grades
For i = 0 To lastExam
total += setOfGrades(i)
Next
Return total / setOfGrades.Length
End Function ' Average
 2002 Prentice Hall.
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' creates String displaying array
Sub BuildString(ByVal grades As Integer()())
Dim i, j As Integer
Outline
JaggedArray.vb
' align column heads
output &= "
"
Appends the two dimensional array to
For i = 0 To lastExam
string
output
output
&= "("in&tabular
i & ")format
"
Next
For i = 0 To lastStudent
output &= vbCrLf & "
(" & i & ")
For j = 0 To lastExam
output &= grades(i)(j) & "
Next
"
"
Next
End Sub ' BuildString
End Module ' modJaggedArray
 2002 Prentice Hall.
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50
7.10 Variable-Length Parameter Lists
• Keyword ParamArray
– Makes it possible to create procedures that receive a variable
number of arguments
– You can not use ParamArray with a multidimensional
array
– You can not use ByRef with ParamArray
– All arguments passed to the ParamArray array must be of
the same type as the array
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1
' Fig. 7.18: ParamArrayTest.vb
2
' Calls
Usingprocedure
ParamArray
to create variable-length
parameter
lists.
AnyNumberArguments,
passing
a
3
different number of arguments each time
4
Module modParamArrayTest
5
6
Sub Main()
7
AnyNumberArguments()
8
AnyNumberArguments(2, 3)
9
AnyNumberArguments(7, 8, 9, 10, 11, 12)
Applies
keyword ParamArray to array1
10
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End Sub ' Main
12
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' receives any number of arguments in array
14
Sub AnyNumberArguments(ByVal ParamArray array1 _
15DeterminesAswhether
Integer())
or not zero arguments where passed, if
16
not displays array1’s elements and their sum
17
Dim i, total As Integer
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total = 0
19
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If array1.Length = 0 Then
21
Console.WriteLine("Procedure AnyNumberArguments" & _
22
" received 0 arguments.")
23
Else
24
Console.Write("The total of ")
25
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For i = 0 To array1.GetUpperBound(0)
27
Console.Write(array1(i) & " ")
28
total += array1(i)
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Next
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Console.WriteLine("is {0}.", total)
32
End If
33
Outline
ParamArrayTest.v
b
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End Sub ' AnyNumberArguments
Outline
End Module ' modParamArrayTest
Procedure AnyNumberArguments received 0 arguments.
The total of 2 3 is 5.
The total of 7 8 9 10 11 12 is 57.
ParamArrayTest.v
b
 2002 Prentice Hall.
All rights reserved.
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7.11 For Each/Next Repetition Structure
• For Each/Next
– Provided to iterate through the values in a data structure,
such as an array
– Instead of a counter, For Each/Next uses a variable to
represent the value of each element
– Useful when the indices of the elements are not important
– Particularly useful for looping through arrays of objects
 2002 Prentice Hall. All rights reserved.
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' Fig. 7.19: ForEach.vb
' Program uses For Each/Next to find a minimum grade.
Module modForEach
Outline
ForEach.vb
Sub Main()
Specifies
a variable grade and an array gradeArray. The structure
Dim gradeArray As Integer(,) = New Integer(,) _
iterates{{77,
through
all86,
the 73},
elements
gradeArray,
sequentially
68,
{98,in87,
89, 81}, {70,
90, 86, 81}}
assigning each value to variable grade
Dim grade As Integer
Dim lowGrade
As Integer
= 100 to
The values
are compared
For Each
variable lowGrade,
whichInstores
the lowest grade in the array
grade
gradeArray
If grade < lowGrade Then
lowGrade = grade
End If
Next
Console.WriteLine("The minimum grade is: {0}", lowGrade)
End Sub ' Main
End Module ' modForEach
The minimum grade is: 68
 2002 Prentice Hall.
All rights reserved.