1. 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

2. 7.2 Arrays Array Position number Length property GetUpperBound method
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

3. 7.2 Arrays
Name of array (note that all elements of this array have the same name, numberArray)
numberArray(0)
-45
numberArray(1) 6
numberArray(2)
numberArray(3) 72
numberArray(4)
1543
numberArray(5)
-89
numberArray(6)
numberArray(7) 62
numberArray(8) -3
Position number (index or subscript) of the element within array numberArray
numberArray(9) 1
numberArray(10)
6453
numberArray(11) 78
Fig. 7.1 Array consisting of 12 elements.

4. 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

5. Several examples that demonstrate
7.4 Examples Using Arrays
Several examples that demonstrate
Declaration
Allocation
Initialization of arrays

6. The length property returns the number of elements in the array
1 ' Fig. 7.2: CreateArray.vb
2 ' Declaring and allocating an array. 3
4 Imports System.Windows.Forms 5
6 Module modCreateArray 7
Sub Main()
Dim output As String
Dim i As Integer 11
Dim array As Integer() ' declare array variable
array = New Integer(9) {} ' allocate memory for array 14
output &= "Subscript " & vbTab & "Value" & vbCrLf 16
' display values in array
For i = 0 To array.GetUpperBound(0)
output &= i & vbTab & array(i) & vbCrLf
Next 21
output &= vbCrLf & "The array contains " & _
array.Length & " elements." 24
MessageBox.Show(output, "Array of Integer Values", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main 28
29 End Module ' modCreateArray
CreateArray.vb
A variable capable of storing a reference to an array of Integer elements
Allocate an array of 10 elements using New and assigns it to array
Appends to output the headings for the columns displayed by the program
For structure is used to append the index number and value of each array element to output
The length property returns the number of elements in the array

7. 7.4 Examples Using Arrays
CreateArray.vb

8. One statement is used to declare the two arrays
1 ' Fig. 7.3: InitArray.vb
2 ' Initializing arrays. 3
4 Imports System.Windows.Forms 5
6 Module modInitArray 7
Sub Main()
Dim output As String
Dim i As Integer 11
Dim array1, array2 As Integer() ' declare two arrays 13
' initializer list specifies number of elements
' and value of each element
array1 = New Integer() {32, 27, 64, 18, 95, _
, 90, 70, 60, 37} 18
' allocate array2 based on length of array1
array2 = New Integer(array1.GetUpperBound(0)) {} 21
' set values in array2 by a calculation
For i = 0 To array2.GetUpperBound(0)
array2(i) = * i
Next 26
output &= "Subscript " & vbTab & "Array1" & vbTab & _
"Array2" & vbCrLf 29
' display values for both arrays
For i = 0 To array1.GetUpperBound(0)
output &= i & vbTab & array1(i) & vbTab & array2(i) & _
vbCrLf
Next 35
InitArray.vb
One statement is used to declare the two arrays
Allocates the 10 elements of array1 with New and initialize the values in the array, using an initializer list
Allocates array2, whose size is determined by arry1.GetUpperBound(0), so that array1 and array2 have the same upper bound
Initializes each element in array2 to the even integers
Uses the values in the arrays to build String output, which is displayed in a MessageBox

9. InitArray.vb 36 MessageBox.Show(output, "Array of Integer Values", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main 39
40 End Module ' modInitArray
InitArray.vb

10. Declares, allocates and initializes the 10-element array, array
1 ' Fig. 7.4: SumArray.vb
2 ' Computing sum of elements in array. 3
4 Imports System.Windows.Forms 5
6 Module modSumArray 7
Sub Main()
Dim array As Integer() = New Integer() _
{1, 2, 3, 4, 5, 6, 7, 8, 9, 10} 11
Dim total As Integer = 0, i As Integer = 0 13
' sum array element values
For i = 0 To array.GetUpperBound(0)
total += array(i)
Next 18
MessageBox.Show("Total of array elements: " & total, _
"Sum the elements of an Array", MessageBoxButtons.OK, _
MessageBoxIcon.Information)
End Sub ' Main 23
24 End Module ' modSumArray
Declares, allocates and initializes the 10-element array, array
SumArray.vb
Performs the addition

11. 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 recieved

12. Appends the five elements of array1 to String output
1 ' Fig. 7.8: PassArray.vb
2 ' Passing arrays and individual array elements to procedures. 3
4 Imports System.Windows.Forms 5
6 Module modPassArray
Dim output As String 8
Sub Main()
Dim array1 As Integer() = New Integer() {1, 2, 3, 4, 5}
Dim i As Integer 12
output = "EFFECTS OF PASSING ENTIRE ARRAY " & _
"BY REFERENCE:" & vbCrLf & vbCrLf & _
"The values of the original array are:" & vbCrLf 16
' display original elements of array1
For i = 0 To array1.GetUpperBound(0)
output &= " " & array1(i)
Next 21
ModifyArray(array1) ' array is passed by reference 23
output &= vbCrLf & _
"The values of the modified array are:" & vbCrLf 26
' display modified elements of array1
For i = 0 To array1.GetUpperBound(0)
output &= " " & array1(i)
Next 31
PassArray.vb
Appends the five elements of array1 to String output
Passes array1 to procedure ModifyArray
Appends the elements of array1 to output

13. Multiplies the elements of arrayParameter by 2
output &= vbCrLf & vbCrLf & _
"EFFECTS OF PASSING ARRAY ELEMENT " & _
"BY VALUE:" & vbCrLf & vbCrLf & "array1(3) " & _
"before ModifyElementByVal: " & array1(3) 36
' array element passed by value
ModifyElementByVal(array1(3)) 39
output &= vbCrLf & "array1(3) after " & _
"ModifyElementByVal: " & array1(3) 42
output &= vbCrLf & vbCrLf & "EFFECTS OF PASSING " & _
"ARRAY ELEMENT BY REFERENCE: " & vbCrLf & vbCrLf & _
"array1(3) before ModifyElementByRef: " & array1(3) 46
' array element passed by reference
ModifyElementByRef(array1(3)) 49
output &= vbCrLf & "array1(3) after " & _
"ModifyElementByRef: " & array1(3) 52
MessageBox.Show(output, "Passing Arrays", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main 56
' procedure modifies array it receives (note ByVal)
Sub ModifyArray(ByVal arrayParameter As Integer())
Dim j As Integer 60
For j = 0 To arrayParameter.GetUpperBound(0)
arrayParameter(j) *= 2
Next 64
End Sub ' ModifyArray 66
PassArray.vb
Multiplies the elements of arrayParameter by 2

14. PassArray.vb 67 ' procedure modifies integer passed to it
' original is not be modified (note ByVal)
Sub ModifyElementByVal(ByVal element As Integer) 70
output &= vbCrLf & "Value received in " & _
"ModifyElementByVal: " & element
element *= 2
output &= vbCrLf & "Value calculated in " & _
"ModifyElementByVal: " & element
End Sub ' ModifyElementByVal 77
' procedure modifies integer passed to it
' original is be modified (note ByRef)
Sub ModifyElementByRef(ByRef element As Integer) 81
output &= vbCrLf & "Value received in " & _
"ModifyElementByRef: " & element
element *= 2
output &= vbCrLf & "Value calculated in " & _
"ModifyElementByRef: " & element
End Sub ' ModifyElementByRef 88
89 End Module ' modPassArray
PassArray.vb

15. 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

16. 7.6 Passing Arrays: ByVal vs. 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

17. firstArray is passed to FirstDouble
1 ' Fig. 7.9: ArrayReferenceTest.vb
2 ' Testing the effects of passing array references using
3 ' ByVal and ByRef. 4
5 Module modArrayReferenceTest 6
Sub Main()
Dim i As Integer 9
' declare array references
Dim firstArray As Integer()
Dim firstArrayCopy As Integer() 13
' allocate firstArray and copy its reference
firstArray = New Integer() {1, 2, 3}
firstArrayCopy = firstArray 17
Console.WriteLine("Test passing array reference " & _
"using ByVal.")
Console.Write("Contents of firstArray before " & _
"calling FirstDouble: ") 22
' print contents of firstArray
For i = 0 To firstArray.GetUpperBound(0)
Console.Write(firstArray(i) & " ")
Next 27
' pass firstArray using ByVal
FirstDouble(firstArray) 30
Console.Write(vbCrLf & "Contents of firstArray after " & _
"calling FirstDouble: ") 33
ArrayReferenceTest.vb
Copies reference firstArray to variable firstArrayCopy, now they reference the same object
Prints contents first to verify that FirstDouble indeed changes the array’s contents
firstArray is passed to FirstDouble

18. Compares references firstArray and firstArrayCopy
' print contents of firstArray
For i = 0 To firstArray.GetUpperBound(0)
Console.Write(firstArray(i) & " ")
Next 38
' 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 47
' declare array references
Dim secondArray As Integer()
Dim secondArrayCopy As Integer() 51
' allocate secondArray and copy its reference
secondArray = New Integer() {1, 2, 3}
secondArrayCopy = secondArray 55
Console.WriteLine(vbCrLf & "Test passing array " & _
"reference using ByRef.")
Console.Write("Contents of secondArray before " & _
"calling SecondDouble: ") 60
' print contents of secondArray before procedure call
For i = 0 To secondArray.GetUpperBound(0)
Console.Write(secondArray(i) & " ")
Next 65
' pass secondArray using ByRef
SecondDouble(secondArray) 68
Compares references firstArray and firstArrayCopy
ArrayReferenceTest.vb

19. Bubble Sort (a.k.a. sinking sort)
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

20. 7.8 Searching Arrays: Linear Search and Binary Search
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

21. 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

22. 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 Two-dimensional array with three rows and four columns.

23. Allocates array1 with six initializers in two sublists
1 ' Fig. 7.16: MultidimensionalArrays.vb
2 ' Initializing multi-dimensional arrays. 3
4 Imports System.Windows.Forms 5
6 Module modMultidimensionalArrays 7
Sub Main()
Dim output As String
Dim i, j As Integer 11
' create rectangular two-dimensional array
Dim array1 As Integer(,)
array1 = New Integer(,) {{1, 2, 3}, {4, 5, 6}} 15
' create jagged two-dimensional array
Dim array2 As Integer()() = New Integer(2)() {} 18
array2(0) = New Integer() {1, 2}
array2(1) = New Integer() {3}
array2(2) = New Integer() {4, 5, 6} 22
output = "Values in array1 by row are " & vbCrLf 24
For i = 0 To array1.GetUpperBound(0) 26
For j = 0 To array1.GetUpperBound(1)
output &= array1(i, j) & " "
Next 30
output &= vbCrLf
Next 33
MultidimensionalArrays.vb
Allocates array1 with six initializers in two sublists
The declaration and allocation of array2 creates a jagged array of 3 arrays
Traverses the array in two dimensions

24. In a jagged two-dimensional array, the second dimension is actually the first dimension of a separate array
output &= vbCrLf & "Values in array2 by row are " & _
vbCrLf 36
For i = 0 To array2.GetUpperBound(0) 38
For j = 0 To array2(i).GetUpperBound(0)
output &= array2(i)(j) & " "
Next 42
output &= vbCrLf
Next 45
MessageBox.Show(output, _
"Initializing Multi-Dimensional Arrays", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main 50
51 End Module ' modMultidimensionalArrays
MultidimensionalArrays.vb

25. 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

26. Applies keyword ParamArray to array1
1 ' Fig. 7.18: ParamArrayTest.vb
2 ' Using ParamArray to create variable-length parameter lists. 3
4 Module modParamArrayTest 5
Sub Main()
AnyNumberArguments()
AnyNumberArguments(2, 3)
AnyNumberArguments(7, 8, 9, 10, 11, 12) 10
End Sub ' Main 12
' receives any number of arguments in array
Sub AnyNumberArguments(ByVal ParamArray array1 _
As Integer()) 16
Dim i, total As Integer
total = 0 19
If array1.Length = 0 Then
Console.WriteLine("Procedure AnyNumberArguments" & _
" received 0 arguments.")
Else
Console.Write("The total of ") 25
For i = 0 To array1.GetUpperBound(0)
Console.Write(array1(i) & " ")
total += array1(i)
Next 30
Console.WriteLine("is {0}.", total)
End If 33
Calls procedure AnyNumberArguments, passing a different number of arguments each time
ParamArrayTest.vb
Applies keyword ParamArray to array1
Determines whether or not zero arguments where passed, if not displays array1’s elements and their sum

27. 34 End Sub ' AnyNumberArguments 35 36 End Module ' modParamArrayTest
ParamArrayTest.vb
Procedure AnyNumberArguments received 0 arguments.
The total of 2 3 is 5.
The total of is 57.

28. 7.11 For Each/Next Repetition Structure
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

29. 1 ' Fig. 7.19: ForEach.vb
2 ' Program uses For Each/Next to find a minimum grade. 3
4 Module modForEach 5
Sub Main()
Dim gradeArray As Integer(,) = New Integer(,) _
{{77, 68, 86, 73}, {98, 87, 89, 81}, {70, 90, 86, 81}} 9
Dim grade As Integer
Dim lowGrade As Integer = 100 12
For Each grade In gradeArray 14
If grade < lowGrade Then
lowGrade = grade
End If 18
Next 20
Console.WriteLine("The minimum grade is: {0}", lowGrade)
End Sub ' Main 23
24 End Module ' modForEach
ForEach.vb
Specifies a variable grade and an array gradeArray. The structure iterates through all the elements in gradeArray, sequentially assigning each value to variable grade
The values are compared to variable lowGrade, which stores the lowest grade in the array
The minimum grade is: 68