1. Programming In Visual Basic .NET
Chapter 8 Arrays
Programming In
Visual Basic .NET

2. Single-Dimension Arrays
List or series of values all referenced by the same name
Similar to list of values for list boxes and combo boxes - without the box
Use an array to store multiple values
May be referred to as a table or subscripted variable
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3. Array Terms Element Subscript (or index) Boundaries
Individual item in the array
Subscript (or index)
Zero based number used to reference the specific elements in the array
Must be an integer
Boundaries
Lower Subscript, 0 by default
Upper Subscript
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4. Array Example nameString Array (0) Janet Baker (1) George Lee (2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
Janet Baker
George Lee
Sue Li
Samuel Hoosier
Sandra Weeks
William Macy
Andy Harrison
Ken Ford
Denny Franks
Shawn James
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5. The Dim Statement for Arrays - General Form
Dim statement allocates storage for specific number of elements and initializes numeric variables to 0 and string array elements to empty string (zero characters)
Elements in an array may be assigned values in the Dim statement, cannot declare upper subscript and initial values
Dim ArrayName(UpperSubscript) As Datatype
Dim ArrayName( ) As Datatype = {InitialValueList}
Dim ArrayName As Datatype( ) = {InitialValueList}
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6. Dim Statement for Arrays Examples
Dim nameString(25) As String
Dim balanceDecimal(10) As Decimal
Dim productString(99) As String
Dim indexInteger( ) As Integer = {1, 5, 12, 18, 20}
Dim indexInteger As Integer( ) = {1, 5, 12, 18, 20}
Dim departmentsString( ) As String = {"Accounting", "Marketing"}
Private categoryString(10) As String
Public idNumberString(5) As String
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7. Valid Subscripts Subscript must reference a valid element of an array
VB rounds fractional subscripts
VB throws exceptions for subscripts that are out of range
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8. For Each/Next Statements
Use Loops to reference each element in the array
For / Next or For Each/Next
VB references EACH element of the array and assigns its value to ElementName
Variable used for ElementName must be same datatype as array elements or an Object datatype
Makes one pass through the loop per element
Use Exit For statement within loop to exit early
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9. The For Each and Next Statements – General Form
For Each ElementName In ArrayName
' Statement(s) in loop.
Next [ElementName]
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10. The For Each and Next Statements - Example
' Assumes array nameString is dimensioned and holds data.
Dim eachNameString As String
For Each eachNameString In nameString
' Write one element of the array.
Debug.WriteLine(eachNameString)
Next eachNameString
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11. Structures Combine multiple fields of data to create a new structure
Similar to defining a new data type
Define using Structure, End Structure
Declaration (by default a Structure is Public)
Cannot be declared inside a procedure
Generally place with module-level declarations
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12. The Structure and End Structure Statements - General Form
[Public|Private] Structure NameOfStructure
Dim FirstField As Datatype
Dim SecondField As Datatype
. . .
End Structure
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13. The Structure and End Structure Statements - Example
Structure Employee
Dim lastnameString As String
Dim firstNameString As String
Dim socialSecurityNumberString As String
Dim streetString As String
Dim stateString As String
Dim zipCodeString As String
Dim hireDate As Date
Dim payCodeInteger As Integer
End Structure
' Declaring a variable based on the Structure.
Dim officeEmployee As Employee
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14. The Structure and End Structure Statements - Example
Public Structure Product
Dim descriptionString As String
Dim idString As String
Dim quantityInteger As Integer
Dim priceDecimal As Decimal
End Structure
' Declaring a variable array based on the structure.
Dim inventoryProduct(100) As Product
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15. Accessing the Elements in a Structure Variable
Each field of data in Structure is an Element
To access specify Variable.Element
Examples
officeEmployee.lastNameString
officeEmployee.hireDate
inventoryProduct(indexInteger).descriptionString
inventoryProduct(indexInteger).quantityInteger
inventoryProduct(indexInteger).priceDecimal
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16. Including An Array In A Structure
Arrays can be included as elements within a Structure
VB does not allow you to declare the number of elements in the array within the Structure declaration
Use the ReDim statement inside a procedure to define the size of the array
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17. ReDim Code Example
' Module-level declarations. Structure SalesDetail Dim saleDecimal( ) As Decimal End Structure
Dim houseWaresSalesDetail As SalesDetail
' Inside a procedure. ' Establish the number of elements in the array. ReDim houseWaresSalesDetail.saleDecimal(6)
' In processing. houseWaresSalesDetail.saleDecimal _ (dayIndexInteger) = currentDaySalesDecimal
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18. Using Array Elements for Accumulators (pgs. 325-327)
groupNumberInteger=(groupTextBox.Text - 1)
totalInteger array
(0)
(1)
(2)
(3)
(4)
(5)
(6)
(7) 10
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19. Debugging Array Programs
View the array elements in break time in the Autos window, click plus sign to left of array name to view individual array elements
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20. Table Lookup (pgs )
Often values used to identify a series of elements are not sequential
Use a table lookup process to find the correct element in the array
Establish a structure and dimension an array of the structure
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21. Table Lookup (continued)
indexInteger=2
arrayGroup array
(0)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
101 0
103 0
110 10
115 0
121 0
123 0
130 0
145 0
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22. Using List Boxes With Arrays
Use List Boxes or Combo Boxes rather than text boxes to look up information in the array
Use the list's SelectedIndex property to determine the array subscript
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23. Using List Boxes With Arrays (continued)
groupNumberInteger = groupListBox.SelectedIndex
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24. Multidimensional Arrays
Dim statement specifies number of rows and columns in two-dimensional array
May specify number of elements OR initial values
Specify row with first subscript, column with second subscript
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25. The Dim Statement for Two-Dimensional Arrays - General Form
Dim ArrayName(HighestSubscript, Highest Subscript) As Datatype
Dim ArrayName( , ) As Datatype = {ListOfValues}
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26. The Dim Statement for Two-Dimensional Arrays - Examples
Dim nameString(2, 3) As String
Dim nameString( , ) As String = {{"James", "Mary", "Sammie", "Sean"}, _ {"Tom", "Lee", "Leon", "Larry"}, {"Maria", "Margaret", "Jill", "John"}}
' Both statements establish an array of 12 elements.
(0, 0)
James
(0, 1)
Mary
(0, 2)
Sammie
(0, 3)
Sean
(1, 0)
Tom
(1, 1)
Lee
(1, 2)
Leon
(1, 3)
Larry
(2, 0)
Maria
(2, 1)
Margaret
(2, 2)
Jill
(2, 3)
John
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27. Initializing Two-Dimensional Arrays
Initializing/Reinitializing
Use nested For/Next loop
Printing a Two-Dimensional Table
Use For Each/Next loop
Summing a Two-Dimensional Table
Include a total field for each row and each column
Sum the figures in both directions (double-check totals)
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28. Nested For/Next Example
Dim rowInteger As Integer
Dim columnInteger As Integer
For rowInteger = 0 To 2
For columnInteger = 0 To 3
' Initialize each element.
nameString(rowInteger, columnInteger) = " "
Next columnInteger
Next rowInteger
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29. Printing a Two-Dimensional Table
' Print one name per line.
For Each elementString In nameString
' Set up a line.
e.Graphics.DrawString(elementString, printFont, _ Brushes.Black, horizontalPrintLocationSingle, _ verticalPrintLocationSingle)
' Increment the Y position for the next line.
verticalPrintLocationSingle += lineHeightSingle
Next elementString
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30. Summing a Two-Dimensional Table
amountDecimal
(0) (1) (2) (3) (4) (5)
rowTotalDecimal
(0)
(1)
(2)
(3)
(0)
(1)
(2)
(3)
ROW TOTALS
COLUMN TOTALS
columnTotalDecimal
(0) (1) (2) (3) (4) (5)
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31. Summing Code Example ' Crossfoot Total a 2D table.
Dim amountDecimal( , ) As Decimal = {{2.5D, 3D, 1.2D, 2.2D, 4.5D, 3.5D}, _ {2D, 2D, 2D, 2D, 2D, 2D}, {3D, 3.1D, 3.2D, 3.3D, 3.4D, 3.5D}, _
{4.4D, 4.5D, 4.6D, 4.7D, 4.8D, 4.9D}}
Dim rowTotalDecimal(3) As Decimal
Dim columnTotalDecimal(5) As Decimal
Dim rowInteger As Integer
Dim columnInteger As Integer
For rowInteger = 0 to 3
For columnInteger = 0 to 5
rowTotalDecimal(rowInteger) += amountDecimal(rowInteger, columnInteger)
columnTotalDecimal(columnInteger) += amountDecimal(rowInteger, columnInteger)
Next columnInteger
Next rowInteger
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32. Lookup Operations for Two-Dimensional Tables
Use same techniques as for single dimensional arrays
Direct Reference (if meaningful row and column subscripts are available)
Table Lookup
Many 2D tables used for lookup will require additional one-dimensional arrays or lists to aid in the lookup process
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33. Lookup Example Using List Box (page 335)
weightIndexInteger uses weightListBox.SelectedIndex
zoneIndexInteger uses
zoneListBox.SelectedIndex
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