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

2. Case Structure
Best alternative for testing a single variable or expression for multiple values
Any decisions coded with nested If statements can also be coded using Case structure
Case Structure is simpler, cleaner, more efficient than the nested If
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

3. Select Case General Form (also notice indenting)
Select Case expression
Case ConstantList
[ code to run]
[Case ConstantList
[ code to run]]
[Case Else ]
[code to run]]
End Select
If expression=value in constant list
If expression=value in constant list
If expression< >values in any of the preceding constant lists
** Case Else is an optional clause
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

4. Select Case - Numeric Value Example 1
Private Function CalculateGrade(ByVal intScore As Integer) as String
Select Case intScore
Case Is >= 90
Return "A"
Case 80 to 89
Return "B"
Case 70 to 79
Return "C"
Case 60 to 69
Return "D“
Case Else 'accommodate all other values
Return "F"
End Select
End Function
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

5. Select Case - Numeric Value Example 2
Select Case intListIndex
Case 0
HandleItemZero( )
Case 1, 2, 3
HandleItems( )
Case Else
HandleNoSelection( )
End Select
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

6. Select Case - String Value Example
Select Case mstrSelectedButton
Case "radQuarter“: intRow = 0
Case "radHalf“: intRow = 1
Case "radFull“ : intRow = 2
Case Else ‘ use default
intRow = 0
End Select
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

7. Sharing an Event Procedure
If the code for multiple controls is very similar,, the controls can share an event procedure
Use the Handles Clause to add multiple controls to a handler
Private Sub radBlack_CheckChanged(ByVal sender as System.Object, _
byVal e as System.Event.Args) Handles radBlack.CheckChanged, _
radBlue.CheckChanged, radRed.CheckChanged, _
radWhite.CheckChanged, radYellow.CheckChanged
[block of code]
End Sub
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

8. sender Argument sender argument is the key to using the shared event
sender is a System.Object type with Name property
Possible Problem
if Option Strict is turned on, reference to sender.Name will cause a compile error for Late Binding (i.e. type cannot be determined until run time rather than at compile time)
Solution
use CType function to convert sender to a specific object type, thus providing Early Binding
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

9. CType Function Converts object from one type to another General Form
CType (ValueToConvert, NewType)
Example
Dim radSelected As RadioButton
radSelected = CType(sender, RadioButton)
Select Case radSelected .Name
Case "radBlue"
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

10. Sharing Event Example
' Declare a module level variable for storing color
Dim mColorNew as Color ‘declare it module level
. . .
Private Sub radBlack_CheckChanged(ByVal sender as System.Object, _
byVal e as System.Event.Args) Handles radBlack.CheckChanged, _ radBlue.CheckChanged, radRed.CheckChanged, _
radWhite.CheckChanged, radYellow.CheckChanged
Dim radSelected as RadioButton
radSelected = CType (sender, RadioButton) ‘early binding
Select Case radSelected.Name
Case "radBlack“ : mColorNew = Color.Black
Case "radBlue“ : mColorNew = Color.Blue
Case "radRed“ : mColorNew = Color.Red
Case "radWhite“ : mColorNew = Color.White
Case "radYellow“ : mColorNew = Color.Yellow
End Select
End Sub
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

11. Arrays
Array is a collection of values referenced in memory by the same name
Similar to list of items for list boxes and combo boxes - without the box
Use an array to keep a series of variable for later processing such as
Reordering
Calculating
Printing
strName
(0)
(1)
(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
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

12. Array Terms strName Element Index (or subscript) Boundaries
(0)
(1)
(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
Element
Individual item in the array
Index (or subscript)
Zero based number used to reference the specific elements in the array
Must be an integer
Boundaries
Lower Subscript, 0 by default
Upper Subscript
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

13. Two Ways to Declare Arrays
Using upper bound versus assigned values
Examples
Dim ArrayName (UpperSubscript ) as Datatype
‘ In this case each element of the array will be assigned a default ‘value: numeric  0, string  “” (no characters)
Dim ArrayName ( ) as Datatype = {InitialValueList}
‘No upper Subscript is allowed
Dim strName (3) as String ‘an array of 4 elements: Dim decBalance(99) as Decimal ‘an array of 100 elements:
Dim strDept ( ) as String = {"ACT", "MKT", "HR", "MIS"} Dim intActCode ( ) as Integer = {10, 20, 30, 40}
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

14. Referencing Array Elements
Use the Index(s) of the Element
strName
(0)
(1)
(2)
(3)
Jill Creech
Paul Fry
Rich Wells
strName(0) : "Sam Smith"
strName(1) : "Jill Creech"
strName(2) : "Paul Fry"
strName(3) : "Rich Wells"
Sam Smith
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

15. For Each / Next Loop General Form Example
For Each ElementName In ArrayName
Statements to execute
Next [ElementName]
' Assumes array intTotal previously dimensioned
Dim intOneTotal As Integer ‘must be the same type as intTotal
For Each intOneTotal In intTotal ‘references EACH element
intOneTotal=0 ' reinitialize element of the array
Next intOneTotal
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

16. Structures Combine multiple fields of data into a single unit
Declaration (by default a Structure is Public)
Cannot be declared inside a procedure
Generally declared in General Declarations
Define using Structure, End Structure
Once created, declare variable of the Structure as if it were another datatype; make up a meaningful prefix
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

17. Structure Declaration
General Form
Example
[Public|Private] Structure NameOfStructure
Dim FirstField As Datatype
Dim SecondField As Datatype
. . .
End Structure
Dim manyStructuredVar As NameOfStructure
Structure CoffeeSale
Dim strType As String
Dim strQuantity As String
Dim decPrice As Decimal
End Structure
Dim mcslTransaction(20) As CoffeeSale
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

18. Accessing the Elements in a Structure Variable
Each field of data in Structure is an Element
To access specify Variable.Element
Examples
empOffice.intEmpID
empOffice.strFName
empOffice.strLName
empOffice.datHireDate
prdInven(intIndex).strDesc
prdInven(intIndex).strID
prdInven(intIndex).intQuan
prdInven(intIndex).decPrice
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

19. Including An Array In A Structure
Arrays can be included as elements within a Structure
VB does not, however, 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
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

20. ReDim Statement Used to redeclare the UpperSubscript/Size of an array
Can preserve original data in the array
General Form (basic)
ReDim [Preserve] ArrayName(UpperSubscript)
Examples
ReDim Preserve strDept(20)
ReDim sdtHousewares.decSale(6)
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

21. Table Lookup Using Structures
Structure Student strStudentID As String strUserName As String End Structure
mstuStudents(99) As Student Dim intIndex As Integer Dim blnFound As Boolean blnFound = False intIndex = 0 Do Until blnFound Or intIndex > If mstuStudents(intIndex).strStudentID = txtID.Text Then blnFound = True lbl .Text = mstuStudents(intIndex).strUserName _ & End If intIndex = intIndex + 1 Loop If blnFound = False Then MsgBox "There is no such student in the list."
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

22. Multidimensional Arrays
Arrays can have more than one dimension
Like a table of values
You must specify the boundaries for each dimension using subscripts
Example: Two Dimensional Array
Dim intScoreBoard (1, 8) as Integer 1
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

23. Referencing Elements in Multidimensional Array
intScoreBoard(row,column) 1
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
1,0
1,1
1,2
1,3
1,4
1,5
1,6
1,7
1,8
intScoreBoard(0,0)
intScoreBoard(0,1)
intScoreBoard(0,2)
intScoreBoard(0,3)
intScoreBoard(0,4)
intScoreBoard(0,5)
intScoreBoard(1,0)
intScoreBoard(1,1)
intScoreBoard(1,2)
intScoreBoard(1,3)
intScoreBoard(1,4)
intScoreBoard(1,5)
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

24. Declaring Two-Dimensional Arrays
General Form
Example
Dim ArrayName(HighestSubscript, Highest Subscript) as Datatype
Dim ArrayName( , ) as Datatype = {ListOfValues}
Dim strName(2, 3) As String
‘ Results in an array of 12 elements: ‘3 rows: 0, 1, 2 and 4 columns: 0, 1, 2, 3
Dim strName( , ) As String = {{"Jim", "Mary", "Sam", "Sean"}, _
{"Tom", "Sue", "Fred", "Paul"}, _
{"Tim", "Al", "Bob", "Pete"}}
‘ Also results in an array of 12 elements: ‘ 3 rows: 0, 1, 2 and 4 columns: 0, 1, 2, 3
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

25. Using Two-Dimensional Arrays
Initializing/Reinitializing
Use Nested For/Next Loops
Use For Each/Next Loop
Printing
Summing
Include a total field for each row and each column
Use For/Next Loop to calculate sums
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

26. Initializing / Reinitializing
Using For/Next loops
Using For Each/Next loops
Dim intRow As Integer
Dim intColumn As Integer
For intRow = 0 to 2
For intColumn = 0 to 3
strName(intRow, intColumn) = " "
Next intColumn
Next intRow
Dim strElement As String
For Each strElement In strName
strElement = " "
Next strElement
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

27. Printing Example 'Print one name per line
For Each strElement In strName
'Set up a line
e.Graphics.DrawString(strElement, fntPrintFont, _ Brushes.Black, sngPrintX, sngPrintY)
'Increment the Y position for the next line
sngPrintY += sngLineHeight
Next strElement
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

28. Summing Example decAmount(3,5) decRowTotal(3) 0 1 2 3 4 5 1 1 1 2 3 1 2 3
ROW TOTALS
COLUMN TOTALS
decColTotal(5)
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

29. Summing Code Example 'Crossfoot Total a 2D table
Dim decAmount(3,5) As Decimal
Dim decRowTotal(3) As Decimal
Dim decColTotal(5) As Decimal
Dim intRowIndex As Integer
Dim intColIndex As Integer
For intRowIndex = 0 to 3
For intColIndex = 0 to 5
decRowTotal(intRowIndex) += decAmount(intRowIndex, intColIndex)
decColTotal(intColIndex) += decAmount(intRowIndex, intColIndex)
Next intColIndex
Next intRowIndex
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

30. Lookup Two-Dimensional Tables
Lookup for an intersection cell (VBMailOrder example)
Lookup for a corresponding value (VBAutoCenter example)
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

31. Lookup For an Intersection Cell
Dim mdecCharge(,) As Decimal = {{1D, 1.5D, 1.65D, 1.85D}, _ 'other elements specified} Dim intCol, intRow As Integer Dim decCharge As Decimal
'Look up the price. intRow = lstWeight.SelectedIndex 'determine the row intCol = lstZone.SelectedIndex 'determine the column decCharge = CDec(mdecCharge(intRow, intCol)) 'find the Charge lblCharge.Text = FormatCurrency(decRate) 'display formatted
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

32. Lookup For a Corresponding Value
'Determine the brand row. intRow for VB Brand is 0. Select Case mstrSelectedRad Case "radA" : intCol = Case "radC" : intCol = Case "radX" : intCol = 3 End Select
'Determine the entered number's row. Dim blnFound As Boolean = False For intRow = 0 To If strParts(intRow, intCol) = txtTheirNumber.Text Then lblVBEquivalent.Text = strParts(intRow, 0) blnFound = True Exit For End If Next
© 2001 by The McGraw-Hill Companies, Inc. All rights reserved.