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2. 8 Arrays Chapter McGraw-Hill
© 2006 The McGraw-Hill Companies, Inc. All rights reserved.

3. Objectives
Establish an array and refer to individual elements in the array with subscripts
Use the For Each/Next to traverse the elements of an array
Create a structure for multiple fields of related data
Accumulate totals using arrays
Distinguish between direct access and indirect access of a table
Write a table lookup for matching an array element
Combine the advantages of list box controls with arrays
Store and look up data in multidimensional arrays

4. 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 a series of variables for later processing
Use an array to store multiple values
May be referred to as a table or subscripted (index) variable
Individual elements are treated the same as any other variable and my be used in any statement

5. 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

6. 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

7. Subscripts
Subscripts may be constants, variables, or numeric expressions
Subscripts must be integers-VB rounds any noninteger subscript
The real advantage of using an array is not realized until you use variables for subscripts in place of constants

8. The Declaration Statements for Arrays - General Form
This 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}
Arrays can be declared by using Dim, Public, Private, or Friend keyword
Just as with any other variable, the location of the declaration determines the scope and lifetime of the array variables
*The next slide displays the Declaration Statements for Arrays Example

9. Dim Statement for Arrays Example(s)
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
Array subscripts are zero bases, so the first element is always element zero
The upper subscript is the highest subscript—one less than the number of elements
You declare a data type for the array—all of the array elements must be the same data type; if the data type is omitted by having Option Strict off, just as single variables, the type defaults to Object

10. 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
Arrays are based on System.Array, which is a collection

11. 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
Best to declare the variable for ElementName as part of the For Each statement to create a block-level variable
Makes one pass through the loop per element
Use Exit For statement within loop to exit early
The significant advatanges of using the For Each and Next (key term) are that subscripts for the array don’t have to be manipulated or the user doesn’t need to know how many elements there are in the array
*The next slide displays the General Form for the For Each and Next Statements

12. The For Each and Next Statements General Form
For Each ElementName [As Datatype] In ArrayName
' Statement(s) in loop.
Next [ElementName]
If the array has 12 elements, the loop will execute 12 times
*The next slide provides an example of the For Each and Next Statements

13. The For Each and Next Statements Example
For Each eachNameString In nameString
' Write one element of the array.
Debug.WriteLine(eachNameString)
Next eachNameString
The For Each loop executes if the array has at least one elements—all the statements within the loop are executed for the first element
If the array has more elements, the loop continues to execute until all the elements are processesd

14. Structures Combine multiple fields of data to create a new structure
Similar to defining a new data type
Combine fields into a structure using the Structure, End Structure
Structure Declaration (by default a Structure is Public)
Cannot be declared inside a procedure
Generally place at the top of a file with module-level declarations
Can also be placed in a separate file
*The next slide displays the general form for the Structure and End Structure Statements

15. The Structure and End Structure Statements - General Form
[Public|Private|Friend] Structure NameOfStructure
Dim FirstField As Datatype
Dim SecondField As Datatype
. . .
End Structure
By default, a structure is public—it can be declared to be Friend or Private if desired

16. The Structure and End Structure Statements – Example (1 of 2)
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
*Continuation of the Structure and End Structure Statement Example is on the next slide

17. The Structure and End Structure Statements – Example (2 of 2)
Friend Structure Product
Dim descriptionString As String
Dim productNumberString As String
Dim quantityInteger As Integer
Dim priceDecimal As Decimal
End Structure
Structure SalesDetail
Dim saleDecimal () As Decimal
EndStructure
Once a structure is created variables of the structure can be declared just as if it were another data type

18. Accessing the Elements in a Structure Variable
Each field of data in Structure is referred to as an element of the structure
To access elements use the dot notation similar to that used for objects--Specify Variable.Element
Examples
officeEmployee.lastNameString
officeEmployee.hireDate
inventoryProduct(indexInteger).descriptionString
inventoryProduct(indexInteger).quantityInteger
inventoryProduct(indexInteger).priceDecimal
A variable that is not an array, does not need an index

19. 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
*The next slide provides an example of the code used to include an Array in a Structure

20. ReDim Code Example
' Module-level declarations. Structure SalesDetail Dim saleDecimal( ) As Decimal End Structure
Private houseWaresSalesDetail As SalesDetail
' Inside a procedure. ' Establish the number of elements in the array. ReDim houseWaresSalesDetail.saleDecimal(6)
' In processing. houseWaresSalesDetail.saleDecimal _ (dayIndexInteger) = currentDaySalesDecimal

21. Using Array Elements for Accumulators
Array elements are regular variables and perform in the same ways as many other variables
Subscripted variables can be used in any choosen such as for counters or total accumulators
*Use example in the textbook on p. 327 to explain this slide

22. Debugging Array Programs
View the array elements in debugging time by setting a breakpoint and view the Autos window; click the plus sign to left of array name to view individual array elements

23. Table Lookup
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
Use the Form_Load event procedure to put numbers in table-executed once the form is loaded into memory
Things don’t always work out so neatly as having sequential group numbers that can be used to access the table directly
Sometimes a little work is involved to find (look up) the correct value and reference the array elements indirectly

24. Coding a Table Lookup
For a table lookup, a Do/Loop works better than For Each
When comparing to element in the array and eventually finding a match the user needs to know the subscript of the matching element
*Example on p. 331 in textbook

25. Lookup Operation Logic
The table-lookup technique will work for any table, numeric or string
It isn’t necessary to arrange the fields being searched in any particular sequence
The comparison is made to one item in the list, then the next, and the next until a match is found
Time can be saved in a large table by arranging the elements with the most-often-used entries at the top so that fewer comparisons must be made

26. Using List Boxes With Arrays (1 of 2)
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
Selected Index property holds the position or index of the selected list item
*The next slide displays an example of using a List Box

27. Using List Boxes With Arrays (1 of 2)
Allow the user to select from a list and the SelectedIndex property can be used as the subscript of the total array.
groupNumberInteger = groupListBox.SelectedIndex

28. Multidimensional Arrays
To define a two-dimensional array or table--
Dim statement specifies number of rows and columns
The row is horizontal and the column is vertical
May specify number of elements –OR-- initial values
Specify row with first subscript, column with second subscript, need to use a comma to specify the dimensions
Generally two subscripts are needed to identify tabular data, where data is arranged in rows and columns

29. The Dim Statement for Two-Dimensional Arrays - General Form
Dim ArrayName(HighestSubscript, Highest Subscript) As Datatype
Dim ArrayName( , ) As Datatype = {ListOfValues}

30. The Dim Statement for Two-Dimensional Arrays – Example(s)
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
The elements of the array may be used in the same ways as any other variable – in accumulators, counts and reference fields for lookup, or in statements like assignment and printing, and as conditions

31. 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)
Numeric array elements are initially set to 0 and string elements are set to empty strings; initial values can be assigned when declaring the array

32. Nested For/Next Example
For rowInteger = 0 To 2
For columnInteger = 0 To 3
' Initialize each element.
nameString(rowInteger, columnInteger) = " "
Next columnInteger
Next rowInteger
The assignment statement will be executed once for each element of nameString

33. 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

34. Summing a Two-Dimensional Table
The sum of a table can be found in various ways; either sume the columns or the rows of the table; or, as sum the figures in both directions and double-check the totals; to sum an array in both directions, each column needs one total variable and each row needs one total variable
Two-one dimensional arrays work well for the totals

35. 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
A table lookup is the most common lookup technique

36. Two Dimensional Array Example
*This example is found in the textbook on p. 337
Many two-dimensional tables used for lookup require additional one-dimensional arrays or lists to aid in the lookup process