1. Tutorial 11 Arrays
Tutorial 11: Arrays

2. Using a One-Dimensional Array Lesson A Objectives
After completing this lesson, you will be able to:
Declare and initialize a one-dimensional array
Assign data to a one-dimensional array
Display the contents of a one-dimensional array
Access an element in a one-dimensional array
Search a one-dimensional array
Compute the average of a one-dimensional array’s contents
Find the highest entry in a one-dimensional array
Update the contents of a one-dimensional array
Sort a one-dimensional array
Tutorial 11: Arrays

3. Arrays
A simple variable, also called a scalar variable, is one that is unrelated to any other variable in memory
An array is a group of variables that have the same name and data type and are related in some way
Although arrays in Visual Basic .NET can have as many as 60 dimensions, the most commonly used arrays are one-dimensional and two-dimensional
Programmers use arrays to store related data in the internal memory of the computer
Tutorial 11: Arrays

4. One-Dimensional Arrays
A one-dimensional array is simply a row (or column) of variables
A two-dimensional array resembles a table in that it has rows and columns
Each element in an array is identified by a subscript, which Visual Basic .NET assigns to the variable when the array is created
You refer to an array element by the array’s name followed by the element’s subscript
Tutorial 11: Arrays

5. One-Dimensional Array
strState(2)
strState(3)
strState(4)
strState(0)
strState(1)
Alaska
Montana
South Carolina
Tennessee
Texas
strState(0)
Alaska
Montana
South Carolina
Tennessee
Texas
strState(1)
strState(2)
strState(3)
strState(4)
Tutorial 11: Arrays

6. Declaring an Array Version 1
accessibility arrayname(highestSubscript) As datatype
Version 2
accessibility arrayname() As datatype = {initialValues}
These statements create and initialize the array variables in memory
accessibility is Dim, Public, or Private
Tutorial 11: Arrays

7. Declaring an array Dim strCitys(3) As String
Private intNumbers(5) As Integer
Private udtItems(4) As ItemStruc
Private strStates() As String = {“Hawaii”, “Alaska”, “Maine”}
Dim intScores() As Integer = {75, 9, 23, 6}
Tutorial 11: Arrays

8. Storing Data in a One-Dimensional Array
You can use a variety of ways to enter data into an array
strMonthArray(0) = “Jan”
strMonthArray(1) = “Feb”
strMonthArray(2) = “Mar”
strMonthArray(3) = “Apr”
strMonthArray(4) = “May”
strMonthArray(5) = “June”
Tutorial 11: Arrays

9. Assigning Values to Array Elements
For intNum = 1 to 6
intSquareArray(intNum - 1) = intNum * intNum
Next intNum
For intNum = 0 to 10
sngNum(intNum) = Val(InputBox(“Enter number”))
udtItems(0).sngPrice = udtItems(0).sngPrice * 1.1
Tutorial 11: Arrays

10. One-Dimensional Array
Dim intX As Integer
Do While (intX <= 5 AndAlso Not EOF(1))
FileGet(1, udtItems(intX), intX + 1)
intX += 1
Loop
Tutorial 11: Arrays

11. Display the Contents of a One-Dimensional Array
Dim strMonths() As String = {“JAN”, “FEB”, “MAR”, “APR”, “MAY”, “JUN”, “JUL”, “AUG”, “SEP”, “OCT”, “NOV”, “DEC”}
Dim intX As Integer
For intX = 0 To strMonths.Length - 1
Me.MonthListBox.Items.Add(strMonths(intX))
Next intX
Tutorial 11: Arrays

12. Searching a One-Dimensional Array
Dim intSales() As Integer = {45000, 35000, 25000, 60000, 23000}
Dim intX As Integer ‘keeps track of subscripts
Dim intCount As Integer ‘counter variable
Dim intSearchFor As Integer ‘number to search for
intSearchFor = Val(InputBox(“Enter sales to search for:”, _
“Sales”))
For intX = 0 To 4
If intSales(intX) > intSearchFor Then
intCount += 1
End If
Next intX
MessageBox.Show(“Count: ” & intCount, “Sales”, _
MessageBoxButtons.OK, MessageBoxIcon.Information)
Tutorial 11: Arrays

13. Calculating the Average Amount Stored in a One-Dimensional Numeric Array
Declare variables
Repeat for each score
add array score to intTotal variable
End repeat for intNum
Calculate the average by dividing intTotal by number of scores
Display the average
Tutorial 11: Arrays

14. Calculating the Average Amount Stored in a One-Dimensional Numeric Array
Dim intScores() As Integer = {98, 100, 56, 74, 35}
Dim intX As Integer ‘keeps track of subscripts
Dim intTotal As Integer ‘accumulator variable
Dim sngAvg As Single ‘average score
For intX = 0 To intScores.Length - 1
intTotal += intScores(intX)
Next intX
sngAvg = intTotal / intScores.Length
MessageBox.Show(“Average: ” & sngAvg, “Average”, _
MessageBoxButtons.OK, MessageBoxIcon.Information)
Tutorial 11: Arrays

15. Determining the Highest Value Stored in a One-Dimensional Array
Declare variables
Assign first array value (zero) to intHigh variable
Initialize the intX variable to 1 (second subscript)
Repeat while intX is less than the number of elements in the array
If current array value > intHigh value then
assign current array value to intHigh
End If
End repeat for intNum
Display the highest value(stored in intHigh)
Tutorial 11: Arrays

16. Updating the Values Stored in a One-Dimensional Array
Declare variables
Prompt user for the value to add
Repeat for each price in the array
add value to current array value
display the contents of the current array element
End repeat
Tutorial 11: Arrays

17. Sorting the Data Stored in a One-Dimensional Array
declare an Integer array named intNumbers
declare an Integer variable named intX
open the random access file named nums.data
repeat while intX is less than or equal to 5 and it is not the end of the nums.data file
read a number from the file and store it in the current array element
display the contents of the current array element in a message box
add 1 to the intX variable
end repeat
close the nums.data file
sort the intNumbers array in ascending order using the Array.Sort method
repeat for each element in the intNumbers array
Tutorial 11: Arrays

18. Summary of Array Methods
Clear
Sets a range of elements in the Array to zero or to a null reference (Nothing in Visual Basic).
Copy
Copies a section of one Array to another Array
IndexOf
Returns the index of the first occurrence of a value in a one-dimensional Array or in a portion of the Array
LastIndexOf
Returns the index of the last occurrence of a value in a one-dimensional Array or in a portion of the Array
Reverse
Reverses the order of the elements in a one-dimensional Array or in a portion of the Array
Sort
Sorts the elements in one-dimensional Array objects
Tutorial 11: Arrays

19. More on One-Dimensional Arrays Lesson B Objectives
After completing this lesson, you will be able to:
Create and manipulate parallel one-dimensional arrays
Create and manipulate a one-dimensional array of structures
Tutorial 11: Arrays

20. Parallel Arrays Product ID Price BX35 13 CR20 10 KW10 24 MM67 4
Arrays that are related by an element’s position (subscript)
Searching one array gives you the subscript for the other array
Dim strId() As String = {"BX35”, “CR20", “FE15”, “KW10”, “MM67”}
Dim intPrice() As Integer = {13, 10, 12, 24, 4}
Dim intX As Integer, strSearchFor As String
strSearchFor = UCase(IdTextBox.Text)
‘search the array
Do While intX < strId.Length AndAlso strSearchFor <> strId(intX)
intX += 1
Loop
Product ID
Price
BX35 13
CR20 10
KW10 24
MM67 4
Tutorial 11: Arrays

21. An Array of Structures Declare an ItemStruc array named udtPriceList
Declare variables intX and strSearchFor
Assign IDs and prices to the udtPriceList array
Assign the product ID entered in the IdTextBox control, converted to uppercase, to the strSearchFor variable
Repeat while intX is less than the list length and the value of strSearchFor variable is not equal to the value stored in the current array element’s strId field
Increment intX
End repeat
If the intX variable contains a number that is less than the lists length
display the appropriate price from the intPrice field in the array
Else
display the message “Product ID is not valid”
End if
Tutorial 11: Arrays

22. An Array of Structs Structure ItemStruc Public strId As String
Public intPrice As Integer
End Structure
Dim udtItem(4) As ItemStruc
‘populate the array
udtItem(0).strId = “BX35”: udtItem(0).intPrice = 13 …
‘search the array
Do While intX <udtItem.length AndAlso strSearchFor <> udtItem(intX).strId
intX = intX + 1
Loop
Tutorial 11: Arrays

23. Using a Two-Dimensional Array Lesson C Objectives
After completing this lesson, you will be able to:
Create and initialize a two-dimensional array
Store data in a two-dimensional array
Manipulate a two-dimensional array
Tutorial 11: Arrays

24. Two-Dimensional Arrays
A two-dimensional array resembles a table in that the variables are in rows and columns
strProducts(0, 0)
strProducts(0, 2)
AC24
Shirt
Red
BD12
Coat
Blue
CP14
Blouse
White
strProducts(1, 2)
strProducts(2, 1)
Tutorial 11: Arrays

25. Two-Dimensional Arrays
Version 1
accessibility arrayname(highestRowSubscript, highestColumnSubscript) As datatype
Version 2
accessibility arrayname(,) As datatype = {{initialValues}, {initialValues}, …{initialValues}}
Dim strCitys(5, 3) As String
Dim intScores(,) As Integer = {{75, 90}, {9, 25}, {23, 56}, {6, 12}}
Tutorial 11: Arrays

26. Storing data in a Two-dimensional Array
Example 1
strCitys(0, 0) = “Madrid”
strCitys(0, 1) = “Paris”
strCitys(0, 2) = “Rome”
strCitys(0, 3) = “London”
Example 2
For intRow = 0 To 3
For intColumn = 0 To 1
intScores(intRow, intColumn) = 0
Next intColumn
Next intRow
Tutorial 11: Arrays

27. Calculating the Total in a Two-Dimensional Array
Dim intSales(,) As Integer = {{12000, 10000}, _
{45000, 56000}, {32000, 42000}, _
{67000, 23000}, {24000, 12000}, _
{55000, 34000}}
Dim intRow, intCol As Integer ‘keeps track of subscripts
Dim intTotal As Integer ‘accumulator variable
For intRow = 0 To 5
For intCol = 0 To 1
intTotal = intTotal + intSales(intRow, intCol)
Next intCol
Next intRow
Tutorial 11: Arrays

28. Multidimensional Array Properties
Length will tell you the total number of elements
intSales.Length will return 12
Use GetLength(dimension) to get the size of a particular dimension
intSales.GetLength(0) will return 6
intSales.GetLength(2) will return 2
For intRow = 0 To intSales.GetLength(0) - 1
For intCol = 0 To intSales.GetLength(1) - 1
intTotal = intTotal + intSales(intRow, intCol)
Next intCol
Next intRow
Tutorial 11: Arrays