Microsoft Visual Basic 2010
Arrays
1
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
2
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 can have as many as 60
dimensions, the most commonly used arrays are onedimensional and two-dimensional
 Programmers use arrays to store related data in the
internal memory of the computer
3
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 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
4
One-Dimensional Array
Alaska Montana
South Carolina
Tennessee
Texas
Alaska
Montana
South Carolina
Tennessee
Texas
5
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
6
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}
7
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”
8
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”))
Next intNum
udtItems(0).sngPrice = udtItems(0).sngPrice * 1.1
9
One-Dimensional Array
Dim intX As Integer
Do While (intX <= 5 AndAlso Not EOF(1))
FileGet(1, udtItems(intX), intX + 1)
intX += 1
Loop
10
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
11
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)
12
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
13
Calculating the Average
Amount Stored in
a One-Dimensional Numeric Array
Dim intScores() As Integer = {98, 100, 56, 74, 35}
Dim intX As Integer
Dim intTotal As Integer
Dim sngAvg As Single
‘keeps track of subscripts
‘accumulator variable
‘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)
14
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)
15
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
16
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
display the contents of the current array element in a message box
end repeat
17
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 onedimensional Array or in a portion of the Array
Sort
Sorts the elements in one-dimensional Array objects
18
Parallel Arrays
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
19
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
20
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
21
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)
22
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}}
23
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
24
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
25
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
26