Chapter Six:
Working With Arrays in Visual Basic
Objectives for Chapter Six
* Understand the use of control, list, and table arrays in Visual Basic
* Use control arrays to work with groups of controls using a single
name.
* Describe the difference between arrays and combo boxes, list boxes,
and similar controls.
* Declare the maximum number of elements or rows and columns for
an array.
* Understand the errors that can occur from exceeding the declared
upper limits on index values.
* Input data into an array from the keyboard or files using loops.
* Manipulate array data to find the sum and average of array values, the
largest or smallest value in an array, or to find a particular value.
* Work with multiple arrays to match values in one array to those in the
other.
* Output the result of array processing to a control, the printer, or the
Immediate window.
* Use Step operations to step though an array operation to find and
correct an error.
Using Control Arrays
•
•
•
•
•
A control array is group of the same type control which is
assigned a single name****
The individual controls are identified by the control array
name and an index value starting with 0.****
The Case decision structure can be useful in working with a
control array.
To create a control array, just enter the same name for more
than one control and replay “yes” to the query.
The order in which the controls are entered determines the
index values for the controls in the control array.
Check Boxes Vs. Option Buttons
• Check box is used to make multiple
selections from a list
• Prefix is chk
• Option button is used to make one selection
from a list.
– Often referred to as radio buttons
• Prefix is opt
• Be able to identify this control from a listing of
controls****
Frame Control
• Option buttons must be within a frame control
which acts as a container .
• Frames have a prefix of fra.
• Recommendation is to add frame first and add the
option button by drawing it in, not double clicking
• All option buttons will have the same name but a
different Index, such as optDemo(0), optDemo(1),
optDemo(2)
• If the frame is moved, option buttons will move
with it
Option Button Array
• Double click any option button to open the code
window and it will have event similar to this
Private Sub optDemo_Click(Index as Integer)
• The Index value is being passed to the event
procedure, in other words, the index of the option
button that was clicked is now known to the event
procedure
• The Index value is used is Select Case statements
VB Code Box 6-2
Code for Option Buttons
Private Sub optDemo_Click(Index As Integer)
Select Case Index
Case 0
MsgBox "Button One selected"
Case 1
MsgBox "Button Two selected"
Case 2
MsgBox "Button Three selected"
End Select
End Sub
Check Box Control Array
• All check boxes will have the same name but a
different Value, such as chkSelect(0).Value,
chkSelect(1).Value, chkSelect(2).value
• The Value will either be True or False. It is True if
the check box is selected and False if not selected
• To determine if it is False use the Not operator
• Code on Next slide is used to check if a value is
True or False
VB Code Box 6-1
Code for Check Box Control Array
Private Sub cmdSelect_Click()
If chkSelect(0).Value And Not chkSelect(1).Value Then
MsgBox "Box One selected"
ElseIf Not chkSelect(0).Value And chkSelect(1).Value Then
MsgBox "Box Two selected"
ElseIf chkSelect(0).Value And chkSelect(1).Value Then
MsgBox "Boxes One and Two selected"
Else
MsgBox "No boxes selected"
End If
End Sub
VB Code Box 6-3
Select Prices Using Option Buttons
(Vintage Video)
Private Sub OptTypes_Click(Index As Integer)
Dim curPrice As Currency
Select Case Index
Case 0’Kids
curPrice = 0.99
Case 1’Regular
curPrice = 1.99
Case 2’Classic
curPrice = 2.99
End Select
txtVideoPrice.text = Format(curPrice, "currency")
End Sub
VB Code Box 6-4
Clear OptTypes Option Buttons
Private Sub cmdClear_Click()
For Counter = 0 to 2’Clear option buttons
OptTypes(Counter).Value = False
Next
End Sub
Using List Arrays
Arrays are lists or tables of data which have single name.
They provide a way of working with long lists in memory versus
working with short lists in a list or combo box
Arrays can only store one type of data
Individual array elements are identified by the array name and
one or more subscripts or index values. For instance:
curPrices(0), curPrices(1), curPrices(2)
The index must be an integer constant, variable or expression
Using List Arrays
• To be used in Visual Basic, an array must be
declared just like any other variable.
• Arrays can be fixed size or dynamic size (we use
only fixed arrays.)
– Fixed size-array- specific amount of memory
set aside for it
– Dynamic array - no fixed amount of memory
Using List Arrays
• Form of array declaration
Dim ArrayName (max index value) as variable type
Dim curPrices(9) as Currency
– Above statement allows for 10 values to be stored (0-9)
• The declaration statement defines the upper limit but by
default the lower limit on an array index is zero but this
can be changed to one or any other value.
• It is not possible to exceed the upper limit or go below the
lower limit on the array index values . Will receive a
“Subscript out of range” error
Entering Event Driven Array Data
Most of the time you want to input multiple values into an array.
Arrays can be input with any of the three types of loops discussed
earlier--event driven, for-next, or while/until loops.
If input is from a keyboard and you don’t know the values to be
input, an event driven loop is most appropriate. Similar to loops
in Chapter 5 except values are entered directly in an array versus
being added to a list box. Values don’t need to be summed
immediately.
Index for the array corresponds to the value of the counting
variable for each value that is input
With an event driven loop, each click of a button increments a
counter and inputs the corresponding array element
Input Using For-Next Loops
• With a For-Next loop, you must input the number of arrays
elements. The array values must be input with an Inputbox
with the For-Next counter variable matching the array
index
• VB Code Box 6-6.
Private Sub Input_Click()
Dim intCounter As Integer
intNumPrices = CInt(InputBox("How many prices?"))
For intCounter = 0 To intNumPrices - 1
curPrices(Counter) = CCur(InputBox("Next price:"))
Next
End Sub
Code to Input Array from Files
With an Do Until loop, you can input from a file. Increment a
counter that matches the index for the array element.
Do Until Loop General Form
intCounter =0
Do Until EOF (n)
Input #n, ArrayName(Counter)
intCounter=intCounter+1
Loop
VB Code Box 6-7
Code to Input Array Elements from a File
Open “A:\chapter6\prices.txt" For Input As #5’open text file
Do Until EOF(5)’ repeat loop until EOF
Input #5, Prices(NumPrices)’Prices is array,Numprices is counter
intNumPrices = intNumPrices + 1 ‘add 1 to counter
Loop
Close #5
Processing Arrays
• Typical array operations include summing and
averaging the array values and finding the largest or
smallest value in the array.
•Working with arrays usually involves a For-Next loop.
•Summing Prices array elements involves using a
statement of the form: Sum = Sum + Prices(Counter)
• Averaging Prices array elements involves dividing the
Sum by the number of elements
Processing Arrays
• Finding the largest or smallest value involves
multiple comparisons of array elements.
• To find the maximum Price, you must compare
each array value to the current highest price; if it is
higher, it becomes the highest price. Do this using
For-Next loop and If-then
VB Code Box 6-8
Compute the Sum and Average in Array
Private Sub CmdSumAverage_Click()
Dim curSum as Currency ’Sum variable
Dim intCounter as Integer ’counter variable
Dim curAverage as Currency ’Average variable
curSum = 0 ’Set sum to 0
For intCounter = 0 to intNumPrices - 1
curSum = curSum + curPrices(intCounter) ’add prices
Next
If intNumPrices >0 then ’check to see if >0
curAverage = curSum/intNumPrices ’true average prices
Else ’if false
MsgBox "No values to average!” ’display Msgbox
Exit Sub
End If
txtSum.Text=Format(curSum, “currency”)
txtAverage.Text = Format (curAverage, “currency”
Pseudocode to Find Maximum Value
Begin procedure to find largest value
Set largest value to first item in list
Repeat beginning with second item to last item
If item in list > largest value then
Largest value = item in list
End decision
End repeat
Display largest value
End procedure
VB Code Box 6-10
Find Maximum Value in List
Private Sub cmdFindMax_Click()
’Declare variables and set largest value to first item in the array
Dim intCounter As Integer, curLargest As Currency
curLargest = curPrices(0)
For intCounter = 1 To intNumPrices - 1
If curPrices(intCounter) >curLargest Then ’if item >largest #
curLargest = curPrices(intCounter) ’ replace it if it is larger
End If
Next
’Display largest number as currency
txtMaxPrice.Text = Format(curLargest, "currency")
End Sub
Code to Find Minimum Value in List
Private Sub cmdFindMax_Click()
’Declare variables and set smallest value to first item in the array
Dim intCounter As Integer, curSmallest As Currency
curSmallest = Prices(0)
For intCounter = 1 To intNumPrices - 1
If curPrices(intCounter) > curSmallest Then ’if item > smallest #
curSmallest = Prices(Counter) ’ replace if it is smaller
End If
Next
’Display smallest number as currency
txtMaxPrice.Text = Format(curSmallest, "currency")
End Sub
Find the Largest/Smallest String Value in
a List
• Collating Sequence - order in which characters are
displayed
• Digits come before alphabetic characters.
• Upper case A is smaller than uppercase B because it
comes first in alphabetical ordering
• Lower case letters come after upper case letters
• Chr() function converts Integer values of the For-Next
variable into the corresponding characters
• To reverse operation use the ASC() function with the
character as the argument
VB Code Box 6-9
Displaying the Collating Sequence
Private Sub Form_Load()
Dim intCounter As Integer
For intCounter = 0 To 255
Debug.Print Chr(intCounter);
Next
End Sub
Finding Items and Working
with Multiple Lists
•The goal of the project is to find a specified part ID and display
the part identifier and the price of the part
•To input both the part identifiers and a price a second array,
PartID needs to be declared as a string in the Form General
declaration section
Dim strPartId(25) as String
•The Input Statement in the Form-Load event must be modified
Input #5, strPartID(intNumPrices), curPrices(intNumPrices)
•For a given part, the index values or the strPartId, and the
curPrices arrays are the same. The index acts as a link between
them.
The Continuation Character
To display the two items in a text box it will be necessary
to modify the cmdDisplay event procedure and it will
require a long line of code.
Must use the _ (continuation character). There must be a
space before this character
The line below add PartsId and price to a list box and
formats the price as currency.
lstParts.AddItem PartId(counter) + “ “ _
& Format(Prices(Counter), “currency”)
Flag Variables
• A flag variable is often used to indicate whether a match
was found
• It is a Boolean data type, so it has a value of True or False
• The Flag variable must be set to False before the For-Next
loop is started
• If the loop finds a match between the PartId that was input
and a PartId on the parts list, the Flag is set to TRUE,
• The program jumps out of the loop through the use of the
Exit For statement and saves the index of the PartID. The
appropriate text box is then updated, otherwise a message
box will appear
Pseudocode to Find Price for Part
Identifier
Begin procedure to find part identifier
Input part identifier
Set Flag to False
Repeat for each part in parts list
If part identifier = identifier on parts list then
Flag = True
Save index of part identifier on parts list
End decision
End repeat
If Flag = True
Use saved index to display part identifier and price
Else
Display message that part not on parts list
End decision
End procedure
VB Code Box 6-11 Find Price for Part ID
Private Sub cmdFind_Click()
Dim intCounter As Integer, intResults As Integer, strFindID as String
Dim blnFound As Boolean ’flag variable
Dim intPriceIndex as Integer
strFindPartID = InputBox("Input part identifier to find")’input Part ID
blnFound = False ’flag set to false
For intCounter = 0 To intNumPrices - 1
If UCase(strFindPartID) = UCase(strPartId(intCounter)) Then ’ if
match
blnFound = True ’flag set to True
intPriceIndex = intCounter ‘Save index of PartId on parts list
Exit For ’jump out of loop
End If
Next
If blnFound Then ’ if a match is found display PartID and price
txtFound.Text = strPartId(intPriceIndex) & " " & _
Format(curPrices(intPriceIndex), "Currency")
Else ’ no match found display the message box
Results = MsgBox("Part not found", VbExclamation, "Price Search")
End If
More on Message Boxes
• The Msgbox can be used as a function by including
multiple parameters within parentheses.
• Syntax: Variable=MsgBox (message, buttons,title)
– buttons=one or more VB constants in table 6-3
– title= title (caption)string for the dialog box
• Example:
MsgBox “Part not found”, vbExclamation, “Price Search”
More on Message Boxes (con’t)
• Msgbox function returns a value which can be checked to
determine which button was clicked
• For instance:
intResults= MsgBox (“Write over old file?”,vbYesNoCancel)
Produces a Message Box with 3 buttons Yes, No, and Cancel
Clicking Yes will return a value of 6, No a value of 7, and
Cancel a value of 2
VB Code Box 6-12
Save Index for Highest Price Part
Modify cmdFindMax button add a statement that stores the index
of the current largest price to the loop that searches for the
maximum price
Private Sub cmdFindMax_Click()
Dim intCounter As Integer, curLargest As Currency, intMaxIndex as Integer
curLargest = curPrices(0)
For intCounter = 1 To intNumPrices - 1
If curPrices(intCounter) > curLargest Then
curLargest = curPrices(intCounter)
intMaxIndex = intCounter
End If
Next
txtMaxPrice = strPartId(intMaxIndex) & " " & _
Format(curPrices(intMaxIndex), “currency")
End Sub
Working with Multiple Forms
(Vintage Video)
It is possible to have multiple forms in a project.
Add a form by clicking Project/AddForm or click on the
Add Form icon on the toolbar .
A blank form replaces the existing form and the form
name is added to Project Explorer window
Working with Multiple Forms
(Vintage Video)
• To display a form and load it into memory, use
formname.Show ****
Example: frmVideos.Show
• To hide the form, but not unload it from memory use
• formname.Hide.
If a control on one form is referred to on another form, the
form name must be included as a part of the control
reference.
• Create the frmVideos form. In addition three arrays will be
needed. Declare variables for curVideoPrice,
strVideoName, strVideoLoc on new form (Figure 6-17)in
General Declarations
Declare Arrays for frmVideos
(Figure 6-17)
Dim striVideos(100) as String, intNumVideos as Integer
Dim curVideoPrice(100) as Currency, strVideoLoc(100) as String
_____________________________________________
After entering above code you would create a file called
videos.txt, that contains the video name, video price, and video
location
Entries in the file must be in the same order as variables are
input , i.e. “Ghost”, 1.99,”Drama”
Next update the Form-Load event ( VB Code Box 6-14)
VB Code Box 6-14
frmVideos Form_Load Event Procedure
Private Sub Form_Load()
’Open file for input
Open "a:\videos.txt" For Input As #2
Do Until EOF(2)’Input list of videos
Input#2,strVideos(intNumVideos), _
curVideoPrice(intnumVideos), _
strVideoLoc(intNumVideos)
intNumVideos = intNumVideos + 1’counter
Loop
Close #2 ’Close file
End Sub
Search in Strings
* To search for a substring within a string, you use the
(Instr(string to search, search string) function.
String to search - character string that is being searched for an
occurrence of of the second parameter search string
For example: Instr(“Ghostbusters”, “Ghost “) returns 1 because “G” is in the 1st
position. If the character does not exist, Instr returns a zero.
*NOTE: Instr is case sensitive!!!
Instr(“Ghostbusters”, “Bust “) will return a value of 0, because Bust in not
in Ghostbusters
•To avoid above problem, search for strings using a loop requires that you use
•UCase or LCase to convert all strings to the same case before comparisons are
•made.
VB Code Box 6-15
Search for Video Name
Private Sub cmdSearch_Click()
Dim strVideoName As String, intCounter As Integer, _
intNumMatches As Integer
strVideoName = txtSearch.Text ’Assign value to variable
lstVideos.Clear ’Clear list box
lstVideos.AddItem "Video Name“ ‘Add string to list box
VB Code Box 6-15
Search for Video Name (Continued)
For intCounter = 0 To intNumVideos – 1 ’Check all titles
If InStr(UCase(strVideos(intCounter)), _
UCase(strVideoName)) > 0 Then
intNumMatches = intNumMatches + 1 ’Count number of matches
lstVideos.AddItem Videos(Counter)’add item to list box
End If
Next
If intNumMatches = 0 Then ’if no matches are found
MsgBox ("No matching videos found! Try again.")’display message
ElseIf intNumMatches <= 5 Then ’<=5 matches display in list box
lstVideos.AddItem Str(intNumMatches) & " videos found"
Else
lstVideos.Clear ’Clear list box when OK is clicked
MsgBox ("Too many matching videos!")’Display this message
End If
End Sub
VB Code Box 6-16
Search for Exact Match of Video Name
Private Sub lstVideos_Click()
Dim strVideoName As String, intCounter As Integer
strVideoName = lstVideos.Text
lstVideos.Clear
For intCounter = 0 To intNumVideos - 1
If strVideoName = strVideos(intCounter) Then
lstVideos.AddItem strVideoName & " " & _
Format(curVideoPrice(intCounter), "currency") & _
" " & strVideoLoc(intCounter)
Exit For
End If
Next
End Sub
*Clicking on a title that appears will give you title,
price and location
VB Code Box 6-17
cmdBack_Click Event Procedure
Private Sub cmdBack_Click()
txtSearch.Text = ""
lstVideos.Clear ’Clear list box
frmVideos.Hide ’Hide video form
End Sub
Two-Dimensional Arrays
To declare a two-dimensional array (a table) you must provide the
maximum row index and the maximum column index. Row and column
indexes begin at 0
General form
Dim ArrayName(max row index, max column index)as var type
Dim sngNumberTable(10,20) as Single
In this example, it will hold 231 elements (11*21)
The table on the next slide will be declared as
Dim curRevenue(2,3) as Currency
Reason it has 3 rows (0,1,2) and 4 columns (0,1,2,3)
Each element of the table is defined by its row and column position
Table 6-6 Product Revenue by Region
(Row,Column)
Product
Northeast SouthEast Midwest
West
Column 0 Column 1 Column 2 Column 3
PC’s
Row 0
53.5
0,0
62.1
0,1
27.1
0,2
41.5
0,3
Storage
Row 1
24.7
1,0
23.5
1,1
27.3
1,2
20.3
1,3
Memory
Row 2
15.1
2,0
11.3
2,1
17.9
2,2
20.7
2,3
VB Code Box 6-19
Form_Load event procedure to Input
Data for Two Dimensional Array
Private Sub Form_Load()
Dim intProduct As Integer, intRegion As Integer
Dim curRevenue(10,10) as Currency
Open "a:\chapter6\revenue.txt" For Input As #10
For intProduct = 0 To 2
For intRegion = 0 To 3
Input #10, curRevenue(intProduct, intRegion)
Next intRegion
Next intProduct
End Sub
Using the Step Commands
Stepout of
Step into
The Step Commands
Step Over
If you select Step Into, you can “step” through the
code, line by line and note the result of the code in the
various windows--Watch, Locals, or Immediate.
You will be asked to identify one of these buttons in a test****