1. Introduction to Computer Programming IT-104
Objectives
Introduction
Loop Types
Determinate
Indeterminate
Event
While-Wend
Do-While
Do-Until
For-Next
Exit
Introduction to Computer Programming IT-104
Unit Six – Arrays
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Intro to Comp. Programming - IT 104

2. Intro to Comp. Programming - IT 104
Objectives
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.
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Intro to Comp. Programming - IT 104

3. Intro to Comp. Programming - IT 104
Objectives
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.
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Intro to Comp. Programming - IT 104

4. Intro to Comp. Programming - IT 104
Objectives
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.
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Intro to Comp. Programming - IT 104

5. Intro to Comp. Programming - IT 104
Introduction
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Arrays are an important part of computer programming. An Array is a special type of variable structure implemented in virtually every computer language. Without the array and the loop collectively, programming a computer would be a daunting task indeed.
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Intro to Comp. Programming - IT 104

6. Intro to Comp. Programming - IT 104
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
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Intro to Comp. Programming - IT 104

7. Intro to Comp. Programming - IT 104
Using Control Arrays
Home
name for more than one control and replay “yes” to the query.
Alternatively, simply copy an existing control and paste it to your existing form, and then answer ‘Yes’ to the ‘Confirm Control Array’ dialog box.
The order in which the controls are entered determines the index values for the controls in the control array.
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Intro to Comp. Programming - IT 104

8. Check Boxes Vs. Option Buttons
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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
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Intro to Comp. Programming - IT 104

9. Intro to Comp. Programming - IT 104
Frame Control
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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.
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Intro to Comp. Programming - IT 104

10. Intro to Comp. Programming - IT 104
Frame Control
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.
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Intro to Comp. Programming - IT 104

11. Intro to Comp. Programming - IT 104
Option Button Array
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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.
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Intro to Comp. Programming - IT 104

12. VB 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
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Intro to Comp. Programming - IT 104

13. 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
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Intro to Comp. Programming - IT 104

14. VB 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
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Intro to Comp. Programming - IT 104

15. VB Code Select Prices Using Option Buttons (Pos demo)
Private Sub OptTypes_Click(Index As Integer)
Dim curItemPrice As Currency
Select Case Index
Case 0 ’Perishables
curItemPrice = 3.99
Case 1 ’Staples
curItemPrice = 1.99
Case 2 ’Hardware
curItemPrice = 5.99
Case 3 ‘Cleaning supplies
curItemPrice = 2.99
End Select
txtItemPrice.text = Format(curItemPrice, "currency")
End Sub
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Intro to Comp. Programming - IT 104

16. VB Code to Clear the OptTypes Option Buttons
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Private Sub cmdClear_Click()
For Counter = 0 to 2 ’Clear option buttons
OptTypes(Counter).Value = False
Next
End Sub
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Intro to Comp. Programming - IT 104

17. Intro to Comp. Programming - IT 104
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
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Intro to Comp. Programming - IT 104

18. Intro to Comp. Programming - IT 104
Using List Arrays
expression.
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 is reserved.
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Intro to Comp. Programming - IT 104

19. Intro to Comp. Programming - IT 104
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
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Intro to Comp. Programming - IT 104

20. Intro to Comp. Programming - IT 104
Using List Arrays
Home
If a lower bound other than zero is desired, the programmer can implement his own numbering scheme as in the following:
Dim sngRate(100 to 199) as Single
This statement allocates 100 elements, but the lower bound is now 100 instead of 0. This gives the programmer the flexibility of matching existing numbering schemes that may exist within files he has been given to process.
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Intro to Comp. Programming - IT 104

21. 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
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Intro to Comp. Programming - IT 104

22. Entering Event Driven Array Data
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.
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Intro to Comp. Programming - IT 104

23. 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
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
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Intro to Comp. Programming - IT 104

24. Intro to Comp. Programming - IT 104
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
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Intro to Comp. Programming - IT 104

25. Intro to Comp. Programming - IT 104
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
8/21/2019
Intro to Comp. Programming - IT 104

26. VB Code to Compute the Sum and Average in Array
Home
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”
End Sub
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Intro to Comp. Programming - IT 104

27. 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
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Intro to Comp. Programming - IT 104

28. VB Code to 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
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Intro to Comp. Programming - IT 104

29. Code to Find Minimum Value in List
Private Sub cmdFindMin_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
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Intro to Comp. Programming - IT 104

30. 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
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Intro to Comp. Programming - IT 104

31. VB Code for Displaying the Collating Sequence
Private Sub Form_Load()
Dim intCounter As Integer
For intCounter = 0 To 255
Debug.Print Chr(intCounter);
Next
End Sub
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Intro to Comp. Programming - IT 104

32. 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.
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Intro to Comp. Programming - IT 104