1. Chapter 7 - Visual Basic Schneider
Arrays
Chapter 7 - Visual Basic Schneider

2. Chapter 7 - Visual Basic Schneider
Outline and Objective
Arrays in Visual Basic
One- dimensional arrays
Control arrays
Searching
Sorting
Chapter 7 - Visual Basic Schneider

3. Array verses Simple Variable
Simple variable is used to store a single value.
Array variable is used to represent many values of the same type with one variable name.
Suppose you want to evaluate the exam grades for 30 students.,this means you have to create 30 string variables for names and 30 single vvariables for their scores
Array holds either all string values or all numeric values.
Chapter 7 - Visual Basic Schneider

4. Chapter 7 - Visual Basic Schneider
Elements of an Array
Array Name: A valid variable name for the structure.
Subscript or Index : A value that refers to a particular array element.
Element: An individual data item within an array.
The elements of an array are assigned successive memory locations.
Chapter 7 - Visual Basic Schneider

5. Chapter 7 - Visual Basic Schneider
Array Declaration
Syntax
Dim arrayname ( n To m) As VarType
Dim grade(1 to 20) as integer
Arrayname follows the same rules as variable names.
Each array has sufffiient memory reserved to hold the number of items of the given type..
Chapter 7 - Visual Basic Schneider

6. Chapter 7 - Visual Basic Schneider
Variable Arrays
A group of variables that have the same name and data type and are related in some way
Programmers use arrays to store related data in the internal memory of the computer
Data stored inside the computer can be both written and read much faster than data stored in a file on a disk
Chapter 7 - Visual Basic Schneider

7. Chapter 7 - Visual Basic Schneider
Variable Arrays
A one-dimensional array is simply a row (or column) of variables
Each element in an array is identified by a subscript
You refer to an array element by the array’s name followed by the element’s subscript
Chapter 7 - Visual Basic Schneider

8. One-dimensional Array
strState(3)
strState(4)
strState(5)
strState(1)
strState(2)
Nebraska
New Jersey
New Mexico
Tennessee
Texas
strState(1)
Nebraska
strState(2)
New Jersey
strState(3)
New Mexico
strState(4)
Tennessee
strState(5)
Texas
Chapter 7 - Visual Basic Schneider

9. Chapter 7 - Visual Basic Schneider
Examples of arrays
Dim intScore (1 To 30) As integer
Dim strStudent (1 To 30 ) As string
Dim employee (101 to 350) as string
Demo Provinces
Chapter 7 - Visual Basic Schneider

10. Initializing an Array by Reading from a File
Dim student ( 1 To 30) As String
Open “STUDENTS.TXT” For Input As #1
For count = 1 To 30
Input #1, student ( count )
Next count
Close #1
Demo Provinces2
Chapter 7 - Visual Basic Schneider

11. Chapter 7 - Visual Basic Schneider
Parallel Arrays
Two arrays are referred to as parallel if subscripted variables having the same subscript (elements) are related.
Chapter 7 - Visual Basic Schneider

12. Example of Parallel Arrays
Dim nom ( 1 To 8) As String , score ( 1 To 8 ) As Integer
Open “SCORE.TXT” For Input As #1
For student = 1 To 8
Input #1, nom(student), score(student)
Next student
Close #1
Chapter 7 - Visual Basic Schneider

13. The Average Program Revisited!
Open “STUDENT.TXT” For Input As #1
For count = 1 To 30
Input #1, student (count), score (count)
Next count
sum = 0
sum = sum + score(count)
average = sum/30
Chapter 7 - Visual Basic Schneider

14. Chapter 7 - Visual Basic Schneider
Unknown Array Size
What do I do if I don’t know the size of a file – and thus the size of the array??
Chapter 7 - Visual Basic Schneider

15. Chapter 7 - Visual Basic Schneider
Unknown Array Size
Dim student() as string
Cannot be used without a redim statement
Redim student(1 to 37) as string
Demo provinces2
Redim preserve student(1 to 38) as string
Local vs Form Level
Chapter 7 - Visual Basic Schneider

16. Chapter 7 - Visual Basic Schneider
Homework!
Go through the seven (7) example programs in section 7.1 of your text book – me – for each program, tell me if you can understand it or not!
Chapter 7 - Visual Basic Schneider

17. Chapter 7 - Visual Basic Schneider
Demo Provinces2
Exercises - Schneider
Chapter 7 - Visual Basic Schneider

18. Chapter 7 - Visual Basic Schneider
Ordered Array
An array is ordered it its values are in either ascending or descending order.
For string arrays, the ANSI table is used to evaluate the “less than or equal to” condition.
Chapter 7 - Visual Basic Schneider

19. Chapter 7 - Visual Basic Schneider
Ordered Array
Ordered
strState(3)
strState(4)
strState(5)
strState(1)
strState(2)
Alabama
Kentucky
New Mexico
Tennessee
Virginia
strState(3)
strState(4)
strState(5)
strState(1)
strState(2)
Tennessee
Virginia
New Mexico
Kentucky
Alabama
Unordered
Chapter 7 - Visual Basic Schneider

20. Chapter 7 - Visual Basic Schneider
Ordered Arrays
Why order arrays?
Chapter 7 - Visual Basic Schneider

21. Chapter 7 - Visual Basic Schneider
Ordered Arrays
Efficiency in searching – on average only half a sorted array has to be searched
Whole array has to be searched for unordered arrays
Chapter 7 - Visual Basic Schneider

22. Chapter 7 - Visual Basic Schneider
Merging
A common practice involving arrays is merging two sorted arrays.
Chapter 7 - Visual Basic Schneider

23. The method for merging two sorted arrays :
1.Compare the two first elements of the first and second arrays.
A. If one name alphabetically precedes the other, copy it onto the third list and cross it off the original array.
B. If the names are the same, copy the name onto the third list and cross out the name from both arrays.
2. Repeat Step 1 with the new name in the array until you reach the end of either array.
3. Copy the names from the remaining array onto the third array.
Demo Merge
Chapter 7 - Visual Basic Schneider

24. Chapter 7 - Visual Basic Schneider
Passing an Array
An array can be passed to another procedure by reference.
Dim scores(1 to 10) as integer
Call sort(scores( ))
Chapter 7 - Visual Basic Schneider

25. Example of Passing an array:
Private Sub cmddisplay_Click()
' Pass array to subprogram and function
Dim score(1 To 5) As Integer
Call FillArray(score( ) )
picAverage.Cls
picAverage.Print ”Average is"; Sum(score( ) ) / 5
End Sub
Passing array score
This array is not dimensioned in the declaration section of General , so is local to this procedure and unknown to other procedures.
Chapter 7 - Visual Basic Schneider

26. Array Score is passed to a Subprogram
Private Sub FillArray(s( ) As Integer)
' Fill array with scores
s(1) = 85
s(2) = 92
s(3) = 75
s(4) = 68
s(5) = 84
End Sub
This array is pointing to the same
location as array score
Total = 404
404/5 =80.8
Chapter 7 - Visual Basic Schneider

27. Array Score is passed to a Function
Private Function Sum(s ( ) As Integer) As Integer
Dim total As Integer, index As Integer
' Add up scores
total = 0
For i = 1 To 5
total = total + s(i)
Next i
Sum = total
End Function
Chapter 7 - Visual Basic Schneider

28. Exercises - Schneider 332 - 337
Chapter 7 - Visual Basic Schneider

29. Chapter 7 - Visual Basic Schneider
Control Arrays
Chapter 7 - Visual Basic Schneider

30. Chapter 7 - Visual Basic Schneider
Control Array
A means of constructing arrays of text boxes, labels, and command buttons.
At least one element of a control array must be created when the form is designed.
The remaining elements can be created either during form design, or with the Load statement.
To create additional elements of the txtBox() Control array during form design, make the control active,press CRTL +C . VB has recorded all the properties associated with textbox(00) . To creat a copy press CTRL + V
The value of the index for the new textbox(1) is 1;
Note all the properties of textbox are being passed to other textboxes.
Chapter 7 - Visual Basic Schneider

31. Creating Control Array during Form Design
Add one instance of the desired control to the form
Set the Index property to a number
Set any other properties that will be common to all other elements
Click on the control and then press Ctrl+C
Press Ctrl + V, to create the next element
Demo
Chapter 7 - Visual Basic Schneider

32. Chapter 7 - Visual Basic Schneider
Review Provinces2
Demo ColourArray
Chapter 7 - Visual Basic Schneider

33. Control Array Event Procedures:
Even though we may have many elements in the txtBox( ) control array, we will have just one txtBox_GotFocus event procedure to deal with.
The value of Index property for the elements of the control array must be passed.
Example:
Private Sub txtBox_GotFocus (Index As Integer)
In chapter 3 we discussed several events related to text boxes. One example was GotFocus event procedure.
An ordinary txtBox wold be Private Sub txtBox_GotFocus( )
But for txtBox a control array the GotFocus begins with Private Sub ttxtBox_GotFocus (Index As Integer)
Chapter 7 - Visual Basic Schneider

34. Control Array Event Procedures:
Demo Elements
Demo GradeArray
Demo CalculatorwithArray
Chapter 7 - Visual Basic Schneider

35. Creating Control Array at Run Time:
You can create elements of a control array via a Load statement at run time.
Demo Load
Copying and positioning control array elements can become tedious if the number of elements is large.
Also the actual number of elements needed in a control array may not be known until a response from the user is processed at run time.
They are 1440 wip to the inch.
You want the new element has its unique location on the form..
Chapter 7 - Visual Basic Schneider

36. Chapter 7 - Visual Basic Schneider
Control Array
All the properties of the first element are passed to other elements of the control array including the Top and Left properties.
The only property that differs from first element is the Visible property.
The Load statement sets the Visible property to False.
Chapter 7 - Visual Basic Schneider

37. Creating Control Array at Run Time:
The standard unit of measurement is called Twip.
To place a new element of a control array, adjust the Top and Left properties during run time.
Set the Visible property to True.
Demo Tax
Before discussing creating arrays at run time, yu must consider- the Left, Top, Width, and Height properties of controls.
They are 1440 Twips to the inch.
When a control ic active, the two panels on the right side of the toolbar give the location and size of the control , respectively..
The location and size properties of a control array ca be altered at run time with statement t such as : Text1.Left = 480
Text2.Top = Text1.Top * Text1.Height ( which places Text2 a comfortable distance below Text1.
Chapter 7 - Visual Basic Schneider

38. Example ( Creating control array during run time)
Private Sub Form_Load()
Dim i As Integer, monthNames As String
monthNames = "FebMarAprMayJunJulAugSepOctNovDec"
For i = 1 To 11
Load lblMonth(i)
Load txtInfo(i)
blMonth(i).Top = lblMonth(i - 1).Top + txtInfo(0).Height
txtInfo(i).Top = txtInfo(i - 1).Top + txtInfo(0).Height
lblMonth(i).Caption = Mid(monthNames, 3 * i - 2, 3)
lblMonth(i).Visible = True
txtInfo(i).Visible = True
Next i
End Sub

39. Chapter 7 - Visual Basic Schneider
Schneider p
Chapter 7 - Visual Basic Schneider

40. Chapter 7 - Visual Basic Schneider
Processing Arrays
Searching successive elements of an array is called Sequential Search.
A Sequential Search examines each element , from the first to the last, until the specified value is found or the end of the array is reached.
Chapter 7 - Visual Basic Schneider

41. Example of Sequential Search (finding the quiz grades greater than 8)
Dim quiz ( 1 To 15) As Single
For position =1 TO 15
If quiz(position) > 8 THEN
picOutput.Print quiz (position)
count = count + 1
End If
Next Position
The variable count keeps track of
Chapter 7 - Visual Basic Schneider

42. Chapter 7 - Visual Basic Schneider
Sequential Search
Useful for short lists.
Very inefficient for long lists ( example names in telephone book).
Use binary search if the list is sorted.
Chapter 7 - Visual Basic Schneider

43. Chapter 7 - Visual Basic Schneider
Binary Search
In binary search, an ordered array is repeatedly divided in half. The half not containing the target value is ignored.
To use binary search, the data in the array must be arranged in ascending or descending order.
Chapter 7 - Visual Basic Schneider

44. Chapter 7 - Visual Basic Schneider
Binary Search
Private Sub BinarySearch(corp As String, result As String
foundFlag = '1 indicates corp found
first = 1
last = numFirms Do While (first <= last) And (foundFlag = 0) middle = Int((first + last) / 2) Select Case UCase(firm(middle)) Case corp foundFlag = Case Is > corp last = middle Case Is < corp first = middle End Select
Loop
End Sub
Chapter 7 - Visual Basic Schneider

45. Chapter 7 - Visual Basic Schneider
Binary Search
If foundFlag = 1 Then
result = "found”
Else
result = "not found
End If
Chapter 7 - Visual Basic Schneider

46. Chapter 7 - Visual Basic Schneider
Sorting
A common practice involving arrays is sorting the elements of the array in either ascending or descending order.
You can sort an array in alphabetic order or numeric order.
There are various methods to sort data items.
Ascending : lowest to highest
descending: highest to lowest
When characters are compared the computer uses the ASCII value of each character to compare if the letter A is less than the letter B
Chapter 7 - Visual Basic Schneider

47. Chapter 7 - Visual Basic Schneider
Types of Sorting
Bubble Sort
Shell Sort
Chapter 7 - Visual Basic Schneider

48. Chapter 7 - Visual Basic Schneider
Bubble Sort
The bubble sort involves comparing adjacent elements and swapping the values of those elements when they are out of order.
One complete time through the array is called a pass.
Notice that the Flag is set to 1 before the loop is entered . Its value is later checked to determine if the entire array is in order.
The Final is set to one less than the number of items to be sorted. This is because two items at a time are compared . And you do not want to go over the boundary of the array
Examine the block IF statement in the FOR… NEXT loop . This statement determines whether two adjacent element should beexchanged.
The following program segment demonstrate SWAP
X = 20
Y = 10
SWAP X, Y
We need a DO WHILE… LOOP to sort the whole list.
As long as FLAG =1 Basic knows switches have been made
When the loop is completed without setting the Flag = 1 - that is when no switches are made
Chapter 7 - Visual Basic Schneider

49. Chapter 7 - Visual Basic Schneider
Bubble Sort
For passNum = 1 To 4 'Number of passes is 1 less than
number of items
For index = 1 To 5 - passNum
If name(index) > name(index + 1) Then
Call SwapData( name( ), index)
End If
Next index
Next passNum
Chapter 7 - Visual Basic Schneider

50. Swapping two variables
Private Sub SwapData ( A ( ) As String, index As Integer)
Dim temp As String
temp = A ( index)
A(index ) = A (index + 1)
A ( index + 1) = temp
End Sub
Chapter 7 - Visual Basic Schneider

51. Chapter 7 - Visual Basic Schneider
Bubble Sort
The maximum number of passes necessary to sort the elements in an array is equal to the number of elements in the array less 1.
The minimum number of passes to sort an array may be one.
It works well for a small number of data items.
It is too slow for really long lists.
Chapter 7 - Visual Basic Schneider

52. Chapter 7 - Visual Basic Schneider
Shell Sort
Is similar to the bubble sort, but instead of comparing and swapping adjacent elements A(count) and A(count+1), it compares and swaps nonadjacent elements A(count) and A(count + Gap) , where Gap starts considerably greater than 1.
Gap is equal to one-half the size of the list.
The elements of the list are separated by the chosen gap and grouped into subsists.
Is more efficient for longer lists (100 or more elements)
Is a good compromise between speed and simplicity.
The shell sort was named for its inventor, Donald Shell, is much more efficient for really long lists
For very short list s, the bubble sort is preferable; however for a lis of 30 items or more, the shell sort will consistently outperform the bubble sort.
Chapter 7 - Visual Basic Schneider

53. Chapter 7 - Visual Basic Schneider
Shell Sort
Gap is set to one-half the length of the array.
After each pass if flag is set to 1, then Gap is halved again for the next pass.
At the end Gap becomes one, and adjacent elements are compared and swapped.
Begin with a gap of g =Int(n/2)
compare items 1 and 1+g , 2 and 2 + g,….. N-g and n. Swap any pairs that are out of order
Repeat step 2 until no swaps are made for gap g
Halve the value of g
Repeat steps 2, 3, 4 until tahe value of gap is 0.
Chapter 7 - Visual Basic Schneider

54. Chapter 7 - Visual Basic Schneider
Shell Sort
gap = Int(numParts / 2)
Do While gap >= 1 Do
doneFlag = 1
For index = 1 To numParts - gap
If part(index) > part(index + gap) Then
Call Swap( part(index), part(index + gap)
doneFlag = 0
End If
Next index
Loop Until doneFlag = 1
gap = Int(gap / 2) 'Halve the length of the gap
Loop
For lists of 3elements or more, the shell sort will consistently outperform
outperform the bubble sort.
Chapter 7 - Visual Basic Schneider

55. Efficiency of Bubble and Shell sort
Array Elements Bubble Sort Shell Sort
, ,517
Chapter 7 - Visual Basic Schneider