1. CSCI 3327 Visual Basic Chapter 7: Data Manipulation in Arrays
UTPA – Fall 2011
Part of the slides is from Dr. John Abraham’s previous lecture slides. – Xiang Lian

2. Objectives In this chapter, you will: Learn sorting data in arrays
Sort method of arrays
Linear search
Binary search
Learn the declaration of rectangular arrays
Know how to resize an array in Visual Basic

3. In the Last Class: Example of an Array
Array: C
Dim C = New Integer(11)
C(0)
-45
C(1) 6
C(2)
C(3) 72
C(4) 34
C(5) 39
C(6) 98
C(7)
-1345
C(8)
939
C(9) 10
C(10) 40
C(11) 33

4. Sort an Array C(0) -45 C(1) 6 C(2) C(3) 72 C(4) 34 C(5) 39 C(6) 98
C(3) 72
C(4) 34
C(5) 39
C(6) 98
C(7)
-1345
C(8)
939
C(9) 10
C(10) 40
C(11) 33
C(0)
-1345
C(1)
-45
C(2)
C(3) 6
C(4) 10
C(5) 33
C(6) 34
C(7) 39
C(8) 40
C(9) 72
C(10) 98
C(11)
939

5. Class Array Array is a class in namespace System
Method for sorting: Array.Sort(arrayName)

6. Example 7.12: SortArray.vb URL: ListBox Button
ListBox
OriginalValuesListBox.Items.Clear()
Button
sortButton.Enabled = True
Array.Sort(integerArray)

7. Sorting and Searching Sorting implementation
You need to implement it
Don’t use the method Sort comes with array class
You may use bubble sort or selection sort
Assume we have an array: CustomerName

8. Bubble Sort Dim sorted As Boolean = False
Dim j As Integer = CustomerName.GetUpperBound(0)
While Not (sorted)
sorted = True
For i = 0 To j - 1
If CustomerName(i) > CustomerName(i + 1) Then
Swap(i)
sorted = False
End If
Next i
j = j - 1
End While

9. Swap Private Sub Swap(ByVal i As Integer) Dim tmp1 As String
tmp1 = CustomerName(i)
CustomerName(i) = CustomerName(i + 1)
CustomerName(i + 1) = tmp1
tmp2 = CustomerTele(i)
CustomerTele(i) = CustomerTele(i + 1)
CustomerTele(i + 1) = tmp2
End Sub

10. Searching
Searching: to determine whether a value (called search key) is in the array
Linear search
Compare each element of the array with the search key
For either sorted or unsorted array
Efficient for small array
Binary search
For sorted array

11. Linear Search search key C(0) -45 C(1) 6 C(2) C(3) 72 C(4) 34 C(5) 39
C(3) 72
C(4) 34
C(5) 39
C(6) 98
C(7)
-1345
C(8)
939
C(9) 10
C(10) 40
C(11) 33

12. Example 7.14: LinearSearchTest.vb
URL:
Code:
If searchData(i) = searchKey Then
index = i
Exit For 'terminate the loop, as the key is found
End If

13. Binary Search first search key: 10 middle last C(0) -1345 C(1) -45
C(3) 6
C(4) 10
C(5) 33
C(6) 34
C(7) 39
C(8) 40
C(9) 72
C(10) 98
C(11)
939
first
search key: 10
middle
last

14. Binary Search first search key: 10 middle last C(0) -1345 C(1) -45
C(3) 6
C(4) 10
C(5) 33
C(6) 34
C(7) 39
C(8) 40
C(9) 72
C(10) 98
C(11)
939
first
search key: 10
middle
last

15. Binary Search first search key: 10 middle last C(0) -1345 C(1) -45
C(3) 6
C(4) 10
C(5) 33
C(6) 34
C(7) 39
C(8) 40
C(9) 72
C(10) 98
C(11)
939
first
search key: 10
middle
last

16. Binary Search first search key: 10 middle last C(0) -1345 C(1) -45
C(3) 6
C(4) 10
C(5) 33
C(6) 34
C(7) 39
C(8) 40
C(9) 72
C(10) 98
C(11)
939
first
search key: 10
middle
last

17. Code of Binary Search Dim Lookfor As String
Dim first, last, middle As Integer
Dim nfound As Boolean
LblName.Caption = "": LblTele.Caption = ""
Lookfor = TxtSearch.Text
nfound = False
first = 1: last = Index
While (Not (nfound) And first <= last)
middle = (first + last) \ 2
If RTrim(Lookfor) = RTrim(CustomerName(middle)) Then
nfound = True
LblName.Caption = CustomerName(middle)
LblTele.Caption = CustomerTele(middle)
ElseIf Lookfor < CustomerName(middle) Then last = middle - 1
Else: first = middle + 1
End If
End While
If Not (nfound) Then LblName.Caption = "Name not in list"

18. Using an Array for a Stack
Keep track of the top
Push: Increase it before adding
Pop: Decrease it after taking
Push or Pop only to or from the top
Examine the stack to see if it is empty or full
For example, if stack.top < 0, then it is empty
You may choose not to use the 0th location for data, then you can say it is empty when stack.top is zero

19. Rectangular Array So far, we have studied one-dimensional array
Dim C = New Integer (11)
Rectangular array is a 2-dimensional array
Column 0
Column 1
Column 2
Column 3
a(0, 0)
a(0, 1)
a(0, 2)
a(0, 3)
a(1, 0)
a(1, 1)
a(1, 2)
a(1, 3)
a(2, 0)
a(2, 1)
a(2, 2)
a(2, 3)
Row 0
Row 1
Row 2

20. Declaration of Rectangular Array
Create a 2-by-2 array
Dim numbers (1, 1) As Integer
Initialize values
numbers (0, 0) = 1
numbers (0, 1) = 2
numbers (1, 0) = 3
numbers (1, 1) = 4
Declare and initialize a rectangular array
Dim numbers = {{1, 2}, {3, 4}}
Dim numbers(,) As Integer = {{1, 2}, {3, 4}}

21. Case Study: Grade Report Using a Rectangular Array
Example 7.20: GradeReport.vb
URL:

22. Resize an Array Keyword: ReDim An array's size cannot be changed
But a new array can be created and assigned to an array variable
Example:
Dim values() As Integer = {1, 2, 3, 4, 5}
ReDim values(6) ' {0, 0, 0, 0, 0, 0, 0}
ReDim Preserve values(6) ' {1, 2, 3, 4, 5, 0, 0}