1. Chapter 7
Arrays

2. Outline and Objective In this chapter we will Learn about arrays
One-dimensional arrays
Two-dimensional arrays
Learn about searching
Learn about sorting

3. Array verses Simple Variable
Simple variable is used to store a single value.
Ex: Dim X as Integer X
Array variable is used to represent many values of the same type with one variable name.
Ex: Dim X(1 to 4) as Integer
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.
X(1)
X(2)
X(3)
X(4) X

4. Elements of an Array
X(1)
X(2)
X(3)
X(4) X
Array Name: A valid variable name for the structure. (X)
Subscript or Index : A value that refers to a particular array element. X(1)
Element or Subscripted variable: An individual data item within an array.
Ex: X(1), X(2)
The elements of an array are assigned successive memory locations.
The dim statement creates an array of 5 elements of type integer with a default value = 0

5. 35 10 5 25 Dim Grade( 1 To 4) As Integer Array Grade() Grade(1)
Array Name
The elements of an array are assigned successive memory location.
Grade(1)
Index 5 5

6. Array Declaration
Syntax Dim arrayName(m To n) As varType where m and n are integers
Declaring arrays - specify:
name
type of array
number of elements
Arrayname follows the same rules as variable names.
Each array has sufffiient memory reserved to hold the number of items of the given type..

7. This statement creates array of 3 integer elements
Array Declaration
Examples
Dim month(1 To 5) As String
Dim stdID(1 To 3) As Integer
Month(1)
Month(2)
Month(3)
Month(4)
Month(5)
Arrayname follows the same rules as variable names.
Each array has sufffiient memory reserved to hold the number of items of the given type..
This statement creates array of 3 integer elements
stdID(1)
stdID(2)
stdID(3) 7 7

8. The Dim Statement Used to declare an array
A Dim statement must occur before the first reference to the array elements.
You can declare arrays in the declaration section of general , which are form level variable or pass them as arguments to different sub program

9. Initializing an Array Private Sub cmdExample_Click()
Grade(1) 5
Private Sub cmdExample_Click()
Dim Grade(1 To 5) As Integer
Grade (1) = 5
Grade (2) = 30
Grade (3) = 25
Grade (4) = 15
Print Grade(1) + Grade(3)
Print Grade(4)
Print Grade(1+2)
End Sub
Grade(2) 30 25
Grade(3) 15
Grade(4)
Grade(5) 30 15 25

10. The statements Dim arrayName(0 to n) as VarType can be placed by the statement Dim arrayName(n) as VarType
Ex. Dim X(0 To 3) As Integer
Ex. Dim X(3) As Integer
x(0)
x(1)
x(2)
x(3)
x(0)
x(1)
x(2)
x(3)

11. Example Dim Y(-1 to 2) As Integer Dim Z(-2 to 0) As Single Y(-1) Y(0)
Dim Z(-2 to 0) As Single
Z(-2)
Z(-1)
Z(0)

12. Example
Dim Y(-1 to -1) As Integer
Y(-1)
Dim Z(2 to 2) As Single
Z(2)

13. Example Dim Y(2) As Integer Dim Z(2 to 2) As Single Y(0) Y(1) Y(2)
Dim Z(2 to 2) As Single
Z(2)

14. Compile ERROR Compile ERROR Example Dim Z(2 to -2) As Single
Dim Y(10 to 1) As Integer
Compile ERROR
Dim Z(2 to -2) As Single
Compile ERROR

15. Example
i = 5
Dim arr(i) As Integer
Invalid statements

16. Example 5

17. Example

18. Example
m, n must be a constant

19. Initializing an Array by Reading from a File
STUDENTS.txt
Dim student (1 To 30) As String
Dim count As Integer
Open “STUDENTS.txt” For Input As #1
For count = 1 To 30
Input #1, student(count)
Next count
Ali
Ahmed ..
Huda 1 2 30
Student
Ali
Ahmed
Huda 19
Chapter 7 - Visual Basic Schneider 19

20. Adding Up Elements in an Array
Dim score(1 To 30) As Single, student(1 To 30) As String
Dim count As Integer, average as Integer, sum As Integer
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
Students.txt
Ali 22
Ahmed 19 ..
Huda 1 2 30
Student
Ali
Ahmed
Huda 1 2 30
Score 19 22 25
Chapter 7 - Visual Basic Schneider 20 20

21. Example Dim XY (1 To 5) As Integer Dim count As Integer count = 1
Open “DATA.TXT” For Input As #1
Do While NOT EOF(1)
Input #1, XY(count)
count= count + 1
Loop
The loop will repeated as long as the end of file is not reached

22. Parallel Arrays
Two arrays are said to be parallel if subscripted variables having the same subscript are related.
Students.txt
Ali 22
Ahmed 19 ..
Huda 1 2 30
Student
Ali
Ahmed
Huda 1 2 30
Score 19 22 25

23. Example of Parallel Arrays
Dim nom(1 To 3) As String, score(1 To 3) As Integer
Dim student As Integer
Open “SCORE.TXT” For Input As #1
For student = 1 To 3
Input #1, nom(student), score(student)
Next student
Close #1

24. Chapter 7 - Visual Basic Schneider
Form_Load()
Use it to Initialize Form Level variables
Use it to initialize Form Level Arrays
Use it to Dim Dynamic Arrays
Chapter 7 - Visual Basic Schneider 24

25. Ordered Array
An array is ordered if 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.
x(0)
x(1)
x(2)
x(3) 10 15 30 40

26. Passing an Array
An array can be passed to another procedure (Only) by reference.
the name of the array, followed by an empty set of parenthesis, must appear as an argument in calling statement, and an array variable name of the same type must appear as corresponding parameters in the procedure definition of the procedure that is to receiver the array
Parenthesis are optional with the arguments

27. Example 27 27

28. Example

29. Example

30. Sorting
A common practice involving arrays is to sort the elements of the array in either ascending or descending order.
A sort is an algorithm for ordering an array
Sorting techniques
Bubble Sort
Shell Sort
Ascending : lowest to highest
descending: highest to lowest
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

31. Bubble Sort
The bubble sort involves comparing adjacent elements and swapping the values of those elements when they are out of order.
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

32. Shell Sort Similar to the bubble sort
Instead of comparing and swapping adjacent elements A(count) and A(count+1), Shell sort compares and swaps non-adjacent elements A(count) and A(count + Gap), where Gap starts at roughly half the size of the array
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.

33. Efficiency of Bubble and Shell sort (average number of comparisons)
Array Elements Bubble Sort Shell Sort
, ,638
, ,517

34. Searching Arrays
The process of finding the position of a value in an array is called searching
For example
Note: search(x) means search about x
Search(-10) = 3
Search (3) = 1
Search (5) = Not Found
stdID(1)
stdID(2)
stdID(3) 3 6
-10

35. Searching techniques
A sequential search examines each element, beginning with the first, until the specified value is found or the end of the array is reached
For example
Search about number 4  Search(4) = 5
stdID(1)
stdID(2)
stdID(3)
stdID(4)
stdID(5)
stdID(6) 3 7
-10 1 4 10
Is 4 = 3:
False
Is 4 = 7:
False
Is 4 = -10:
False
Is 4 = 1:
False
Is 4 = 4:
True
The number of comparisons to find the value 4 = 5 35 35

36. Sequential Search Useful for small arrays.
Very inefficient for large arrays (for example, names in a telephone book).
For any size array, if the array is ordered, the more efficient binary search can be used.

37. Binary Search
In a binary search, an ordered array is repeatedly divided in half. The half not containing the target value is ignored.

38. Two-Dimensional Arrays
Store values as a table, grouped into rows and columns.
The first subscript of a two-dimensional array refers to the row and the second subscript to the column.

39. Declaration of Two-Dimensional Array
Syntax:
Dim arrayName(m1 To m2, n1 To n2) As varType
Example:
Dim rm(1 To 4, 1 To 4) As Single
column
row

40. Manipulating a Two-Dimensional Array
Use nested For … Next loops to assign or access elements of a two-dimensional array.
Example:
For row = 1 To 4
For col = 1 To 4
Input #1, rm(row, col)
Next col
Next row

41. Examples: How many elements?
Dim rm(0 To 3, 97 To 99) As Integer 97 98 99 1 2 3
 12 elements 41

42. 1 2 3 2 4 6 3 6 9 What is the output of: The output is
Dim (1 to 3 , 1 to 3) as integer
For i = 1 To 3
For j = 1 To 3
a(i, j) = i * j
Print a(i, j);
Next j
Print
Next i
The output is
1 2 3
2 4 6
3 6 9

43. Examples: How many elements?
Dim rm(1 To 4) As Single
rm(1)
rm(2)
rm(3)
rm(4)
 4 elements

44. Examples: How many elements?
Dim arr(4, 1 To 4) As Single 1 2 3 4 1 2 3 4
 20 elements 44

45. Examples: How many elements?
Dim arr(-5 To -3, 5 To 5) As String 5 -5 -4 -3
 3 elements 45

46. Examples: How many elements?
Dim xy(-3 To -5) As Integer
 ERROR 46

47. Examples Dim arr(0 To 3, 97 To 99) As Integer arr(1,98)= 20
arr(0,2)  Error: index out of range
arr(-1,99)  Error: index out of range 97 98 99 1 20 2 3 15 47

48. Examples Dim arr(0 To 3, 97 To 99) As Integer For i = 97 To 99 Next i
arr(1,i) = 10
Next i 97 98 99 1 10 10 10 2 3 48