1. 1 Chapter 7 Arrays

2. 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 0 X 0000 X(1) X(2) X(3) X(4) 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

4. 4 Elements of an Array 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) 0000 X(1) X(2) X(3) X(4) X

5. 5 Array Grade() Dim Grade( 1 To 4) As Integer 35 10 5 25 Grade(1 ) Array Name Index

6. 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

7. 7 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) 000 stdID(1) stdID(2)stdID(3) This statement creates array of 3 integer elements

8. 8 The Dim Statement Used to declare an array A Dim statement must occur before the first reference to the array elements.

9. 9 Initializing an Array 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 0 0 0 0 0 Grade(1) Grade(2) Grade(3) Grade(4) Grade(5) 5 30 25 15 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 0000 x(0) x(1)x(2)x(3) 0000 x(0) x(1)x(2)x(3)

11. Example Dim Y(-1 to 2) As Integer 0000 Y(-1) Y(0)Y(1)Y(2) Dim Z(-2 to 0) As Single 000 Z(-2) Z(-1)Z(0)

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

13. Example Dim Y(2) As Integer Dim Z(2 to 2) As Single 0 Z(2) 000 Y(0)Y(1)Y(2)

14. Example 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 500500

18. m, n must be a constant

19. Chapter 7 - Visual Basic Schneider 19 Initializing an Array by Reading from a File 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 STUDENTS.txt AliAhmed Huda Student 12 30

20. Chapter 7 - Visual Basic Schneider20 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 For count = 1 To 30 sum = sum + score(count) Next count average = sum/30 AliAhmed Huda Student 1230 22 19 25 Score 1230 Ali 22 Ahmed 19.. Huda 25 Students.txt

21. 21 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 Example

22. 22 Parallel Arrays Two arrays are said to be parallel if subscripted variables having the same subscript are related. AliAhmed Huda Student 1230 22 19 25 Score 1230 Ali 22 Ahmed 19.. Huda 25 Students.txt

23. 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. 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 Schneider24

25. 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. 40301015 x(0) x(1)x(2)x(3)

26. 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. 27 Example

30. 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

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

32. 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

33. 33 Efficiency of Bubble and Shell sort (average number of comparisons) Array Elements Bubble Sort Shell Sort 51015 15105115 25300302 30435364 1004,9502,638 500124,75022,517

34. 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 -1036 stdID(1) stdID(2)stdID(3)

35. 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 -1037 stdID(1) stdID(2)stdID(3) 1014 stdID(4) stdID(5)stdID(6) 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

36. 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. 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. 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. 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. 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 41 000 000 000 000 999798 0 1 2 3  12 elements

42. What is the output of: 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 43 000 rm(1) rm(2)rm(3) 0 rm(4)  4 elements

44. Examples: How many elements? Dim arr(4, 1 To 4) As Single 44 000 000 000 000 312 0 1 2 3 0 0 0 0 4 0000 4  20 elements

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

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

47. Examples Dim arr(0 To 3, 97 To 99) As Integer arr(1,98)= 20 arr(3,99)=15 arr(0,2)  Error: index out of range arr(-1,99)  Error: index out of range 47 000 0020 000 1500 999798 0 1 2 3

48. Examples Dim arr(0 To 3, 97 To 99) As Integer For i = 97 To 99 arr(1,i) = 10 Next i 48 000 10 000 000 999798 0 1 2 3