Arrays

1. Arrays • Group of variables that have a similar type • Integers • Strings • Doubles • An array of states, tax rates, social security numbers

2. Arrays • Arrays can be in one dimension or two dimensions (actually you can have up to 60 dimensions) • 1D --- myarray(4) as string can contain: NJ(0), NY(1), DE(2), PA(3)

3. Arrays • 2D --- myarray(3,3) can contain a tic-tac-toe board: X (0,0) O (0,1) X (0,2) O X O X (2,0) O (2,1) X (2,2)

4. Arrays • 1D Array: Dim arrayname(lower subscript TO upper subscript) as datatype *** lower subscript is set to 0

5. Arrays - Examples Dim statearray(0 to 4) as string • Creates a string array that will contain state ids • Statearray(3) equals ‘DE’

6. Arrays - Examples Dim montharray(0 to 11) as string • Creates a string array that will contain months in the year

7. Arrays - Examples Dim numberarray(1 to 10) as Integer • Creates an integer array that will contain 10 numbers

8. Arrays - Examples Dim ArrayVariable() as Integer • no set range of elements • Elements in this array are from 0 to n

9. Arrays - Examples Dim myarray(5) as Integer For x = 0 to 4 myarray(x) = x+1 Form1.Print “array(“ & x & “) = “ & array(x) Next x

10. Arrays - Examples Dim myarray(50) as string myarray(0) = “hello”

11. Arrays - Examples Valuing an array: Default values of arrays are: 0 for numeric arrays spaces for string arrays false for boolean arrays

12. Arrays - Examples Valuing an array: (element by element hard coded) Montharray(11) = “December” Numberarray(5) = 21

13. Arrays - Examples Valuing an array: (use a loop) For x = 1 to 10 Myarray(x) = Val(Inputbox(“Enter a _ Number”)) Next x

14. Arrays - Examples Dim myarray(5) as Integer For x = 1 to 5 Myarray(x) = x+1 Form1.Print “array(“ & x & “) = “ & array(x) Next x

15. Arrays - Examples Getting array data: Txt1.text = montharray(5) ‘ displays ‘ MAY Text2.text = numberarray(5) ‘display 21

16. Arrays - Examples PRACTICE: ZAK p. 724 “The Presidents” Write an application that allows a user to guess the first 10 US Presidents. Create a string array of the presidents (form load) and randomly ask the user to guess the 1st, 2nd, etc… president. Continued...

17. Arrays - Examples PRACTICE: ZAK p. 724 “The Presidents” Have them select from a radio button control array of 15 unordered presidents. One they click on a “GUESS” button, examine their choice and match it to the string array. Let them know if they are right or wrong and keep track of their choices. Once they successfully selected a president, disable that choice and DO NOT allow that number to be used again

18. Arrays - RANGES Lbound --- identifies and returns the lowest index in the array (usually 0) Lbound(arrayname, DIM) ‘ DIM identifies the dimension of the array 1 is ‘ default  EXAMPLE: Result = Lbound(myarray)

19. Arrays - RANGES Ubound --- identifies and returns the highest index in the array Ubound(arrayname, DIM) ‘ DIM identifies the dimension of the array 1 is default EXAMPLE: Result = Ubound(myarray) for x = 1 to Result … Next x

20. Arrays - RANGES EXAMPLE: Dim mystring(10) as String For count = Lbound(mystring) TO ubound(mystring) mystring(count) = InputBox(“Enter a Name:”) Next count

21. Arrays - RANGES EXAMPLE: RANGE Errors: Dim myarray(5) as integer Myarray(6) = 200 ‘ SUBSCRIPT ERROR

22. Arrays - Unbounded • Unbounded/Dynamic Array: • Declare an array with no predefined size. It can vary in size during run time. Dim myarray() as Integer

23. Arrays - Redim • REDIM --- allocates/resets the size of an unbounded/dynamic array Redim myarray(10) ---- clears out the array and resizes it to the number of Elements • ONLY USE THIS ON LOCALLY SCOPED ARRAYS !!!

24. Arrays - Redim • REDIM • To Preserve the existing array when redimming: • Keeps existing values when redimming. • Can only do when resetting the UPPERBOUNDRY of the array.

25. Arrays - Redim • REDIM Redim Preserve myarray(10) • preserves the existing contents of the array Redim Preserve myarray Ubound(myarray) + 1) • dynamically adds 1 element to the array size

26. Arrays - Redim • REDIM • Erase --- deallocates an array space if its dynamically allocated. Reinitializes the elements of a fixed sized array. Erase myarray

27. Arrays - Redim • PRACTICE: Thompson (p. 9-6) Count the freequency of dice roll outcomes

28. Arrays - Searching • Searching and Array: Linear • Iterate thru each array element looking for a specifice value, Example: ‘ find a given number in an integer array searchnum = 5 dim intarray(20) as integer do while (intarray(I) <> searchnum) AND (I < Ubound(intarray)) I = I + 1 loop

29. Arrays - 2 D Array • 2 Dimensional Array: • a matrix is a multidimensonal array used to store related information. • Checkerboard, tic-tac-toe board.

30. Arrays - 2 D Array • Dim my2darray(3,3) as Integer (X,Y) X = rows Y = columns R 0,0 0,1 0,2 0,3 O 1,0 1,1 1,2 1,3 W 2,0 2,1 2,2 2,3 S 3,0 3,1 3,2 3,3 COLUMNS (Y)

31. Arrays - 2 D Array • EXAMPLE: Dim a2d(3, 3) a2d(0, 0) = 1 a2d(2, 2) = 5 a2d(3, 3) = 9

32. Bubble Sort For x = Lbound(array) to Ubound(array) For y = Lbound(array) to Ubound(array)-1 if array(y) > array(y+1) then temp = array(y) array(y) = array(y+1) array(y+1) = temp end if Next Next

33. Binary Search Dim lowi ,highi, midi as integer Lowi = Lbound(array) Highi = Ubound(array)

34. Binary Search Do While Not boolfound AND lowi <= highi midi = Int((highi + lowi) / 2) if array(midi) = TARGETNUM then boolfound = TRUE elseif array(midi) > TARGETNUM then highi = midi -1 else lowi = mid + 1 end if loop

35. Binary Search If boolfound = TRUE then “FOUND” else “NOT FOUND” End if

36. ArrayList • The ArrayList is a “class” that allows you to maintain an “array” of objects and have the ArrayList do all of the organizing of the data.

37. ArrayList • You can perform the following types of actions with an ArrayList: • Add • Count • Remove • Sort • Search

38. ArrayList • You can perform the following types of actions with an ArrayList: • Get an Item from the list (Item) • Clear the list • Determine if 2 elements are EQUAL (equal) • Obtain the value at a specific index in the arraylist (IndexOf)

39. ArrayList • The following are examples on how to use each of these actions:

40. ArrayList • Create the ArrayList: Dim myAL As ArrayList = New ArrayList

41. ArrayList • Add elements to the ArrayList: Dim cc As Integer = 10 myAL.Add(cc) myAL.Add(20)

42. ArrayList • iterate thru all elements of the ArrayList (Count and Item): Dim z As Integer z = 0 Do While z < myAL.Count Button3.Text = Val(Button3.Text) + myAL.Item(z) z += 1 Loop

43. ArrayList • Remove elements from the ArrayList: myAL.Remove(20)

44. ArrayList • Check the list to see if a specific ob ject is in the ArrayList: TextBox1.Text = myAL.Contains(15)

45. ArrayList • Return a specific element from the ArrayList: myAL.Item(0) = 40

46. ArrayList • Sort elements of the ArrayList: myAL.Sort()

47. ArrayList • Search for an element in the ArrayList: TextBox2.Text = myAL.BinarySearch(40)

48. ArrayList • Check to see if 2 objects are equal: TextBox3.Text = myAL(0).Equals(myAL(0))

49. ArrayList • Empty the ArrayList: myAL.Clear()

50. PRACTICE: Thompson (p. 9-26) Exercise 3 “Generated Numbers” • PRACTICE: Thompson (p. 9-27) Exercise 5a “Generated Numbers” (5b advanced) • PRACTICE: Thompson (p. 9-28) Exercise 8 “Duplicate Values” • PRACTICE: Thompson (p. 9-29) Exercise 10 “Lockers” continued...