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+1Form1.Print “array(“ & x & “) = “ & array(x)

Next x 

10

Arrays - Examples

Dim myarray(50) as string

 

myarray(0) = “hello” 

11

Arrays - ExamplesValuing an array:

Default values of arrays are:

0 for numeric arrays

spaces for string arrays

false for boolean arrays  

12

Arrays - ExamplesValuing an array:

(element by element hard coded)

Montharray(11) = “December”

 

Numberarray(5) = 21 

13

Arrays - ExamplesValuing an array:

(use a loop)

For x = 1 to 10Myarray(x) = Val(Inputbox(“Enter a _

Number”))Next x

 

14

Arrays - ExamplesDim myarray(5) as Integer

 

For x = 1 to 5

Myarray(x) = x+1

Form1.Print “array(“ & x & “) = “ & array(x)

Next x

 

15

Arrays - ExamplesGetting 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...

51

PRACTICE: Thompson (p. 9-30) Exercise 12 “Game Board 16” (12b advanced)

PRACTICE: Thompson (p. 9-31 to 33) Exercises 13, 14, 15 and 16 (ADVANCED)