Arrays

Code: Arrays Controls: Control Arrays, PictureBox, Timer

Seeding Random Number Generators Because the numbers are given by an

algorithm, the same numbers come up each time the algorithm runs

A “seed” is a parameter in the random number generator; changing the seed, changes algorithm results

Randomize seeds the generator off the clock so the program is different at different times Randomize should only be done once, perhaps

in a form_initialize method

Variable Arrays If a group of variables are

of the same type (e.g. all int’s) (Note: same type does not mean same value)

and play a similar role (i.e. the code for them is nearly identical),

it is convenient to make them an array For example, grade1, grade2, …

becomes grade(0), grade(1), …. Chapter 7 in Deitel, Deitel and Nieto

Arrays in Memory Recall variables correspond to

memory locations The elements of an array are

stored in consecutive memory locations

When you refer to the entire array, you “point” to the first memory location

Before ArraysDim Grade1 As IntegerDim Grade2 As IntegerDim Grade3 As IntegerDim Grade4 As IntegerDim Grade5 As IntegerDim Grade6 As Integer

BECOMES

Dim Grade(5) As Integer

After ArraysAverage = (Grade1 + Grade2 + Grade3 +

_ Grade4 + Grade5 + Grade6) / 6

BECOMES

Average = 0For i = 0 To 5 Average = Average + Grade(i)Next iAverage = Average / 6

Array Vocabulary Array: refers to the entire set of related

variables Element: refers to one member of the

array Index: (a.k.a. subscript) is an integer

(0,1,2,…) that is associated with each element

Grade is the array, Grade(3) is an element in that array, that element has an index 3 (note: it is the fourth item)

More Array Vocabulary Option Base:

If you declare Grade(5), VB makes an array with six elements Grade(0) through Grade(5), that is, it starts indexing at 0

If you want to start indexing at 1, you can type Option Base 1 (just below Option Explicit)

Note: Control Arrays are always zero based (regardless of Option Base)

Average, High and Low

Average, High and Low

Average, High and Low

Average, High and LowOption ExplicitConst SCORENUMBER As Integer = 5

Private Sub cmdEnter_Click() Dim Score(SCORENUMBER - 1) As Integer Dim i As Integer Dim Sum As Integer Dim Min As Integer Dim Max As Integer Dim Average As Double

Average, High and Low

Score(0) = InputBox("Enter Score 1: ")

Sum = Score(0) Min = Score(0) Max = Score(0)

‘Enter first score outside of loop and make it the ‘min and the max

Average, High and LowFor i = 1 To SCORENUMBER - 1 Score(i) = InputBox("Enter Score " & i + 1 & ": ") Sum = Sum + Score(i) If Score(i) < Min Then Min = Score(i) End If If Score(i) > Max Then Max = Score(i) End If Next i

Average, High and LowAverage = Sum / SCORENUMBER

txtAverage.Text = Average txtHigh.Text = Max txtLow.Text = MinEnd Sub

Private Sub Form_Load() lblInstruct.Caption = "Click the button below to begin " & _ "entering the " & SCORENUMBER & " scores and “ &

_ “calculate " & “their average, high and low."End Sub

Scaling To scale something is to change its size

(e.g. the number of elements in an array) If a program is written in a way which

facilitates various size changes, it is said to be “scalable”

The use of the constant SCORENUMBER in the previous code made it scalable, since the code would only one change if the size of the score array was varied

Array as argument of function 1

Const NUMBEROFGRADES As Integer = 5Private Sub cmdEnter_Click() Dim Grades(NUMBEROFGRADES-1) As Integer Dim Ave As Double Dim i As Integer For i = 0 To NUMBEROFGRADES-1 Grades(i) = InputBox("Enter Grade " & i, "Grades") Next i Ave = Average(Grades) txtAverage.Text = AveEnd Sub

Array as argument of function 2

Private Function Average(mArray() As Integer) As Double Dim i As Integer Average = 0.0 For i = LBound(mArray) To UBound(mArray) Average = Average + mArray(i) Next i Average = Average / (UBound(mArray) -

LBound(mArray) + 1)End Function

Bounds The Lower Bound is the lowest

index in an array The Upper Bound is the highest

index in an array Lbound(ArrayName) finds the

lower bound Ubound(ArrayName) finds the

upper bound of an array

Shuffle'randomly shuffles an array of stringsPrivate Sub Shuffle(mArray() As String) ‘Strings only Dim i As Integer Dim Swap As String Dim j As Integer dim lb as Integer lb = LBound(mArray) dim ub as Integer ub = UBound(mArray)

For i = lb To ub j = lb + Int((ub - lb + 1) * Rnd()) Swap = mArray(i) mArray(i) = mArray(j) mArray(j) = Swap Next iEnd Sub

By Reference In VB the default situation is that

variables are passed to a function “by reference” (whether or not they are arrays)

That is, if the variable is changed in the function, it is also changed in the caller

More about this in a future lecture

Control array If a group of controls are

of the same type (e.g. all CommandButtons)

and play a similar role (i.e. the code for them is nearly identical),

it is convenient to make them an array

(p. 274 in Deitel, Deitel and Nieto)

Array of TextBoxes

Code for Array of Textboxes

Option Explicit

Private Sub cmdSumHours_Click() Dim i As Integer 'Counter Dim Total As Integer Total = 0 For i = 0 To txtHours.Ubound ‘Ubound is a property NOT

function

Total = Total + txtHours(i).Text Next i txtSum.Text = TotalEnd Sub

Which button was pressed?

Which button revisited (code)

Option ExplicitDim StoreButtonIndex As Integer

Private Sub cmdButton_Click(Index As Integer) StoreButtonIndex = IndexEnd Sub

Private Sub cmdWhich_Click() txtWhich.Text = cmdButton(StoreButtonIndex).Caption

& _ " was last pressed."End Sub

Comes automatically and tells us which button was pressed

Collection of Forms The index property comes into play when a

control is an element in an array Notice that forms do not have an index

property However there is a way to apply these

scaling ideas to forms Forms have an order, the order in which

they are loaded The third form loaded can be referred to as

Forms(2) (zero-based counting) Doesn’t matter what it was named

Toward Scaling with Forms

Option ExplicitDim FormIndex As Integer

Private Sub optForm_Click(Index As Integer) FormIndex = Index + 1End Sub

Private Sub cmdGoToForm_Click() Me.Hide Forms(FormIndex).ShowEnd Sub

Private Sub Form_Load() 'the order in which forms are loaded 'is their order in the collection Call Load(frmNumber1) Call Load(frmNumber2) Load frmNumber3 ‘note alternate syntax for calling subsEnd Sub

PictureBox The pictureBox control (not Image control)

is found near the top of the control in the VB IDE

The properties we will use Picture: refers to the picture to be shown

We’ll load the pictures during runtime instead of during development

Index: since we will make an array of PictureBoxes

Tag: an internal labeling, we can give matching PictureBoxes the same Tag and use that property to test for a match

PictureBox (Cont.) We will load the picture using the

function LoadPicture(filename) which loads an image file include “the complete path” e.g. LoadPicture(“a:\dice2.gif”) If the image files are in the project folder,

one can use App.Path e.g. LoadPicture(App.Path & “\dice2.gif”)

LoadPicture() empties the PictureBox Note: no argument in LoadPicture()

Craps Example

Craps codeOption Explicit

Private Sub cmdRoll_Click() Dim i As Integer Dim Die_Value As Integer For i = 0 To picDie.UBound Die_Value = Int(Rnd() * 6 + 1) picDie(i).Picture = LoadPicture(App.Path & "\dice" & Die_Value & ".gif") Next iEnd Sub

Private Sub cmdClear_Click() Dim i As Integer For i = 0 To picDie.UBound picDie(i).Picture = LoadPicture() Next iEnd Sub

Timer Important Properties

Interval: the amount of time in milliseconds between Timer events

Enabled: When True, Timer events occur, when False, no Timer events occur

Events/Methods Timer: when the timer is enabled a

Timer event occurs roughly every N milliseconds, where N is the Interval property

Stop Watch

Stop Watch CodeOption ExplicitPrivate Sub cmdStart_Click() tmrStopWatch.Enabled = Not tmrStopWatch.Enabled If tmrStopWatch.Enabled Then cmdStart.Caption = "Stop" Else cmdStart.Caption = "Start" End IfEnd Sub

Private Sub tmrStopWatch_Timer() txtTimer.Text = txtTimer.Text + 0.1 ‘interval = 100End Sub