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Arrays

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;

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Arrays

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  1. Arrays Code: Arrays Controls: Control Arrays, PictureBox, Timer

  2. 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

  3. 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

  4. 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

  5. Before Arrays Dim Grade1 As Integer Dim Grade2 As Integer Dim Grade3 As Integer Dim Grade4 As Integer Dim Grade5 As Integer Dim Grade6 As Integer BECOMES Dim Grade(5) As Integer

  6. After Arrays Average = (Grade1 + Grade2 + Grade3 + _ Grade4 + Grade5 + Grade6) / 6 BECOMES Average = 0 For i = 0 To 5 Average = Average + Grade(i) Next i Average = Average / 6

  7. 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)

  8. 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)

  9. Average, High and Low

  10. Average, High and Low

  11. Average, High and Low

  12. Average, High and Low Option Explicit Const 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

  13. 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

  14. Average, High and Low For 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

  15. Average, High and Low Average = Sum / SCORENUMBER txtAverage.Text = Average txtHigh.Text = Max txtLow.Text = Min End 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

  16. 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

  17. Array as argument of function 1 Const NUMBEROFGRADES As Integer = 5 Private 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 = Ave End Sub

  18. 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

  19. 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

  20. Shuffle 'randomly shuffles an array of strings Private 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 i End Sub

  21. 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

  22. 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)

  23. Array of TextBoxes

  24. 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 = Total End Sub

  25. Which button was pressed?

  26. Which button revisited (code) Option Explicit Dim StoreButtonIndex As Integer Private Sub cmdButton_Click(Index As Integer) StoreButtonIndex = Index End Sub Private Sub cmdWhich_Click() txtWhich.Text = cmdButton(StoreButtonIndex).Caption & _ " was last pressed." End Sub Comes automatically and tells us which button was pressed

  27. 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

  28. Toward Scaling with Forms

  29. Option Explicit Dim FormIndex As Integer Private Sub optForm_Click(Index As Integer) FormIndex = Index + 1 End Sub Private Sub cmdGoToForm_Click() Me.Hide Forms(FormIndex).Show End 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 subs End Sub

  30. 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

  31. 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()

  32. Craps Example

  33. Craps code Option 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 i End Sub Private Sub cmdClear_Click() Dim i As Integer For i = 0 To picDie.UBound picDie(i).Picture = LoadPicture() Next i End Sub

  34. 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

  35. Stop Watch

  36. Stop Watch Code Option Explicit Private Sub cmdStart_Click() tmrStopWatch.Enabled = Not tmrStopWatch.Enabled If tmrStopWatch.Enabled Then cmdStart.Caption = "Stop" Else cmdStart.Caption = "Start" End If End Sub Private Sub tmrStopWatch_Timer() txtTimer.Text = txtTimer.Text + 0.1 ‘interval = 100 End Sub

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