Arrays

One dimensional arrays

Index of projects

• Random picture display

• Sum array values

• Display names in listbox

• Name search

• Largest/smallest

• Car sales

arrays

• Arrays are multi-entry data structures.• One dimensional arrays have a fixed length

associated with the array name, once they have been built. – For this reason (one-dim) arrays are called “linear”

data storage– For this reason arrays are called “static” data storage

– the allocation may not be changed later.• One dimensional arrays have a datatype

associated with them, the type they may hold. For this reason arrays are called “homogeneous”.

Arrays

• Arrays are declared specifying a size.• Examples might be:

Dim calendarEntries(365) as DateDim bestFriends(3) as StringDim list(5) as integerDim values(25) as Double

• Arrays can be allocated at compile time, in which case their size is calculated based on how many entries are provided, as inDim numbers as double()={1.1,2.2,3.3}

arrays

• Because arrays have fixed size, once allocated, loops are useful for processing them.

• Array indices are zero-based (count subscripts starting at zero) just as String indices are in VB.

• There are a number of fields/methods useful for arrays such as: length, getType, initialize(), reverse(), lastIndexOf

A loop is generally used to process an array

‘ if we have built an array:Dim list(5),i as integer‘ then later….

For i=0 to list.length-1‘ process elements here… for exampleList(i)=0 ‘a typical initializationNext

We could “glue together” names

Dim longstring as string=“ “

Dim picnames As String() = {"lisa", "bart", "dollars", "robot“_ ,"booper", "shakespeare", "nerd"}

For i=0 to picnames.length-1

Longstring = longstring & “ “ & picnames(i)

Next

We could search for a name

Dim picnames As String() = {"lisa", "bart", "dollars", "robot“_ ,"booper", "shakespeare", "nerd"}

Dim name as string

Dim found as boolean=false

Name=txtinput.text

For i=0 to picnames.length-1

If name= picnames(i) then

Found=true

End if

Next

A form which displays random pictures

• Uses our array of names since I found those gif files.

• Uses techniques we used in our “flags-of-the-world” application to display pictures

A form which displays random pictures

Clicking random button

This form uses

• A string array declared as a field value and initialized at time of declaration

• A random object to pick random entries – remember parens are used when allocating an object with the new keyword

• A picture box to display pictures• Gets the image from a file using system.io

Dim randomguy As Random = New Random() Dim picnames As String() = {"lisa", "bart", "dollars", "robot", "booper",

"shakespeare", "nerd"}

Random class

• The next (or nextint()) function gets the next random value.

• You can give the next a start and final value and it will pick a random int from start to final-1

• If you use random class to generate reals, it gives reals in the range (0,1). To get other reals multiply and shift.

Code for btnrandom

Private Sub btnRandom_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRandom.Click

Dim val As Integer val = randomguy.Next(0, picnames.Length)picture.Image =

Image.FromFile(directory.GetCurrentDirectory & picnames(val) & ".gif")

End Sub

Debugger note

• In VB 2003 the debugger expects files to be named “bin”&name.gif since the debug version of your project is in a bin subdirectory

• We noticed in VB2005 it didn’t work the same.

More on arrays and the debug window

For each item in array…next

• For each is a useful mechanism when the number of items in an array is not known: Private Sub Btndisplay_Click(ByVal sender As

System.Object, ByVal e As System.EventArgs) Handles btndisplay.Click

Dim Name As String For Each Name In names Debug.WriteLine(Name) ’write to debug

window Next End Sub

Now display to listbox

Array allocation and button code

Dim names As String() = {"bob", "sue", "mary", "jeremiah", "opie", "jezebel"} ‘put on one line or use line continue

‘this is compile time array allocation Private Sub Btndisplay_Click(ByVal sender As

System.Object, ByVal e As System.EventArgs) Handles btndisplay.Click

Dim Name As String For Each Name In names Debug.WriteLine(Name) lstdisplay.Items.Add(Name) Next End Sub

Common activites

• Arrays often need to be searched for a specific value

• Largest or smallest value may be sought.• Arrays may need to be summed (if contents are

numeric)

Allocate an array and sum its contents

Dim values As Double() = {1.2, 2.3, 3.4, 5.6, 6.7, 7.8, 8.9, 9.0} Private Sub Form1_Load(ByVal sender As System.Object, ByVal e

As System.EventArgs) Handles MyBase.Load Dim sum As Double = 0 'set sum to zero…additive identity element Dim guy As Double For Each guy In values sum += guy Next MessageBox.Show("sum is" & sum, "The sum",

MessageBoxButtons.OK, MessageBoxIcon.Hand)

End Sub

Find the largest (or smallest)

Revised loadform code

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Dim big As Double = values(0) 'set big to first one Dim guy As Double For Each guy In values If guy > big Then big = guy End If Next MessageBox.Show("largest is" & big, "findbiggest",

MessageBoxButtons.OK, MessageBoxIcon.Hand) End Sub

Look for mary

Mary found

Look for bozo

Can’t find him

One version of search code: remember, the user may need a reminder about case-sensitivity

Private Sub btnfind_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnfind.Click

Dim search, guy As String Dim found As Boolean = False

search = txtguy.Text ‘value in textbox For Each guy In names If guy = search Then MessageBox.Show(search & "is found", "results",

MessageBoxButtons.OK, MessageBoxIcon.Hand) found = True End If Next 'after loop you'll know if he's not there If Not found Then MessageBox.Show(search & "is not found", "results",

MessageBoxButtons.OK, MessageBoxIcon.Hand) End If End Sub

Another version of search code Private Sub btnfind_Click(ByVal sender As System.Object, ByVal e As

System.EventArgs) Handles btnfind.Click Dim search, guy As String Dim found As Boolean = False search = txtguy.Text ‘value in textbox For Each guy In names If guy = search Then

found = True End If Next 'after loop you'll know if he's not there If found ThenMessageBox.Show(search & "is found", "results",

MessageBoxButtons.OK, MessageBoxIcon.Hand)else MessageBox.Show(search & "is not found", "results",

MessageBoxButtons.OK, MessageBoxIcon.Hand) End If End Sub

Yet another version of search code Private Sub btnfind_Click(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles btnfind.Click Dim search, guy As String Dim message as String = “Not there” ‘ must assume

won’t be found search = txtguy.Text ‘value in textbox For Each guy In names If guy = search Then

Message=“Is there”

End If Next 'after loop you'll know if he's not there…no if neededMessageBox.Show(search & message, "results",

MessageBoxButtons.OK, MessageBoxIcon.Hand)End Sub

Car sales

We have several employees and car models

• This application uses a combobox

• You can populate it from the properties window by clicking the ellipsis and entering strings into the dialog box

combobox

combobox

Arrays needed for car sales‘which one? Dim list As Integer() = {0, 0, 0, 0}‘ name of car sold Dim values(4) As String’car costsDim prices as

double={50000,200000,30000,12000} ‘worker namesDim employees() as String={“names”,”go”,”here”}

Keep track of individual employee sales