Arrays in Visual Basic

Week 9CM30104-1

What is an array ?

An array is a data structure that enables us to store a list of values that can be thought of as a table

Enables us to reference several data values by one variable name

Types of Arrays

There are 2 types of arrays in VB :

Data Arrays

Control Arrays

Two types of Arrays in VBData Arrays

Primarily used to store data which is related in some way and of the same type, e.g: student grades for a class of twenty students weather details for a series of places.

Control Arrays

A mechanism for duplicating controls and allowing the same event coding to be triggered by an action to any of the elements of the control array.

Data arrays ~ example

iNos

1

2

3

4

5

iNos (3)

Array name

Array index

Array elementsCoding to reference each element

42

31

98

Array Declaration

Arrays are declared in the same way as for variables.

Dim iNos (1 To 5) As Integer

or : Dim iNos (5) As Integer

1 42

2 98

3 21

4 77

5 30

0 42

1 98

2 21

3 77

4 30When no start number specifiedarray index begins at 0

An example - Finding largest of a sequence of numbers

Using several variables … iNum1, iNum2, iNum3 etcand a complicated Nested If ………….

If (iNum1 > iNum2) And (iNum1 > iNum2) And … … And (iNum1 > iNum5) Then

iLargest = iNum1Else

If (iNum2 > iNum1) And (iNum2 > iNum3) …… …….. etc

An example - Finding largest of a sequence of numbers

Using a For loop and one variable, iNum

For iLoopCount = 1 To 5

iNum = InputBox (“Enter next number”)

If iNum > iLargest TheniLargest = iNum

End If

Next iLoopCount

Give iLargest an initialvery small value

iLargest = 0

Finding largest of a sequence of numbers - using an Array

Dim iNos (1 To 5) as Integer

iLargest = 0

For iCount = 1 To 5

iNos (iCount) = InputBox (“Enter next number”)

If iNos (iCount) > iLargest TheniLargest = iNos (iCount)

End If

Next iCount

iNos

45132

2

71

94

iLargest

132

Finding largest of a sequence of marks & also storing names associated with each mark

iMarks(1 To 5)

42

98

21

77

30

sNames(1 To 5)

Fred

Sue

Bill

Amy

Jonathon

iHighestMark

98

sBestStudent

Sue

Finding largest of a sequence of marks & also storing names associated with each mark

iMarks(1 To 5) sNames(1 To 5)

42

98

21

77

30

Fred

Sue

Bill

Amy

Jonathon

Fill the arrays first …

For iLoop = 1 To 5

sNames(iLoop) = …. iMarks(iLoop) = ….

Next iLoop

then have other loops to process the data in the arrays

Arrays have many advantages –e.g, we can then sort & list students in order

98

77

42

30

21

Sue

Amy

Fred

Jonathon

Bill

42

98

21

77

30

Fred

Sue

Bill

Amy

Jonathon

ORDER OF INPUT ARRAYS AFTER SORTING

Example coding

‘fill arraysFor iCount = 1 to 5

sNames(iCount) = InputBox(“Name”)iMarks(iCount) = InputBox(“Mark”)

Next iCount

‘display to listboxesFor iCount = 1 to 5

lstNames.AddItem sNames(iCount)lstMarks.AddItem iMarks(iCount)

Next iCount

42

98

21

77

30

Fred

Sue

Bill

Amy

Jonathon

Payroll example

Min = 0; Max = 9 Vertical Scroll Bar

scrEmployee

Caption = “Add Employee”

Command Button

cmdEmployee

Caption = “”LabellblPayroll

Text = “”Text BoxtxtSalary

Text = “”Text BoxtxtName

PropertiesControlName

• Using a form like this to:

• Input name & salary• Store data in an array

• Scroll through previous data entered

Payroll example

• Scroll bar set at design stage to

• min = 0

• max = 9

sName cSalary

Fred Bloggs 0 10,200John Smith 1 14,000Jim Brown 2 8,250Dave Boss 3 25,600

456789

• Data stored in 2 arrays:

sName (10) As String sSalary (10) As Currency

Payroll example

Defining the variables:

Private sName (10) As StringPrivate cSalary (10) As Currency

Private ID As Integer

Private cTotalPayroll As Currency

sName cSalary

Fred Bloggs 0 10,200John Smith 1 14,000Jim Brown 2 8,250Dave Boss 3 25,600

456789

Program code

Private Sub cmdEmployee_Click()

ID = scrEmployee.Value ‘Set array index ‘depending on scroll bar

sName(ID) = txtName.Text ‘Enter data from text cSalary(ID) = txtSalary.Text ‘boxes into arrays

cTotalPayroll = cTotalPayroll + cSalary(ID) ‘Add to total pay scrEmployee.Value = scrEmployee.Value + 1 ‘Move scroll bar ‘on 1 position

End Sub

Private sName (10) As StringPrivate cSalary (10) As CurrencyPrivate ID As IntegerPrivate cTotalPayroll As Currency

Program code Private sName (10) As StringPrivate cSalary (10) As CurrencyPrivate ID As IntegerPrivate cTotalPayroll As Currency

 

When the scroll bar is moved :

Private Sub scrEmployee_Change()

ID = scrEmployee.Value ‘Set array index depending ‘on scroll bar

‘Display name & salary from ‘appropriate position of arrays txtName.Text = sNames(ID) txtSalary.Text = Format(cSalary(ID), "Currency")

End Sub

Arrays can have more than 1 dimension

Occasionally information can often be presented more clearly by using arrays with more than one dimension.

23232323233

45454545452

888881

Col 1 2 3 4 5

4 100 41

18 15 13

Row

Arrays can have more than 1 dimension

E.g Dim iAllMarks (1 To 5, 1 To 4) As Integer

columns rows

23232323233

45454545452

888881

Col 1 2 3 4 5

4 100 41 18 15 13

Row

iAllMarks (2, 4) = 41

Accessing 2-D arrays

Usually done using two nested loops

For col 1 to 5For row 1 to 3Store input in cell (col,row)Next row

Next col

For row 1 to 3For col 1 to 5Store input in cell (col,row)Next col

Next row

Single line or column?By keeping the column number the same and varying row – access a single column e.g.txtOutput.Text = marks(3,row) [in loop]

By keeping the row number the same and varying col – access a single row e.g.txtOutput.Text = marks(col,1) [in loop]

Array example - sorting

In this example a simple set of inputs are set up.

Clicking the top button allows data entered to be stored in the array

The middle one sorts the data

The bottom button puts sorted data in the text boxes

Set Global variables and Initialise data

Const cmin = 0Const cmax = 4 ‘declare data array’ Private iNumbers(cmin To cmax) As Integer

 Sub Form_Load ()Dim i As Integer ‘initialise array elements to zero For i = cmin To cmax iNumbers(i) = 0 Next i ‘initialise text boxes text1 = iNumbers(0) text2 = iNumbers(1) text3 = iNumbers(2) text4 = iNumbers(3) text5 = iNumbers(4)End Sub

Store Numbers

Sub cmdAssign_Click ()

If (text1.Text = "") Or (text2.Text = "") Or (text3.Text = "") Or (text4.Text = "") Or (text5.Text = "") Then Beep MsgBox ("a zero length string is present") Else ‘store data from textboxes into array iNumbers(0) = CInt(text1.Text) iNumbers(1) = CInt(text2.Text) iNumbers(2) = CInt(text3.Text) iNumbers(3) = CInt(text4.Text) iNumbers(4) = CInt(text5.Text) End If

End Sub

Sort Numbers

Sub cmdRearrange_Click ()Dim i As IntegerDim iPass As IntegerDim iTemp As IntegerDim iNoSwitches As Integer

iPass = 0Do iPass = iPass + 1 iNoSwitches = 1 For i = cmin To (cmax - iPass) If iNumbers(i) > iNumbers(i + 1) Then iNoSwitches = 0 iTemp = iNumbers(i) iNumbers(i) = iNumbers(i + 1) iNumbers(i + 1) = iTemp End If Next iLoop Until NoSwitches = 1

End Sub

Redisplay numbers

Sub cmdRetrieve_Click ()

label1.Caption = iNumbers(0) label2.Caption = iNumbers(1) label3.Caption = iNumbers(2) label4.Caption = iNumbers(3) label5.Caption = iNumbers(4)

End Sub

Summing up

Simple data arrays can be thought of as tables of data

Arrays enable us to reference several data items using one variable name

They can be 2-dimensional (or 3, or 4 …)

They are almost always processed using loops