Arrays

Overview

General Discussion Uses Structure Declaration

Searching Control Arrays

Arrays

From time to time an object (a variable, a picture, a label or a command) does not serve as well as a set of objects of a similar kind addressed with a common name.

For example, in the grade point calculator, rather than having hamburgers, fries and drinks each with its own price and quantity measures, we might better describe the situation as an array of elements

3

Data Arrays A variable like Stuff

defines a data object into which a single quantity can be placed

A variable like Product defines a data object into which an array of information can be placed

210 Product

Stuff

Arrays

Arrays are useful for when there are many instances of similar data

Instead of ten integer variables holding ten values, a single array can handle all ten

intdintc inte

intj

intf

intb

intainti

inthintgintArray

Arrays

Each variable location in an array is called an element Use Dim statement to create, define dimension and type

Dim intArray(1 to 10) as Integer creates the structure below

Treat as normal variables; Reference using subscripts: intArray(4) = “114”

intArray

114

Arrays

Arrays allow programmers to write code once, but have it applied to many different data elements

Compare adding all the integers stored in the variables…

intdintc inte

intj

intf

intb

intainti

inthintgintArray

intSum = inta + intb + intc _+ intd + inte + intf + intg _+ inth + inti + inj

Arrays

Arrays allow programmers to write code once, but have it applied to many different data elements

…to adding all the elements of the array

intdintc inte

intj

intf

intb

intainti

inthintgintArray

For intI = 1 to 10 intSum = intSum + intArray(intI)Next

Arrays Arrays come in different

dimensions. Two dimensional arrays

require two subscripts elements are listed (row, column)

Example DIM intSales(1 to 3, 1 to 4) as

integer What is intSales(2, 3)?

1

2

3

1 2 3 4

1402

7532

Arrays

Three dimensional arrays require three subscripts

Example Dim intSales (1 to 3, 1 to 4, 1 to 2) as Integer

1402

2134

4521

3425

So the number 2134 is found where? the number 4521 is ______ the number 1402 is ______ the number 3425 is ______

Parallel Arrays

Dim strName (1 to 5) as String

Dim intSales (1 to 5) as Integer

So, if we know that Smith is in strName(2), we also know his or her sales is in intSales(2)

strName intSales

Jones

Smith

Frank

Able

Zean

1402

2301

0231

6762

0199

Creating Arrays Dim statement

Array name; Dimensions; Bounds; TypeDim strName (1 to 3, 1 to 4) as String

Using Any integer literal or variable can be used to subscript Must stay within the bounds Must have the correct number of subscripts Must assign the correct type of data

Given: Dim strName (1 to 3, 1 to 4) as String Is strName (0,0) = “Jones” valid? Is strName (2) = “Smith” valid? Is strName (4,3) = “Larry” valid? Is strName(3,4) = 1402 valid?

Searching Arrays

strTarget = “Q” intFound = 0For intI = 1 to 10 If strTarget = strArray(intI) Then intFound = intI Exit For End IfNext strArray

A F S V W Q Z X Y L

• Searching implies looking for a target• A simple sequential search looks through the

array for the target

Dynamic Arrays VB allows a programming to re-dimension arrays during

the run of the program. Rules for Dynamic Arrays

Use empty dimension list: intArray() as Integer Use ReDim to assign dimensions:

ReDim intArray (1 to intN, 1 to 2) Use ReDim to change Bounds

ReDim intArray (1 to (intN + 10), 1 to 3)

Use Preserve keyword to save data in arrayReDim Preserve intArray(1 to intN, 1 to

5)Preserve only allows changes in the last dimension

Control Arrays

VB allows the programmer to create arrays of controls on the form Just as there are data arrays, there may be arrays of objects, such

as command buttons, labels or picture boxes An array of labels might be made with one label for each product,

or for each price An array of command might be made to handle adding products

Characteristics Name with subscripted elements .Index property is the subscript

Control Arrays

Create an toolbox object, perhaps a command button, changing its (name) and caption.

Control Arrays1. Copy and paste the object (Ctrl-C)(Ctrl-V) or Edit/Copy then Edit/Paste

2. The message “Do you want to create a control array?” appears. Answer “yes”

3. Type Edit/Paste or (Ctrl-V) several more times to make an array of commands

Control Arrays

The Properties Window shows it all.

Note that the 4th command created is shown as “cmdButn(3)”

Control Arrays

Arrange the buttons on the form as desired

Double clicking on any one of them opens the code window

Control Arrays

The event handler is a bit strange. There is now a “parameter” inside the normally blank parentheses:

Private Sub cmdButn_Click(Index As Integer)

lblOutput.Caption = "## " & Index & " ##"

End Sub

Control Arrays

Run the process

Click each button

Observe the effect

Control Arrays

Using the same procedure, you can make arrays of labels, or of pictures, or of check boxes, etc.

You can change the GPA calculator program to make arrays of products, commands, product counts, and total costs

Summary Arrays are sets of variables know as elements These elements operate just like simple variables Arrays are created with a DIM statement that defines; boundaries,

dimensions and type When referencing elements in an array, you must have the correct

number of subscripts and their values must be within the bounds of the dimensions

The operation of looking through an array for a “target” is called searching