Arrays

1
Arrays
Chapter 8
2
Overview

• General discussion
• Variable arrays
• Control arrays
• Multi-dimensional variable arrays
• Two-dimensional
• Three-dimensional
• Parallel arrays
• Dynamic arrays

3
Arrays

• Often a set of objects or variables of the same
  type are used to hold related data
• Prices of food items at a fast food restaurant
• Scores on programming assignments
• In the GPA calculator, rather than having five
  textboxes with different names to enter the
  grades, we might better describe the situation as
  an array of elements
• Many data containers
• One name

4
Variable 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

Stuff
3
2
1
0 Product
5
Declaring Variable Arrays

• An array is declared using the following syntax
• Dim ArrayName(LowerBound To UpperBound) as
  VariableType
• The LowerBound of the array is the lowest index
  in the array, while the UpperBound is the highest
  index in the array

6
Variable Array Example (1)

• 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

intd
intc
inte
intb
intf
inti
inta
inth
intg
intj
7
Variable Array Example (2)

• Each variable location in an array is called an
  element
• Use Dim statement to define size and type
• Dim intArray(1 to 10) as Integer creates the
  structure below
• Treat as normal variables
• Reference using subscripts intArray(4) 114

8
Variable Array Example (3)

• 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

intd
intc
inte
intb
intSum inta intb intc _ intd inte
intf intg _ inth inti inj
intf
inti
inta
inth
intg
intj
9
Variable Array Example (4)

• Arrays allow programmers to write code once, but
  have it applied to many different data elements
• to adding all the elements of the array

intd
intc
inte
intb
For intI 1 to 10 intSum intSum
intArray(intI) Next intI
intf
inti
inta
inth
intg
intj
10
Control Arrays

• VB allows the programmer to create arrays of
  controls on the form
• Just as there are variable arrays, there may be
  arrays of objects, such as command buttons,
  labels, textboxes or picture boxes
• An array of labels might be made with one label
  for each grade point
• An array of textboxes might be made with one
  textbox for each grade, or credits
• Characteristics
• Name with subscripted elements
• .Index property is the subscript (Properties
  Window)

11
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 grades, credits and grade points

12
Creating a Control Array Example

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

13
Creating a Control Array Example

• 1. 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

14
Creating a Control Array Example

• The Properties Window shows it all.
• Note that the 4th command created is shown as
  cmdButn(3)

15
Creating a Control Array Example

• Arrange the buttons on the form as desired
• Double clicking on any one of them opens the code
  window

16
Creating a Control Array Example

• 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

17
Creating a Control Array Example

• Run the process
• Click each button
• Observe the effect

18
Creating Multi-dimensional variable Arrays

• Arrays can come in different dimensions
• You need to specify the lower and upper bounds
  for each dimension
• Array name Dimensions Bounds Type
• An example of a two-dimensional array
• Dim strName (1 to 3, 1 to 4) as String

19
Advanced Variable Arrays

• Multi-dimensional arrays
• Parallel arrays
• Searching arrays
• Dynamic Arrays

20
Creating Multi-dimensional variable Arrays

• When accessing/storing elements in the array
• Any integer literal, variable or expression can
  be used to subscript
• Must stay within the bounds
• Must have the correct number of subscripts
• If storing, 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?

21
Two-dimensional variable Arrays

• 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)?

22
Three-dimensional variable Arrays

• Three dimensional arrays
• require three subscripts (row, column, depth)
• Example
• Dim intSales (1 to 3, 1 to 4, 1 to 2) as Integer

1402
So the number 2134 is found where? the
number 4521 is ______ the number 1402 is
______ the number 3425 is ______
4521
2134
3425
23
Parallel Arrays
strName intSales

• Parallel arrays are used to hold related data
  with different types
• 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)

Jones Smith Frank Able Zean
1402 2301 0231 6762 0199
24
Searching Arrays

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

• strTarget "Q"
• intFound 0
• For intI 1 to 10
• If strTarget strArray(intI) Then
• intFound intI
• Exit For
• End If
• Next intI

25
Dynamic Arrays

• You can re-dimension an array at run-time
• Rules for resizing arrays
• Use can empty dimension list Dim 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 array
• ReDim Preserve intArray(1 to intN, 1 to 5)