lesson 8 arrays

7/26/2019 Lesson 8 Arrays

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ARRAYS


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PREVIEWINGTHETREASURESGIFTSHOP

APPLICATION

Treasures application

Allows the user to enter a product ID

Displays the products price

Open the Treasures.exe file

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PREVIEWINGTHETREASURESGIFTSHOP

APPLICATION(CONTD.)

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Figure 9-1 Interface showing the products price


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LESSONA OBJECTIVES

After studying Lesson A, you should be able to:

Declare and initialize a one-dimensional array

Store data in a one-dimensional array

Determine the number of array elements and thehighest subscript

Traverse a one-dimensional array

Code a loop using the For EachNext statement

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LESSONA OBJECTIVES(CONTD.)

Compute the total and average of a one-

dimensional arrays contents

Find the highest value in a one-dimensional

array

Associate a list box with a one-dimensional array

Use a one-dimensional array as an accumulator

or a counter

Sort a one-dimensional array

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USINGARRAYS

Simple (scalar) variable

One that is unrelated to any other variable in

memory

Array

Group of related variables

Variables have same name and data type

Reasons to use arrays

Simplifies process of coding application

Increases run-time efficiency of program

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ONE-DIMENSIONALARRAYS

One-dimensional array

Variables stored in consecutive memory locations

Visualized as a column of variables

Subscript

Indicates variables position in the array

Starts at 0 for first array variable

Refer to array variable by array name and

subscript

Example: strCities(0)is first variable in

strCities array

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ONE-DIMENSIONALARRAYS(CONTD.)

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Figure 9-2 Illustration of the one-dimensional strCitiesarray


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9Figure 9-3 Syntax versions and examples of declaring a one-dimensional array


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Element: Refers to individual array variable

Arrays are initialized by computer when created

Arrays of numeric variables are initialized to 0

Arrays of string variables are initialized usingkeyword Nothing

Arrays of Boolean variables are initialized to False

Arrays of Date variables are initialized to 12:00 AM

January 1, 0001

Populating the array Assigning initial values

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After array is declared, you can store data in

array

To enter data into array:

Use assignment statement

Use TryParse statement

Example syntax using assignment statement

arrayname(subscript) = value

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12Figure 9-4 Examples of statements used to store data in a one-dimensional array


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DETERMININGTHENUMBEROF

ELEMENTSANDTHEHIGHESTSUBSCRIPT

Arrays Length property

Stores number of elements in array

Number is an integer

Highest subscript in a one-dimensional array

Subtract 1 from arrays Length property

GetUpperBound method

Returns an integer that represents highest subscript

in specified array dimension

For one-dimensional array, specified dimension is 0

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DETERMININGTHENUMBEROFELEMENTS

ANDTHEHIGHESTSUBSCRIPT(CONTD.)

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Figure 9-5 Syntax and an example of a one-dimensional arrays Length property


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DETERMININGTHENUMBEROFELEMENTS

ANDTHEHIGHESTSUBSCRIPT(CONTD.)

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Figure 9-6 Syntax and an example of a one-dimensional arrays GetUpperBound method


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TRAVERSINGAONE-DIMENSIONALARRAY

Traversing an array

Look at each array element, one by one

Beginning with first element

Ending with last element

Figure 9-7 shows two examples

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TRAVERSINGAONE-DIMENSIONALARRAY

(CONTD.)

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Figure 9-7 Examples of loops used to traverse a one-dimensional array


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THEFOREACHNEXTSTATEMENT

For EachNext statement

Used to process each element in array

Unlike ForNext statement:

You do not have to keep track of array subscripts

Can only read array values, not permanently modify

them

Declare variable within For EachNext

statement to refer to each array element, one at a

time

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Figure 9-9 Syntax and an example of the For EachNext statement


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CALCULATINGTHETOTALANDAVERAGE

VALUES

Sweet Tooth Chocolate application

Displays total number of pounds of chocolate sold

during six month period

Displays average number of pounds sold each month

btnCalc controls Click event procedure

Adds array element values

Divides total by number of array elements

Displays average amount on form

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Figure 9-11

Examples of code for the

btnCalc_Click event procedure

(continues)


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Figure 9-11

Examples of code for the btnCalc_Click event procedure (contd.)


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FINDINGTHEHIGHESTVALUE

Cycles Galore application

Displays highest bonus amount earned during the

month

Displays number of salespeople who earned that

amount

Get Highest Bonus buttons Click event

procedure

Code shown in Figure 9-16

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24Figure 9-16 Get Highest Bonus buttons Click event procedure


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ARRAYSANDCOLLECTIONS

Items in a list box belong to a collection

Collections and arrays

Group of individual objects treated as one unit

Each object identified by unique number

First index in a collection and first array subscript

are both 0

List boxes can be associated with arrays

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ARRAYSANDCOLLECTIONS(CONTD.)

Prairie Auditorium application

26Figure 9-17 Problem specification for the Prairie Auditorium application


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ARRAYSANDCOLLECTIONS(CONTD.)

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Figure 9-18 Illustration of the relationship between the list box and array


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Figure 9-19 Most of the code for the Prairie Auditorium application


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ACCUMULATORANDCOUNTERARRAYS

One-dimensional arrays

Often used to either accumulate or count related

values

Warren School application

Uses an accumulator array

Allows user to enter amount of candy sold for each

student

Displays total number sold for each candy

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Figure 9-24 btnAdd controls Click event procedure


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SORTINGAONE-DIMENSIONALARRAY

Sorting

Arranging data in a specific order

Array.Sort method

Sorts elements of one-dimensional array in ascending

order

Syntax: Array.Sort(arrayname)

To sort array in descending order:

First use Array.Sort to sort in ascending order

Then useArray.Reverseto reverse order of array

elements

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32Figure 9-26 Syntax and examples of the Array.Sort and Array.Reverse methods


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SORTINGAONE-DIMENSIONALARRAY

(CONTD.)

33Figure 9-28 State names displayed in ascending order


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LESSONA SUMMARY

An array groups variables with same data type

under one name

Individual array variables also called elements

Arrays may be declared with or without list of

initial values

Values can be assigned after declaration

Arrays Length property returns array size

Can also use GetUpperBound method

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LESSONA SUMMARY(CONTD.)

To traverse each element in a one-dimensional

array

Use a loop coded with one of the following

statements:

DoLoop, ForNext, For EachNext

To associate list box with array:

Use list box items index and array elements

subscript

Array.Sort: Sorts elements in ascending orderArray.Reverse: Reverses order of array elements

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LESSONB OBJECTIVES

After studying Lesson B, you should be able to:

Explain the relationship between the elements in

parallel one-dimensional arrays

Create parallel one-dimensional arrays

Locate information in two parallel one-

dimensional arrays

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PARALLELONE-DIMENSIONALARRAYS

Parallel arrays

Two or more arrays whose elements are related by

their position in arrays (by their subscripts)

Arrays may be different data types

Scenario involving two parallel arrays Parallel arrays named strIdsand intPrices

Each strIdselement corresponds to intPrices

element located in same position

Search strIdsarray for product ID View corresponding element in intPricesarray

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(CONTD.)

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Figure 9-31 Illustration of two parallel one-dimensional arrays


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Figure 9-32 btnDisplay controls Click event procedure

using parallel one-dimensional arrays (continues)


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Figure 9-32 btnDisplay controls Click event procedure

using parallel one-dimensional arrays (contd.)


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(CONTD.)

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Figure 9-33 Interface showing the price for product ID CR20


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LESSONB SUMMARY

To create parallel one-dimensional arrays:

Create two or more one-dimensional arrays

Ensure value stored in first element in first array

corresponds to value stored in same element in other

arrays

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LESSONC OBJECTIVES

After studying Lesson C, you should be able to:

Declare and initialize a two-dimensional array

Store data in a two-dimensional array

Sum the values in a two-dimensional array Search a two-dimensional array

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TWO-DIMENSIONALARRAYS

Two-dimensional array

Resembles a table

Storing variables (elements) in rows and columns

Identifying a two-dimensional array element

Use unique combination of two subscripts to specify

elements row and column position

Subscripts begin at 0

Example: strProducts(1,2)refers to second row, third

column

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TWO-DIMENSIONALARRAYS(CONTD.)

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Figure 9-37 Names of some of the elements in the strProducts array


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46Figure 9-38 Syntax versions and examples of declaring a two-dimensional array (continues)


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Figure 9-38 Syntax versions and examples of declaring a two-dimensional array (contd.)


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Figure 9-39

Examples of

statements used to

store data in a two-dimensional array

(continues)


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Figure 9-39 Examples of statements used to store data in a two-dimensional array (contd.)


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Figure 9-40 Syntax and an example of a two-dimensional arrays GetUpperBound method


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TRAVERSINGATWO-DIMENSIONALARRAY

One loop used to traverse one-dimensional array

Two loops used to traverse two-dimensional array

Outer loop and nested loop

One keeps track of row subscript

One keeps track of column subscript

Can also traverse two-dimensional array using:

One For EachNext loop

This method cannot permanently modify values

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Figure 9-41 Examples of loops used to traverse a two-dimensional array (continues)


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53Figure 9-41 Examples of loops used to traverse a two-dimensional array (contd.)


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SEARCHINGATWO-DIMENSIONALARRAY

Two-dimensional arrays versus parallel arrays

Both can represent data in tabular format

All data in two-dimensional array must be same type

New version of Treasures application

Use one two-dimensional array to store price list

2-D array replaces two parallel arrays in first version

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Figure 9-45 btnDisplay controls Click event procedure using a

two-dimensional array (continues)


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Figure 9-45 btnDisplay controls Click event procedure using a

two-dimensional array (contd.)


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LESSONC SUMMARY

To declare a two-dimensional array:

Use either syntax:

To refer to two-dimensional array element:

Use syntax:

arrayName(rowSubscript, columnSubscript)

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LESSONC SUMMARY(CONTD.)

To determine highest row and column subscripts

in a two-dimensional array:

Use GetUpperBound method

Syntax:

arrayName.GetUpperBound(0)

arrayName.GetUpperBound(1)

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lesson 8 arrays

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