Arrays Chapter Microsoft Visual Basic.NET: Reloaded 1.

transcript

Arrays

Chapter Microsoft Visual Basic .NET: Reloaded

2Microsoft Visual Basic .NET: Reloaded

Objectives

• Declare and initialize a one-dimensional array

• Store data in a one-dimensional array

• Display the contents of a one-dimensional array

• Code a loop using the For Each…Next statement

• Access an element in a one-dimensional array

Objectives (continued)

• Search a one-dimensional array

• Compute the average of a one-dimensional array’s contents

• Find the highest entry in a one-dimensional array

• Update the contents of a one-dimensional array

• Sort a one-dimensional array

Objectives (continued)

• Enter code in the form’s Load event procedure

• Create and manipulate parallel one-dimensional arrays

• Create and initialize a two-dimensional array

• Store data in a two-dimensional array

• Search a two-dimensional array

Using Arrays

• Simple variable

• Also called scalar variable

• Is unrelated to any other variable in memory

• Array

• A group of variables that have the same name and data type and are related in some way

• You can picture an array as a group of small adjacent boxes inside the computer’s memory

One-Dimensional Arrays

• One-dimensional array

• Visualize as a column of variables

• Each variable is identified by a unique number

• Unique number is called “subscript”

• Subscript is placed inside parentheses immediately following array name

• Example strStates(1) – read “strStates sub one”

• Individual variables referred to as “elements”

One-Dimensional Arrays (continued)

• Declare using keywords Dim or Private

• highestSubscript argument in declaration used to specify the number of elements in the array

• number of array elements is 1 more than the value in highestSubscript argument

One-Dimensional Arrays (continued)

HOW TO…

Storing Data in a One-Dimensional Array

Manipulating One-Dimensional Arrays

• Sample procedures will demonstrate how to perform tasks using a one-dimensional array• Display contents of an array

• Access an array element using its subscript

• Search the array

• Calculate the average of the data stored in a numeric array

• Find the highest value stored in an array

• Update the array elements

• Sort the array elements

Displaying the Contents of a One-Dimensional Array

Displaying the Contents of a One-Dimensional Array (continued)

The For Each…Next Statement

• Use to code a loop containing instructions to be processed for each element in a group

• Syntax template shown in next slide contains words “element” and “group”• “element”

• Declare a variable of the same data type as the elements of the array and place this variable in the “element” position of the template

• “group” • The variable name of the array

HOW TO…

Using the Subscript to Access an Element in a One-Dimensional Array

Display salary amount corresponding to code entered by user

Searching a One-Dimensional Array

• Determine number of salespeople selling above a certain amount

Calculating the Average Amount Stored in a One-Dimensional Numeric Array

• Calculate and display average test score earned by students on final exam

Determining the Highest Value Stored in a One-Dimensional Array

• Display highest amount earned in a week

Updating the Values Stored in a One-Dimensional Array

• Procedure allows manager to increase price of each item and display item’s new price

Sorting the Data Stored in a One-Dimensional Array

• Array.Sort(arrayName) method

• Sorts the elements of a one-dimensional array in “ascending order”

• First element contains smallest value

• Last element contains largest value

• To sort in descending order

• First sort in ascending order

• Then use Array.Reverse(arrayname) method to reverse the position of the elements in the array

Sorting the Data Stored in a One-Dimensional Array (continued)

• btnSortAscending_Click procedure sorts intNumbers array into ascending order

• Method sorts array in descending order and displays the results

Using a Module-Level One-Dimensional Array

• Application displays names contained in a sequential access file, giving user choice of ascending or descending order of display

• First, declare array variable in the Form’s general declarations section

• Then, fill array from data in file using code in the form’s Load event procedure

• Load event occurs before the first time a form is displayed

Using a Module-Level One-Dimensional Array (continued)

Parallel One-Dimensional Arrays

• Two or more one-dimensional arrays whose elements are related by their position (subscript)

• Called parallel because element at subscript 0 in first array corresponds to element at subscript 0 in another array

• Example:

• strID(0) corresponds to intPrice(0) and

• strID(1) corresponds to intPrice(1),

• and so on…

Parallel One-Dimensional Arrays (continued)

Two-Dimensional Arrays

• Resemble a table in that variables are store in rows and columns

• Each element is identified by a unique combination of two subscripts

• The first subscript indicates the element’s row

• The second subscript indicates the column

• Each subscript begins with 0

• The element in the first row and column has a subscript of (0,0)

Two-Dimensional Arrays (continued)

HOW TO…

Storing Data in a Two-Dimensional Array

Searching a Two-Dimensional Array

Programming Example – Perrytown Gift Shop Application

• Application is to assist in employee weekly payroll process

• Calculates and displays the federal withholding tax (FWT)

• Gets and displays taxable wages

• Gets and displays marital status

TOE Chart

User Interface

Objects, Properties, and Settings

Objects, Properties, and Settings (continued)

Tab Order

Pseudocode

btnExit Click event procedure

close application

btnCalc Click event procedure

Include the following in a Try/Catch block:

remove any dollar signs and spaces from the txtTaxable control

assign the taxable wages store in txtTaxable to a variable

assign the marital status entered in txtStatus to a variable

if marital status is not either M or S

display an appropriate message

if marital status is M

use the Married tax table, stored in an array

use the singles tax table, stored in an array

Pseudocode (continued)

end ifend if

Repeat while there are still rows in the tax table to search and taxable wages have not been foundif taxable wages are less than or equal to value stored in the first column of the current row in tax table

use information stored in 2nd, 3rd, and 4th columns in taxtable to calculate the federal withholding taxindicate that the taxable wages were found by assigning

thevalue True to blnFound variable

elseadd 1 to the contents of the intRow variable to continue

the searchrow in the tax table

Display the federal withholding tax in the lblFwt controlUse general Catch statement to handle and display any errors

Code (continued)

Summary

• Programmers use arrays to temporarily store related data in computer’s internal memory

• All variables in an array have the same name and data type

• Each element in a one-dimensional array is identified by a unique subscript

• Appears in parentheses after array’s name

Summary (continued)

• Each element in a two-dimensional array is identified by a unique combination of two subscripts:• Row subscript

• Column subscript

• Subscripts appear in parentheses after the array’s name

• You list the row subscript first, followed by a comma and the column subscript

• The first subscript in a one-dimensional array is 0 (zero)

Summary (continued)

• First row subscript in a two-dimensional array is 0 (zero) likewise, the first column subscript also is 0 (zero)

• When declaring a one-dimensional array, provide either highest subscript or initial values

• When declaring a two-dimensional array, you provide either the highest row and column subscripts or the initial values

Summary (continued)

• The number of elements in a one-dimensional array is one more than its highest subscript

• The number of rows in a two-dimensional array is one more than its highest row subscript likewise, the number of columns is one more than its highest column subscript

• You usually use an assignment statement to store data in an array

• You refer to an element in a one-dimensional array using the array’s name followed by the element’s subscript

Summary (continued)

• You refer to an element in a two-dimensional array using the array’s name followed by the element’s row and column subscripts, which are separated by a comma

• You can use the For Each…Next statement to code a loop whose instructions you want processed for each element in an array

• You can use the Length property to determine the number of elements in the array

Summary (continued)

• You use the Array.Sort method to sort the elements in a one-dimensional array

• You use the Array.Reverse method to reverse the order of the elements in an array

• The elements in parallel arrays are related by their subscript (or position) in each array

Arrays Chapter Microsoft Visual Basic.NET: Reloaded 1.

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