microsoft visual basic 2015 chapter 08

► An array variable is simply a variable that can store more than one value► Each individual item in array that contains a value is called an element ► Arrays provide access to data by u

Microsoft Visual Basic 2015

CHAPTER EIGHT

Using Arrays

and File Handling

► Initialize an array with default values

► Access array elements using a loop

► Use ReDim to resize an array

► Determine the number of elements in an array using the Length command

►Use the For Each loop

► Initialize two-dimensional arrays

► Read a text file

► Write to a text file

► Calculate depreciation

► Use multiple Form objects

►Access variable objects on other forms

► An array variable is simply a variable that can store more than one value

► Each individual item in array that contains a value is called an element

► Arrays provide access to data by using a numeric index, or subscript, to identify

each element in the array

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Accessing Array Elements Using a Loop

► An array can use a constant value representing its upper-bound index

► Every array in Visual Basic is considered dynamic, which means that you can resize it at run time

► The ReDim statement assigns a new array size to the specified array variable

• All data in the array will be lost

► If you want to preserve the existing data you can use the keyword Preserve

• Ex: ReDim Preserve

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Using the Length Property

►The Length property of an array contains the number of elements in an array

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

The For Each Loop

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

The For Each Loop

► Searching each element in an array is called a sequential search

► The BinarySearch method searches a sorted array for a value using a binary search

algorithm

• The binary search algorithm searches an array by repeatedly dividing the search interval in half

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Creating a Two-Dimensional Array

►A two-dimensional array holds data that is arranged in rows and columns

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Creating a Two-Dimensional Array

► Text files have a txt extension

►A simple text file is called a sequential file

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Reading a Text File

► To open a text file, you need an object available in the System.IO called a

StreamReader

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Reading a Text File

► To determine whether the end of the file has been reached, use the Peek procedure

of the StreamReader object

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Reading a Text File

► Open the code window by tapping or clicking the View Code button on the Solution Explorer toolbar Tap or click inside the frmDepreciation_Load event

► Initialize the variables Assign an object variable to the IO.StreamReader object Initialize the

StreamReader object by typing Dim objReader As IO An IntelliSense window opens Select StreamReader Press ENTER Finish declaring the rest of the variable names

► Verify that the inventory.txt data file is available by typing If IO to open an IntelliSense window Complete the rest of the line using IntelliSense as shown on the following slide Assign the

objReader variable by typing objR and then pressing CTRL + SPACEBAR to complete the variable name Type = IO and IntelliSense opens Type F

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Reading a Text File

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Reading a Text File

► Select File by typing a period and select OpenText from the IntelliSense list Type

(“e:\inventory.txt”) to access the inventory text file from the USB drive (drive E)

► To read each line of the text file, insert a Do While loop that continues until the Peek procedure returns the value of -1 Specify that the ReadLine() procedure reads each line of the text file Use the variable intCount to determine the index of each array element

► After the data file has been read, close the file Insert an Else statement that informs the user if the file cannot be opened and closes the application

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Reading a Text File

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Writing to a Text File

► Writing to a text file is similar to reading a text file The System.IO namespace also

includes the StreamWriter, which is used to write a stream of text to a file

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Writing to a Text File

► Depreciation is the decrease in property value and the reduction in the balance sheet

value of a company asset to reflect its age and prolonged use

► The simplest and most common method, straight-line depreciation, is calculated by

dividing the purchase or acquisition price of an asset by the total productive years it can reasonably be expected to benefit the company, which is called the life of the asset

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Using Multiple Form Objects

► Tap or click Project on the menu bar, and then tap or click Add Windows Form

► In the Add New Item dialog box, tap or click Windows Form, and then type

frmDisplayInventory.vb in the Name text box

► Click the Add button in the Add New Item dialog box A second Form object named

frmDisplayInventory.vb opens in the Visual Basic 2015 window In the Properties window, change the Text property of the frmDisplayInventory object to Sorted Inventory Listing

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Using Multiple Form Objects

► Every application begins executing a project by displaying the object designated as

the Startup object

of a Windows Form Object

► To display a second or subsequent form, the initial step is to create an instance of the Windows

Form object

► When creating multiple Windows Form objects, Visual Basic allows you to generate two types of

forms: modal and modeless

• A modal form retains the input focus while open

• A modeless form allows you to switch the input focus to another window

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Accessing Variables on Other Forms

► You control the availability of a variable by specifying its access level, or access

specifier

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Designing the Program Processing Objects

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Designing the Program Processing Objects

© 2016 Cengage Learning® May not be scanned, copied or duplicated, or posted to a publicly accessible website,

in whole or in part

Designing the Program Processing Objects

► Initialize an array with default values

► Access array elements using a loop

► Use ReDim to resize an array

► Determine the number of elements in an array using the Length command

►Use the For Each loop

► Initialize two-dimensional arrays

► Read a text file

► Write to a text file

► Calculate depreciation

► Use multiple Form objects

►Access variable objects on other forms

Microsoft Visual Basic 2015

CHAPTER EIGHT COMPLETE

Using Arrays

and File Handling