microsoft visual basic 2012 chapter eight using arrays and file handling
TRANSCRIPT
Microsoft Visual Basic 2012
CHAPTER EIGHT
Using Arraysand File Handling
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Chapter 8: Using Arrays and File Handling 2
Objectives
►Initialize an array►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
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Chapter 8: Using Arrays and File Handling 3
Objectives
►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
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Chapter 8: Using Arrays and File Handling 4
Introduction
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Introduction to Arrays
►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
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Initializing an Array
►To declare an array in a program, you must include an array declaration statement, which states the name of the array, how many items it can store, and what sort of data it can store
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Initializing an Array
►Parallel arrays store related data in two or more arrays
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Accessing Array Elements Using a Loop
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Introduction to Arrays
►The Visual Basic compiler determines if each subscript is within the boundaries set when you initialized the array
►An array can use a constant value representing the 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
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Using the Length Property
►The Length property of an array contains the number of elements in an array
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Using Arrays
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The For Each Loop
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The For Each Loop
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Scope of Arrays
►The scope of an array declared within a procedure is local to that procedure, but an array can be declared as a class level variable
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Passing an Array
►An array can be passed as an argument to a Sub procedure or a Function procedure
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Sorting an Array
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Searching an Array
►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
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Creating a Two-Dimensional Array
►A two-dimensional array holds data that is arranged in rows and columns
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Creating a Two-Dimensional Array
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File Handling
►To process data more efficiently, many developers use text files to store and access information to use within an application
►Text files have a .txt extension►A simple text file is called a sequential file
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Reading a Text File
►To open a text file, you need an object available in the System.IO called a StreamReader
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Reading a Text File
►To determine whether the end of the file has been reached, use the Peek procedure of the StreamReader object
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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
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Reading a Text File
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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
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Reading a Text File
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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
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Writing to a Text File
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Computing Depreciation
►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 the asset can reasonably be expected to benefit the company, which is called the life of the asset
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Computing Depreciation
►The double-declining balance depreciation method is like the straight-line method doubled
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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 2012 window. In the Properties window, change the Text property of the frmDisplayInventory object to Sorted Inventory Listing
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Using Multiple Form Objects
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Startup Objects
►Every application begins executing a project by displaying the object designated as the Startup object
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Creating an Instance of a Windows Form Object
►To display a second or subsequent form, the initial step in displaying the form 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
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Creating an Instance of a Windows Form Object
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Accessing Variables on Other Forms
►You control the availability of a variable by specifying its access level, or access specifier
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Program Design
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Program Design
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Designing the Program Processing Objects
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Designing the Program Processing Objects
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Designing the Program Processing Objects
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Designing the Program Processing Objects
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Summary
►Initialize an array►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
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Chapter 8: Using Arrays and File Handling 44
Summary
►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 2012
CHAPTER EIGHT COMPLETE
Using Arraysand File Handling