Chapter nine
This presentation is the property of its rightful owner.
Sponsored Links
1 / 48

CHAPTER NINE PowerPoint PPT Presentation


  • 83 Views
  • Uploaded on
  • Presentation posted in: General

CHAPTER NINE. Using Arrays and File Handling. 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. Objectives.

Download Presentation

CHAPTER NINE

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Chapter nine

CHAPTER NINE

Using Arraysand File Handling


Objectives

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

Chapter 9: Using Arrays and File Handling


Objectives1

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

Chapter 9: Using Arrays and File Handling


Introduction

Introduction

Chapter 9: Using Arrays and File Handling


Preview the chapter project

Preview the Chapter Project

Chapter 9: Using Arrays and File Handling


Introduction to arrays

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

Chapter 9: Using Arrays and File Handling


Initializing an array

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

Chapter 9: Using Arrays and File Handling


Initializing an array1

Initializing an Array

  • Parallel arrays store related data in two or more arrays

Chapter 9: Using Arrays and File Handling


Accessing array elements using a loop

Accessing Array Elements Using a Loop

Chapter 9: Using Arrays and File Handling


Introduction to arrays1

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 of the array

  • Every array in Visual Basic is considered dynamic, which means that you can resize the array 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

Chapter 9: Using Arrays and File Handling


Using the length property

Using the Length Property

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

Chapter 9: Using Arrays and File Handling


Using arrays

Using Arrays

Chapter 9: Using Arrays and File Handling


The for each loop

The For Each Loop

Chapter 9: Using Arrays and File Handling


The for each loop1

The For Each Loop

Chapter 9: Using Arrays and File Handling


Scope of arrays

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

Chapter 9: Using Arrays and File Handling


Passing an array

Passing an Array

  • An array can be passed as an argument to a Sub procedure or a Function procedure

Chapter 9: Using Arrays and File Handling


Sorting an array

Sorting an Array

Chapter 9: Using Arrays and File Handling


Searching an array

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

Chapter 9: Using Arrays and File Handling


Creating a two dimensional array

Creating a Two-Dimensional Array

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

Chapter 9: Using Arrays and File Handling


Creating a two dimensional array1

Creating a Two-Dimensional Array

Chapter 9: Using Arrays and File Handling


File handling

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 an extension that ends in .txt

  • A simple text file is called a sequential file

Chapter 9: Using Arrays and File Handling


Reading a text file

Reading a Text File

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

Chapter 9: Using Arrays and File Handling


Reading a text file1

Reading a Text File

  • To determine whether the end of the file has been reached, use the Peek procedure of the StreamReader object

Chapter 9: Using Arrays and File Handling


Reading a text file2

Reading a Text File

  • Open the code editing window by clicking the View Code button on the Solution Explorer toolbar. 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 AsIO. and 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. and an IntelliSense window opens. 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

Chapter 9: Using Arrays and File Handling


Reading a text file3

Reading a Text File

Chapter 9: Using Arrays and File Handling


Reading a text file4

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

Chapter 9: Using Arrays and File Handling


Reading a text file5

Reading a Text File

Chapter 9: Using Arrays and File Handling


Reading a text file6

Reading a Text File

Chapter 9: Using Arrays and File Handling


Writing to a text file

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

Chapter 9: Using Arrays and File Handling


Writing to a text file1

Writing to a Text File

Chapter 9: Using Arrays and File Handling


Computing depreciation

Computing Depreciation

  • Depreciation is the decrease in property value and the reduction in the balance sheet value of a company asset to reflect its loss of value through age and wear and tear

  • The simplest and most common, 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

Chapter 9: Using Arrays and File Handling


Computing depreciation1

Computing Depreciation

  • The double-declining balance depreciation method is like the straight-line method doubled

Chapter 9: Using Arrays and File Handling


Using multiple form objects

Using Multiple Form Objects

  • Click Project on the menu bar, and then select Add Windows Form

  • In the Add New Item dialog box, 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 opens in the Visual Basic 2010 window named frmDisplayInventory.vb. In the Properties window, change the Text property of the frmDisplayInventory object to Sorted Inventory Listing

Chapter 9: Using Arrays and File Handling


Using multiple form objects1

Using Multiple Form Objects

Chapter 9: Using Arrays and File Handling


Using multiple form objects2

Using Multiple Form Objects

Chapter 9: Using Arrays and File Handling


Startup objects

Startup Objects

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

Chapter 9: Using Arrays and File Handling


Creating an instance of a windows form object

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

Chapter 9: Using Arrays and File Handling


Creating an instance of a windows form object1

Creating an Instance of a Windows Form Object

Chapter 9: Using Arrays and File Handling


Accessing variables on other forms

Accessing Variables on Other Forms

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

Chapter 9: Using Arrays and File Handling


Program design

Program Design

Chapter 9: Using Arrays and File Handling


Program design1

Program Design

Chapter 9: Using Arrays and File Handling


Designing the program processing objects

Designing the Program Processing Objects

Chapter 9: Using Arrays and File Handling


Designing the program processing objects1

Designing the Program Processing Objects

Chapter 9: Using Arrays and File Handling


Designing the program processing objects2

Designing the Program Processing Objects

Chapter 9: Using Arrays and File Handling


Designing the program processing objects3

Designing the Program Processing Objects

Chapter 9: Using Arrays and File Handling


Summary

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

Chapter 9: Using Arrays and File Handling


Summary1

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

Chapter 9: Using Arrays and File Handling


Chapter nine complete

CHAPTER NINE COMPLETE

Using Arraysand File Handling


  • Login