programming with microsoft visual basic 2010 5 th edition

Chapter TenStructures and Sequential Access

Files

Programming with Microsoft Visual Basic 2010

5th Edition

Programming with Microsoft Visual Basic 2010, 5th Edition

Previewing the CD Collection Application

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CD Collection applicationKeeps track of person’s CD collectionSaves each CD’s name, artist’s name, and

priceUses sequential access file named CDs.txtCan add to or remove information from file

Open the CD.exe file


Previewing the CD Collection Application (cont’d.)

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Figure 10-1 CD information added to the list box


Previewing the CD Collection Application (cont’d.)

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Figure 10-2 Contents of the CDs.txt file


Lesson A Objectives

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After studying Lesson A, you should be able to:

Create a structureDeclare and use a structure variablePass a structure variable to a procedureCreate an array of structure variables


Structures

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Structure statementEnables you to create your own data typesUsed to group related items of different data

types into one unitTypically appears in form’s Declaration

section Structure (or user-defined data type)

Data type created with Structure statementMember variables

Variables, constants, or procedures declared within structure declaration


Structures (cont’d.)

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Figure 10-3 Syntax and an example of the Structure statement


Declaring and Using a Structure Variable

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Structure variables: Declared using structureStructure is data type for variable

Example: Dim hourly As Employee hourly is variable declared with Employee

structure type Accessing member variable in code

Use structureVariableName. memberVariableName

Example: hourly.dblPay = 26 Member variables are used like scalar variables


Declaring and Using a Structure Variable (cont’d.)

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Figure 10-4 Syntax and examples of declaring a structure variable

Programming with Microsoft Visual Basic 2010, 5th Edition10

Figure 10-5 Examples of using a member variable


Passing a Structure Variable to a Procedure

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Application for sales manager at Willow PoolsAllows user to enter length, width, and depthCalculates gallons of water to fill pool

Advantages of using structure to group dimensionsThree inputs are stored in one structure

variableYou pass single structure variable to procedure

instead of three scalar variablesYour code is structured in more readable form


Figure 10-7 Code for the Willow Pools application (without a structure)


Figure 10-8 Code for the Willow Pools application (with a structure)


Lesson A Summary

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Structures: User-defined data typesStructure members can be variables,

constants, or proceduresRefer to member within structure variable

using structureVariableName.memberVariableName

To create an array of structure variables:Declare array using structure as data type

Refer to member within structure variable stored in an array using: arrayName(subscript).memberVariableName


Lesson B Objectives

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After studying Lesson B, you should be able to:

Open and close a sequential access fileWrite data to a sequential access fileRead data from a sequential access fileDetermine whether a sequential access file

existsTest for the end of a sequential access file


Sequential Access Files

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Reading a file: Getting data from a fileWriting to a file: Sending data to a fileOutput files: Store application outputInput files: Application uses data in these

filesSequential access files

Composed of lines of text that are both read and written in consecutive order

Also called text files


Writing Data to a Sequential Access File

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Stream of charactersSequence of characters

StreamWriter objectUsed to write stream of characters to

sequential access fileMust declare StreamWriter variable

Game Show Contestants applicationUses StreamWriter variable


Writing Data to a Sequential Access File (cont’d.)

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Figure 10-15 Syntax and an example of declaring a StreamWriter variable


Figure 10-17 Syntax and examples of the CreateText and AppendText methods


Figure 10-18 Syntax and examples of the Write and WriteLine methods


Closing an Output Sequential Access File

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Close methodUsed to close an output sequential access file

Figure 10-19 Syntax and an example of closing an output sequential access file


Reading Data from a Sequential Access File

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StreamReader objectUsed to read data from sequential access fileMust declare StreamReader variable

OpenText methodUsed to open sequential access file for inputCan use this method to automatically create

StreamReader objectExists method

Used to determine if file existsReturns True if file exists, otherwise False


Figure 10-21 Syntax and an example of declaring a StreamReader variable


Figure 10-22 Syntax and an example of the OpenText method


Figure 10-23 Syntax and an example of the Exists method


Figure 10-24 Additional code entered in the procedure


Reading Data from a Sequential Access File (cont’d.)

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Line: Sequence (stream) of characters followed by newline character

ReadLine methodUsed to read contents of file, one line at a timeReturns String value containing data in current

lineReturns only data, not including newline

characterPeek method

Determines whether file contains another character to read


Figure 10-25 Syntax and an example of the ReadLine method


Figure 10-26 Syntax and an example of the Peek method


Closing an Input Sequential Access File

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Close methodUsed to close input sequential access files

Figure 10-27 Syntax and an example of closing an input sequential access file

programming with microsoft visual basic 2010 5 th edition

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