programming with microsoft visual basic 2010 5 th edition
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Programming with Microsoft Visual Basic 2010 5 th Edition. Chapter Ten Structures and Sequential Access Files. Previewing the CD Collection Application. CD Collection application Keeps track of person’s CD collection Saves each CD’s name, artist’s name, and price - PowerPoint PPT PresentationTRANSCRIPT
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Chapter TenStructures and Sequential Access
Files
Programming with Microsoft Visual Basic 2010
5th Edition
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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
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Programming with Microsoft Visual Basic 2010, 5th Edition
Previewing the CD Collection Application (cont’d.)
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Figure 10-1 CD information added to the list box
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Programming with Microsoft Visual Basic 2010, 5th Edition
Previewing the CD Collection Application (cont’d.)
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Figure 10-2 Contents of the CDs.txt file
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Programming with Microsoft Visual Basic 2010, 5th Edition
Lesson A Objectives
5
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
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition
Structures (cont’d.)
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Figure 10-3 Syntax and an example of the Structure statement
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition
Declaring and Using a Structure Variable (cont’d.)
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Figure 10-4 Syntax and examples of declaring a structure variable
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Programming with Microsoft Visual Basic 2010, 5th Edition10
Figure 10-5 Examples of using a member variable
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Figure 10-7 Code for the Willow Pools application (without a structure)
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Figure 10-8 Code for the Willow Pools application (with a structure)
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition19
Figure 10-17 Syntax and examples of the CreateText and AppendText methods
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Figure 10-18 Syntax and examples of the Write and WriteLine methods
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Figure 10-21 Syntax and an example of declaring a StreamReader variable
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Figure 10-22 Syntax and an example of the OpenText method
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Figure 10-23 Syntax and an example of the Exists method
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Figure 10-24 Additional code entered in the procedure
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Figure 10-25 Syntax and an example of the ReadLine method
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Figure 10-26 Syntax and an example of the Peek method
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Programming with Microsoft Visual Basic 2010, 5th Edition
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