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Microsoft Visual Basic 2005: Reloaded Second Edition

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Structures and Sequential Access Files. Microsoft Visual Basic 2005: Reloaded, Second Edition ... Writes information to a sequential access file ... – PowerPoint PPT presentation

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Title: Microsoft Visual Basic 2005: Reloaded Second Edition


1
Microsoft Visual Basic 2005 Reloaded Second
Edition
  • Chapter 9
  • Structures and Sequential Access Files

2
Structures
  • Structure statement creates your own data type
  • User-defined data type (or structure) data types
    created by using the Structure statement
  • Member variables variables defined within a
    structure
  • Structure can include member variables of
  • Any of the standard data types
  • Other structure types

3
Structures (continued)
4
Using a Structure to Declare a Variable
  • Structure variables variables declared using a
    structure
  • Refer to an entire structure in code using its
    name
  • Refer to a member variable using the structure
    name with the dot operator and the member
    variable name
  • Member variables can be used like any other
    variables
  • Structures are used to group related items into
    one unit

5
Using a Structure to Declare a Variable
(continued)
6
Using a Structure to Declare a Variable
(continued)
7
Passing a Structure Variable to a Procedure
Open the Pool program and Flow Chart
8
Passing a Structure Variable to a Procedure
(continued)
  • Sample application using a structure
  • Less code to pass a structure variable to a
    procedure
  • Stores all of the data in a single unit

9
Creating an Array of Structure Variables
  • Use a one-dimensional array of structure
    variables instead of two-dimensional or parallel
    one-dimensional arrays
  • Refer to a member variable in an array element
    by
  • arrayname(subscript).memberVariableName

10
Creating an Array of Structure Variables
(continued)
11
Creating an Array of Structure Variables
(continued)
12
Creating an Array of Structure Variables
(continued)
13
Creating an Array of Structure Variables
(continued)
14
File Types
  • Reading a file getting information from a file
  • Writing to a file sending information to a file
  • Output files files to which information is
    written
  • Input files files that are read by the computer
  • Three types of files in Visual Basic
  • Sequential
  • Random
  • Binary

15
File Types (continued)
  • Sequential file data is accessed sequentially,
    in consecutive order from the beginning to the
    end
  • Random file data can be accessed in consecutive
    or random order
  • Binary file data is accessed by its byte
    location in the file

16
Sequential Access Files
  • Sequential access file often called a text file
    because it is composed of lines of text
  • Data must be read sequentially from beginning to
    end

17
Sequential Access Files (continued)
18
Writing Information to a Sequential Access File
  • WriteAllText method
  • Writes information to a sequential access file
  • File argument contains the name of the file to
    be used
  • Text argument contains the data to be written
  • Append argument if True, data is added to end of
    existing file otherwise all existing data is
    erased

19
Writing Information to a Sequential Access File
(continued)
  • My feature exposes a set of commonly used
    objects to the programmer
  • My.Computer object allows access to objects and
    methods to manipulate files
  • Computer uses a file pointer to trace where the
    next character will be read from or written to a
    file
  • Strings.Space method writes a specific number of
    spaces to a file

20
Writing Information to a Sequential Access File
(continued)
21
Aligning Columns of Information in a Sequential
Access File
  • PadLeft, PadRight methods
  • Pads a string with a specified number of
    characters based on current length of the string
    being padded
  • Aligns columns of information written to a
    sequential access file
  • Aligns columns of numeric information by the
    decimal point

22
Aligning Columns of Information in a Sequential
Access File (continued)
23
Aligning Columns of Information in a Sequential
Access File (continued)
24
Reading Information from a Sequential Access File
  • ReadAllText method reads information stored in a
    sequential access file
  • File argument contains the name of the
    sequential access file

25
Reading Information from a Sequential Access File
(continued)
26
Determining Whether a File Exists
  • An attempt to read a file that does not exist
    will cause an error
  • FileExists method determines if the file exists
    before attempting to read it
  • File argument contains the name of the file

27
Determining Whether a File Exists (continued)
28
The FormClosing Event
  • FormClosing event
  • Occurs when a form is about to be closed by the
    program code or by the user
  • Allows you to trap the closing action and take
    any necessary actions such as saving data
  • Can be used to cancel the close action
  • Set e.Cancel True to cancel the closing action

29
The FormClosing Event (continued)
30
The Friends Application
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