Microsoft Visual Basic 2005: Reloaded Second Edition

1
Microsoft Visual Basic 2005 Reloaded Second
Edition

• Chapter 9
• Structures and Sequential Access Files

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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

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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

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Using a Structure to Declare a Variable
(continued)
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Using a Structure to Declare a Variable
(continued)
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Passing a Structure Variable to a Procedure
Open the Pool program and Flow Chart
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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

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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

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Creating an Array of Structure Variables
(continued)
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Creating an Array of Structure Variables
(continued)
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Creating an Array of Structure Variables
(continued)
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Creating an Array of Structure Variables
(continued)
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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

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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

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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

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Sequential Access Files (continued)
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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

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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

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Writing Information to a Sequential Access File
(continued)
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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

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Aligning Columns of Information in a Sequential
Access File (continued)
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Aligning Columns of Information in a Sequential
Access File (continued)
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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

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Reading Information from a Sequential Access File
(continued)
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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

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Determining Whether a File Exists (continued)
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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

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The FormClosing Event (continued)
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The Friends Application