Tutorial 9
Sequential Access Files and Printing
Tutorial 9: Sequential Access Files and Printing
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Sequential Access Files
Lesson A Objectives
After completing this lesson, you will be able to:
 Declare StreamReader and StreamWriter object variables
 Open a sequential access file
 Determine whether a sequential file exists
 Write information to a sequential access file
 Align the text written to a sequential access file
 Read information from a sequential access file
 Determine whether the computer has finished reading a
sequential access file
 Close a sequential access file
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File Types
 Files to which information is written are called
output files, because the files store the output
produced by an application
 Files that are read by the computer are called
input files, because an application uses the
information in these files as input
 Here is a list of different file types:
 Sequential access files
 Random access files
 Binary access files
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Using Sequential Access Files
 A sequential access file is often referred
to as a text file, because it is composed of
lines of text
 Sequential access files are similar to
cassette tapes in that each line in the file,
like each song on a cassette tape, is both
stored and retrieved in consecutive order
(sequentially)
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Procedure for Using a
Sequential Access File
1. Declare either a StreamWriter or StreamReader
object variable
2. Create a StreamWriter or StreamReader object
by opening a file; assign the object’s address to
the object variable declared in Step 1
3. Use the StreamWriter object to write one or more
lines of text to the file, or use the StreamReader
object to read one or more lines of text from the
file
4. Use the StreamWriter or StreamReader object to
close the file
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Opening a Sequential File
 Refer to Figure 9-7 in the textbook, which illustrates all
of the methods used to open a sequential access file
CreateText method – Creates a file for writing a text stream
objStreamWriter = System.IO.File.CreateText(“memo.txt”)
AppendText method – Opens a file appending text to the end of the
file
objStreamWriter = System.IO.File.AppendText(“sales.txt”)
OpenText method – Opens a file to read a stream of text
objStreamReader = System.IO.File.OpenText(“a:\reports\pay.txt”)
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Does the file exist?
 Avoid errors by using the Exists method
If System.IO.File.Exists(“pay.txt”) Then
 Returns True or False
 The Exists method returns the Boolean value True if
filename exists; otherwise, it returns the Boolean value
False
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Writing to a Sequential File
Write method
Leaves the file pointer after last character
objStreamWriter.Write(“Good”)
objStreamWriter.Write(“ Morning”) ‘ Writes on the same line
Good Morning
WriteLine method
Appends the line terminator to the end of
line and leaves the file pointer ready for
next line
objStreamWriter.WriteLine(“Good”)
objStreamWriter.WriteLine(“ Morning”) ’ Each is on a separate line
Good
Morning
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Formatting String Data
 The Space function inserts spaces
objStreamWriter.Write(Space(10) & “A” & Space(5) & “B”
 PadLeft – Pads a string on the left with specified character
Dim sngNetPay As Single = 767.89, strNet As String
strNet = FormatCurrency (sngNetPay)
strNet = strNet.PadLeft(15, “*”)
Results in “********$767.89”
 PadRight – Pads a string on the right with specified
character
Dim strName As String = “Sue”
strName = strName.PadRight(10)
Results in “Sue
” (the string “Sue” and seven spaces)
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Aligning Data in a Sequential File
For intRegion = 1 To 3
strSales = InputBox(“Sales amount”, “Sales”)
strSales = Format(strSales, “standard”)
objStreamWriter.WriteLine(strSales.PadLeft(8))
Next intRegion
Result (assuming the following sales amounts: 645.75, 1200, 40.80
645.75
1,200.00
40.80
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Reading from a Sequential File
 ReadLine Method – Read a line of text from the
file
strLine = objStreamReader.ReadLine()
 Peek method – Looks to see if there is another
character to read
Do Until objStreamReader.Peek = -1
 Close method – Close the file when you are finished
objStreamReader.Close()
objStreamWriter.Close()
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Using a DateTimePicker Control
Lesson B Objectives
After completing this lesson, you will be able to:
 Add a DateTimePicker control to a form
 Control the appearance of a DateTimePicker control
 Format the text that appears in a DateTimePicker
control
 Set and retrieve the information stored in a
DateTimePicker control
 Retrieve the system date and time
 Display a form immediately
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Adding a DateTimePicker
Control to a Form
 The
DateTimePicker
control allows the
user to select either
a date or time, and
then displays the
selected
information in a
specified format
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DateTimePicker Properties
 The DateTimePicker control’s ShowUpDown property
determines whether a list arrow button (default) or up and
down arrow button appear on the control
 You can use the Format property to control the format
(style) of the date or time displayed in the
DateTimePicker control
 When you add a DateTimePicker control to a form, Visual
Basic .NET retrieves the current date and time from your
computer system’s clock, and assigns both values to the
DateTimePicker control’s Value property
 The text that appears in a DateTimePicker control is
stored in the control’s Text property
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The Value Property
Example
Results
Me.PayDateTimePicker.Value
11/12/2004 9:07:00 AM
Me.PayDateTimePicker.Value.ToLongDateString
Friday, November 12, 2004
Me.PayDateTimePicker.Value.ToShortDateString
11/12/2004
Me.PayDateTimePicker.Value.ToLongTimeString
9:08:00 AM
Me.PayDateTimePicker.Value.ToShortTimeString
9:08 AM
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Using the DateTime Object
objectname.Value = New DateTime(year, month, day[, hour, minute, second])
Me.PayDateTimePicker.Value = New DateTime(2004, 2, 3)
Me.PayDateTimePicker.Value = New DateTime(2004, 9, 7, 5, 30, 18)
Me.PayDateTimePicker.Value = New DateTime(2004, 1, 6, 17, 30, 18)
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Retrieving the Information
Stored in the Value Property
Example using “11/12/2004 9:07 AM”
Results
Me.PayDateTimePicker.Value.Month
11
Me.PayDateTimePicker.Value.Day
12
Me.PayDateTimePicker.Value.Year
2004
Me.PayDateTimePicker.Value.DayOfWeek
5
Me.PayDateTimePicker.Value.DayOfWeek.ToString
Friday
Me.PayDateTimePicker.Value.Hour
9
Me.PayDateTimePicker.Value.Minute
7
Me.PayDateTimePicker.Value.Second
0
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