1. Input and Output

2. Input and Output Input Output Reading Data from Files
Getting Input from an Input Dialog Box
Formatting Output with Format Functions
Formatting Output with Zones
Using a Message Dialog Box for Output
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Input and Output

3. Input

4. Input data from a file
Establish a communication link between computer and the disk drive for reading data from disk
Dim readerVar As IO.StreamReader = _
IO.File.OpenText(filespec)
Read data in order, one at a time, from the file with the ReadLine method assuming the file contains one item of data per line.
strVar = readerVar.ReadLine
terminate the communications link
readerVar.Close()
1. Execute a statement of the form
Dim readerVar As IO.StreamReader
A StreamReader is an object from the Input/Output class that can read a stream of
characters coming from a disk or coming over the Internet. The Dim statement
declares the variable readerVar to be of type StreamReader.
2. Execute a statement of the form
readerVar = IO.File.OpenText(filespec)
where filespec identifies the file to be read. This statement establishes a communi-cations
link between the computer and the disk drive for reading data from the disk.
Data then can be input from the specified file and assigned to variables in the pro-gram.
This assignment statement is said to “open the file for input.”
Just as with other variables, the declaration and assignment statements in Steps
2 and 3 can be combined into the single statement
Dim readerVar As IO.StreamReader = IO.File.OpenText(filespec)
3. Read items of data in order, one at a time, from the file with the ReadLine method.
Each datum is retrieved as a string. A statement of the form
strVar = readerVar.ReadLine
causes the program to look in the file for the next unread line of data and assign it
to the variable strVar. The data can be assigned to a numeric variable if it is first
converted to a numeric type with a statement such as
numVar = CDbl(readerVar.ReadLine)
Note: If all the data in a file have been read by ReadLine statements and another item
is requested by a ReadLine statement, the item retrieved will have the value Nothing.
4. After the desired items have been read from the file, terminate the communications
link set in Step 3 with the statement
readerVar.Close()
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Input and Output

5. Input Data From A File filespec – the path to find the file.
A:\Grades.txt, C:\Grades.txt
Default folder is bin folder
Each datum is retrieved as a String
The item retrieved will have value Nothing if it is the end of the file
The data can be assigned to a numeric variable if converted into a numeric data type
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Input and Output

6. Code
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Input and Output

7. Code ' Read data from a file and display in a list box
Private Sub btnRead_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRead.Click
' Establish a communication link
Dim sr As IO.StreamReader = IO.File.OpenText("Grades.txt")
' Read data line by line and display them
lstDisplay.Items.Clear()
lstDisplay.Items.Add(sr.ReadLine())
' Terminate the communication link
sr.Close()
End Sub
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Input and Output

8. Input Dialog Box strVar = InputBox(prompt, title) 1/2/2019
Input and Output

9. Code 1/2/2019 Input and Output
' Read data from a file ans display in a list box
Private Sub btnRead_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRead.Click
Dim fileName As String
Dim sr As IO.StreamReader
' Get the file name from user
fileName = InputBox("Enter the file name", "Enter file name")
' establish a communication link
sr = IO.File.OpenText(fileName)
' Read data line by line, display them and the average
lstDisplay.Items.Clear()
lstDisplay.Items.Add(sr.ReadLine())
' Terminate the communication link
sr.Close()
End Sub
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Input and Output

10. Output

11. Format Functions FormatNumber(n,r) FormatCurrency(n,r)
FormatPercent(n,r)
return a string value
n - a number, an numeric expression or a
string to be formatted
r - the number of decimal places
default value is 2
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Input and Output

12. Formatting Output with Format Functions
String Value
FormatNumber( ,1)
FormatNumber(1 + 2)
12,345.6
3.00
FormatCurrency( ,2)
FormatCurrency(-100)
$12,345.63
($100.00)
FormatPercent(0.185,2)
FormatPercent(“0.07”)
18.50%
7.00%
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Input and Output

13. Code
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Input and Output

14. Code ' Format data using format functions
Private Sub btnFormat_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnFormat.Click
lstDisplay.Items.Add(FormatNumber( , 1))
lstDisplay.Items.Add(FormatNumber(1 + 2))
lstDisplay.Items.Add(FormatCurrency( ,2)) lstDisplay.Items.Add(FormatCurrency(-100)) lstDisplay.Items.Add(FormatPercent(0.185,2)) lstDisplay.Items.Add(FormatPercent("0.07"))
End Sub
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Input and Output

15. Formatting Output with Zones
Line up items in columns
Use a fixed-width font such as Courier New
Divide the characters into zones with a format string.
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Input and Output

16. Formatting output with zones
Zone width
Dim fmtStr As String = "{0, 15}{1, 10}{2, 8}“
lstOutput.Items.Add(String.Format(fmtStr, _
data0, data1, data2))
Zone number
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Input and Output

17. Formatting output with zones
A colon and formatting symbol after width to specially format numeric data
Zone Format
Term
Number to be formatted
Number displayed
{1,12:N3}
{1,12:N0}
34.6 34
{1,12:C1}
$1234.6
{1,-12:P}
0.569
56.90%
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Input and Output

18. Formatting Output with Zones
Zone width
left adjusted if preceded with minus sign, right adjusted otherwise
Spaces between the successive pairs of brackets will be displayed in the corresponding zones in the output.
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Input and Output

19. Code
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Input and Output

20. Code 1/2/2019 Input and Output
' Read data from a file ans display in a list box
Private Sub btnRead_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnRead.Click
Dim fileName As String
Dim sr As IO.StreamReader
Dim fmtStr As String = "{0,-15}{1,15}{2,15}"
' Get the file name from user
fileName = InputBox("Enter the file name", "Enter file name")
' Establish a communication link
sr = IO.File.OpenText(fileName)
' Read data line by line, display them and the average
lstDisplay.Items.Clear()
lstDisplay.Items.Add(String.Format(fmtStr, "First Grade", "Second Grade",
"Third Grade"))
lstDisplay.Items.Add(String.Format(fmtStr, sr.ReadLine(), sr.ReadLine(),
sr.ReadLine()))
' Terminate the communication link
sr.Close()
End Sub
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Input and Output

21. Using a Message Dialog Box for Output
MsgBox(prompt,title)
MsgBox(prompt, , title)
is executed, where prompt and title are strings, a message dialog box appears with prompt
displayed and the title bar caption title and stays on the screen until the user presses
Enter, clicks on the box in the upper-right corner, or clicks OK. For instance, the state-ment
MsgBox("Nice try, but no cigar.", , "Consolation")
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Input and Output

22. Code 'Message are sent before clearing the items in the list box
Private Sub Button1_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles Button1.Click
MsgBox(" All items will be deleted", , "Delete items")
lstDisplay.Items.Clear()
End Sub
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Input and Output