The document discusses sequential file handling in Visual Basic. It describes how to create and read files using the Open, Print, and Input statements. It also introduces the Common Dialog control, which allows displaying standard dialog boxes for opening, saving, and printing files. The control simplifies file operations by handling dialog display and file access through its methods like ShowOpen and ShowSave. The example program demonstrates using the Common Dialog control to open a file, read its contents, and save text back to a file.

2. Sequential file handling

3. Creating a File
To create a file , we use the following command
Open "fileName" For Output As #fileNumber
Each file created must have a file name and a file number for
identification. As for the file name, you must also specify the path
where the file will reside. For example:
Open "c:My Documentssample.txt" For Output As #1
will create a text file by the name of sample.txt in My Document
folder in C drive. The accompanied file number is 1. If you wish to
create a HTML file , simply change the extension to .html
Open "c:My Documentssample.html" For Output As # 2

4. Sample Program : Creating a text file
Private Sub cmdCreate_Click() Dim intMsg As String
Dim StudentName As String
Open "c:My Documentssample.txt" For Output As #1
intMsg = MsgBox("File sample.txt opened")
StudentName = InputBox("Enter the student Name")
Print #1, StudentName
intMsg = MsgBox("Writing a" & StudentName & " to
sample.txt ")
Close #1
intMsg = MsgBox("File sample.txt closed")
End Sub

5. Reading a file
To read a file created, you can use the input # statement. However, we
can only read the file according to the format when it was written. You
have to open the file according to its file number and the variable that
hold the data. We also need to declare the variable using the DIM
command.
Sample Program: Reading file
Private Sub cmdReading_Click() Dim variable1 As String
Open "c:My Documentssample.txt" For Input As #1 Input #1,
variable1
Text1.Text = variable1 Close #1
End Sub
This program will open the sample.txt file and display its contents in
the Text1 textbox.

6. Common Dialog Control
The common dialog control provides a standard set of dialog boxes for operations
such as opening and saving files, setting print options, and selecting colors and
fonts. The control also has the ability to display Help by running the Windows Help
engine.
Figure 7.11 The common dialog control
The common dialog control provides an interface between Visual Basic and the
procedures in the Microsoft Windows dynamic-link library Commdlg.dll. To create a
dialog box using this control, Commdlg.dll must be in your Microsoft Windows
System directory.
You use the common dialog control in your application by adding it to a form and
setting its properties. The dialog displayed by the control is determined by the
methods of the control.
At run time, a dialog box is displayed or the Help engine is executed when the
appropriate method is invoked; at design time, the common dialog control is
displayed as an icon on a form. This icon can't be sized.

7. The common dialog control allows you to display these commonly used dialog
boxes:
 Open
 Save As
 Color
 Font
 Print
To use the common dialog control
1. If you haven't already done so, add the common dialog control to the toolbox by
selecting Components from the Project menu. Locate and select the control in
the Controls tabbed dialog, then click the OK button.
2. On the toolbox, click the CommonDialog control and draw it on a form.
When you draw a common dialog control on a form, it automatically resizes
itself. Like the timer control, the common dialog control is invisible at run time.
3. At run time, use the appropriate method, as listed in the following table, to
display the desired dialog.

8. Method Dialog
ShowOpen Open
ShowSave Save As
ShowColor Color
ShowFont Font
ShowPrinter Print
ShowHelp Invokes Windows

9. Creating and Reading files using Common Dialog Box
This example uses the common dialog box to create and read the text file, which is much easier than
the previous examples.Many operations are handled by the common dialog box. The following is the
program:
Dim linetext As String
Private Sub cmdOpen_Click()
CommonDialog1.Filter = "Text files{*.txt)|*.txt"
CommonDialog1.ShowOpen
If CommonDialog1.FileName <> "" Then
Form1.Caption = CommonDialog1.FileName
Open CommonDialog1.FileName For Input As #1
Do
Input #1, linetext
Text1.Text = Text1.Text & linetext
Loop Until EOF(1)
End If Close #1
End Sub

10. Private Sub cmdSave_Click()
CommonDialog1.Filter = "Text files{*.txt)|*.txt"
CommonDialog1.ShowSave
If CommonDialog1.FileName <> "" Then
Open CommonDialog1.FileName For Output As #1
Print #1, Text1.Text
Close #1 End If
Form1.Caption = "Saved to " & CommonDialog1.FileName
End Sub
The syntax CommonDialog1.Filter = "Text files{*.txt)|*.txt" ensures that
only the textfile is read or saved .The statement CommonDialog1.ShowOpen is
to display the open file dialog box and the
statementCommonDialog1.ShowSave is to display the save file dialog box.
Text1.Text = Text1.Text & linetext is to read the data and display them in the
Text1 textbox
The Output window is shown below: