Manipulating With Data From Files

8/8/2019 Manipulating With Data From Files

1/39

1

Manipulating with

Data from Files

Reading and writing text files


2/39

2

Understanding Computer Files

and How They are Stored Random access memory (RAM): temporary storage

Example: storing a value in a variable Volatile storage

Nonvolatile storage is permanent Example: saving a program to disk

Permanent storage devices: hard disks, floppy disks,magnetic tapes, compact discs

Sequential file: records are stored one after anotherin some order


3/39

3

Data files contain facts and figures

Program files (application files) storesoftware instructions

Files occupy space on a section of a

storage deviceEach has a name and a creation time

Write to the file: store data in a file on

persistent storage device


4/39

4

Manipulation with Files

Open the file: locate file on storage device,

associate a variable name with it Read from the file or write to a file: copy data

from the file on storage device into RAM

Close the file: make the file unavailable to theprogram


5/39

5


6/39

6

1. Create a text file (using Notepad)

2. Start writing a Program (VB)

3. To read form the file to a program declare and open a

StreamReader.

4. To write to the file from a program declare and open a

StreamWriter.

FILE

PROGRAM

StreamReader

StreamWriter


7/39

7

Reading from a file (1)

1. Declare a StreamReader

DimsrAs IO.StreamReader

2. Connect the StreamReader with the specified

file (the file you want to read)

sr = IO.File.OpenText(FileName.txt)

* File path. To avoid problems with accessing file

store the text file in the Bin folder of the

project


8/39

8

Reading from a file (2)

3. Read the file

DimlineAs String

Do While (sr.Peek -1)line = sr.ReadLine()

Loop4. Close the StreamReader

sr.Close()


9/39

9


DimlineAs String

sr = IO.File.OpenText

(FileName.txt)

Do While (sr.Peek -1)

line = sr.ReadLine()lstBox.Items.Add(line)

Loop

sr.Close()


10/39

10

Writing into a File

1. Declare a StreamWriterDim sw As IO.StreamReader

2. Connect the StreamWriter with the specified file(the file you want to write into)

sw = IO.File.CreateText(FileName.txt)

or

sw = IO.File.AppendText(FileName.txt)


11/39

11

Writing into a File

3. Write line into a file:

sw.WriteLine(Hello)

4. Close the StreamWriter

sw.Close()


12/39

12

Writing into a File

sw = IO.File.CreateText(FileName.txt)

Creates a new file. If file already exists this command will delete old

information, and record the new one.


13/39

13

Writing into a File

Dim sw As StreamWritersw=IO.File.CreateText(FName.txt)

sw.WriteLine(A)

sw.WriteLine(B)

sw.WriteLine(C)

sw.WriteLine(D)

Sw.Close()


14/39

14

Writing into a File

sw = IO.File.AppendText(FileName.txt)

This command can work only withalready existing files. It will append

new information to the existing part of

the file.


15/39

15

File can have only one stream open at a

time. To make sure if a certain stream is open

or not, you can use Flag variable, that willhold the status of the Streams.

Before you open a stream make sure thatthere is no other stream attached to thisfile

And if there is a stream attached close itfirst.


16/39

16


DimlineAs String

DimsrOpen As Boolean = False

sr = IO.File.OpenText

(FileName.txt)

srOpen = True


line = sr.ReadLine()lstBox.Items.Add(line)

Loop

If srOpen = True

sr.Close()EndIf


17/39

17

Plan for Week 1

1. Create a VB project called Students2. Design and create GUI (name all the controls

properly)

3. Create a text file on Notepad called Students.txt;

add at least 20 entries (records) in the fileMike Connor T127 123-234-2334 mconnor&bell.ca 2.8

Ann Smith T201 416-354-6345 [email protected] 2.4

Kate Wheeler T201 416-490-3551 [email protected] 3.4

Cathy McDonald T127 416-406-3616 [email protected] 3.5

Peter Black T127 321-597-2345 [email protected] 3.6

4. Save this file in the project folder under Bin/Debugfolder


18/39

18

5. In your project provide a functionality (button) to display all records

into a list box.

6. Provide a functionality (button) to display record by record into

separate text boxes.


19/39

19

Validation Functions

7. Write a separate program (this program is not connected withyour assignment) to validate e-mail, phone number, group, GPA


20/39

20

Add new record into a file8. In your assignment provide a functionality (button) to add a

student to a file (without validation). You will be able to do itonly on local drives.

9. Make validations into functions and add validations to a project


21/39

21

Structures

When we need to bind two or more pieces

of related data, we can use STRUCTURE

Structure is a way to package as a singleunit several related variables of different

type.

Structure is a User-Defined Data Type(UDT)


22/39

22

Structures Declaration

Structure Student

DimnameAs String

DimGPAAs Double

End Structure

The structure must be declaredoutside of all procedures (inside aclass), like a sub or function

name and GPAare members ofStructureStudent


23/39

23

Structures

1. Declaration of a variable

Dim st1 As Student

2. Manipulating with Structure members:

st1.name = Mary

st1.GPA = 3.9


24/39


25/39

25

Student Structure for the Project

Structure Student

Dim first As String

Dim last As String Dim majorAs String

Dim phone As String

Dim email As String

Dim gpa As Double

End Structure


26/39

26

Dim array() As String

array = line.Split(" ")txtFirst.Text = array(0)

txtLast.Text = array(1)

txtMajor.Text = array(2)txtPhone.Text = array(3)

txtEmail.Text = array(4)

txtGpa.Text = array(5)


27/39

27

Calculating Number Of Records

Function NumberOfRecords(ByVal fileAs String) As Integer

Dim n As Integer = 0

sr= IO.File.OpenText(filespec)


line = sr.ReadLine

n += 1

Loopsr.Close()

Return n

End Function


28/39

28

Read File Into Array

Private Sub ReadToArray(ByRef s() As Student, ByVal num As Integer)Dim index As Integer

Dim a() As String

Dim record As String

sr = IO.File.OpenText(filename)

For index = 0 To num - 1record = sr.ReadLine

a = record.Split(" ")

s(index).first = a(0)

s(index).last = a(1)

s(index).major = a(2)

s(index).phone = a(3)s(index).gpa = a(4)

Next

sr.Close()

End Sub


29/39

29

Read File Into Array

Dim n As Integer =

NumberOfRecords(file)

Dim a As Integer

Dim stud(n - 1) As Student

ReadToArray(stud, n)


30/39

30

Multiple Forms

1. Create both Forms.

2. Give a meaningful name for the second

Form (in the Name property)

frmSearch, frmSort, ect.3. In both form place buttons that allow to

go from one form to the other.


31/39

31

Form1

frmSource

Name: secondForm


32/39

32

Public Class Form1

Public n As String

Private Sub

btnCalc_Click(..)n = txtName.Text

Dim secondForm As NewfrmSources()

secondForm.n2 = n

secondForm.ShowDialog()

txtIncome.Text =FormatCurrency

(secondForm.sum)

End Sub

End Class

Public Class frmSources

Public sum As Double

Public n2 As String

Private SubbtnComput_Click(..)

sum = CDbl(txtWages.Text) +CDbl(txtInterest.Text)

+ CDbl(txtDivident.Text)

Me.Close()End Sub

Private SubfrmSources_Load(..)

txtName.Text = n2

End SubEnd Class


33/39

33

Deleting record from the file. (1)

1. Read the whole file into the array ofstrings or structures

2. Search the array for the particular record

3. Create 2nd array of the same data typeas the 1st, but one size smaller

4. Copy all the elements from the 1st arraybefore the selected element and after theselected element.

5. Write file from the 2nd array.


34/39

34

Deleting record from the file. (2)

Through Second File1. Open the original file for reading

2. Open new file for writingsw=File.CreateText(Temp.txt)

3. Read from old file, compare line, if the line doesnt matchthe one youve selected to be deleted, then write this lineinto a new file

4. Close both streams

5. Delete old File

File.Delete(Student.txt)

6. Rename new file.

File.Move(Temp.txt,Student.txt)


35/39

35

Sort file in ascending order:

1. Define number of records in the file (27).2. Create an array of structures (Student).

The size of the array is equals the numberof records in the file.

3. Read (copy) date from the file into thearray (28,29).

4. Sort array in ascending order (36).

5. Write the information from the array intothe file (37).

6. Display the sorted file into the list box


36/39

36

Sort array in ascending orderDim index As IntegerDim temp As Student

For i = 0 To n - 2

For index = i + 1 To n - 1

If stud(index).last


37/39


38/39

38

Search the file

1. Repeat steps 1, 2, and 3 from Sortingprocedure.

2. Search the array (in this example the

search is done by the last name):


39/39

39

Dim found As Boolean = False

Dim index As Integer

ln = InputBox("Enter Last Name:", "Last Name")

For index = 0 To n 1If stud (index).last = ln Then

found = True

line = stud (index).first & " " &

stud(index).last & " " &

stud(index).major & " " &

stud (index).phone &

" " & stud (index).email & " " &

stud (index).gpa

lstResult.Items.Add(line)

End If

NextIf found = False Then

MsgBox("ITEM WAS NOT FOUND")

End If

Date post:	09-Apr-2018
Category:	Documents
Upload:	jonathan-velasquez
View:	229 times
Download:	0 times

Manipulating With Data From Files

Documents