All information in a file is always in binary form or a series of ones and zeros. A document includes any file you have created. It can be a true text document, sound file, graphics, images, or any other type of information the computer can create, store, or size from the internet.
COMPUTER FILES I
Wednesday, November 2, 2016
At the end of the lesson, I should be able to:
a. Identify computer file contents
b. Identifying and organizing files
c. Semantics of computer files
d. Basic operation on computer files
e. Steps involved in creating
All information in a file is always in binary form or a series of
ones and zeros. A document includes any file you have
created. It can be a true text document, sound file, graphics,
images, or any other type of information the computer can
create, store, or size from the internet.
They contain instructions for the computer’s microprocessor
and tell the computer what to do.
These include all other files on disk that are not exactly
programs or documents. These include support files for
programs, temporary files, and other random stuff that must
be saved inside the computer.
Although the way programs manipulate files varies according
to the operating system and file system involved, the following
operations are typical:
(i) Creating a file with a given name.
(ii) Setting attributes that control operations on the file.
(iii) Opening a file to use its content.
(iv) Reading or updating the content.
(v) Committing updated contents to durable storage
Closing the file, thereby losing access until it is opened again.
In modern computer system, files are typically accessed using
names also known as file name. Most computers organize files
into hierarchies using folders, directories or catalogs. The
concept is the same irrespective of the terminology used. Each
folder can contain an arbitrary number of files, and it can also
contain other folders. These other folders are referred to as
sub folders. Sub folders can contain still more files and folders
and so on, thus building a tree–like structure in which one
“master folder” can contain any number of levels of other
folders and files.
BASIC FILE OPERATIONS
The basic file operations are:
i. Create (The act of making new file).
ii. Delete (To remove a file from a disk).
iii. Retrieve (To find a file and bring it back).
iv. Copy (To produce something so that it is the same as an original
piece of work)
v. View (See the file in a folder).
vi. Update (To make something more suitable for use now by
adding new information or changing design).
vii. Open (To open a file for editing).
viii. Close (To close the edited file).
CREATING A SEQUENTIAL FILE
These are the ways to organize data in a sequential file:
1. Choose a DOS file name. Some examples are INCOME.86, CUSTOMER.DAT and FORT500.
2. Choose a number from 1 through 255 to be the reference number of the file. While the file is in use,
it will be identified by this number.
3. Execute the statement
OPEN filename FOR OUTPUT AS #n
Where n is the reference number.
4. Place data into the file with the WRITE*statement. If a$ is a string, then the statement
WRITE #n, a$
writes string a$ surrounded by quotation marks into the file . If c is a number then the statement
WRITE #n, c
writes the number c, without any leading or trailing spaces, into file number n. The statement
WRITE #n, a$, c
writes a$ and c as before, but comma separating them. Similarly, if the statement WRITE*n is followed by
a list of several strings and / or numbers separated by commas, then all the string and numbers appear as
before, separated by commas. After each WRITE* statement is executed, the characters f and El are
placed into the file.
5. After all the data have been recorded in the file, execute
Where n is the reference number. This statement breaks the communication
line with the file and dissociates the number n from the file.
Example: Write a program to create the file. Use EOD as a sentinel to
indicate that all the data has been read.
REM Create the file YOB.DAT and record some data into it
OPEN “YOB.DAT” FOR OUTPUT AS #1
READ name$, year
DO WHILE name$, year <> “EOD”
WRITE #1, name$, year
READ name$, year LOOP
REM ----Data: name, year of birth
DATA Barbra, 1942
DATA Ringo, 1940
DATA Sylvester, 1946
DATA EOD, 0
1. EOF – end of file
2. EOD – end of document
COMPUTER FILES II
Wednesday, November 2, 2016
At the end of the lesson, I should be able to:
a. Access sequential file
b. State effects of file insecurity
c. Identify file security methods
d. Advantages of computerized files
e. State limitations of computerized files
ACCESS A SEQUENTIAL FILE
Data stored in a sequential file can read in order and assigned to
variables with the following steps:
1. Choose a number from 1 through 255 to be the reference number
of the file. This number is not necessary to be the same number that
was used when the file was recorded.
2. Execute the statement
OPEN filename FOR INPUT AS #n
Where n is the reference number. This procedure is referred to as
opening a file for input. It establishes a communication line between
the computer and the disk drive for reading data from the diskette.
3. Read data from the file with the INPUT* statement. INPUT*
statement assigns data from file to variable.
INPUT #n. var1, var2, ……
4. After the desired items have been found or all the data has been
read from the file, close the file with the statement CLOSE #n.
5. Basic function EOF; it tells us if we have reached the end of a file.
For example the condition EOF (n) will be true if the end of file n has
been reached and false otherwise.
EXAMPLE: Write a program to display a table showing the ages in 1991 of the people in the
sequential file YOB.DAT.
REM Process data from YOB.DAT file to find ages in 1991
OPEN “YOB.DAT” FOR INPUT AS #5
PRINT “NAME”, “Age in 1991”
DO WHILE NOT EOF (5)
REM Process the entire file
INPUT #5, name$, year
PRINT name$, 1991 – year
REM Display name and age in 1991
Name Age in 1991
Many modern computer systems provide methods for
protecting files against accidental and deliberate damage.
Computer with multi users implement file permissions to
control who may or may not modify, delete or create files and
folders. A user may be given permission to modify a file or
folder, but not to delete while some may be permitted to only
read the contents and not permitted to modify or delete the
File security is a feature of your file system which controls which
users can access which files, and places limitations on what
users can do to files.
Effects of file insecurity
(a) Data loss: Computer users and many experts often loss data
permanently destroyed, with no hope of recovery.
CAUSES OF DATA LOSS
Hardware or System Problem
Software Corruption or Program Problem
This is a process of writing a binary set of data on a memory.
Data that has been overwritten is generally considered to be
FILE SECURITY METHODS
(i) BACK UP: This is refers to making copies of data so that these
additional copies are used to restore the original after loss event. It is
also a method of making copies of the file in a separate location so
that they can be restored if something happen to the computer. This
can be done by using removable media such as rewritable CD,
memory card, flash etc.
(ii) VIRUS: This is a self – replicating program that copies itself and
that can infect other programs by modifying them or their
environment such that a call to an infected program implies a call to
ANTIVIRUS: This is software to protect your computer from viruses
that may try to infect your computer or might have done so.
(iii) PASSWORD PROTECTION: It can prevent people accessing
computer system, account files or parts of files by requiring a user to
(iv) STORAGE DEVICE LABELING: You should label your storage
devices like floppies, CDs, DVDs, Pen drivers etc. So that you know
what is exactly stored in them and so as not to accidentally delete of
ADVANTAGES OF COMPUTERIZED FILES
(i) Computer can form calculations quickly and
(ii) Data can be retrieved quickly and easily.
(iii) Documents that are lost can often be
(iv) Security is tight and hard to break into.
(v) Makes work easier.
(vi) Quicker to find things and sort things.
(vii) Transactions, accounts can be handled more
properly by computers than manually.
i. Computerized filing system is expensive to set up.
ii. Not effective where there is irregular electric supply.
iii. Skilled labor with proficiency in computers is required.
iv. Data are separated and isolated
v. Data are often duplicated
vi. Application program dependent
vii. Incompatible data files
viii. They are vulnerable to virus and hacker attacks
Itemize the differences between computer files and manual
3. File access
4. Back up
Do not copy this following notes. They are for practice
BASIC OPERATION ON
Operations on computer files include the following:
CREATING A SEQUENTIAL
The following statements and functions are used with
LINE INPUT# PRINT# USING
STEPS INVOLVED IN
CREATING SEQUENTIAL FILE
The following program steps are required to create a
sequential file and access the data in the file:
1.Open the file in output (O) mode. The current program will
use this file first for output:
2.Write data to the file using the PRINT# or WRITE#
PRINT#1,A$ PRINT#1,B$ PRINT#1,C$
3.To access the data in the file, you must close the file and
reopen it in input (I) mode:
CLOSE #1 OPEN "I",#1,"filename
4.Use the INPUT# or LINE INPUT# statement to read data
from the sequential file into the program:
10 OPEN "O",#1,"DATA"
20 INPUT "NAME";N$
30 IF N$="DONE" THEN END
40 INPUT "DEPARTMENT";D$
50 INPUT "DATE HIRED";H$
70 PRINT:GOTO 20
NAME? MICKEY MOUSE
DEPARTMENT? AUDIO/VISUAL AIDS
DATE HIRED? 01/12/72
NAME? SHERLOCK HOLMES
DATE HIRED? 12/03/65
NAME? EBENEEZER SCROOGE
DATE HIRED? 04/27/78
NAME? SUPER MANN
DATE HIRED? 08/16/78
ACCESSING A SEQUENTIAL
The program in Example 2 accesses the file data, created in the program
in Example 1, and displays the name of everyone hired in 1978.
10 OPEN "I",#1,"DATA"
30 IF RIGHT$(H$,2)="78" THEN PRINT N$
40 GOTO 20
50 CLOSE #1
Input past end in 20
BASIC FILE PROCESSING
To read and display files:
The table below would be used with a file name “EXAMFILE”.
Matric No. Math English Total Score
0001 50 90 140
0002 70 40 110
0003 80 60 150
20 OPEN “EXAMFILE.TXT” FOR INPUT AS #1
30 PRINT #1 “Matric No. Maths English Total Score”
40 PRINT #1 “0001 50 90 140”
50 PRINT #1 “0002 70 40 110”
60 PRINT #1 “0003 80 60 160”
70 CLOSE #1
80 OPEN “EXAMFILE.TXT” FOR OUTPUT AS #1
90 DO WHILE NOT EOF(1)
100 INPUT #1, text$
110 PRINT text$
130 CLOSE #1