#File: A file is a collection of related information that is stored in a disk under a unique file name.
A file can be categorized as:
(i)Data file
(ii)Program file
1.Data File: A data file contains real data of any person, thing or entity. The data is stored under different attributes such as name, address, phone, etc.
2.Progam File: A program file consists of set of program codes and instructions. The instructions are written in a computer language. Program files in QBASIC have extension .BAS.
#File Handling: It is a process to create a data file, write data to the data file and read data from the specified data file.
Types of data files in QBASIC:
(i)Sequential data file
(ii)Random access data file
1.Sequential data file: In a sequential access data file, data are stored in
sequential order.
· Performs reading and writing sequentially from the beginning to the end of a file.
· Records need to be accessed in the same order as they are stored.
Advantages of sequential access files:
· File design is simple and easy.
· Due to sequential storage nature, tapes can be used for storing data.
· It is very efficient when all the records need to be processed during run time.
Disadvantages of sequential data files:
· In order to search a single record, the entire file needs to be accessed.
· The file is never up-to-date.
· Overall processing is slow.
2. Random Access data file: In a random-access file, data are stored and accessed randomly.
Features:
· Performs reading and writing operations randomly in any order.
· Records can be accessed directly in any order.
Advantages of random-access file:
· Any record can be accessed directly.
· It has fast accessing speed.
· Files can be kept up to date.
Disadvantages of random-access files:
· It does not use all the locations.
· Creates backup and security problem.
#File mode: The purpose of opening a data file is known as file mode.
Types of file mode:
(i)OUTPUT mode: To create new data file and write data in it. [store, create]
(ii)INPUT mode: To read/ retrieve contents from already existing data file. [display, view]
(iii)APPEND mode: To add records in the already existing data file. [add]
#EOF: This function is the abbreviation of the End Of File which is used for testing the end of a file. If the record pointer reaches at the end of a record it returns True(-1). If there are more records to be read from a data file, it returns False(0).
Syntax: EOF(file name)
Differences between WRITE# and PRINT# mode:
| WRITE# | PRINT# |
| · This statement stores values to a file as a separate data, so data in row can be read individually. | · This statement writes values to a file as a single data, so data in row can’t be read individually. |
| · This statement inserts commas between the data items and enclosed strings quotation. | · This statement adds spaces between data item and does not encloses strings. |
Differences between OUTPUT and APPEND mode:
| OUTPUT mode | APPEND mode |
| · OUTPUT mode creates a new sequential data file. | · APPEND mode adds more records to an existing sequential data file. |
| · If the file is already present, the previous file is deleted and a new file with the same name is created. | · If the file is already present, the new records are added to the last of the previous records. |
