LSP_COBOL_Tutorial for BCA Students of M G University

COBOL TUTORIAL FOR BCA STUDENTS OF M G UNIVERSITY

UNIT 3: INTRODUCTION TO COBOL . . .

ENVIRONMENT DIVISION

The ENVIRONMENT DIVISION is the second division in a COBOL source program. It is the most machine-dependent division. The computer and all peripheral devices required by the program are described in this division.

This division contains two sections: CONFIGURATION SECTION
INPUT-OUTPUT SECTION

Of these the CONFIGURATION SECTION appears first. The outline of the sections and paragraphs of this division is shown below:

ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. source-computer-entry.
OBJECT-COMPUTER. object-computer-entry.
[SPECIAL NAMES. special-computer-entry].
[ INPUT-OUTPUT SECTION.
FILE CONTROL. {file-control-entry}….
[I-O-CONTROL. input-output-control-entry]].

For most compilers the COBOL source program must at least include the two section headings and the three paragraphs-SOURCE-COMPUTER, OBJECT-COMPUTER and FILE-CONTROL.

The division headings, section headings and the paragraph headings should be coded as Margin A entries. The paragraph headings must be followed by a period and then a space. The entries in the paragraphs are Margin B entries and can start in the same line with the paragraph heading.

CONFIGURATION SECTION

This section contains an overall specification of the computer used for the purpose of compilation and execution of the program. There are in all three paragraphs in this section, namely, source-computer, object-computer and special names.

SOURCE-COMPUTER

This paragraph specifies the name of the computer used to compile the COBOL program. The following is the form of this paragraph:

SOURCE-COMPUTER. computer-name.

For example, if THOSHIBA Satellite is to be used for compiling the COBOL source program, this paragraph should be as follows:

SOURCE-COMPUTER. THOSHIBA-SATELLITE.

OBJECT-COMPUTER

The OBJECT-COMPUTER paragraph describes the computer on which the program is to be executed. The following shows the syntax for this paragraph:

The computer name specifies a particular computer on which the object program is to be executed.

The MEMORY SIZE is used to indicate the amount of storage available to the object program. This clause is also used in conjunction with the SORT verb.

The PROGRAM COLLATING SEQUENCE clause specifies the collating sequence that is to be used to compare nonnumeric data items. The alphabet name in this clause should be defined in the SPECIAL-NAMES paragraph to specify a collating sequence. If this clause is absent, the machine’s own collating sequence called NATIVE, is assumed.

The SEGMENT-LIMIT clause is used in most of the compilers to indicate that the sections having segment number less that the number specified in integer-2 should be held in the permanent area of storage and should not be transferred to and from the virtual memory.

All the entries in this paragraph are terminated using period ( a dot). The following is an example of the OBJECT-COMPUTER paragraph.

OBJECT-COMPUTER. THOSHIBA-SATELLITE.
MEMORY SIZE 8000 WORDS.

SPECIAL-NAMES

This paragraph is used to relate some hardware names to user-specified mnemonic
names. This paragraph is optional in all compilers. The following is the format of this
paragraph.

INPUT-OUTPUT SECTION

This section contains information regarding files to be used in the program. There are two paragraphs in this section: FILE-CONTROL and I-O-CONTROL.

FILE-CONTROL

The FILE-CONTROL paragraph names each file and identifies the first medium through file control entries. The simplified format of a file control entry is given below.

SELECT [OPTIONAL] file-name ASSIGN TO hardware-name.

In general, a COBOL source program uses some files. For each of these files, there must be a FILE-CONTROL entry. This entry names the file and assigns a peripheral device which holds that particular file. The file names that appear in the SELECT clauses must be unique and all these files must be described in DATA DIVISION. The file name should be formed according to the rules of data names.

The word OPTIONAL may be used only for input files. When the object program is executed, the optional files need not be present on every occasion. If the optional clause is omitted for a particular file, the file must be present during the execution of the program. If the file is absent, an execution error will occur. On the other hand, if an optional file is absent, any attempt to open the file for reading will not result in an error. But the absent file will be considered to be an empty file which means that the file does not contain any record.

The assign clause assigns a particular physical peripheral device name to a file. The physical peripheral device names are machine-dependent. We shall use the device names READER, PRINTER, TAPE and DISK to mean card reader, line printer, magnetic tape and magnetic disk device respectively.

An example of the FILE-CONTROL paragraph is given below:

FILE-CONTROL.
	SELECT STU-FILE ASSIGN TO DISK.
	SELECT REPORT-FILE ASSIGN TO PRINTER.

This paragraph indicates that there are two files: STU-FILE and REPORT-FILE. The file named STU-FILE is a disk file, while the other is a report file to be printed on a line printer.

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