Cobol

COBOL

Introduction:-

                  The word COBOL is an acronym for COmmon Business Oriented Language. COBOL is designed for developing business, typically file-oriented, applications. It is not designed for writing systems programs. COBOL is a high-level programming language first developed by the CODASYL Committee (Conference on Data Systems Languages) in 1960.

History:-

                 The first COBOL compiler became available in early 1962. The next version with some new additions was published in 1965. In August 1968 a standard version of the language was approved by the American National  Standard Institute (ANSI). This standard version was again modified in 1974 and is known as ANSI-74 COBOL or COBOL -74.

Importance of COBOL Program:-

COBOL was the first widely used high-level programming language. It is an English-like language which is user friendly. All the instructions can be coded in simple English words.

·         COBOL is also used as a self-documenting language.

·         COBOL can handle huge data processing.

·         COBOL is compatible with its previous versions.

·         COBOL has effective error messages and so, resolution of bugs is easier.

Features of Cobol Program:-

1.      Standard Language :- COBOL is a standard language that can be compiled and executed on machines such as IBM AS/400, personal computers, etc.

2.      Business Oriented :- COBOL was designed for business-oriented applications related to financial domain, defense domain, etc. It can handle huge volumes of data because of its advanced file handling capabilities.

3.      Robust Language :- COBOL is a robust language as its numerous debugging and testing tools are available for almost all computer platforms.

4.      Structured Language :- Logical control structures are available in COBOL which makes it easier to read and modify. COBOL has different divisions, so it is easy to debug.

Format of COBOL Program:-

               COBOL programs are written in coding sheets. There are 80 columns in a line of the  coding sheet. The page number is coded in columns.

             Column                                        Field

              1-3                                               Page Number

              4-6                                               Line Number (1-6 Sequence Number)

              7                                                  Continuation / Comment

             8-11                                              A – Margin / Area A

             12-72                                             B- Margin /Area B

             73-80                                             Identification

                In COBOL there are two types of entries known as margin A and margin B entries.

Margin A entries start from column 8, 9, 10 or 11 and margin B entries start from column 12

or anywhere after 12. An asterisk (*) in column 7 indicates a comment line and the entry is not compiled to produce object code.

Structure of COBOL Program:-

A COBOL program structure consists of divisions as shown in the following image:

                                              

·         Sections are the logical subdivision of program logic. A section is a collection of paragraphs.

·         Paragraphs are the subdivision of a section or division. It is either a user-defined or a predefined name followed by a period, and consists of zero or more sentences/entries.

·         Sentences are the combination of one or more statements. Sentences appear only in the Procedure division. A sentence must end with a period.

·         Statements are meaningful COBOL statements that perform some processing.

·         Characters are the lowest in the hierarchy and cannot be divisible.

The COBOL program consists of the following Divisions:-

1.      Identification Division

2.      Environment  Division

3.      Data  Division

4.      Procedure Division

1 . Identification  Division :-  

                         The details about the author, date of writing the program etc will be specified. It is the first and only mandatory division of every COBOL program.

                         The programmer and the compiler use this division to identify the program. In this division, PROGRAM-ID is the only mandatory paragraph. PROGRAM-ID specifies the program name that can consist 1 to 30 characters.

2 . Environment   Division :-

                        The details about the computer environment under which the program was written and compiled  etc will be notified. Environment division is used to specify input and output files to the program. It consists of two sections:

·         Configuration section provides information about the system on which the program is written and executed. It consists of two paragraphs:

Ø  Source computer : System used to compile the program.

Ø  Object computer : System used to execute the program.

·         Input-Output section provides information about the files to be used in the program. It consists of two paragraphs:

Ø  File control : Provides information of external data sets used in the program.

Ø  I-O control : Provides information of files used in the program.

3. Data Division :- The variables that are used by the program will be defined and it is

an important division for the program. Data division is used to define the variables used in the program. It consists of four sections:

·         File section is used to define the record structure of the file.

·         Working-Storage section is used to declare temporary variables and file structures which are used in the program.

·         Local-Storage section is similar to Working-Storage section. The only difference is that the variables will be allocated and initialized every time a program starts execution.

·       Linkage section is used to describe the data names that are received from an external program.

4.Procedure Division:-  All the programming statements (Executable Cobol statements) will be written and it is the most important division. Procedure division is used to include the logic of the program. It consists of executable statements using variables defined in the data division. In this division, paragraph and section names are user-defined.

There must be at least one statement in the procedure division. The last statement to end the execution in this division is either STOP RUN which is used in the calling programs or EXIT PROGRAM which is used in the called programs.