Structured programming language

Lecture-1 : INTRODUCTION• To provide brief history of COBOL • To learn the capabilities and limitations of COBOL • To present the program layout of COBOL • To discuss the structure of a

Structured Programming

Language

ITSS113

Lecture-1 : INTRODUCTION

• To provide brief history of COBOL

• To learn the capabilities and limitations of COBOL

• To present the program layout of COBOL

• To discuss the structure of a COBOL program

• To determine the difference between COBOL Literal Set, COBOL Words, COBOL Literals

Learning Objectives:

Introduction to COBOL

• COBOL

– Common Business Oriented Language

– A third-generation programming language,

– Was one of the earliest high-level programming languages; still widely used today

– First proposed in 1959 by the Conference on Data Systems

Languages (CODASYL)

– Three ANSI standards for COBOL have been produced in 1968,

1974 and 1985

– Object-oriented COBOL is the fourth edition in the continuing evolution of ANSI/ISO standard COBOL.

Underlining Philosophy

• Like the name suggests, COBOL was meant to be

‘common’ or compatible among a significant group of

manufacturers

• COBOL is designed for developing business, typically

file-oriented, applications, and is not designed for writing

systems programs

• Primary domain in business, finance, and administrative systems for companies and governments.

Pro’s and Con’s

- Disadvantages

- very wordy

- has a very rigid format

- not designed to handle scientific applications

- Advantages

- Simple

- Portable

- Maintainable

Distinct features

• The language is simple

• No pointers

• No user defined types

• No user defined functions

• ‘Structure like’ data types

• File records are also described with great detail,

as are lines to be output to a printer

• COBOL is self documenting

COBOL PROGRAM LAYOUT

The layout, or format, or a COBOL program follows

certain simple rules, which originated long ago when

programs were punched onto 80-column punch cards.

COBOL programs are written in coding sheets There are

80 columns in a line of the coding sheet.

COBOL PROGRAM LAYOUT

(CONTINUED)

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

Structure of COBOL Program

• COBOL programs are hierarchical in structure.

– Each element of the hierarchy consists of one or more

subordinate elements

• The levels of hierarchy are Divisions, Sections,

Paragraphs, Sentences and Statements

• There are 4 main divisions and each division provides

an essential part of the information required by the

complier

Structure of COBOL Program (continued)

• At the top of the COBOL hierarchy are the four divisions

• The sequence in which they are specified is fixed, and must follow the order:

– IDENTIFICATION DIVISION This division’s primary purpose is to name the

program

– ENVIRONMENT DIVISION This division is primarily used to tell the computer

about the input and output devices such files or printers.

– DATA DIVISION provides descriptions of the data-items/fields processed by the

program

– PROCEDURE DIVISION contains the code used to manipulate the data described

in the DATA DIVISION It is here that the programmer describes his algorithm.

Note:

Some COBOL compilers require that all the divisions be present in a

program while others only require the IDENTIFICATION DIVISION and the

PROCEDURE DIVISION

Hello World Example

000100 IDENTIFICATION DIVISION.

000200 PROGRAM-ID HELLOWORLD.

000300

000400 ENVIRONMENT DIVISION.

000500 CONFIGURATION SECTION.

000600 SOURCE-COMPUTER RM-COBOL.

000700 OBJECT-COMPUTER RM-COBOL 000800

000900 DATA DIVISION.

001000 FILE SECTION.

001100

101200 PROCEDURE DIVISION.

101300

101400 MAIN-LOGIC SECTION.

101500 DISPLAY "Hello world!"

101600 STOP RUN.

Character Set

There are 50 different characters in

COBOL character set.

0-9 (10 numerals)

A-Z (26 English alphabets-only

capital letters) – (minus sign or hyphen)

+ (Plus sign)

* (Asterisk)

= (Equal sign)

$ (Currency sign)

; (Semi colon)

(Period or decimal point)

“ (Quotation mark)

( (Left Parenthesis ) ) (Right Parenthesis)

> (Greater than symbol)

< (Less than symbol)

Character Set (continued)

The characters 0-9 are called numeric characters or digits

The characters A-Z are called letters

The remaining characters are called special characters The space or blank character in certain cases is treated as a

letter.

COBOL WORDS

A COBOL word can be formed using the following characters:

0-9 A-Z (a-z)

- (hyphen)

There are 2 types of words in COBOL:

1.) Reserved word 2.) User-defined word

COBOL WORDS (continued)

The following rules must be adhered in forming COBOL user-defined words:

1.) A word cannot begin or end with a hyphen

2.) A word can have at the maximum 30 characters

3.) One of the characters must be a letter

(Some compilers put the additional restrictions that the first character must be a letter.)

4.) Except hyphen (-) no special character allowed

5.) Cannot be a COBOL reserved word

•Paragraph names, Identifiers, File names can be defined by users

COBOL WORDS (continued)

Examples

The actual values can also appear in a program Such values are known as literals

A data name may have different values at different points of time whereas a literal means the specific value which remains

unchanged throughout the execution of the program

For this reason a literal is often called a constant Moreover the

literal is not given a name; it represents itself and does not require

to be defined in the DATA DIVISION

Literals (continued)

There are 3 types of literals:

a)Numeric Formed by digits only It can have a sign (+ or

-) and can have a decimal point also.

b) Nonnumeric Use in general to output messages or

headings Characters that are enclosed between “ “

constitute nonnumeric literal.

c) Figurative Constants Have some fixed names and

the compiler recognizes these names and it sets up

corresponding values in the object program.

Literals (continued)

Figurative Constant Meaning

ZERO ZEROS ZEROES

value 0

SPACE SPACES One or more blanks HIGH-VALUE

HIGH-VALUES Highest value in theCollating sequence LOW-VALUE

LOW-VALUES Lowest value in theCollating sequence QUOTE

QUOTES one or more of “ ALL literal one or more of the string characters

comprising the literal

Summary