Chapter 1
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To familiarize you with
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Why COBOL is a popular business-oriented
language.
Programming practices and techniques
History of COBOL
Use of the current ANSI standard versions of
COBOL
Four divisions of a COBOL program
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Computer Programming: An Overview
Applications Program Development Process
Nature of COBOL
History of COBOL and the ANS Versions
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Techniques for Improving Program Design
Sample Programs
Entering and Running a COBOL Program on
Your Computer
◦ This is particular to our system
◦ We’ll be using the “Alpha” which is a VAX
◦ Telnet into it, you’ll love the editor.
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Machine language
 Only language computer understands
 All programs executed on computer must
be in machine language
 Machine language programs difficult to
write
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Symbolic language (like COBOL)
 English-like languages used to write
programs
 Easier than writing programs in machine
language
 Must be translated or compiled into machine
language to run on computer
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Determine Program Specifications
Design Program Using Program Planning
Tools
Code and Enter Program
Compile Program
Test Program
Document Program
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Systems analysts, users and programmers
develop specifications
Specifications include:
• Description of input and output data
• Step-by-step processing required to convert
input to output
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Record layout forms describe format of input
and output data
 Data names of each data item in record
 Location of each data item in record
 Size of each data item
 Number of decimal positions (for numeric
data items)
 Note that this is different than what you are
used to in C++
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Printer spacing charts describe
 Spacing
 Layout of printed output
 Heading, detail, total lines
 Error messages
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Program planning tools used to map out
structure and logic of program
 Flowcharts use block diagrams to represent
logic
 Pseudocode uses English-like statements
 Hierarchy charts show relationships among
sections of program
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Programmer writes and enters program into
computer
Program written in symbolic language (like
COBOL)
Called source program
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You all already know this
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112
Compiler is program that
 Checks source program for rule violations
 Translates source program into object
program
 Next class we’ll try this out
Source program in
symbolic language
Translated
by compiler
Object program in
machine language
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Test or debug program to ensure it contains
no errors
Check for two types of errors
◦ Compile-Time Errors
◦ Execution Errors
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Errors detected by compiler during
translation from COBOL to machine language
Detects violations of programming rules
◦ Misspelled reserved words
◦ Missing punctuation
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Also called syntax errors
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Detected when program is run
Logic error causes incorrect output
◦ Sequence of instructions incorrect
◦ Wrong instruction coded
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Run-time error if computer cannot execute
instruction
◦ Attempt to divide by zero
◦ Attempt to read a file that cannot be found
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Desk checking
Correcting syntax errors
Program walkthroughs
Executing the program
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Documentation - formal set of procedures
and instructions to specify how to use
program
Written for
◦ Those working with output
◦ Computer operators who run program
◦ Maintenance programmers who make modifications
to program
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This was a big part of the design of COBOL,
Self documenting code
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Business-oriented language
Standard language
English-like language
Relatively easy to understand
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Distinct Features of COBOL
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
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Advantages
-Simple
-Portable
-Maintainable
Disadvantages
-very wordy
-very rigid format
-not designed to handle scientific
applications
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Developed in 1959 as standard language
to meet needs of business
Committee to develop language convened
by Department of Defense
Included representatives from academia,
business, computer manufacturers
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1960s
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1968
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1974
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1985
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wide variations in COBOL
compilers
first COBOL standard set by
American National Standards
Institute (ANSI)
second ANSI standard to make
COBOL more efficient,
standardized
this ANSI standard incorporated
structured programming
techniques
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1985 currently the most widely used
The book mentions 2008 as the latest
standard but looks like 2002 may be
So the book mentions 2008 conventions,
seems they work on our compiler.
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Likely to remain important language
 Older COBOL programs need to be updated
 Still used by many for new program
development
 Mostly maintaining existing code, that’s why
you’re here.
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About 200 billion lines of COBOL source code
in use
New lines added each year
Used by many application programmers in
medium to large U.S. companies
How about the Y2K Problem?
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Two techniques used to develop programs
that are easier to understand, test, debug
and modify
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Structured Programming
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Top-Down Programming
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Eliminates use of GO TO statements
◦ Allowed skipping to different sections of
program without returning to starting point
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Program logic easier to follow with "GOTO-less" programming
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Program divided into paragraphs
 Main paragraph or module controls logic flow
using PERFORM statements
 Main module "performs" other modules when
instructions in that module required
 Each module can be written and tested
independently of others
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Another technique to make programs easier
to understand, test, debug and modify
Develop program like term paper
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Develop outline first
Add details for each of main steps
Add further refinement for more complex steps
Use of stubs
For COBOL program
 Code main modules or routines first
 Code intermediate modules next
 Details deferred to minor modules and coded
last
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Cobol suited for developing both types of
programs
Interactive programs
 Accept input data from keyboard
 Input data processed immediately
 Output (results) displayed on screen
immediately
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Batch programs
 Process large volumes of input at periodic
intervals
 Input data read in from files
 Output written to files
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Every COBOL program contains up to four
separate divisions in the following order:
IDENTIFICATION DIVISION
ENVIRONMENT DIVISION
DATA DIVISION
PROCEDURE DIVISION
Specific to COBOL
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IDENTIFICATION DIVISION
◦ Identifies program to operating system
◦ Provides documentation about program
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ENVIRONMENT DIVISION
◦ Defines file-names
◦ Describes devices used to store them
◦ Not included in fully interactive programs
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DATA DIVISION
◦ Describes input and output format of data in files
◦ Defines any constants and work areas
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PROCEDURE DIVISION
◦ Contains instructions to read input, process it and
create output
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Purpose
◦ to compute employee WAGES
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Input from keyboard
◦ HOURS and RATE
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Processing
◦ compute WAGES as HOURS x RATE
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Output displayed on screen
◦ WAGES
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Sample on Page 17 of book
136
IDENTIFICATION DIVISION.
PROGRAM-ID. WAGES1.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 HOURS
PIC 99.
01 RATE
PIC 99V99.
01 WAGES
PIC 999.99.
01 MORE-DATA
PIC XXX VALUE 'YES'.
PROCEDURE DIVISION.
100-MAIN.
PERFORM UNTIL MORE-DATA = 'NO'
DISPLAY 'ENTER HOURS AS A TWO DIGIT NUMBER'
ACCEPT HOURS
DISPLAY 'ENTER RATE IN NN.NN FORMAT (2 DECIMAL DIGITS)'
ACCEPT RATE
MULTIPLY RATE BY HOURS GIVING WAGES
DISPLAY 'WAGES ARE ', WAGES
DISPLAY 'IS THER MORE DATA (YES OR NO)?'
ACCEPT MORE-DATA
END-PERFORM
STOP RUN.
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IDENTIFICATION DIVISION
◦ One required entry, PROGRAM-ID
◦ Names the program
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DATA DIVISION
◦ Describes and defines storage for all data
◦ Data defined in WORKING-STORAGE SECTION for
interactive program
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Keyed input fields (HOURS, RATE)
Output fields (WAGES)
Other fields used for processing (MOREDATA)
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01 level begins definition of each field
PICTURE or PIC clause describes
◦ Type of data
 Numeric (PIC 9)
 Nonnumeric (PIC X)
◦ Size of field - determined by number of 9’s or
X’s
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RATE with PIC 99V99 includes V to show
assumed decimal point position
User enters data with decimal point
◦ Program uses V to align data
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WAGES includes actual decimal point
◦ Shown when value displayed on screen
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MORE-DATA with PIC XXX is nonnumeric
field
Assigned initial contents of YES by use of
VALUE clause
Value must be in quotation marks since
MORE-DATA is nonnumeric field
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Set of instructions to be executed by
program
Organization of instructions planned
before coding begins
Pseudocode, an English-like description of
program instructions, used for planning
Describes program logic and order in
which instructions will be executed
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PROCEDURE DIVISION includes one paragraph
100-MAIN
List of instructions that follow make up
paragraph
Period follows last statement in paragraph
(STOP RUN.)
Main processing controlled by PERFORM …
END-PERFORM loop
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Repeats set of instructions as long as user
enters YES in response to prompt
"IS THERE MORE DATA (YES/NO)?"
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MORE-DATA initially contains YES so
instructions in loop executed first time
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When user enters NO as response
◦ MORE-DATA set to "NO" and loop ends
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After loop, STOP RUN is executed, ending
program
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Statements in loop executed in order they
are listed
 DISPLAY displays value in quotes or value
of field on screen
 ACCEPT stores value user enters from
keyboard in field
 MULTIPLY performs calculation to find
WAGES
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In batch mode, data comes from input file
instead of keyboard
Data for each employee stored in a record in
file on disk
Employee name, hours and rate data called
fields
Page 30
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Calculated results (Wages) stored in file
instead of displayed on screen
For each input record
◦ Record created and stored in output file
◦ Includes employee name, hours, rate and
computed wages
◦ File intended for printing so spacing added
between fields for readability
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All four divisions included for batch programs
IDENTIFICATION DIVISION first with required
PROGRAM-ID paragraph
ENVIRONMENT DIVISION
◦ INPUT-OUTPUT SECTION assigns input and output
files to specific devices
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FILE SECTION describes format of input and
output files
Fields in records described using PICTURE
clause
Decimal point not stored in input records
◦ Use V for implied decimal for alignment
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Use actual decimal point for fields in output
record so it is printed
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Contains instructions to be executed by
computer
Instructions executed in order they appear
Includes two paragraphs with period at end of
each
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OPENs files to be used by program
Repeatedly READs in records (PERFORM …
END-PERFORM) until there are no more
Calls second paragraph 200-WAGE-ROUTINE
to process each record
CLOSEs files after all records read
Ends program (STOP RUN)
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Reads one record into program storage area
Record must be in storage to use it
Takes one of two actions depending on
whether record was read
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PERFORM instruction after NOT AT END
executed when record read
◦ Statements in paragraph 200-WAGE-ROUTINE
executed to process record
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If no more records to be read, MOVE
instruction after AT END executed
◦ 'NO ' moved to ARE-THERE-MORE-RECORDS, ends
loop
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First MOVE initializes PRINT-REC to blanks
Then MOVEs name, hours, wages to output
fields
Calculates WAGES with MULTIPLY statement,
MOVES it to output field
WRITEs data in employee output record to
print file
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To type in and run a COBOL program on
your computer system, you need to know
how to:
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Log on and off of the computer
Name COBOL files on the computer
Use a text editor to key in, modify and save files
Compile a COBOL source program to translate it
into machine language
Link or load the object program
Run the object program
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The Nature of COBOL
◦ English-like language
◦ Used widely for business programming
◦ With new standard coming out soon, it is likely to
remain important language
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COBOL programs divided into four divisions
 IDENTIFICATION DIVISION identifies program
to operating system
 ENVIRONMENT DIVISION required for batch
programs that operate on files
 DATA DIVISION defines formats for all input,
output and work areas needed
◦ FILE SECTION required for batch programs that
operate on files
◦ WORKING-STORAGE SECTION for work fields or
fields used in interactive programs
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PROCEDURE DIVISION
◦ Contains instructions to process input and produce
output
◦ Divided into paragraphs or modules
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