1. An Introduction to Structured Program Design in COBOL
Chapter 1
An Introduction to Structured Program Design in COBOL

2. Chapter Objectives To familiarize you with
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

3. Chapter Contents Computer Programming: An Overview
Applications Program Development Process
Nature of COBOL
History of COBOL and the ANS Versions

4. Chapter Contents 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.

5. Program Languages Machine language Only language computer understands
All programs executed on computer must be in machine language
Machine language programs difficult to write

6. Program Languages 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

7. Program Development Process
Determine Program Specifications
Design Program Using Program Planning Tools
Code and Enter Program
Compile Program
Test Program
Document Program

8. 1. Program Specifications
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

9. 1. Program Specifications
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++

10. 1. Program Specifications
Printer spacing charts describe
Spacing
Layout of printed output
Heading, detail, total lines
Error messages

11. 2. Design the Program
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

12. 3. Code and Enter Program
Programmer writes and enters program into computer
Program written in symbolic language (like COBOL)
Called source program
You all already know this

13. 4. Compile Source Program
Compiler is program that
Checks source program for rule violations
Translates source program into object program
Thursday we’ll meet in Dundee and try this out
Source program in symbolic language
Translated by compiler
Object program in machine language

14. 5. Test Program Test or debug program to ensure it contains no errors
Check for two types of errors
Compile-Time Errors
Execution Errors

15. Compile-Time Errors
Errors detected by compiler during translation from COBOL to machine language
Detects violations of programming rules
Misspelled reserved words
Missing punctuation
Also called syntax errors

16. Execution Errors Detected when program is run
Logic error causes incorrect output
Sequence of instructions incorrect
Wrong instruction coded
Run-time error if computer cannot execute instruction
Attempt to divide by zero
Attempt to read a file that cannot be found

17. Debugging Techniques Desk checking Correcting syntax errors
Program walkthroughs
Executing the program

18. 6. Document the Program
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
This was a big part of the design of COBOL, Self documenting code

19. Nature of COBOL Business-oriented language Standard language
English-like language
Relatively easy to understand

20. History of COBOL
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

21. Standard Versions of COBOL
1968
1974
1985
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

22. Current and Future Standards
1985 currently the most widely used
2008 is next standard
Approval expected in 2008 or so
Information on 2008 COBOL standard at

23. Future of COBOL 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.

24. Use of COBOL About 200 billion lines of COBOL source code in use
5 billion new lines added each year
Used by 42.7% of application programmers in medium to large U.S. companies
$200 million in expected revenues for 2001
Y2K Problem

25. Improving Program Design
Two techniques used to develop programs that are easier to understand, test, debug and modify
Structured Programming
Top-Down Programming

26. Structured Programming
Eliminates use of GO TO statements
Allowed skipping to different sections of program without returning to starting point
Program logic easier to follow with "GO- TO-less" programming

27. Structured Programming
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

28. Top-Down Programming
Another technique to make programs easier to understand, test, debug and modify
Develop program like term paper
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

29. Interactive vs Batch Programs
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

30. Interactive vs Batch Programs
Process large volumes of input at periodic intervals
Input data read in from files
Output written to files

31. Overview of the Four Divisions
Every COBOL program contains up to four separate divisions in the following order:
IDENTIFICATION DIVISION
ENVIRONMENT DIVISION
DATA DIVISION
PROCEDURE DIVISION
Specific to COBOL

32. Overview of the Four Divisions
IDENTIFICATION DIVISION
Identifies program to operating system
Provides documentation about program
ENVIRONMENT DIVISION
Defines file-names
Describes devices used to store them
Not included in fully interactive programs

33. Overview of the Four Divisions
DATA DIVISION
Describes input and output format of data in files
Defines any constants and work areas
PROCEDURE DIVISION
Contains instructions to read input, process it and create output

34. Sample Interactive Program
Purpose
to compute employee WAGES
Input from keyboard
HOURS and RATE
Processing
compute WAGES as HOURS x RATE
Output displayed on screen
WAGES
Page 17 of book

35. Sample Interactive Program
IDENTIFICATION DIVISION
One required entry, PROGRAM-ID
Names the program
DATA DIVISION
Describes and defines storage for all data
Data defined in WORKING-STORAGE SECTION for interactive program

36. Data Defined in Sample Program
Keyed input fields (HOURS, RATE)
Output fields (WAGES)
Other fields used for processing (MORE- DATA)

37. PICTURE Clause 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

38. PICTURE Clauses
RATE with PIC 99V99 includes V to show assumed decimal point position
User enters data with decimal point
Program uses V to align data
WAGES includes actual decimal point
Shown when value displayed on screen

39. Giving Field Initial Value
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

40. PROCEDURE DIVISION 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

41. PROCEDURE DIVISION 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

42. PERFORM … END-PERFORM
Repeats set of instructions as long as user enters YES in response to prompt
"IS THERE MORE DATA (YES/NO)?"
MORE-DATA initially contains YES so instructions in loop executed first time

43. PERFORM … END-PERFORM When user enters NO as response
MORE-DATA set to "NO" and loop ends
After loop, STOP RUN is executed, ending program

44. PERFORM … END-PERFORM
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

45. Sample Batch Program
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

46. Sample Batch Program
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

47. COBOL Divisions 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

48. DATA DIVISION 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
Use actual decimal point for fields in output record so it is printed

49. PROCEDURE DIVISION Contains instructions to be executed by computer
Instructions executed in order they appear
Includes two paragraphs with period at end of each

50. 100-MAIN-MODULE 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)

51. READ Statement 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

52. READ Statement
PERFORM instruction after NOT AT END executed when record read
Statements in paragraph 200-WAGE-ROUTINE executed to process record
If no more records to be read, MOVE instruction after AT END executed
'NO ' moved to ARE-THERE-MORE-RECORDS, ends loop

53. 200-WAGE-ROUTINE 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

54. Entering & Running a Program
To type in and run a COBOL program on your computer system, you need to know how to:
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

55. Chapter Summary 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

56. Chapter Summary 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

57. Chapter Summary PROCEDURE DIVISION
Contains instructions to process input and produce output
Divided into paragraphs or modules