COBOL Structured Programming

1
COBOL - Structured Programming

• Structured programming use logical control
  structures to specify the order in which
  instructions are executed.
• These structures are the same for all languages
• The four logical structures are
• Sequence
• Selection
• Iteration
• Case structure

2
COBOL - Introduction

• A program - is a set of instructions that enable
  a computer to process data.
• There are two types of programs
• Operating System programs
• Application programs
• Operating Systems
• All programs run under the control of an
  operating system
• This program monitors and control the overall
  operation of the computer
• Application programs
• Takes input data and converts it to meaningful
  output information

3
COBOL - History

• COBOL is an acronym that stands for Common
  Business Oriented Language.
• COBOL was developed in the 1950s and was
  designed for applications with large volumes of
  Data
• To date over 50 of computer code in existence is
  in COBOL

4
COBOL - History

• COBOLs popularity is due largely to the USAs
  Department of Defense which played in leading
  role in standardizing the COBOL language

5
Steps in program Development- COBOL programming
context

• Read and understand program specifications
• Draw hierarchy charts
• Draw program flowcharts
• Write program code
• Compile a program and correct errors
• Test-run the program with test data
• Document the program

6
Divisions and Programming Area

• There are four main divisions in a COBOL program
• IDENTIFICATION DIVISION
• ENVIRONMENT DIVISION
• DATA DIVISION
• PROCEDURE DIVISION

7
Notes to remember about Divisions

• The divisions are coded in a text Editor.
• The divisions are coded in that particular order
• Name of the division and actual word DIVISION
  are coded separated by a single space
• Each division plays a specific role in the COBOL
  program

8
Rules for the Coding a COBOL program

• columns 1-6
• Optional sequence number
• column 7
• Comment line (with an )
• (ignored by compiler)
• columns 8-11
• Area A (division heads, paragraphs, FD,
  01entries)
• columns 12-72
• Area B (All other entries)
• columns 73-80
• Program identification(also ignored by the
  compiler)

9
1.0 IDENTIFICATION DIVISION

• Identifies the program
• Example

IDENTIFICATION DIVISION. PROGRAM-ID. PRGM01.
10
2.0 ENVIRONMENT DIVISION

• There are two sections in this division
• Configuration section (Hardware details this
  section is NOT NEEDED)
• Input-Output section(File details)

INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT
SALES-FILE ASSIGN TO DISK-SALEFLE. SELECT
PRNT-FILE ASSIGN TO PRINTER-QPRINT.
11
3.0 DATA DIVISION

• This DIVISION typically contains two sections
• FILE SECTION, and
• WORKING-STORAGE SECTION
• File section deals with Input and Output file
  descriptions
• FD- File description (starts in Area A)
• 01 - to describe the record layout (also in area
  A)
• Working Storage section
• Is the section where the input and output records
  are manipulated and all other variables needed
  are defined.
• Typically contains the variables, heading lines
  and detail record

12
COBOL Language Elements

• In a COBOL program, youll find the following
  words
• Words
• Reserved words
• User Defined words
• Constants or Literals
• Non-Numeric
• Numeric
• Figurative constants
• Note Reserve words, and User Defined words are
  case NON-sensitive

13
COBOL Language Elements

• Reserved words
• See Appendix B, page 700
• User Defined words (page 85)
• These are data names for storage, paragraph, and
  section names
• Examples
• EMPLOYEE-NAME-OUT
• WS-END-OF-FILE-INDICATOR
• Rules
• max 30 characters
• A-Z, 0-9, and hyphen (-)
• must start and end with A-Z, or 0-9 (paragraph ad
  section name are the only user defined words that
  are allowed to start with 0-9)
• cannot begin or end with hyphen
• must be at least one alphabetic character
• cannot be a reserved word

14
COBOL Language Elements

• Non-Numeric Literals
• these are string constants
• Examples
• Summary of Loans Report
• ABC
• Rules
• max 160 characters
• quotation marks are required before and after
  (single or double - compiler option)
• contents between the quotes are case-sensitive

15
COBOL Language Elements

• Numeric Literals
• these are hard-coded numbers
• Examples
• 12.45
• -1
• Rules
• max 18 digits
• , - must appear on the left of the number

16
Non-Edited Picture Characters

• X Alpha-numeric (1 byte)
• 9 Numeric (1 bytes)
• S Operational SIGN (does not take up any space)
• e.g. 05 WS-CREDIT PIC S9(3)
• V Implied Decimal Point
• e.g. 05 WS-SALARY PIC 9(5)V9(02)

17
Example Input file and File Description

• Data File of SALEFILE
• 111111111MOOING MARTY
  001451255000
• 222222222PATSY POTATO
  450003569050
• 333333333ROWDY RODENT
  205001259020
• 444444444STARING STACEY
  000090000650
• The File Description
• FD SALES-FILE
• RECORD CONTAINS 80 CHARACTERS
• DATA RECORD IS SALES-REC.
• 01 SALES-REC.
• 05 EMPLOYEE-NUM-IN PIC 9(09).
• 05 NAME-IN PIC X(20).
• 05 QUANTITY-IN PIC 9(05).
• 05 AMOUNT-IN PIC 9(05)V99.
• 05 FILLER PIC X(39)
• Note the use of X and 9 and numbers in
  parentheses

18
Example Input file and File Description

• Main Memory

Disk
.
Program Executable Code
ENVIRONMENT DIVISION. INPUT-OUTPUT
SECTION. FILE-CONTROL. SELECT SALES-FILE
ASSIGN TO DISK-SALEFLE. DATA DIVISION. FILE
SECTION. FD FD SALES-FILE RECORD CONTAINS
80 CHARACTERS DATA RECORD IS SALES-REC.
SALEFLE file
Buffer
01 SALES-REC. 05 EMPLOYEE-NUM-IN PIC
9(09). 05 NAME-IN PIC X(20). 05
QUANTITY-IN PIC 9(05). 05 AMOUNT-IN PIC
9(05)V99. 05 FILLER PIC X(39)
AS400 Operating System
Working Storage
19
Working Storage Section

• Purpose
• to save, or store temporary data for use in the
  program
• Records and variables
• consist of Group and Elementary items
• Elementary items MUST HAVE a PIC clause
• Group items may consist of one or more elementary
  item, or other Group items
• Group items are consider alphanumeric always
• To show groupings, LEVEL numbers are used
• Rules
• In sequence (from smaller numbers to larger)
• But dont have to be consecutive
• Also, not required to jump by any given interval
  can be random
• Record level is 01 level
• Valid numbers are 01 through 49 inclusive
• 66, 77, 88 have special purpose usage

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Working Storage Section

• VALUE clauses are ONLY allowed in Working Storage
  (not allow in FILE section.
• Used to initial elementary data items
• Cannot be used for group items
• can take a
• literal
• Figurative constant
• the word ALL
• Examples
• 05 WS-RPT-TITLE PIC X(20) VALUE SALES REPORT.
• 05 WS-CHRISTMAS-DAY.
• 10 XMAS-YR PIC 9(04) VALUE 2002.
• 10 XMAS-MM PIC 9(02) VALUE 12.
• 10 XMAS-DD PIC 9(02) VALUE 25.
• 01 DRAW-LINE PIC X(133) VALUE ALL .

21
4.0 Procedure Division

• Its very important to be precise while dealing
  with the procedure division.
• This is the only division that requires hierarchy
  chart, pseudocode, and program flowcharts.
• Hierarchy chart Overview of the process.
• Pseudocode Near COBOL code without syntax.
• Flowchart Graphical representation of program
  flow.

22
Hierarchy Chart

• Level1
• Level2
• Level3

MAIN-RTN
HDG-RTN
READ-RTN
DETAIL-RTN
READ-RTN
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Pseudocode
MAIN PROCESS OPEN FILES WRITE
HEADINGS READ FIRST RECORD PROCESS
RECORDS UNTIL NO MORE RECORDS CLOSE FILES
STOP PROCESSING WRITE HEADINGS
MOVE AND WRITE HEADING LINE 1 MOVE AND WRITE
HEADING LINE 2 PROCESS RECORDS MOVE AND
WRITE DETAIL RECORDS READ NEXT
RECORD
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FLOWCHART
PROGRAM FLOW
START
OPEN FILES
READ- RTN
HDG- RTN
UNTIL WS- EOFY
CLOSE FILES
DETAIL- RTN
STOP