4-1

Coding Complete COBOL Programs: The PROCEDURE DIVISION

Chapter 4

4-2

Chapter Objectives

To familiarize you with methods used to

1. Access input and output files

2. Read data from an input file

3. Perform simple move operations

4. Write information to an output file

5. Accomplish end-of-job operations

6. Execute paragraphs from main module, return control to that main module

4-3

Review of First Three Divisions

• IDENTIFICATION DIVISION

– Identifies program name

• ENVIRONMENT DIVISION

– Defines files and equipment used by batch

programs

– Associates a logical / programmer-defined

file name with a physical (device-oriented)

file name.

4-4

Review of First Three Divisions

• DATA DIVISION

– FILE SECTION

• Detailed description of input/output records

– WORKING-STORAGE SECTION

• Defines keyed input, displayed output

Defines fields needed for processing but not

part of input/output records

4-5

PROCEDURE DIVISION

Contains instructions to

• Read data

• Process data

• Produce output

• Perform end-of-job operations

4-6

PROCEDURE DIVISION

• Interactive processing instructions

– Accept input from keyboard

– Display output on screen

• Batch processing instructions

– Access files and read them

– Write output to files

4-7

Paragraphs

• PROCEDURE DIVISION divided into

paragraphs

• Each is independent module or routine

• I will use these terms interchangeably.

• Made up of series of instructions to

perform specific set of operations

4-8

Rules for Paragraph-Names

• Coded in Area A, followed by period

• Follow rules for forming data-names

except may be all digits

– 1010, 1020, 1030, etc. are valid paragraph

names

– We will use combinations of digits and

letters as will be appropriate.

• Must be unique

4-9

Rules for Paragraph-Names

• Examples – of ‘high level modules’– 0000-Main– 1000-initialize– 2000-process– 3000-terminate– x000-edit– x000-update, etc.– At the main module level, we will use

paragraphs in the thousands….

4-10

Procedure Division Statements

• All statements coded in Area B

– Start in position 12.

• Statement begins with verb (READ, MOVE)

Last statement in paragraph ends with

period

• Sentence - series of statements ending with

period

4-11

Batch Program Instructions

• OPEN - to open files to be processed

– “Connect” with files (logical to physical)

• PERFORM UNTIL … END-PERFORM

– Loop to continually READ and process

input records and WRITE results to output

file until there are no more records

• CLOSE - to close files when done processing

• STOP RUN - to end program

4-12

OPEN Statement

• Accesses and makes files available for processing

• Identifies whether files will be used for input or output

• If the machine cannot ‘find’ a file, you will get a notice. Check spellings and path!!! This is an easy error to get.

4-13

OPEN Statement

INPUT file-name-1 … OPEN OUTPUT file-name-2 …

• File-names used must appear in SELECT statement

• File must be accessed with OPEN before reading from or writing to it

• as we have said a number of times.

FORMAT Explain this syntax!!

4-14

OPEN statement example

• May use a single OPEN statement

Open Input Payroll-File Output PayChecks, Err-List

• May use multiple OPEN statements

Open Input Payroll-File Open Output PayChecks Open Output Err-List

4-15

PERFORM UNTIL … END-PERFORM

PERFORM UNTIL condition-1 statement-1 ... [END-PERFORM]

• Repeatedly executes statement(s) between PERFORM UNTIL … END-PERFORM until condition specified in UNTIL clause is met

FORMAT Explain syntax!!

Note: scope terminator

4-16

PERFORM UNTIL … END-PERFORM

• In typical batch program, instructions repeated until no more records in file

• When condition met, program continues with statement following END-PERFORM

4-17

PERFORM UNTIL … END-PERFORM

Perform Until WS-More-Data = 'NO'Read Payroll-File

At EndMove 'NO' To WS-More-Data

Not At EndPerform 200-Process-Record

End-ReadEnd-Perform

EXAMPLENote: indentation, scope terminators,‘pre-condition,’ and ‘post-condition.’

4-18

PERFORM UNTIL … END-PERFORM

• Assume WS-More-Data initially = 'YES'– Condition not met, so statements in PERFORM loop

will be executed

• WS-More-Data set to 'NO' when MOVE statement executed– When condition checked again loop ends since

condition has been met

• I prefer f-eof (flag, end of file) set to 0 initially via a value statement. At End? Move 1 to f-eof. Then, Perform … Until F-EOF=1.

• This is merely a stylistic choice. You may choose what you wish, but use the ‘f’ prefix.

4-19

READ Statement

• Reads one record from file opened for input each time Read statement is executed.

• Transfers record to input storage area– Actually, data is made available via the 01

entry.

• Makes one record available at a time, not entire file

4-20

READ Statement

• READ file-name-1 AT END statement-1 … [NOT AT END statement-2 …] [END-READ]

File-name appears in SELECT statement, FD entry and OPEN

• AT END tests if there are more records

FORMAT Explain the syntax! What is required? not?

4-21

READ Statement• If no more records

– Executes statement(s) after AT END– Typically statement(s) to cause loop containing READ

to end ONCE THE NEXT TEST VIA THE PERFORM IS EXECUTED! THE READ DOES NOT CAUSE THE LOOP TO TERMINATE. THE PERFORM DOES!!

• If more records– Reads in next record– Executes statement(s) after NOT AT END– Typically statement(s) to process record just read – No. Poor style. Abstraction!! Execute a couple of

statements; if more, Perform them via paragraph!

4-22

Simple PERFORM

PERFORM paragraph-name

• To execute instructions in separate paragraph or module one time

• Transfers control to named paragraph• Executes all instructions in paragraph• Control returns to statement following

PERFORM

FORMAT Syntax? This is one form of the Perform.

4-23

Out-Of-Line PERFORM

PERFORM paragraph-name UNTIL condition

• Repeats paragraph until condition met

• Control transfers to named paragraph

• Executes instructions in paragraph and returns

• May loop over and over until ‘true.’

FORMAT

4-24

Out-Of-Line PERFORM - example

…

perform 2000-Process.

<more statements>

2000-Process.

<statements>

3000-Next-Paragraph…

4-25

In-Line PERFORM

PERFORM UNTIL condition statement(s) END-PERFORM

• Repeats statement(s) until condition met • Statement(s) to be executed are in-line, not in

separate paragraph• Statements follow the Perform until ‘header’ and

stop prior to the End-Perform scope terminator.

FORMAT

4-26

In-Line PERFORMPerform until amount = 45

<statements>

<more statements>

end-perform.

no ‘branch’

may be preferable or not – depending on the volume of statements and level of abstraction desired.

4-27

End-Of-Job Processing

• Steps performed after all records processed

• Release all files

• Terminate processing

• Often (not always) done in a paragraph by itself – high level module.

4-28

CLOSE statement

• CLOSE file-name-1 ...

• Close all files opened

• Indicates files no longer needed for processing

• Releases files and deactivates devices

• Always close your files explicitly.

FORMAT

4-29

Closing multiple files

May use a single CLOSE statement Close Payroll-File PayChecks align these Err-List

• May use multiple CLOSE statements Close Payroll-File Close PayChecks Close Err-List

4-30

STOP RUN

• Terminates the program– last ‘executable’ statement in program– last ‘logical’ statement (not physical) in

pgm.

• Usually last instruction in main module

• Execution continues with next paragraph if STOP RUN is omitted– Yes, possible error!

4-31

Interactive Program Statements

• DISPLAY to prompt for input

• ACCEPT to store input in WORKING-STORAGE areas

• Various statements to process input

• DISPLAY to show output

• DISPLAY to ask if there is more input

• ACCEPT to get response

4-32

Interactive Program Statements

• Statements coded in an in-line PERFORM loop

• Repeated until user responds that there is no more input. Use appropriate flag.

• Like batch programs, loop may include simple PERFORM to execute instructions for processing input that are in a separate paragraph

4-33

MOVE statement

MOVE Identifier-1 TO identifier-2

• Copies (not moves) contents of identifier-1 to identifier-2

• Many forms of the ‘move’

FORMAT Syntax???

4-34

WRITE statement

• WRITE record-name-1

• Transmits data from output record area to associated file on device specified

• Record-name is 01 level name following FD for a file opened for output

• READ file-name, WRITE record-name

FORMAT

4-35

Comments in COBOL

• Start with asterisk (*) in column 7

• Use as reminders and explanations of processing performed by program

• Use to describe program in IDENTIFICATION DIVISION

• Use to describe each module in PROCEDURE DIVISION

• We use ‘flower boxes.’ See Standards.

4-36

Batch Programs Review

• Programs that process large quantity of data stored in files

• Require ENVIRONMENT DIVISION

• Require FILE SECTION in DATA DIVISION

• Use OPEN, READ, WRITE, CLOSE verbs to process files

4-37

Interactive Programs Review

• Programs that process individual items rather than large group of items

• Provide quick solution to ACCEPT data, process it and DISPLAY results

4-38

Chapter Summary

• Batch Program Structure– Main module's in-line PERFORM UNTIL

repeatedly executes READ statement– READ gets and processes next record until

there are no more– Files are opened before PERFORM loop

and closed after loop ends

4-39

Chapter Summary

• Interactive Program Structure– Main module's in-line PERFORM UNTIL

repeatedly• Prompts user for input and accepts it• PERFORMs other paragraphs as needed to

process input• Asks user if there is more input

– Loop repeats until user indicates there is no more data

4-40

Chapter Summary

• Paragraph-names coded in Area A and end with period

• All other PROCEDURE DIVISION statements coded in Area B

• Statements executed in order unless– PERFORM UNTIL loop executes– PERFORM transfers control to another

paragraph

4-41

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