1. 4-1 Coding Complete COBOL Programs: The PROCEDURE DIVISION Chapter 4

2. 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

3. 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. 4-4 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

5. 4-5 PROCEDURE DIVISION Contains instructions to Read data Process data Produce output Perform end-of-job operations

6. 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

7. 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

8. 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

9. 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….

10. 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

11. 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

12. 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.

13. 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!!

14. 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

15. 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

16. 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

17. 4-17 PERFORM UNTIL … END-PERFORM Perform Until WS-More-Data = 'NO' Read Payroll-File At End Move 'NO' To WS-More-Data Not At End Perform 200-Process-Record End-Read End-Perform EXAMPLE Note: indentation, scope terminators, ‘pre-condition,’ and ‘post-condition.’

18. 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.

19. 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

20. 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?

21. 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!

22. 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.

23. 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

24. 4-24 Out-Of-Line PERFORM - example … perform 2000-Process. 2000-Process. 3000-Next-Paragraph…

25. 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

26. 4-26 In-Line PERFORM Perform until amount = 45 end-perform. no ‘branch’ may be preferable or not – depending on the volume of statements and level of abstraction desired.

27. 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.

28. 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

29. 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

30. 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!

31. 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

32. 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

33. 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???

34. 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

35. 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.

36. 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

37. 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

38. 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

39. 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

40. 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

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