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The Procedure Division

The Procedure Division. Chapter 4. Main Two Sections. File Section Used to define files and record formats Field names within records Working Storage Section All accumulators, counters, subscripts, flags, tables, etc.

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The Procedure Division

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  1. The Procedure Division Chapter 4

  2. Main Two Sections • File Section • Used to define files and record formats • Field names within records • Working Storage Section • All accumulators, counters, subscripts, flags, tables, etc. • All constant records, such as print header records and other constant or near-constant records. • But first:

  3. PROCEDURE DIVISION. Contains all the instructions that the computer will execute. Other divisions: identification, environment, data (all i/o areas (file section) and Other data areas (working-storage section) remaining chapters - mostly procedure division... FORMAT OF PROCEDURE DIVISION. . Procedure division divided into paragraphs (modules/routines/functions) . Designed to perform a specific function . Set of operations ===> one function. . A area = paragraph names only . all instructions - b area. RULES FOR PARAGRAPH NAMES: . Must be unique names . Should be descriptive . See our "standards" <<<======yes yes!! . Numbering of modules - four digits

  4. e.g. 1000-initialize; 2000-read, ... From structured design: Statements and sentences: . Verbs start statements. . Statements followed by period = sentence . Paragraphs consist of sentences Sequences of instructions . Statements are executed in order (sequence) unless a "transfer of control" type statement is executed, such as a perform, goto. Well-written programs - written "top-down" . Code main module first. . Lower level modules next. . Progress to lower levels (more detailed)

  5. STRUCTURE OF PROCEDURE DIVISION: PROCEDURE DIVISION. 0000-MAIN. ..... .... 1000-INITIALIZE-TIME-DATE. .... 2000-INITIALIZE-READS. .... ETC. PARAGRAPH NAMES COINCIDE WITH MODULES IN STRUCTURE CHART MAIN + FOUR SUBORDINATE FUNCTIONS ==> FIVE PARAGRAPHS.

  6. PROCEDURE DIVISION STATEMENTS - MAIN MODULE OPEN STATEMENT SYNTAX: OPENINPUT filename1… OUTPUT . UPPERCASE = COBOL RESERVED WORD . UNDERLINE = REQUIRED { } MUST SELECT SOMETHING INSIDE ... MEANS ANY NUMBER OF PRECEDING ITEMS. MUST SAY: OPEN “INPUT” OR “OUTPUT” EACH MUST BE FOLLOWED BY ANY NUMBER OF FILE NAMES... (BUT AT LEAST ONE...) CAN SAY OPEN INPUT FILENAME-1, FILENAME-2. OR OPEN INPUT FILENAME-1. OPEN INPUT FILENAME-2.

  7. A FILE MUST BE (OPENED) BEFORE IT CAN BE PROCESSED! . EVERY FILE NAMED IN A SELECT STATEMENT WILL HAVE AN FD. THIS IMPLIES THAT EACH FILE WILL BE OPENED FOR EITHER INPUT OR OUTPUT. OPEN DESIGNATES THE FILE AS “INPUT” OR “OUTPUT” OPEN CAUSES THE DEVICE (TAPE OR DISK) TO BE ACCESSED TO FIND AND LOCATE FILE. IF OPEN INPUT WITH LABELS (TYPICALLY TAPES OR DISKS) THE HEADER LABEL (IN FRONT OF FILE) IS CHECKED TO SEE IF THIS IS THE CORRECT FILE. IF OPEN OUTPUT WITH LABELS DEVICE IS ACCESSED AND HEADER LABEL IS WRITTEN TO THE FRONT OF THE FILE TO BE CREATED. THEREFORE, LABELS ARE CREATED OR CHECKED.

  8. The Read Statement Transfers data (a record) from input device to the input storage area. (The 01 - process area) Format: (older versions of Cobol) READ filename AT END STATEMENT(S). OR READ filename (COBOL 85) AT END STATEMENT STATEMENT STATEMENT... END-READ. Fourth time we have seen the filename. Transfers one record into the process area: the 01. Read also checks length of record inputted against record description. The At End ==> Did I hit EOF or unsuccessful read? If so,do what follows the at end entry:

  9. In COBOL-85, we have a newer READ statement: READ filename AT END STATEMENTS [ NOT AT END STATEMENTS] [END-READ] EITHER MUST END IN PERIOD OR END-READ. EXAMPLE: Here are two READ statements…. 1. READ SALES-FILE AT END PERFORM 2000-BEGIN-PROCESS PERFORM 2100-CONTINUE. <------ (period) OR (BOOK [ BUT I CHANGED EOF FLAG....] 2. IF AMT = ZERO READ IN-FILE AT END MOVE 1 TO F-EOF END-READ END-IF NOTE THE SCOPE TERMINATORS. GIVEN THE CHOICE, USE OF THE SCOPE TERMINATORS IS STRONGLY ENCOURAGED.

  10. THE PERFORM ... UNTIL FORMAT: (THE ‘TRANSFER OF CONTROL’ PERFORM:) PERFORM procedure-name-1 UNTIL condition OR COBOL 85: (THE ‘IN-LINE’ PERFORM) PERFORM UNTIL condition STATEMENTS STATEMENTS END-PERFORM The Perform is critical for implementing structured design and programming techniques FIRST FORMAT: . The Perform is thee mechanism by which control is transferred from a higher level module to a lower level module. . Perform transfers control to a procedure and repeatedly executes the procedure (module, paragraph...) ‘until’ the cited condition becomes true. . Then, control returns to the next sequential instruction following the perform. (We will spend considerable time on this verb.)

  11. THE PERFORM ... UNTIL Example: (Traditional Perform) 100-SOME-PARAGRAPH. … <Preceding statements> PERFORM 200-CALCULATE-TOTALS UNTIL X > 25 <Next statements following the perform> … 200-CALCULATE-TOTALS. <Statements> <More statements> <SOME STATEMENT THAT ADJUSTS VALUE OF X TOO…> 300-DO-MORE. EXPLAIN…

  12. “IN-LINE PERFORM” (COBOL 85 AND 2002 VERSIONS) PERFORM UNTIL condition .... .... .... END-PERFORM. HERE, USE OF THE SCOPE TERMINATOR IS ESSENTIAL. EXAMPLE: MOVE INPUTFIELD-A TO OUTPUTFIELD-B PERFORM UNTIL F-EOF = 1 READ EMPLOYEE-FILE AT END ... NOT AT END ... END-READ MOVE fields... WRITE some printline... END-PERFORM. Can readily see the “scope” of the Perform via the scope terminators. Called “in line” Perform because there is no explicit branching to a paragraph and returning.

  13. THE NOTION OF THE "PRETEST" AND POST-TEST": Consider: PERFORM 2000-CALCULATE UNTIL EOF = 1. Condition: (EOF = 1) is tested before loop is ever executed. (Pretest). Then, aftereach iteration, the condition is tested repeatedly. (Post-test) Here, EOF is assumed to be set initially to 0 (or at least not 1) 05 F-EOF PIC 9 VALUE 0. OR 05 F-EOF PIC XXX VALUE "YES".

  14. More on Pretest and Post-test Let's consider the notions of 1.. THE PERFORM ... UNTIL AND THE READ STATEMENT (WITH BAD CODING APPROACH ... ) 2. THE PERFORM ... UNTIL AND THE READ STATEMENT (GOOD CODING TECHNIQUE) Poorly-written code: 0000-MAIN-MODULE. OPEN INPUT .... PERFORM 2000-CALC-ROUTINE UNTIL EOF=1. .... 2000-CALC-ROUTINE. READ INPUT-FILE AT END MOVE 1 TO F-EOF END-READ MOVE... COMPUTE…. Are there potential problems?? 2100-NEXT-PARA. Discuss pre-test and post-test…

  15. BETTER WAY TO GO..... 1. SCOPE TERMINATORS; 2..PRIMING READ 0000-MAIN-MODULE. OPEN INPUT .... ... READ INPUT-FILE <---- PRIMING READ (ONE TIME) AT END MOVE 1 TO F-EOF END-READ PERFORM 2000-CALC-ROUTINE <--- PRETEST; POST TEST UNTIL EOF=1 END-PERFORM <--- NICE SCOPE TERMINATOR PERFORM 4000-SUMMARY-ROUTINE CLOSE.... STOP RUN. 2000-CALC-ROUTINE. MOVE... ... <all other computations and /or data manipulations > ... READ INPUT-FILE <--- THE "MAIN" READING OF THE FILE AT END MOVE 1 TO F-EOF <---- MERELY SETS A SWITCH END-READ. DOES NOT STOP LOOP ITERATION LAST STATEMENT IN PARAGRAPH 2100-NEXT-PARA.

  16. END-OF-JOB PROCESSING The Close and Stop Run statements. Typically have two statements part of every EOJ routine: Close files and Stop Run. CLOSE: Releases files and "deactivates" the devices (Releases devices for other assignments....) Format: Close filename1, filename2, ... .. Creates trailer labels (and more on old technologies) .. No "input" or "output" cited. .. Use separate Closes if appropriate to close files in different parts of a larger program. STOP RUN . Last executable statement of program . In Cobol 85 and 2002, the Stop Run will close any opened files, but explicitly Close them anyway.

  17. . THE SIMPLIFIED MOVE. SYNTAX: MOVE identifier-1 TO identifier-2 . Moves data from first field to second . First field remains unchanged EXAMPLES: MOVE ER-NAME-IN TO PR-NAME-OUT MOVE ER-AMT-OF-CREDIT-IN TO PR-AMT-OF-CREDIT-OUT Assumption: fields are of same type (size is also a consideration - later...)

  18. THE WRITE STATEMENT WE READ FILES AND WRITE RECORDS READ a filename. WRITE a record name THE WRITE SPECIFIES WHICH FORMAT IS TO BE WRITTEN We can have multiple output formats (detail records, column headers, report headers, page trailers, etc. We use the FD name (file name) when we Read We use a record name when we Write.

  19. We use the 01 name (record name) when we write. Now: let's look at multiple record format - for output. FD PRINTFILE ... . 01 REPORT-HDR. .... 01 COLUMN-HDR. .... 01 DETAIL REC. ... All are output record formats What are “report headers” and “column headers?” What are “footer” records (“trailer” records) What are “detail” records? Explain.... ____________________________________________________________ INVENTORY REPORT STOCK NUMBER QTY-ON-HAND REORDER POINT UNIT COST WAREHOUSE ....................... ........... .................. .............. .............. ....................... ........... .................. .............. .............. ....................... ........... .................. .............. .............. ....................... ........... .................. .............. .............. ....................... ........... .................. .............. .............. PAGE NO: 14

  20. Where are they written from?

  21. Writing Records So, we must WRITE all records from the single output process area, that is, the 01 area – FOR EACH FILE. Because of the availability of the Value clause, however, we can set up these "constant records" in working-storage, and move them to the print area and ‘write’ them as needed. (Set up records already ‘built’ and ready to be printed…) Otherwise, we would have to build up these constant records each time we wish to write the report trailers and the report header(s)... (since we have but a single output area from which Writing will occur. Do, however, use the file section’s 01 for the detail record (variable data). Why? Explain? Important to note... Looking ahead: Two classes of verbs: 1... Arithmetic, and 2… Conditional Statements

  22. BASIC FORMATS: ADD identifier-1 TO identifier-2 … literal-1 SUBTRACT identifier-1 FROM identifier-2… literal-1 MULTIPLY identifier-1 BY identifier-2 literal-1 DIVIDE identifier-1 INTO identifier-2 literal-1 BASIC IF FORMAT: IF (condition) (statement-1) … [ELSE (statement-2) … END-IF]

  23. Examples Add 1 to Counter Add over-time-pay to regular-pay Subtract 1 from Total Subtract discount-amt from sub-total Multiply amt by 1.05 Divide temp into field-total If a > b Move ….. Write ….. Else Move… Add… End-if IF C = D Write printrec from hdr-1 after advancing Page End-if.

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