1 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

2 Interactive vs Batch Programs Batch programs Process large volumes of input at periodic intervals Input data read in from files Output written to files Can be files on disk, print files, files to be transmitted to a remote location: but files.

3 Files, Records, Fields Field – a single data item: your name; salary; Record – everything to do with a specific topic, such as all the information about YOU to generate your pay check: Your name, ssan, deductions, address, bank account number, hours worked, overtime hours…. File – The grouping of individual records of all employees working in a corporation for whom you want to generate a pay check. Typically read a single record, prepare the output, read next record, and continue until EOF. Book definitions: p. 21

4 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

5 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

6 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

7 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

8 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

9 IDENTIFICATION DIVISION. PROGRAM-ID. CH0102. DATA DIVISION. WORKING-STORAGE SECTION. 01 SALES-AMOUNT PIC 999V SALES-TAX PIC Fields; sizes; numeric 01 MORE-DATA PIC XXX VALUE 'YES'. Field; alphanumeric PROCEDURE DIVISION.instructions: operate on data 100-MAIN. PERFORM UNTIL MORE-DATA = 'NO' DISPLAY 'ENTER SALES AMOUNT AS DOLLARS AND CENTS' ACCEPT SALES-AMOUNTreads / accepts from keyboard COMPUTE SALES-TAX = SALES-AMOUNT *.08 DISPLAY SALES-TAXwrites to keyboard DISPLAY 'IS THER MORE INPUT (YES OR NO)?‘ prompts user ACCEPT MORE-DATAaccepts keyboard input END-PERFORM STOP RUN. Sample COBOL Program – Interactive (no Environment Division)

10 Data Defined in Sample Program Keyed input fields (HOURS, RATE) Output fields (WAGES) Other fields used for processing (MORE- DATA) Wages (not shown) 01 WAGESPIC

11 PICTURE Clause 01 level begins definition of each field much more later on this… 01 has special significance. PICTURE or PIC clause describes Type of data Numeric (PIC 9) Nonnumeric (PIC X) (alphanumeric) Size of field - determined by number of 9’s or X’s

12 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 Wages (not shown) 01 WAGESPIC

13 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

14 PROCEDURE DIVISION Set of instructions to be executed by program Organization of instructions planned before coding begins Pseudo-code, an English-like description of program instructions, used for planning Describes program logic and order in which instructions will be executed

15 PROCEDURE DIVISION PROCEDURE DIVISION includes one paragraph 100- MAIN Note: program here is horribly simple, as we would expect at this time. There is only one paragraph (module) and a structure chart (architectural design) is almost meaningless – would contain a single box… List of instructions that follow make up paragraph Period follows last statement in paragraph (STOP RUN.) Main processing controlled by PERFORM … END- PERFORM loop END-PERFORM is called a ‘scope terminator.’ VERY important!

16 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

17 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 (Note the indentation of code within the loop. This is essential to good programming style!)

18 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

19 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 (see page 21) Employee name, hours and rate data called fields

20 Sample Batch Program Calculated results (Wages) stored in file instead of displayed on screen (but can be both displayed as well as stored in a 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 I disagree. Most input data is NOT spaced for printing!!! Fields are all contiguous for important reasons! (will discuss)

21 COBOL Divisions All four divisions included for batch programs IDENTIFICATION DIVISION first with required PROGRAM-ID paragraph ENVIRONMENT DIVISION CONFIGURATION SECTION – not required. INPUT-OUTPUT SECTION assigns input and output files to specific devices. required to name (called logical file names or programmer-defined file names) files and associate them with specific devices, such as a CD or disk or …

22 DATA DIVISION (will be repeating this many times) FILE SECTION describes format of input and output files Characteristics of the file itself Characteristics of the records and their fields. 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

23 PROCEDURE DIVISION Contains instructions to be executed by computer Instructions executed in order they appear Includes two paragraphs with period at end of each. Let’s consider the program in your textbook. This is also assignment #1 to be turned in later. First, let’s overview…

24 IDENTIFICATION DIVISION. PROGRAM-ID. SAMPLE AUTHOR. YOUR-NAME-PLEASE. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT EMPLOYEE-DATA ASSIGN TO EMP-DAT. SELECT PAYROLL-LISTING ASSIGN TO PRINTER. DATA DIVISION. FILE SECTION. FDEMPLOYEE-DATA. 01EMPLOYEE-RECORD. 05EMPLOYEE-NAME-INPIC X(20). 05HOURS-WORKED-INPIC HOURLY-RATE-INPIC 9V99. FDPAYROLL-LISTING. 01PRINT-REC. 05PIC X(20). 05NAME-OUTPIC X(20). 05PIC X(10). 05HOURS-OUTPIC PIC X(8). 05RATE-OUTPIC PIC XXXXXX. 05WEEKLY-WAGES-OUTPIC WORKING-STORAGE SECTION. 01ARE-THERE-MORE-RECORDSPIC XXX VALUE ‘YES’.

25 PROCEDURE DIVISION. 100-MAIN-MODULE. OPEN INPUT EMPLOYEE-DATA OUTPUT PAYROLL-LISTING. PERFORM UNTIL ARE-THERE-MORE-RECORDS = ‘NO’ READ EMPLOYEE-DATA AT END MOVE ‘NO’ TO ARE-THERE-MORE-RECORDS NOT AT END PERFORM 200-WAGE-ROUTINE END-READ END-PERFORM CLOSE EMPLOYEE-DATA PAYROLL-LISTING STOP RUN. 200-WAGE-ROUTINE. MOVE SPACES TO PRINT-REC MOVE EMPLOYEE-NAME-IN TO NAME-OUT MOVE HOURS-WORKED-IN TO HOURS-OUT MOVE HOURLY-RATE-IN TO RATE-OUT MULTIPLY HOURS-WORKED-IN BY HOURLY-RATE-IN GIVING WEEKLY-WAGES-OUT WRITE PRINT-REC. OBSERVE INPUT AND OUTPUT ON P. 24.

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)

27 READ Statement Reads one record into program storage area Record must be in storage to use it Entire record ‘read into’ the Process Area (the 01 area) Takes one of two actions depending on whether record was read

28 READ Statement - 1 PERFORM instruction after NOT AT END executed when a successful read occurs: Statements in paragraph 200-WAGE-ROUTINE executed to process record Control remains within the Perform. Condition is evaluated and is false, so the loop iterates.

29 READ Statement - 2 If no more records are available, MOVE instruction after AT END executed 'NO ' moved to ARE-THERE-MORE- RECORDS, ends loop Control returns to the Perform which determines that the condition is now True and control passes to the statement following the Perform.

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

31  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

32 COMMENTS1 Interactive Programs don’t need Environment Division Batch Programs Need all four divisions – in order Environment Division names / associates files with devices. machine / implementation dependent. Assign to clauses will differ (will inform you…)

33 COMMENTS2 Data Division will always have a File Section describes the file in general and the records with their fields in particular. Provides the sizes and classification of fields and relative placement of data in input and output records All data fields are named! (Constants {later} are treated separately) All fields must be defined with their sizes and type of data expected. Name files with meaningful names.

34 COMMENTS3 Filler – reserved word Many reserved words – have special meanings. ARE-THERE-MORE-RECORDS is really a flag field. I prefer EOF. Will discuss more later. types of data: numeric pic 9 alphanumeric pic x (non-numeric) alphabetic pic A (not used much anymore). Data name rules – later Editing characters (decimals, commas…) later.