Transcript Interactive vs Batch Programs

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
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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.
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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
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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
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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
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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
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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
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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
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IDENTIFICATION DIVISION.
PROGRAM-ID. CH0102.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 SALES-AMOUNT PIC 999V99.
01 SALES-TAX
PIC 99.99.
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-AMOUNT
reads / accepts from keyboard
COMPUTE SALES-TAX = SALES-AMOUNT * .08
DISPLAY SALES-TAX
writes to keyboard
DISPLAY 'IS THER MORE INPUT (YES OR NO)?‘ prompts user
ACCEPT MORE-DATA
accepts keyboard input
END-PERFORM
STOP RUN.
Sample COBOL Program – Interactive (no Environment Division)
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Data Defined in Sample Program
 Keyed input fields (HOURS, RATE)
 Output fields (WAGES)
 Other fields used for processing (MORE-
DATA)
 Wages (not shown)
01 WAGES
PIC 999.99.
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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
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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 WAGES
PIC 999.99.
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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
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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
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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!
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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
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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!)
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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
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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
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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)
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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 …
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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
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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…
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IDENTIFICATION DIVISION. <alignment and indentation!>
PROGRAM-ID. SAMPLE
<divisions, sections, paragraphs, sentences statements>
AUTHOR. YOUR-NAME-PLEASE.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL. SELECT EMPLOYEE-DATA ASSIGN TO EMP-DAT.
SELECT PAYROLL-LISTING ASSIGN TO PRINTER. <will change>
DATA DIVISION.
<input and output files and formats; working storage…>
FILE SECTION.
FD
EMPLOYEE-DATA.
01
EMPLOYEE-RECORD.
05
EMPLOYEE-NAME-IN
PIC X(20).
05
HOURS-WORKED-IN
PIC 99.
05
HOURLY-RATE-IN
PIC 9V99. <alignment; pic clauses>
FD
PAYROLL-LISTING.
01
PRINT-REC.
05
PIC X(20).
05
NAME-OUT
PIC X(20).
05
PIC X(10).
05
HOURS-OUT
PIC 99.
05
PIC X(8).
05
RATE-OUT
PIC 9.99.
05
PIC XXXXXX.
05
WEEKLY-WAGES-OUT
PIC 999.99.
WORKING-STORAGE SECTION.
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01
ARE-THERE-MORE-RECORDS
PIC XXX VALUE ‘YES’. <Value clause>
PROCEDURE DIVISION. <instructions to operate (read. print) / manipulate data>
100-MAIN-MODULE.
OPEN
INPUT EMPLOYEE-DATA
<must have for files>
OUTPUT PAYROLL-LISTING.
PERFORM UNTIL ARE-THERE-MORE-RECORDS = ‘NO’ <loop construct>
READ EMPLOYEE-DATA
<note the indentation!!!>
AT END
MOVE ‘NO’ TO ARE-THERE-MORE-RECORDS
NOT AT END
PERFORM 200-WAGE-ROUTINE
END-READ
<note the ‘control’ here – not detail!>
END-PERFORM
<note: scope terminators end-read; end-perform>
CLOSE EMPLOYEE-DATA
PAYROLL-LISTING
STOP RUN.
<last logical executable statement in program>
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.
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100-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-WAGEROUTINE to process each record
 CLOSEs files after all records read
 Ends program (STOP RUN)
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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
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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.
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READ Statement - 2
 If no more records are available, MOVE
instruction after AT END executed


'NO ' moved to ARE-THERE-MORERECORDS, ends loop
Control returns to the Perform which
determines that the condition is now True and
control passes to the statement following the
Perform.
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200-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
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 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
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COMMENTS
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 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…)
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COMMENTS
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 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.
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COMMENTS
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 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.
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