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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.01 ARE-THERE-MORE-RECORDS PIC XXX VALUE ‘YES’. <Value clause>
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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 ENDMOVE ‘NO’ TO ARE-THERE-MORE-RECORDS
NOT AT ENDPERFORM 200-WAGE-ROUTINE
END-READ <note the ‘control’ here – not detail!>END-PERFORM <note: scope terminators end-read; end-perform>CLOSE EMPLOYEE-DATA
PAYROLL-LISTINGSTOP RUN. <last logical executable statement in program>
200-WAGE-ROUTINE.MOVE SPACES TO PRINT-RECMOVE EMPLOYEE-NAME-IN TO NAME-OUTMOVE HOURS-WORKED-IN TO HOURS-OUTMOVE HOURLY-RATE-IN TO RATE-OUTMULTIPLY HOURS-WORKED-IN BY HOURLY-RATE-IN
GIVING WEEKLY-WAGES-OUTWRITE 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-WAGE-
ROUTINE 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-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.
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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 1
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 2 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 3 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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