CHAPTER 4 Coding Complete COBOL Programs

1
CHAPTER 4Coding Complete COBOL Programs

• A Closer Look at the PROCEDURE DIVISION and the
  PERFORM Statement

2
A REVIEW OF THE FIRST THREE DIVISIONS

• The IDENTIFICATION and ENVIRONMENT DIVISIONs
  supply information about the nature of the
  program and the specific equipment and files.
• The FILE SECTION of the DATA DIVISION defines the
  input and output records.

3
A REVIEW OF THE FIRST THREE DIVISIONS

• The WORKING-STORAGE SECTION of the DATA DIVISION
  is used for defining any areas not part of input
  and output files.
• The instructions in the PROCEDURE DIVISION read
  and process the data and produce the output
  information.

4
THE FORMAT OF THE PROCEDURE DIVISION

• PARAGRAPHS THAT SERVE AS MODULES Structure
  Chart documentation serves as the basis for
  determining paragraphs needed
• The PROCEDURE DIVISION is divided into
  paragraphs.
• Each paragraph is an independent module or
  routine that includes a series of instructions
  designed to perform a specific set of operations.
• Using the structure chart as a guide paragraphs
  are written from the top down left to right -
  ie. 100s, 200s, 300s etc.

5
THE FORMAT OF THE PROCEDURE DIVISION

• Paragraph-names, like the PROCEDURE DIVISION
  entry itself, are coded in Area A.
• All other entries in the PROCEDURE DIVISION are
  coded in Area B.
• Paragraph-names, like the PROCEDURE DIVISION
  entry, end with a period.

6
THE FORMAT OF THE PROCEDURE DIVISION

• PARAGRAPHS THAT SERVE AS MODULES
• Rules for forming paragraph-names are the same as
  rules for forming data-names except that a
  paragraph-name may have all digits.
• Paragraph-names must be unique, meaning that two
  paragraphs may not have the same name.
• Paragraph names must be meaningful ie. Reflect
  the purpose of the paragraph
• Similarly, a data-name cannot also serve as a
  paragraph-name.

7
Paragraphs That Serve as Modules

• We will use descriptive paragraph-names along
  with a numeric prefix such as 200-PROCESS-RTN to
  identify the type of paragraph.
• A paragraph with a prefix of 200- is located
  after paragraph 100--XXX and before paragraph
  300-- YYY.

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Statements within Paragraphs

• Each paragraph in a COBOL program consists of
  statements, where a statement begins with a verb
  such as READ, MOVE, or WRITE, or a condition such
  as IF A B ....
• As noted, all COBOL statements are coded in Area
  B whereas paragraph-names are coded in Area A.
• Statements that end with a period are called
  sentences.
• Use periods only
• After Paragraph Names
• After the last statement in a paragraph

9
Statements within Paragraphs

• With COBOL 85 only the last statement in a
  paragraph ends with a period.
• With COBOL 74, each statement typically ends
  with a period.
• Recommended that each statement be coded on an
  individual line. And use of indentation
• Makes programs much easier to read and debug.

10
THE SEQUENCE OF INSTRUCTIONS IN A PROGRAM

• Instructions are typically executed in sequence
• Unless a PERFORM statement is encountered.
• PERFORM UNTIL ... END-PERFORM
• A loop that repeatedly executes
• All the statements between PERFORM and
  END-PERFORM
• Until some condition is met
• Instruction within the loop must do something to
  be sure the condition is met
• Known as an inline PERFORM
• A PERFORM paragraph-name UNTIL ....
• Another form of using PERFORM to implement a loop

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PERFORM .... UNTIL

• Pretest loop the condition stated is tested
• If condition is not met paragraph / instructions
  are executed
• Upon return - start over at Step 1
• If condition is met execution of statements
  continues with the statement following the LOOP

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PERFORM UNTIL . . . END-PERFORM Statement A
Structured Programming Technique

• The basic instruction format of the PERFORM UNTIL
  ... END- PERFORM statement is as follows
• PERFORM
• UNTIL condition-1
• .
• .
• .
• END-PERFORM COBOL 85 only

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THE SEQUENCE OF INSTRUCTIONS IN A PROGRAM

• A PERFORM paragraph-name
• An instruction that temporarily transfers control
  to another paragraph
• Instructions are executed 1 time
• Program control is returned to statement
  following the PERFORM
• Program knows when to return when
• A new PARAGRAPH is encountered or
• No more program statements to execute

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The Top-Down Approach for Coding Paragraphs

• Well-designed programs are written using a
  top-down approach.
• This means that the main module is coded first
• subsequent modules are coded from the major
  level to the detail level.
• Endeavor to code the more general paragraphs
  first and end with the most detailed ones.
• Facilitates incremental testing
• Write the paragraphs at one level
• Lower level paragraphs at stubs (ie. No code)
• Test
• Proceed to write paragraphs at next level
• Go step 2

15
STATEMENTS TYPICALLY CODED IN THE MAIN MODULE OF
BATCH PROGRAMS
16
OPEN Statement

• The OPEN statement accesses the files in a
  program and indicates which are input and which
  are output. It has the following instruction
  format
• Format
• OPEN INPUT file-name-1 . . .
• OUTPUT file-name-2 . . .
• OPEN INPUT file-name-1 ...
• OPEN OUTPUT file-name-2 ...

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OPEN
OPEN INPUT file-name-1 ...
OUTPUT file-name-2 ...
18
OPEN STATEMENT

• A REVIEW OF INSTRUCTION FORMAT SPECIFICATIONS
• 1. Uppercase words are COBOL reserved words.
• 2. Underlined words are required in the
  statement or option specified.
• 3. Lowercase entries are user-defined words.
• 4. Braces denote that at least one of the
  enclosed items is required.

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OPEN STATEMENT

• A REVIEW OF INSTRUCTION FORMAT SPECIFICATIONS
• 5. Brackets denote that the enclosed item is
  optional.
• 6. Punctuation, when included in the format, is
  required.
• 7. The use of three dots or ellipses (. . .)
  indicates that additional entries of the same
  type (a file-name in this case) may be repeated
  if desired.

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OPEN STATEMENT

• FUNCTIONS OF THE OPEN STATEMENT
• 1. Indicates which files will be input and which
  will be output.
• 2. Makes the files available for
  processing Locates INPUT file if not found a
  runtime error Allocates space for the
  OUPUT filr
• 3. Performs header label routines if label
  records are STANDARD.

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OPEN STATEMENT

• DEBUGGING TIPS CODING GUIDELINES
• Indent each line within an OPEN sentence.
• This makes a program more readable.
• For the OPEN sentence, we typically indent so
  that the words INPUT and OUTPUT are aligned.
  For other entries we indent four spaces.

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OPEN STATEMENT

• DEBUGGING TIPS CODING GUIDELINES
• AN EXAMPLE
• OPEN INPUT OLD-MASTER-IN
• TRANS-FILE
• OUTPUT NEW-MASTER-OUT
• ERROR-LIST.

23
OPEN STATEMENT

• DEBUGGING TIPS CODING GUIDELINES
• For output disk files, the ASSIGN clause of a
  SELECT statement often specifies the name the
  file is to be saved as
• SELECT SALES-FILE ASSIGN TO A\DATA100.DAT
  ORGANIZATION IS LINE SEQUENTIAL.

24
READ Statement

• Typically, after an input file has been opened,
  the PERFORM ... END-PERFORM loop, which begins
  with a READ, is executed.
• A READ statement transmits data from the input
  device, assigned in the ENVIRONMENT DIVISION, to
  the input storage area, defined in the FILE
  SECTION of the DATA DIVISION.

25
READ Statement

• The following is a partial instruction format for
  a READ statement
• Format
• READ file-name-1
• AT END statement-1 . . .
• NOT AT END statement-2 . . .
• END-READ COBOL 85 ONLY

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READ Statement

• AT END
• READ test to see if there are more records on the
  file if not the instruction(s) following the AT
  END clause are executed
• NOT AT END
• If a successful READ the instruction(s) following
  the NOT AT END are executed
• Program execution then continues with the
  instruction following the END-READ

27
READ Statement

• The file-name specified in the READ statement
  appears in three previous places in the program
• 1. The SELECT statement, indicating the file-name
  and the device or implementor-name assigned to
  the file.
• If a file is stored on a disk, for example, a
  READ operation transmits data from the disk to
  the input area.
• 2. The FD entry, describing the file and its
  format.
• 3. The OPEN statement, accessing the file and
  activating the device.

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READ Statement

• The primary function of the READ statement is to
  transmit one data record to the input area
  reserved for that file.
• Each time a READ statement is executed, one
  record is read into primary storage - not the
  entire file.

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DEBUGGING TIP

• Code the AT END and NOT AT END clause on separate
  lines and indent them for readability.
• If an error occurs, you will be able to more
  easily identify the problem because the line
  number of the error is specified.
• Common programming error trying to continued to
  process records whrn END-OF-FILE has been
  encountered

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QUESTIONS?
31
End-of-Job Processing The CLOSE and STOP RUN
Statements

• The CLOSE Statement
• Files must be accessed or activated by an OPEN
  statement before data may be read or written.
• Similarly, a CLOSE statement is coded at the end
  of the job after all records have been processed
  to release these files and deactivate the devices.

32
End-of-Job Processing The CLOSE and STOP RUN
Statements

• The format of the CLOSE is
• CLOSE file-name-1 . . .

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End-of-Job Processing The CLOSE and STOP RUN
Statements

• The STOP RUN Statement
• The STOP RUN instruction tells the computer to
  terminate the program.
• All programs should include a STOP RUN statement
  to end the run.
• The STOP RUN is usually the last instruction in
  the main module.

34
STATEMENTS TYPICALLY CODED FOR PROCESSING INPUT
RECORDS AND PRODUCING OUTPUT RECORDS
35
Simplified MOVE Statement

• A simple MOVE statement has the following basic
  instruction format
• MOVE identifier-1 TO identifier-2
• Fields in main memory may be moved to other
  fields with the use of the MOVE instruction.
• The word identifier'' means data-name''.

36
WRITE Statement

• The WRITE instruction takes data in the output
  area defined in the DATA DIVISION and transmits
  it to the device specified in the ENVIRONMENT
  DIVISION.
• A simple WRITE statement has the following
  format
• WRITE record-name-1

37
WRITE Statement

• Format
• WRITE record-name-1 AFTER ADVANCING n
  LINE(S) AFTER ADVANCING PAGE
• Note that although files are read, we write
  records.
• The record-name appears on the 01 level and is
  generally subdivided into fields. The record
  description specifies the format of the output.
• With each WRITE instruction, we tell the computer
  to write data that is in the output area.

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NOTE Carefully

• You READ a file
• You WRITE a record

39
LOOKING AHEAD AN INTRODUCTION TO ARITHMETIC and
CONDITIONAL verbs
40
The four basic arithmetic verbs have the
following simple formats

• ADD identifier-1 literal-1 TO
  identifier-2
• SUBTRACT identifier-1 literal-1 FROM
  identifier-2
• MULTIPLY identifier-1 literal-1 BY
  identifier-2
• DIVIDE identifier-1 literal-1 INTO
  identifier-2
• Result always stored in last identifier.

41
The four basic arithmetic verbs have the
following another format

• ADD identifier-1 literal-1 TO identifier-2
  GIVING indentifer-3
• SUBTRACT identifier-1 literal-1 FROM
  identifier-2 GIVING indentifer-3
• MULTIPLY identifier-1 literal-1 BY
  identifier-2 GIVING indentifer-3
• DIVIDE identifier-1 literal-1 INTO
  identifier-2 GIVING indentifer-3
• Result always stored in last identifier.

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The basic instruction format for a conditional IF
is as follows

• Format
  
  IF condition-1
• THEN imperative-statement-1. . .
• ELSE
  
  imperative-statement-2 . . .
• END-IF
• Note that the ELSE clause is optional. Numerous
  statements can follow each IF or ELSE clause.

43
The simple conditions that can be tested are as
follows

• (identifier-1)
• (or IS EQUAL TO) identifier-2
• lt (or IS LESS THAN) literal-1
• gt (or IS GREATER THAN)

44
REVIEW OF COMMENTS IN COBOL
45
COMMENTS IN COBOL

• An asterisk () in column 7 (the continuation
  position) of any line makes the entire line a
  comment
• Use comments freely to make your program
  user-friendly and easier to understand.

46
Coding Guidelines for PROCEDURE DIVISION Entries

• 1. Each clause should be on a separate line
  indented for readability. For example
• READ ...
• AT END ...
• NOT AT END ...
• END-READ.

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Coding Guidelines for PROCEDURE DIVISION Entries

• 2. Each paragraph-name should begin with a
  sequence number that helps to pinpoint the
  location of the paragraph
• a descriptive name should follow this number
  (e.g., 100-MAIN-MODULE, 200-CALC-RTN).
• 3. The last statement in a paragraph should
  always end with a period.

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COBOL 2000 CHANGES

• You will be able to code comments on a line, even
  those with instructions
• gt will be used to add a comment to a line.
• After gt appears, characters to the end of the
  line will not be compiled.

49
YEAR 2000-COMPLIANT DATE FIELDS

• Older, legacy programs, using only two-digit for
  the year, will no longer accurately depict the
  date beginning in the year 2000.
• Problems associated with dates after this are
  referred to as the Year 2000 Problem or Y2K
  Problem.

50
YEAR 2000-COMPLIANT DATE FIELDS

• Fixes for the Y2K problem are not all that
  difficult
• They are just costly and time-consuming.
• In addition to program source changes, all files
  on which they operate will also need to be
  modified.

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CHAPTER SUMMARY

• COBOL 85
  PROCEDURE DIVISION.
  paragraph-name-1.
  
  OPEN INPUT file-name-1
  OUTPUT file-name-2
  PERFORM
  UNTIL ARE-THERE-MORE-RECORDS 'NO
• READ file-name-1
  AT END
  MOVE 'NO ' TO ARE-
  THERE-MORE-RECORDS NOT AT END
  PERFORM paragraph-name-2
  
  END-READ
  
  END-PERFORM
  
  CLOSE file-name-1
  
  file-name-2
  
  STOP RUN.

52
CHAPTER SUMMARY

• A. Paragraph-names are coded in Area A and end
  with a period.
• Rules for forming paragraph-names are the same as
  for data-names except that a paragraph-name can
  have all digits.
• We use a prefix such as 100-, 200- , 300-, along
  with a descriptive name such as HEADING- RTN or
  MAIN-MODULE.
• A paragraph with a prefix of 200- is located
  after a paragraph with prefix 100- and before a
  paragraph with prefix 300-.

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CHAPTER SUMMARY

• B. All statements are coded in Area B.
• We recommend coding one statement per line.
• C. Instructions are executed in the order in
  which they appear unless a PERFORM statement
  executes a loop or transfers control.

54
CHAPTER SUMMARY

• D. When the main module's
• PERFORM UNTIL ... END-PERFORM
• is encountered, the loop specified is executed
  repeatedly until the condition most often that
  condition is met when there are no more input
  records.