COBOL Lecture 5

-----------------------------------------------------------------------
PERFORM Statement -- is used to execute a module repeatedly from multiple locations in the program.

The PERFORM paragraph-name statement jumps "out-of-line" by transferring control to the first executable statement in the paragraph referenced.

When the last statement of the PERFORMed procedure is complete, or an EXIT statement is executed, control jumps back to the statement immediately following the calling PERFORM.
-----------------------------------------------------------------------
The EXIT statement. When reached, the EXIT becomes the end point in a paragraph and the remaining statements in the paragraph are bypassed.

A-A-CALCULATIONS.
    IF REGION-A-CALLS-IN = ZERO
       EXIT.
    COMPUTE REGION-A-CHARGE-OUT WS-AREA-A-CHARGE
          = REGION-A-CALLS-IN   * .05
          + REGION-A-MINUTES-IN * .03.
-------------------------------------------------------
Format for a simple PERFORM.

PERFORM paragraph-name.

This performs PARA-A a single time.

PERFORM PARA-A.
- - - - - - - - - - - - - - - - - - - - - - - - - - - -
PERFORM paragraph-name THRU paragraph-name-2

This performs PARA-A through PARA-C a single time.

PERFORM PARA-A THRU PARA-C
- - - - - - -- - - - - - - - - - - - - - - - - - - - -
PERFORM paragraph-name THRU paragraph-name-2 [ {identifier } TIMES ]
[{numeric }]

PARA-A is performed 5 times each with either of the following code segments

    PERFORM PARA-A 5 TIMES
    or
    MOVE 5 TO LOOP-CONTROL (define LOOP-CONTROL in working-storage)
    PERFORM PARA-A LOOP-CONTROL TIMES
--------------------------------------------------------------------
PERFORM paragraph-name UNTIL some-condition-is-met

This format is a method of performing the paragraph-name a variable number of times until some condition is true.

The condition is a test of the value within a variable.

        UNTIL SWITCH = 'YES'
        UNTIL REC-COUNT > 20
        UNTIL END-OF-FILE OR TOTAL-INPUT > 100

Initialize the tested variable(s) prior to the PERFORM statement.

MOVE 'NO' TO SWITCH.
PERFORM PARA-A UNTIL SWITCH = 'YES'

If the test is false, the paragraph will be performed.

MOVE ZERO TO REC-COUNT
PERFORM PARA-A UNTIL REC-COUNT > 9

If the test is true, the loop will not be performed

MOVE 10 TO REC-COUNT
PERFORM PARA-A UNTIL REC-COUNT > 9

The test is done first but could be done after execution of the paragraph if "WITH TEST AFTER" is used.

        MOVE 10 TO REC-COUNT
        PERFORM PARA-A WITH TEST AFTER
        UNTIL REC-COUNT > 9

IMPORTANT! A statement in the performed paragraph is needed that will eventually turn off the loop by satisfying the condition tested

If the condition is a count, then there should be a count increment.

UNTIL REC-COUNT > 10 should have an ADD 1 TO REC-COUNT

If the condition is a switch, then the switch should be set in the loop.

        UNTIL SWITCH = 'YES'   should have a   MOVE 'YES' TO SWITCH
-----------------------------------------------------------------------
        PERFORM paragraph-name
            VARYING a-variable-value FROM start-value BY increment-value
            UNTIL some-condition-is-met

    The advantage of this statement is that it offers a good
    "locality of reference." The variable and its increment are
    close together. The other PERFORM statements might have the
    initializing statement, the increment statement and the PERFORM
    far from each other and therefore difficult to trace..

With variables of

01 TEST-1 PIC S999.
01 FILE-SWITCH PIC XXX VALUE SPACES.

The following will execute 10 times.

        PERFORM PARA-A
            VARYING TEST-1 FROM 1 BY 1
            UNTIL TEST-1 > 10

The increment value could also be a negative value

        PERFORM PARA-A
            VARYING TEST-1 FROM 100 BY -1
            UNTIL TEST-1 = ZEROS.

The condition tested could be complex and controlled by the increment value as well as other switches set within PARA-A.

        PERFORM PARA-A
            VARYING TEST-1 FROM 1 BY 1
            UNTIL TEST-1 > 1000
             OR FILE-SWITCH = 'EOF'

In addition to the counter countrolled by the VARYING, this code depends on a statement somewhere in PARA-A that moves 'EOF' to FILE-switch.

-----------------------------------------------------------------------------
With nested PERFORMS, every single execution of the outer PERFORM causes a complete looping of the inner PERFORM.

01 INNER-1 PIC 9.
01 OUTER-1 PIC 9.

     PERFORM    WITH TEST AFTER
         VARYING OUTER-1 FROM 0 BY 1
         UNTIL OUTER-1 = 9

         PERFORM WITH TEST AFTER
             VARYING INNER-1 FROM 0 BY 1
             UNTIL INNER-1 = 9

DISPLAY OUTER-1 INNER-1

END-PERFORM

The above displays what starting value ____
through what ending value____?
------------------------------------------------------------------
The above example utilizes "in-line" PERFORMS which do not require a named paragraph to refer to.

The range of statements for "in-line" PERFORMS

start at the PERFORM and
stop at the END-PERFORM.

Every PERFORM format discussed for the "out-of-line" PERFORM
is also applicable to the "in-line" PERFORM.
----------------------------------------------------------------
The CLASS tests are

        NUMERIC              ALPHABETIC
        ALPHABETIC-LOWER     ALPHABETIC-UPPER
        ALPHANUMERIC         ALPHANUMERIC-EDITED
----------------------------------------------------------------
    The SIGN tests are

POSITIVE NEGATIVE ZERO
---------------------------------------------------------------
Reference modification --

can be used to manipulate part of a field.

FORMAT

field-name (location-of-starting-position : length)

If fields are

    01 GROUP-OF-FIELDS.
        05 NUMERIC-1 PIC 9(10) VALUE ZEROS.
        05 FIELD-A PIC X(11) VALUE 'START VALUE'
        05 FIELD-B PIC X(11) VALUE 'START VALUE'

This will alter FIELD-A to 'START-VALUE'

MOVE '-' TO FIELD-A (6:1)

This will alter FIELD-A to 'VALUE-START'

        MOVE FIELD-B (7:5) TO FIELD-A (1:5)
        MOVE FIELD-B (1:5) TO FIELD-B (7:5)
        MOVE '-' TO FIELD-A (6:1)

This will alter FIELD-A to '**TRY IT***"

MOVE ALL '*' TO FIELD-A
MOVE 'TRY IT' TO FIELD-A (3:6)

The following will make NUMERIC-1 contain "0500000010".

MOVE 1 TO NUMERIC-VALUE1(9:1)
MOVE 5 TO NUMERIC-VALUE1 (2:1)

The following will make NUMERIC-1 contain " 5 1 ".

INSPECT GROUP-OF-FIELDS REPLACING ALL "0" BY SPACES.

INSPECT can count parts of field that match a comparison string.

--------------------------------------------------------------------
INSPECT field TALLYING add-to-field FOR CHARACTERS
ALL 'comparison'
LEADING 'comparison'

field is either a group item or an elementary USAGE DISPLAY item

add-to-field is a counter that is incremented by the INSPECT. If the programmer wants accumulations to start a zero, then MOVE ZERO TO add-to-field prior to executing the INSPECT.

CHARACTERS is the number of positions counted in the field inspected

'comparison' is either a constant of 1 or more characters

such as 'A' or 'ABC' or 1 or 321.

Or an elementary USAGE DISPLAY field of 1 or more

characters containing values used for the match.

Or a figurative constant treated as a 1 character match.

ALL to examine the entire field for a match

LEADING to examine the leading matches in a field

BEFORE stop-string

Starts at the left of a string and stops when the stop-string
or end of field is encountered.

AFTER start-string

Starts to the right of the start-string and stops at the end of
the field.

---------------------------------------------------------------------------

Starting with the following fields

        01 COUNT-1 PIC 99 VALUE ZEROS.
        01 FIELD-1 PIC X(11) VALUE 'ACHIEVEMENT'.
        01 COUNT-2 PIC 99 VALUE ZEROS.

After execution of the following, COUNT-1 will be at 3.

MOVE ZEROS TO COUNT-1
INSPECT FIELD-1 TALLYING COUNT-1 FOR ALL 'E'.

After the following, COUNT-1 will be at 4.

INSPECT FIELD-1 TALLYING COUNT-1 FOR LEADING 'ACH'.

After the following, COUNT-1 will be at 2.

MOVE ZEROS TO FIELD-1
INSPECT FIELD-1 TALLYING COUNT-1 FOR ALL 'M' ALL 'T'

After the following, COUNT-1 will be at 3, COUNT-2 will be at 1.

INSPECT FIELD-1 TALLYING COUNT-1 FOR ALL 'C'
COUNT-2 FOR ALL 'T'

After the following, COUNT-1 will be at 3.

INSPECT FIELD-1 TALLYING COUNT-1 FOR ALL 'C'
AFTER INITIAL 'I'

---------------------------------------------------------------

Start with the following fields

        01 FIELD-1 PIC X(11) VALUE 'ACHIUVUMUNT'.
        01 FIELD-2 PIC X(11) VALUE 'PPPORTUNITY'.
        01 FIELD-3 PIC X(11) VALUE 'PERSISTLNCE'.

What is the value in the proceeding fields after execution of the INSPECT statements that follow?

         INSPECT FIELD-1 REPLACING ALL 'U' BY 'E'
         INSPECT FIELD-2 REPLACING FIRST 'P' BY 'O'
         INSPECT FIELD-3 REPLACING 'L' BY 'E' AFTER INITIAL 'T'
------------------------------------------------------------------

        INSPECT field REPLACING CHARACTERS
                                 ALL 'comparison'
                                 LEADING 'comparison'
                                 FIRST 'comparison'
                       BY new-string

This INSPECT replaces parts of field that match the comparison. The comparison and new string should have the same number of characters.

BEFORE INITIAL stop-string

Starts at the left of a string and stops when the stop-string or
end of field is encountered.

AFTER INITIAL start-string

Starts to the right of the start-string and stops at the end of
the field.
-----------------------------------------------------------------------------------------------------------

REDEFINES CLAUSE -- a STORAGE space can have multiple definitions.

        01 GROUP-1.
            05 NUMBER-1                  PIC 9(5).
            05 AN-1 REDEFINES NUMBER-1   PIC X(5).
            05 SUB-GROUP-1 REDEFINES NUMBER-1.
                10 SUB-1-NUMBER          PIC 99.
                10 SUB-1-CODE            PIC XXX.
        01 ERROR-FIELD                   PIC X(5).
        01 ANSWER-FIELD                  PIC 9(5)V99.

The multiple definitions of a single storage space are useful because the data in that storage can be manipulated according to its data type.

The picture of NUMBER-1 leads the system to expect a 5 digit number.

If the actual contents of NUMBER-1 is not NUMERIC, then any calculation using NUMBER-1 or any move of NUMBER-1 to a number would crash the program.

The programmer has options to treat the storage location as an alpha field or as a alphanumeric field or as a group item segmented into a number and a alphanumeric code.

IF NUMBER-1 NOT NUMERIC
MOVE AN-1 TO ERROR-FIELD.
ELSE
COMPUTE ANSWER-FIELD = NUMBER-1 * 1.6

-----------------------------------------------------------------------------------------------------------