One of the first you learn in #Cobol, especially back in the day when indexed files where a common practice, is the use of SW-FIRST-READ.
In a program flow most probably there’s a loop on a cursor or a file. Many programmers inside that main loop they use an IF for controlling the first read. For example, if you want to match previous and current row/record. The COBOL code would be something like:
01 SW-FIRST-READ PIC X VALUE ‘Y’.
88 FIRST-READ-YES VALUE ‘Y’.
88 FIRST-READ-NOT VALUE ‘N’.
MAIN-ROUTE.
PERFORM READ-ROUTE
#PERFORM UNTIL EOF
#IF FIRST-READ-YES
SET FIRST-READ-NOT TO TRUE
MOVE CURRENT-RECORD TO PREVIOUS-RECORD
END-IF
IF CURRENT-RECORD = PREVIOUS-RECORD
DISPLAY ‘SAME ACCOUNT’
PERFORM SAME-ACCOUNT-ROUTE
ELSE
DISPLAY ‘NEW ACCOUNT’
PERFORM NEW-ACCOUNT-ROUTE
END-IF
PERFORM READ-ROUTE
END-PERFORM
IF EOF AND SW-FIRST-READ
DISPLAY ‘NO RECORDS/ROWS IN FILE/CURSOR’
PERFORM EMPY-FILE-OR-CURSOR-ROUTE
END-IF .
READ-ROUTE.
READ FILE NEXT AT END SET SW-EOF TO TRUE
(OR)
FETCH CURSOR
IF SQLCODE = NOT-FOUND-NEXT
SET SW-EOF TO TRUE
END-IF
IF SQLCODE/FILE-STATUS NOT-OK
ERROR-HANDLING-ROUTE
END-IF.
This is a very common practice with one fault for performance. The IF SW-FIRST-READ will execute as many times as the ROWS/RECORDS of the CURSOR/FILE – 1.000.000 or 50.000.000 times, and IF statement is not a fast one.
My recommendation would have some more code to be written, some paragraph rearrangements and involve a bit more thinking. But it will have 1.000.000 IFs less.
You will have to have separate paragraphs for #READ / #FETCH, for error handling and PERFORM these paragraphs twice, once before the main loop. That one would be the first time and will be executed only once. There’s no need to ask again. The code would look like this:
MAIN-ROUTE.
PERFORM READ-ROUTE
IF NOT-EOF
MOVE CURRENT-RECORD TO PREVIOUS-RECORD
ELSE
DISPLAY ‘NO RECORDS/ROWS IN FILE/CURSOR’
PERFORM EMPY-FILE-OR-CURSOR-ROUTE
END-IF
PERFORM UNTIL EOF
IF CURRENT-RECORD = PREVIOUS-RECORD
DISPLAY ‘SAME ACCOUNT’
PERFORM SAME-ACCOUNT-ROUTE
ELSE
DISPLAY ‘NEW ACCOUNT’
PERFORM NEW-ACCOUNT-ROUTE
END-IF
END-PERFORM
PERFORM END-ROUTE .
READ-ROUTE.
READ FILE NEXT AT END SET SW-EOF TO TRUE
(OR)
#FETCH #CURSOR
IF SQLCODE = NOT-FOUND-NEXT
SET SW-EOF TO TRUE
END-IF
IF SQLCODE/FILE-STATUS NOT-OK
#ERRORHANDLING-ROUTE
END-IF.
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