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menu_book Course Curriculum (COBOL) expand_more
Program Structure
IDENTIFICATION DIVISION PROGRAM-ID paragraph ENVIRONMENT DIVISION DATA DIVISION PROCEDURE DIVISION WORKING-STORAGE SECTION LOCAL-STORAGE SECTION LINKAGE SECTION Paragraphs Sections
Data Description
PIC X alphanumeric PIC 9 numeric Signed numeric pictures Decimal pictures VALUE clauses REDEFINES RENAMES level 66 Condition names level 88 Group items FILLER items
Statements
MOVE DISPLAY ACCEPT INITIALIZE COMPUTE ADD SUBTRACT MULTIPLY DIVIDE STRING
Control Flow
IF ELSE END-IF EVALUATE PERFORM paragraph PERFORM THRU PERFORM TIMES PERFORM UNTIL PERFORM VARYING CONTINUE GO TO EXIT paragraph
Tables and Strings
OCCURS tables Indexed tables Subscript access SEARCH SEARCH ALL INSPECT TALLYING INSPECT REPLACING UNSTRING Reference modification FUNCTION LENGTH
Files
SELECT file FD file description OPEN INPUT OPEN OUTPUT READ WRITE REWRITE DELETE records START indexed file CLOSE
Numeric and Dates
COMP storage COMP-3 packed decimal ROUNDED ON SIZE ERROR Intrinsic FUNCTION CURRENT-DATE FUNCTION NUMVAL FUNCTION INTEGER-OF-DATE FUNCTION DATE-OF-INTEGER Class tests NUMERIC Sign handling
Subprograms and Quality
CALL subprogram USING parameters RETURNING values BY REFERENCE BY CONTENT COPY copybooks REPLACE directive DECLARATIVES File status codes GnuCOBOL compile command
COBOL / Control Flow

PERFORM THRU

Learn PERFORM THRU in COBOL through a focused explanation, a dedicated topic-specific example, an engineering boundary, and a mastery check.

12 min read • Intermediate

PERFORM THRU is a focused COBOL lesson inside Control Flow. The example uses the construct named in the lesson directly rather than reusing a generic placeholder.

Trace the example from its inputs through PERFORM THRU and identify the behavior that would change if that construct were removed or replaced. Pay attention to the language-specific rules shown by the syntax, because neighboring lessons intentionally exercise different mechanisms.

Topic-specific example

cobol-0034-2b6150ca2b.cbl
cobol Try It Live 
       PERFORM VARYING WS-I FROM 1 BY 1 UNTIL WS-I > 3
           DISPLAY WS-I
       END-PERFORM.
       SUBTRACT 1 FROM WS-COUNT
Edge case / engineering note

For PERFORM THRU, test one realistic boundary: empty data, invalid input, unavailable resources, lifetime/cleanup, type constraints, or concurrency timing where applicable. A successful happy path is not enough to prove the construct is used correctly.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

PERFORM THRU Mastery Check →
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PERFORM TIMES