COBOL by Example: Tables
Defining fixed-size arrays called tables using the OCCURS clause with 1-based indexing, implementing variable-length tables with OCCURS DEPENDING ON clause, accessing table elements with parentheses notation, and creating multi-dimensional tables for matrices and complex data structures.
Code
IDENTIFICATION DIVISION.
PROGRAM-ID. TABLES-DEMO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WEEK-TABLE.
05 DAY-NAME PIC X(10) OCCURS 7 TIMES.
01 I PIC 99.
PROCEDURE DIVISION.
MOVE "Monday" TO DAY-NAME(1).
MOVE "Tuesday" TO DAY-NAME(2).
MOVE "Wednesday" TO DAY-NAME(3).
PERFORM VARYING I FROM 1 BY 1 UNTIL I > 3
DISPLAY "Day " I ": " DAY-NAME(I)
END-PERFORM.
STOP RUN.Explanation
In COBOL, arrays are called Tables. They are defined using the OCCURS clause, which specifies how many times a data item repeats. Tables are strictly fixed-size; you must define the maximum number of elements at compile time (though modern COBOL supports dynamic allocation with OCCURS DEPENDING ON).
Tables are 1-indexed, meaning the first element is at index 1, not 0. You access elements using parentheses, e.g., DAY-NAME(1). You can iterate through tables using a PERFORM VARYING loop with a subscript variable.
COBOL tables can also be multi-dimensional. You can nest an OCCURS clause inside another group item that also has an OCCURS clause, allowing for matrices and complex data structures. Accessing these requires multiple subscripts, like MY-TABLE(ROW, COL).