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Module 9: Array processing and Table handling


ARRAY INDEX and INDEXING

  • Array INDEX is one of the good alternative to subscripting
  • An INDEX denotes displacement of the element from the beginning of array
  • An INDEX is data item which is associated with an array or particular dimension of an array through the use of INDEXED BY phrase of OCCURS clause
  • Example:-

    01 COMPANY-TABLE. 05 DEPARTMENT OCCURS 3 TIMES INDEXED BY D1. 10 EMPLOYEE OCCURS 6 TIMES INDEXED BY E1. 15 SALES PIC 9(4) TIMES OCCRUS 4 TIMES INDEXED BY S1.

  • In above example, D1, E1 and S1 are index names.
  • These index names need not be defined in DATA DIVISION
  • Array element can be referenced as SALES(D1,E1,S1)
  • General format of using INDEXED BY phrase with OCCURS clause:-

    OCCURS integer TIMES   [INDEXED BY index-name-1 [, index-name-2]…]

  • Some points to be considered while using INDEXED BY phrase:-
    • If INDEXED BY used for any one level of array, then INDEXED BY must be used for all levels
    • INDEX item cannot be used in combination with subscript data item
    • INDEX defined for one array cannot be used for another array. The index name should be unique
    • Since INDEX items are coded with INDEXED BY phrase, it should not appear in DATA DIVISION
    • INDEX items can be manipulated using SET, SEARCH and PERFORM statements
    • Use of INDEX with plus or minus to any integer is valid. For example, SALES(D1+2,E1-1,S2) is valid
    • More than one index item can be coded for each level of array

What other kind of INDEX exist?

  • There is one more kind of INDEX items exist which are declared in DATA DIVISION by specifying USAGE IS INDEX clause
  • And INDEX declared with ‘USAGE IS INDEX’ clause must not have PIC clause
  • Example:-

    77 INDEX-SALES USAGE IS INDEX.

    This defines Index ‘INDEX-SALES’.
  • Such kind of data items are called as Index Data item
  • This kind of index data item can be used to temporarily store the index values.
  • With help of SET verb, the actual index value can be transferred to the index data item(and vice-versa) without conversion (to occurrence number). SET verb is explained in next section.
  • When the clause is specified for a group item, it applies to all elementary items contained in it. However, the group itself is not an index data item
  • For example,
    In DATA DIVISION,

    01 TEMP-INDEX. 02 A-INDEX USAGE IS INDEX. 01 PERM-INDEX. 02 INDEX-VALUE PIC S9(6) COMP.

    Now, In PROCEDURE DIVISION

    MOVE A-INDEX TO PERM-INDEX MOVE A-INDEX TO INDEX-VALUE

    are both invalid statements. However, the following statement is valid

    MOVE TEMP-INDEX TO PERM-INDEX

Difference between Subscript and Index is explained in next article


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