Restrictions on Subscripting
- A data-name must not be subscripted or indexed when it is being used as
a subscript or qualifier.
- An index may be modified only by a PERFORM, SEARCH, or SET statement.
- When a literal is used in a subscript, it must be a positive or unsigned
integer.
- When a literal is used in relative subscripting and indexing, it must
be an unsigned integer.