SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
The utility and application of this feature are best described in a series of examples.
1. It can be used to construct a "ragged table," a two-dimensional array with a different number
of elements in each row. The construction follows:
(a) Set up a base pointer and an array of row pointers:
reserve TABLE(*,*) as 5 by *
This statement assigns an array of five elements, each of which contains an unassigned pointer, to
the base pointer TABLE(*,*). The asterisk in the array assignment clause 5 by * indicates that
only pointers, not data values, are to be stored. After execution of this statement, the structure
shown in figure 6-4 exists in memory. The base pointer points to the array of row pointers. The
row pointers do not yet point to anything because arrays have not been assigned to them.
ROW POINTERS
⎧
TABLE(1,*)
BASE POINTER ⎪ TABLE(2,*)
TABLE(*,*) ⎨ TABLE(3,*)
⎪
TABLE(4,*)
⎩
TABLE(5,*)
Figure 6-4. Memory Structure After Reserve Statement
(b) Assign data arrays to each of the row pointers. A dimension must be given for each
row, by reading a data value for each row. For example:
for I = 1 to 5,
do
read D
reserve TABLE(I,*) as D
loop
The reserve statement assigns an array of D elements to each of the row pointers TABLE(I,*),
as I varies from 1 to 5. If the values of D read are 4, 2, 6, 1, and 3, respectively, the final ragged
table structure appears as shown in figure 6-5.
The ragged array TABLE(I,J) may be used in the same way as any rectangular array, with the only
restriction that care must be taken not to reference a nonexistent array element, as, for example,
TABLE(4,3) in figure 6-5.
2. The pointer mechanism may be used to make the processing of multiple-dimensioned arrays
more efficient, eliminating the recomputation of unchanging subscripts when processing
elements of a single dimension in some regular fashion. For example, the program
segment described in (a) below can be made more efficient by rewriting it as shown in (b).
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