SIMSCRIPT II.5 Programming Language

Advanced Topics
(a) for I = 1 to 10, read CUBE(J+7,K+L,I)
(b) let DUMMY(*) = CUBE(J+7,K+L,*)
for I=1 to 10, read DUMMY(I)
where DUMMY has been defined as a one-dimensional array, of the same mode as CUBE, but has not
been reserved. The revised statement eliminates the need for recomputing the subscripts of CUBE
not affected by the for loop every time a new element is accessed. Little additional memory space
is taken, for the array DUMMY never has more space allocated than is needed for its base pointer.
DATA ELEMENTS
⎧ TABLE(1,1)
⎨ TABLE(1,2)
⎪ TABLE(1,3)
⎩ TABLE(1,4)
⎧ TABLE(2,1)
⎨ TABLE(2,2)
ROW POINTERS
⎩
⎧ TABLE(1,*) ⎧ TABLE(3,1)
BASE POINTER ⎪ TABLE(2,*) ⎪ TABLE(3,2)
TABLE(*,*) ⎨ TABLE(3,*) ⎨ TABLE(3,3)
⎪ TABLE(4,*) ⎪ TABLE(3,4)
⎩ TABLE(5,*) ⎪ TABLE(3,5)
⎩ TABLE(3,6)
{ TABLE(4,1)
⎧ TABLE(5,1)
⎨ TABLE(5,2)
⎩ TABLE(5,3)
Figure 6-5. Memory Structure After Assignment of Data Arrays to Row Pointers
3. It has already been stated that once an array has been reserved, it cannot be reserved
again. The SIMSCRIPT II.5 system ignores instructions to reserve an array when the
pointer to the array already has a value. When a program is first initialized, all array
pointers are zero, making the first reserve possible. After this, the presence of a nonzero
value in a pointer variable dictates whether or not a reserve will be executed. This
makes it possible to use a reserve statement more than once to reserve multiple instances
of an array by saving the value of the array base pointer and then resetting it to zero
before the second and subsequent reserves. Any specific instance of the array may be
accessed by restoring the value of the appropriate base pointer. The example below illustrates
how such a mechanism can be employed:
A program is to be developed to store genealogical information in the form of a
family tree. Such a tree has an individual at its apex, his parents at the next level,
his parents' parents below that, and so on. Figure 6-6 illustrates a family tree containing
four levels of genealogical information.
This information can be stored in a rectangular array, as depicted in figure 6-7.
While simple enough to do, there is a waste of computer memory because of all the
empty cells.
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