SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
for I = 1 to N
read LIST(I)
If N were the reserved dimension of the array, this statement has the same effect as the statement
read LIST.
A more complex example demonstrates the use of nested control phrases to govern the repetition of
a do loop. The loop reads and assigns data values to only the lower triangular elements (i.e., those
that lie below the diagonal) of a square two-dimensional array or matrix. For example:
reserve MATRIX(*,*) as N by N
for I = 1 to N
for J = 1 to N
do
if I gt J
read MATRIX(I,J)
always
loop
While the subscripts, in turn, take on the values to address each element, the read statement is
executed only when the if condition is satisfied. The data values supplied would be the values for
MATRIX(2,1), MATRIX(3,1), MATRIX(3,2), MATRIX(4,1), MATRIX(4,2),
MATRIX(4,3), etc.
2.7 Using Subscripted Variables In Expressions
Recall that parentheses are also used to clarify the desired evaluation order in complex arithmetic
expressions. Subscripted variables may appear in such expressions. In these cases, the evaluation
of subscripts and the selection of the array elements may be considered to take precedence over other
arithmetic evaluations. Note that subscripts may themselves involve expression evaluations.
Thus, in the statement:
let Z = X(I + 1) * Y(J + 1)
the subscript expressions I + 1 and J + 1 are evaluated first, thus selecting the two elements of
arrays X and Y that are to be multiplied. The subscript expressions may even involve subscripted
variables. The same procedure, applied to these expressions, ensures that these are evaluated first:
let Z = X(Y(I + 1) + 1) * 2
The subscript I + 1 is evaluated to select an element from Y; 1 is added to the value of this element
to form the indexing value for the array X; and the selected element of X is then multiplied before
assignment to Z. After conversion to integer mode (if necessary), the subscript expression should
always evaluate in the range of 1 to the size given in the reserve statement. Out-of-range subscripts
will produce execution errors that either terminate the program or introduce undesirable
side-effects, depending on the implementation.
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