SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
It is common to indent in some regular way the statements that are to be repeated within the control
structure of a do loop (as for the statement groups in an if statement) drawing attention to the departure
from normal sequential flow of control.
The following program uses a number of terms from an infinite series to estimate an approximate
value for the irrational number PI. The value of PI, approximately 3.14159..., can be represented
by the infinite series:
PI/4 = 1 - 1/3 + 1/5 - 1/7 + 1/9 ...
The accuracy of the approximation is controlled by a variable read from input data. This data value
sets a limiting value on the size of the divisor in the terms of the series. The summation is halted
when the values of subsequent terms become too small to affect the desired accuracy of the result.
For example:
read LIMIT
let VALUE = 0
let SIGN = +1
for DIVISOR = 1 to LIMIT by 2
do
add SIGN/DIVISOR to VALUE
let SIGN = -SIGN
loop
print 1 line with VALUE*4 as
The Approximate Value of Pi is *.******
stop
The variable DIVISOR takes the values 1,3,5,... until it exceeds the limiting value. Note the
use of the unary operators to control the sign of successive terms.
1.15 Logical Control Phrases
Normally, a do loop, controlled by a for statement, is executed over the entire range of values of
the control variable generated. An alternative is to control the repetition of statements using some
logical condition that may be evaluated during the execution of the controlled statements.
A logical control phrase contains a logical control operator and a logical expression and may be
used to control a do loop. The logical control phrases are:
while logical expression
and
until logical expression
The following example illustrates the use of a logical control phrase in a program:
22