SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
and
normally, mode is double
2.3 Expression Modes
Although statements that combine integer and real variables are allowed, a programmer should
be aware of the way in which computations are carried out whenever using "mixed mode" expressions.
When A and B represent two variables, constants, or sub-expressions, then:
1. Arithmetic expressions of the form A op B, where A and B represent variables of specified
mode, or constants of that mode, and op is any of the arithmetic operations +, -, and *, are
integer if both A and B are integer, and real if either A or B is real.
2. Expressions of the form A/B are always real (Two integer expressions can be divided to
yield a truncated integer result by a library function called div.f. Library functions are
described in paragraph 2.15).
3. Expressions of the form A**B are always real.
Compound expressions are evaluated from left to right as a sequence of simple expressions that are
evaluated according to the above rules. In the following examples, if A, B, and C are integer,
then:
A/B + C
A + B + C
A**B + C
is real
is integer
is real
When an expression appears on the right-hand side of a let statement or in an add or subtract
statement, and its mode differs from the mode of the variable on the left-hand side, the expression
is converted to the mode of the variable before the value of the variable is changed. When the arithmetic
expression constituents of logical expressions differ in mode, all integer expressions are
converted to real before evaluating the logical expression as true or false.
Conversions from integer to real are straightforward. An integer to real conversion takes
the whole number that is the value of an integer variable and converts it to a real number with
the same value; 25 becomes 25.0, -11 becomes -11.0, and so forth.
Real to integer conversions are more complex. Obviously, any fractional part cannot be represented
by the integer. Real values are rounded to whole numbers by adding +0.5 to the variable
if its value is positive or -0.5 if it is negative, and truncating the result. If X is integer and e is
some real-valued expression (formed according to the above rules), then:
let X = e sets X = 0 if e = 0.2 since 0.2 + 0.5 = 0.7 → 0
let X = e sets X = 1 if e = 1.4999 since 1.4999 + 0.5 = 1.9999 → 1
let X = e sets X = 2 if e = 1.50000 since 1.50000 + 0.5 = 2.0000 → 2
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