SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
quantities is an attractive idea. However, both the range and number of real numbers are infinite,
while a computer has a finite range of representations.
The enumeration of items, or iterations, requires the exact representation of a sizable range of integer
numbers. Many other calculations require the representation of a potentially greater range in
magnitude of the real numbers but are necessarily limited in accuracy.
Most computer systems, therefore, provide two internal representations for numeric data — one
trading some exactness of representation for increased range. These representations may vary between
different computer systems. The precise limitations pertaining to any SIMSCRIPT II.5 implementation
may be found in the appropriate user's guide. A programming language is used to
describe both the actions and the data on which these actions are to be performed. In this chapter,
some of the ways in which data are described are discussed.
A variable definition statement serves to declare the properties of a variable. This information is
used to determine the way in which the variable may be manipulated.
2.2.1 REAL and INTEGER Variables
SIMSCRIPT II.5 numeric variables may be declared to be integer or real. Variables declared
as integer represent only whole numbers. Variables declared as real represent numbers that can
have fractional values. Note that a whole number, lying within an established range of the integer
values, may be represented either by an integer or real variable. It is the possibility of a fractional
value, and not any particular value, that makes a variable require a real definition. The
numbers 56, -6745, 91, -1, and 0 are integer-valued. The numbers 56.0, 35.7846, 0.999876, -
27.45, and 0.0. are real-valued.
Every SIMSCRIPT II.5 program has a preamble that contains variable definition information. In
some cases, as in the previous examples, this preamble is implied but need not be written as all
variables are treated as real. Whenever a variable has a property that differs from one that
SIMSCRIPT II.5 assumes, a variable definition statement must be used. Programs containing an
explicit preamble begin with the one-word statement preamble. This section, containing variable
definition statements, is separated from succeeding program action statements by the word end.
As stated, the mode of a numeric variable is assumed real unless otherwise specified. The "normal
form" of SIMSCRIPT II.5 variables is real numbers. The assumed real condition can be changed
by using the statement:
mode is integer
This statement resets the compiler's "background conditions" so that all following program variables
are assumed integer unless otherwise specified. Mode is but one of several properties that
can be used to describe variables. Hence, the general form of the normally statement is:
normally, specification phrase list
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