SIMSCRIPT II.5 Programming Language

Programming Language Concepts
Where double variables are supported, conversions between double and integer modes follow
the same procedures as conversions between integer and real. Hence, expressions mixing
integer and double arithmetic operations follow the procedure outlined above for mixed
integer and real expressions.
Expressions containing mixed double and real variables are evaluated to yield a double precision
result, which may be automatically converted to the real mode, if necessary. When required
by context, as in mixed real and double mode expressions, real values are automatically converted
to double before evaluation.
If, in the following examples, R has been defined as a real variable and D as a double variable,
then in executing the statement:
let D = D + R
R is converted to double before the addition, which produces a double precision result, while:
let R = R * D
converts R to double before the multiplication, but the result is truncated to real before reassignment.
As may be seen, the provision of different modes of variable representation brings with it some additional
complexity. A variable defined with a certain mode can only be used in ways consistent
with its definition. In some cases, automatic conversion between modes is performed as indicated
above, although information may be lost as in the case of real to integer conversion, where the
fractional value may no longer be represented. Be aware of such implied conversions and their effect
on program behavior.
One particular potential source of error, however, is the attempted assignment of variable values
read from input data to variables defined with conflicting internal representation. Specifically, a
data field containing a noninteger format number should not be assigned to an integer variable
in a read statement. This will result in loss of information and is therefore treated as an error condition.
Table 2-2 specifies the actions taken when different combinations of data and variable definitions
occur.
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