Order of Evaluation
When
an
expression
has
multiple operations.
as
in:
A+C*10/212
there
is
a built-in hierarchy for evaluating the expression. First
is
exponentiation
(l).
followed by unary minus (-1. followed by multiplication and division
(*/1.
followed by addition and subtraction
(+
-).
Operators of the same hierarchy are
evaluated from left to right.
This natural order of operation can be overridden by the use of
parentheses. Any operation
within
parentheses
is
performed first.
Examples:
4+1.2
(4+1).2
100·4/2-1
100.(4/2-1
)
100.(4/(2-1))
results
in
6
results
in
10
results
in
199
results in 100
results in
400
When
parentheses are present.
PET
BASIC evaluates the innermost set first.
then the next innermost. etc. Parentheses can
be
nested to any level and may
be
used freely
to
clarify the order of operations being performed
in
an
expression.
Relational Operators
A relational operator specifies a
"true"
or
"fa
Ise"
relationship
between
adjacent terms. The specified comparison
is
made. and then the relational
expression
is
replaced by a value of true
(-1)
or
false (0). Relational operators
are listed in Table 3-4 at the end of this chapter. Relational operators are evalu-
ated after ail
arithmetic
operations have been performed.
Examples:
1=5-4
14>66
15>
=15
A<
>B
resultsin
true
(-1)
resu
Its
in
fa
Ise
(0)
results
in
true
(-1)
Relational operators can
be
used to compare strings. For comparison pur-
poses. the letters of the alphabet have the order A
<
B.
B<
C.
C<
D.
etc. Strings
are compared by comparing their stored character values. Characters are stored
using a special binary code called "ASCI!." Appendix A lists the ASCII code
assigned to every
PET
character.
Examples:
"A"<"B"
"X"="XX"
C$=A$+B$
results
in
true
(-1)
results
in
false
(0)
65
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