Propeller Manual

Operators – Spin Language Reference
Here are assignment operator examples:
Count++ ' (Unary) evaluate Count + 1
' and write result to Count
Data >>= 3 ' (Binary) shift Data right 3 bits
' and write result to Data
Binary operators have special forms that end in equal ‘=’ to make them assignment operators.
Unary operators do not have a special assignment form; some always assign while others
assign only in special situations. See Table 2-9 above and the operator’s explanation, for
more information.
Most assignment operators can only be used within methods (
PUB and PRI blocks). The only
exception is the constant assignment operator ‘
=’ which can only be used in CON blocks.
Constant and/or Variable Expression
Operators which have the integer-constant-expression attribute can be used both at run time
in variable expressions, and at compile time in constant expressions. Operators that have the
float-constant-expression attribute can be used in compile-time constant expressions.
Operators without either of the constant-expression attributes can only be used at run time in
variable expressions. Most operators have a normal, non-assignment form that allows them
to be used in both constant and variable expressions.
Level of Precedence
Each operator has an assigned level of precedence that determines when it will take action in
relation to other operators within the same expression. For example, it is commonly known
that Algebraic rules require multiply and divide operations to be performed before add and
subtract operations. The multiply and divide operators are said to have a “higher level of
precedence” than add and subtract. Additionally, multiply and divide are commutable; both
are on the same precedence level, so their operations result in the same value regardless of the
order it is performed (multiply first, then divide, or vice versa). Commutative operators are
always evaluated left to right except where parentheses override that rule.
The Propeller chip applies the order-of-operations rules as does Algebra: expressions are
evaluated left-to-right, except where parentheses and differing levels of precedence exist.
Following these rules, the Propeller will evaluate:
X = 20 + 8 * 4 – 6 / 2
Page 146 · Propeller Manual v1.1