Operator Precedence

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Operator Precedence

When several operations occur in a single expression, each operation is evaluated and resolved in a predetermined order. This is called the order of operation or operator precedence.

If an operator in an expression has a higher precedence, it is evaluated before an operator of lower precedence.

If operators have equal precedence, they then are evaluated in the order in of their associativity. The associativity may be Left-to-Right or Right-to-Left order.

As a rule, binary operators (such as +, ^) and unary postfix operators (such as (), ->) are evaluated Left-to-Right, and unary prefix operators (such as Not, @) are evaluated Right-to-Left.

Operators that have an associativity of "N/A" indicate that there is no expression in which the operator can be used where its order of operation would need to be checked, either by precedence or by associativity. Function-like operators such as Cast are always the first to be evaluated due to the parentheses required in their syntax. And assignment operators are always the last to be evaluated.

Parentheses can be used to override operator precedence. Operations within parentheses are performed before other operations. Within the parentheses normal operator precedence is used.

The following table lists operator precedence from highest to lowest. Breaks in the table mark the groups of operators having equal precedence.

Highest Precedence

Operator	Description	Associativity
CAST	Type Conversion	N/A
PROCPTR	Procedure pointer	N/A
STRPTR	String pointer	N/A
VARPTR	Variable pointer	N/A
[]	String index	Left-to-Right
[]	Pointer index	Left-to-Right
()	Array index	Left-to-Right
()	Function Call	Left-to-Right
.	Member access	Left-to-Right
->	Pointer to member access	Left-to-Right
@	Address of	Right-to-Left
*	Value of	Right-to-Left
New	Allocate Memory	Right-to-Left
Delete	Deallocate Memory	Right-to-Left
^	Exponentiate	Left-to-Right
-	Negate	Right-to-Left
*	Multiply	Left-to-Right
/	Divide	Left-to-Right
\	Integer divide	Left-to-Right
MOD	Modulus	Left-to-Right
SHL	Shift left	Left-to-Right
SHR	Shift right	Left-to-Right
+	Add	Left-to-Right
-	Subtract	Left-to-Right
&	String concatenation	Left-to-Right
Is	Run-time type information check	N/A
=	Equal	Left-to-Right
<>	Not equal	Left-to-Right
<	Less than	Left-to-Right
<=	Less than or equal	Left-to-Right
>=	Greater than or equal	Left-to-Right
>	Greater than	Left-to-Right
NOT	Complement	Right-to-Left
AND	Conjunction	Left-to-Right
OR	Inclusive Disjunction	Left-to-Right
EQV	Equivalence	Left-to-Right
IMP	Implication	Left-to-Right
XOR	Exclusive Disjunction	Left-to-Right
ANDALSO	Short Circuit Conjunction	Left-to-Right
ORELSE	Short Circuit Inclusive Disjunction	Left-to-Right
=[>]	Assignment	N/A
&=	Concatenate and Assign	N/A
+=	Add and Assign	N/A
-=	Subtract and Assign	N/A
*=	Multiply and Assign	N/A
/=	Divide and Assign	N/A
\=	Integer Divide and Assign	N/A
^=	Exponentiate and Assign	N/A
MOD=	Modulus and Assign	N/A
AND=	Conjunction and Assign	N/A
EQV=	Equivalence and Assign	N/A
IMP=	Implication and Assign	N/A
OR=	Inclusive Disjunction and Assign	N/A
XOR=	Exclusive Disjunction and Assign	N/A
SHL=	Shift Left and Assign	N/A
SHR=	Shift Right and Assign	N/A
LET	Assignment	N/A
LET()	Assignment	N/A

In some cases, the order of precedence can cause confusing or counter-intuitive results. Here are some examples:

'' trying to raise a negated number to a power

-2 ^ 2

Desired result: (-2) ^ 2 = 4

Actual result:   -(2 ^ 2) = -4

'' trying to test a bit in a number

n And 1  <>  0

Desired result: (n And 1) <> 0

Actual result:   n And (1 <> 0)

'' trying to shift a number by n+1 bits

a Shl n+1

Desired result: a Shl (n + 1)

Actual result: (a Shl n) + 1

For expressions where the operator precedence may be ambiguous, it is recommended to wrap parts of the expression in parentheses, in order both to minimise the possibility of error and to aid comprehension for people reading the code.

See also

• Operators

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