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:
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