Expressions and Operators

An expression is a bit of PHP that can be evaluated to produce a value. The simplest expressions are literal values and variables. A literal value evaluates to itself, while a variable evaluates to the value stored in the variable. More complex expressions can be formed using simple expressions and operators .

An operator takes some values (the operands) and does something (for instance, adds them together). Operators are written as punctuation symbols—for instance, the + and - familiar to us from math. Some operators modify their operands, while most do not.

Table 2-3 summarizes the operators in PHP, many of which were borrowed from C and Perl. The column labeled “P” gives the operator’s precedence; the operators are listed in precedence order, from highest to lowest. The column labeled “A” gives the operator’s associativity, which can be L (left-to-right), R (right-to-left), or N (non-associative).

Table 2-3. PHP operators

P

A

Operator

Operation

19

N

new

Create new object

18

 

[

Array subscript

17

R

!

Logical NOT

 

R

~

Bitwise NOT

 

R

++

Increment

 

R

--

Decrement

 

R

(int), (double), (string), (array), (object)

Cast

 

R

@

Inhibit errors

16

L

*

Multiplication

 

L

/

Division

 

L

%

Modulus

15

L

+

Addition

 

L

-

Subtraction

 

L

.

String concatenation

14

L

<<

Bitwise shift left

 

L

>>

Bitwise shift right

13

N

<, <=

Less than, less than or equal

 

N

>, >=

Greater than, greater than or equal

12

N

==

Value equality

 

N

!=, <>

Inequality

 

N

===

Type and value equality

 

N

!==

Type and value inequality

11

L

&

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