Page 85 - Beginning PHP 5.3

Chapter 3: PHP Language Basics
In fact, there is one other string operator — the combined assignment operator .= — which was
mentioned earlier in the chapter. It ’ s useful when you want to join a new string onto the end of an
existing string variable. For example, the following two lines of code both do the same thing — they
change the string variable $x by adding the string variable $y to the end of it:

$x = $x . $y;

$x .= $y;

Understanding Operator Precedence
With simple expressions, such as 3 + 4 , it ’ s clear what needs to be done (in this case, “ add 3 and 4 to
produce 7 ” ). Once you start using more than one operator in an expression, however, things aren ’ t so
clear - cut. Consider the following example:

3 + 4 * 5

Is PHP supposed to add 3 to 4 to produce 7, then multiply the result by 5 to produce a final figure of 35?
Or should it multiply 4 by 5 first to get 20, then add 3 to make 23?

This is where operator precedence comes into play. All PHP operators are ordered according to
precedence. An operator with a higher precedence is executed before an operator with lower precedence.
In the case of the example, * has a higher precedence than + , so PHP multiplies 4 by 5 first, then adds 3
to the result to get 23.

Here ’ s a list of all the operators you ’ ve encountered so far, in order of precedence (highest first):

Precedence of Some PHP Operators (Highest First)
++ - - (increment/decrement)

(int) (float) (string) (array) (object) (bool) (casting)
! (not)
* / % (arithmetic)

+ - . (arithmetic)
< < = > > = < > (comparison)

== != === !== (comparison)
& & (and)

|| (or)
= += - = *= /= .= %= (assignment)
and
xor

or

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