Control Structures

????

if

else

elseif

Alternative syntax for control structures

while

do-while

for

foreach

break

continue

switch

declare

return

require()

include()

require_once()

include_once()

Any PHP script is built out of a series of statements. A statement can be an assignment, a function call, a loop, a conditional statement of even a statement that does nothing (an empty statement). Statements usually end with a semicolon. In addition, statements can be grouped into a statement-group by encapsulating a group of statements with curly braces. A statement-group is a statement by itself as well. The various statement types are described in this chapter.

if

The if construct is one of the most important features of many languages, PHP included. It allows for conditional execution of code fragments. PHP features an if structure that is similar to that of C:

if (expression) statement ?>

As described in the section about expressions, expr is evaluated to its Boolean value. If expr evaluates to TRUE, PHP will execute statement, and if it evaluates to FALSE - it'll ignore it. More information about what values evaluate to FALSE can be found in the 'Converting to boolean' section.

The following example would display a is bigger than b if $a is bigger than $b:

if ($a > $b) echo "a is bigger than b"; ?>

Often you'd want to have more than one statement to be executed conditionally. Of course, there's no need to wrap each statement with an if clause. Instead, you can group several statements into a statement group. For example, this code would display a is bigger than b if $a is bigger than $b, and would then assign the value of $a into $b:

if ($a > $b) { echo "a is bigger than b"; $b = $a; } ?>

If statements can be nested indefinitely within other if statements, which provides you with complete flexibility for conditional execution of the various parts of your program.

Type Operators

PHP has a single type operator: instanceof. instanceof is used to determine whether a given object is of a specified object class.

The instanceof operator was introduced in PHP 5. Before this time is_a() was used but is_a() has since been deprecated in favor of instanceof.

class A { } class B { } $thing = new A; if ($thing instanceof A) { echo 'A'; } if ($thing instanceof B) { echo 'B'; } ?>

As $thing is an object of type A, but not B, only the block dependent on the A type will be executed:

A

See also get_class() and is_a().

Array Operators

???? 15-8. Array Operators

Example	Name	Result
$a + $b	Union	Union of $a and $b.
$a == $b	Equality	TRUE if $a and $b have the same key/value pairs.
$a === $b	Identity	TRUE if $a and $b have the same key/value pairs in the same order and of the same types.
$a != $b	Inequality	TRUE if $a is not equal to $b.
$a <> $b	Inequality	TRUE if $a is not equal to $b.
$a !== $b	Non-identity	TRUE if $a is not identical to $b.

The + operator appends the right handed array to the left handed, whereas duplicated keys are NOT overwritten.

$a = array("a" => "apple", "b" => "banana"); $b = array("a" => "pear", "b" => "strawberry", "c" => "cherry"); $c = $a + $b; // Union of $a and $b echo "Union of \$a and \$b: \n"; var_dump($c); $c = $b + $a; // Union of $b and $a echo "Union of \$b and \$a: \n"; var_dump($c); ?>

When executed, this script will print the following:

Union of $a and $b: array(3) { ["a"]=> string(5) "apple" ["b"]=> string(6) "banana" ["c"]=> string(6) "cherry" } Union of $b and $a: array(3) { ["a"]=> string(4) "pear" ["b"]=> string(10) "strawberry" ["c"]=> string(6) "cherry" }

Elements of arrays are equal for the comparison if they have the same key and value.

????? 15-5. Comparing arrays $a = array("apple", "banana"); $b = array(1 => "banana", "0" => "apple"); var_dump($a == $b); // bool(true) var_dump($a === $b); // bool(false) ?>

See also the manual sections on the Array type and Array functions.

String Operators

There are two string operators. The first is the concatenation operator ('.'), which returns the concatenation of its right and left arguments. The second is the concatenating assignment operator ('.='), which appends the argument on the right side to the argument on the left side. Please read Assignment Operators for more information.

$a = "Hello "; $b = $a . "World!"; // now $b contains "Hello World!" $a = "Hello "; $a .= "World!"; // now $a contains "Hello World!" ?>

See also the manual sections on the String type and String functions.

Logical Operators

???? 15-7. Logical Operators

Example	Name	Result
$a and $b	And	TRUE if both $a and $b are TRUE.
$a or $b	Or	TRUE if either $a or $b is TRUE.
$a xor $b	Xor	TRUE if either $a or $b is TRUE, but not both.
! $a	Not	TRUE if $a is not TRUE.
$a && $b	And	TRUE if both $a and $b are TRUE.
$a || $b	Or	TRUE if either $a or $b is TRUE.

The reason for the two different variations of "and" and "or" operators is that they operate at different precedences. (See Operator Precedence.)

Incrementing/Decrementing Operators

PHP supports C-style pre- and post-increment and decrement operators.

????: The increment/decrement operators do not affect boolean values. Decrementing NULL values has no effect too, but incrementing them results in 1.

???? 15-6. Increment/decrement Operators

Example	Name	Effect
++$a	Pre-increment	Increments $a by one, then returns $a.
$a++	Post-increment	Returns $a, then increments $a by one.
--$a	Pre-decrement	Decrements $a by one, then returns $a.
$a--	Post-decrement	Returns $a, then decrements $a by one.

Here's a simple example script:

echo " Postincrement "; $a = 5; echo "Should be 5: " . $a++ . " \n"; echo "Should be 6: " . $a . " \n"; echo " Preincrement "; $a = 5; echo "Should be 6: " . ++$a . " \n"; echo "Should be 6: " . $a . " \n"; echo " Postdecrement "; $a = 5; echo "Should be 5: " . $a-- . " \n"; echo "Should be 4: " . $a . " \n"; echo " Predecrement "; $a = 5; echo "Should be 4: " . --$a . " \n"; echo "Should be 4: " . $a . " \n"; ?>

PHP follows Perl's convention when dealing with arithmetic operations on character variables and not C's. For example, in Perl 'Z'+1 turns into 'AA', while in C 'Z'+1 turns into '[' ( ord('Z') == 90, ord('[') == 91 ). Note that character variables can be incremented but not decremented.

????? 15-4. Arithmetic Operations on Character Variables $i = 'W'; for ($n=0; $n<6; $n++) { echo ++$i . "\n"; } ?> The above example will output: X Y Z AA AB AC

Incrementing or decrementing booleans has no effect.

Execution Operators

PHP supports one execution operator: backticks (``). Note that these are not single-quotes! PHP will attempt to execute the contents of the backticks as a shell command; the output will be returned (i.e., it won't simply be dumped to output; it can be assigned to a variable). Use of the backtick operator is identical to shell_exec().

$output = `ls -al`; echo " $output "; ?>

????: The backtick operator is disabled when safe mode is enabled or shell_exec() is disabled.

See also the manual section on Program Execution functions, popen() proc_open(), and Using PHP from the commandline.