Data Types
integer, float, boolean, string, array, object, resource, NULL

Variable Declarations

$variablename = <value>;

$anothervariable =& $variablename; (Assign by Reference)

Declare Array

$arrayname = array();

Initialize Array

$arrayname = array(<value1>, <value2>, <value3>);

$arrayname = array(<key> => <value>, <key> => <value>); (Define Keys)

$multiarray = array(<key> => array(<value1>,<value2>)); (Multi-dimensional)

Common Array Functions

sort(<array>); (Sort array assigns new keys)

asort(<array>); (Sort array maintain keys)

rsort(<array>); (Sort array in reverse, new keys)

arsort(<array>); (Sort array in reverse, maintain keys)

count(<array>); (Count elements)

count(<array>,COUNT_RECURSIVE); (Count multidimensional array)

array_push(<array>,<value>); (Push item onto end of array)

array_pop(<array>); (Pop item off end of array)

Comments  
// Comment text
/* Multi-line comment text */
# Comment text

Arithmetic Operators
+ (Addition), - (Subtraction), * (Multiplication), / (Division), % (Modulus)

Relational Operators
== (Equal), === (Equal with type comparison), != (Not equal), <> (Not equal), !== (Not Equal with type comparison), < (Less than), > (Greater than), <= (Less than or equal to), >= (Greater than or equal to)

Logical Operators
! (logical NOT), && (logical AND), || (logical OR), xor (logical XOR)

Assignment Operators

= (Assign), += (Addition), -= (Subtraction), *= (Multiplication), /= (Division), .= (Concatenation), %= (Modulus), &= (And), |= (Or), ^= (Exclusive Or), <<= (Left Shift), >>= (Right Shift)

String Concatenation

. (Period)

String Manipulation

substr(<string>,<start>,[<length>]);

strlen(<string>);

trim(<string>);

ltrim(<string>); // Trim left

rtrim(<string>); // Trim right

strtolower(<string>);

strtoupper(<string>);

str_replace(<search>,<replace>,<string>,[<count>]);

strpos(<string>, <search>);

strcmp(<string1>,<string2>); (Binary safe string comparison)

strcasecmp(<string1>,<string2>); (Binary safe case-insensitive comparison)

explode(<delim>,<string>,[<limit>]); (Break string into array)

implode(<delim>,<array>); (Join array into string separated by delim)

Super Globals

$GLOBALS (Access all global variables in script)
$_SERVER (Access web server variables)
$_GET (Values passed to script through URL)
$_POST (Values passed to script through HTTP Post)
$_COOKIES (Values passed by user cookie)
$_FILES (Values passed by HTTP Post File Uploads)
$_ENV (Values passed to script via the environment)
$_REQUEST (Values passed by URL, HTTP Post, or user Cookies)
$_SESSION (Values passed through user's session)

Cookies

setcookie (<cookiename>, [<value>],[<expire_time_in_secs_since_epoch>]);

$_COOKIE['cookiename']; (Returns value of cookie)

Sessions

session_start(); (Create session)

$_SESSION['key_name'] = value; (Set session variable)

$variablename = $_SESSION['key_name']; (Retrieve value from session variable)

session_destroy(); (Destroy session)

Error Handling

try {

     <statements that may cause error>;

}

catch (<Exception Class> $exception_name) {

    <statements to execute when error is caught>;

}

If Else

if (<condition 1>)   
    { <statement 1>; }
elseif (<condition 2>)   
    { <statement 2>; }

else

    { <statement 3>; }

Inline If (Ternary)

<condition> ? true : false;

For Loop
for (<initialize>;<condition>;<update>)

{

    <statements>;

}

For Each Loop

foreach (<array> as [<value> |<key> => <value>])

{

    <statements>;

    [break];

    [continue];

}

While Loop
while (<condition>)

{

    <statements>;

}

Do-While Loop
do

{

    <statements>;

} while (<condition>);

Switch

switch (<expression>)

{

    case <literal or type>:

        <statements>;

        [break;]

    case <literal or type>:

        <statements>;

        [break;]

    default:

        <statements>;

}

Function Structure

function <function_name>([<parameters>])

{

    <statements>;

    [return <value>;]

}

Class Structure

class <class_name> [<extends base_class>]

{

    [var | <modifiers*>] [<class member variables>];

    [<modifiers*>] function <function_name>([<parameters>])

    {

         <statements>;

    }

}

* Modifiers <public | private | static> are implemented in PHP5

Declare and Use Class

$variable = new class_name();

$variable->function_name();

class_name::function_name(); (Static call)