[PHP] Cheat sheet, part 1 - basics

I know there are dozens of similar stuff on net, but none would be as good for me as one made by myself. Created while reading (mainly) a brick called PHP and MySQL Web Development: Vademecum.

Putting PHP into HTML

<?php
echo "<p>Text bla bla bla</p>";
?>

<?php echo '<p>Text bla bla bla</p>'; ?>

Comments

/*
long
comments
*/

echo '<p>Text bla bla bla.'; // short comment
echo '<p>Text bla bla bla.'; # short comment

. – bonds 2 strings

Date

<?php
echo '<p>' . date('H:i. jS F Y') . '</p>' ;
?>

result: 14:32. 19th June 2010

date formatting
H – 24-hour format of an hour with leading zeros
i – minutes
j – day (without zero)
S – +th
F – month (verbal)
Y – year
more here

variables – access, displaying, types

access to the content of $tyresamount

$_POST[‘tyresamount’]

displaying

echo $tyresamount.' tyres<br /> ' ;
echo "$tyresamount tyres< br />" ;

interpolation – inside a string, replacing a variable by its content, works with "

types
• Integer - integers; -2, 3
• Float (called also Double) - real number; 2.4, 0.3
• String - text; boobphysicist
• Boolean - 0 or 1
• Array - used to store many variables
• Object - used to store objects

logical operators

$a and $b	TRUE if both $a and $b are TRUE.
$a or $b	TRUE if either $a or $b is TRUE.
$a xor $b	TRUE if either $a or $b is TRUE, but not both.
! $a	TRUE if $a is not TRUE.
$a && $b	TRUE if both $a and $b are TRUE.
$a || $b	TRUE if either $a or $b is TRUE.

formatting variables

$amount = 0;
$value = (float)$amount;

formats 0 to real number

assignment operators – shortened operations

$a  +=  $b	$a  = $a  + $b
$a  -= $b	$a  = $a  - $b
$a  *=  $b	$a  = $a  *  $b
$a  /= $b	$a  = $a /  $b
$a %=  $b	$a  = $a %  $b
$a  .= $b	$a  = $a  $b

reference operator – „combining” variables

$a = 5;
$b = &$a;
$a = 7; // both $a and $b has value 7

unset($a) ; - undos it

comparison operators
== - is equal? (= is an assignment operator!)
=== - is identical?
!= - isn’t equal?
!== - isn’t identical?
<> - inequality
< >
<= >=

dividing 1 variable into 2

( $mark > 2 ? . ‘positive' : 'negative' );

Divides students’ marks into ‘positive’ and ‘negative’.

ignoring errors
$a = @(57/0);

listing folders

<?php
$out = `dir c:` ;
echo "<pre>".$out."</pre>";
?>

Checking and setting the type of a variable
$a = 56;

echo gettype($a).’’; // tells that $a is an integer number
settype($a, ‘double’); // turns it into real number, $a = 56.0
echo gettype($a).’’; // tells that $a is a real number

checks if the variable is a...
is_array()
is_double(), is_float(), is_real() – real number
is_long(), is_int(), is_integer – integer number
is_string()
is_bool()
is_object()
is_resource()
is_null()
is_scalar()
is_numeric() – has a numeric value
is_callable() – is a name of an existing function

useful while checking if the user filled specific places correctly

echo 'isset( $ema):'. isset($ema). '': // returns true if the variable exists
echo 'empty($tyresamount):'. empty($tyresamount). '': // true, if doesn’t exist or is empty

Control structures

if($amount==0)
echo 'No order placed on the previous site!' ;

To be continued.
btw. haven't I mentioned before that blogger's text formatting sucks badly?
price for being too lazy to build an own site, I guess >.>