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PHP Language Basics
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PHP code starts with <?php
and ends with ?> written to a .php file <?php // statements ?>
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anywhere in an HTML content
PHP code can be placed anywhere in an HTML content <?php // PHP can be placed here ?> <html><head> </head><body> <?php // or here... ?> </body></html> <?php // or even here ?>
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To put a string into the HTML of a PHP-generated page, use echo
(It’s like Java’s System.out.println) echo “Printy”; echo(“Printy”); // also valid
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You can specify multiple items to print by separating them with commas
echo “First”, “second”, “third”; Firstsecondthird
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There is a shorter way to
echo a variable <span><?php echo $name; ?></span> // shorter <span><?=$name?></span>
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To check the type and content of a variable, use the var_dump() function
var_dump($a); // int(10)
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We can easily put multiline strings into your program with a heredoc
(here documents) $html = <<< EndOfQuote <html><head> </head><body> Hello World! </body></html> EndOfQuote;
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The names of user-defined classes and functions, as well as
built-in constructs and keywords are case-insensitive
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Thus, these three lines are equivalent: echo(“hello, world”);
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Null keywords are also case-insensitive $val = null; // same
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Variables, on the other hand, are case-sensitive.
That is, $name, $NAME, and $NaME are three different variables
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to separate statements
PHP uses semicolons to separate statements
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echo “Hello, world”; myFunction(42, “O'Reilly”); $a = 1; $name = “Elphaba”; $b = $a / 25.0; if ($a == $b) { echo “Rhyme? And Reason?”; }
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Whitespace doesn’t matter
in a PHP program
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For example, this statement: could just as well be written
raisePrices($inventory, $inflation, $costOfLiving, $greed); could just as well be written with more whitespace: raisePrices ( $inventory , $inflation , $costOfLiving , $greed ) ; or with less whitespace: raisePrices($inventory,$inflation,$costOfLiving,$greed);
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PHP provides several ways to include comments within your code
(all of which are borrowed from existing languages such as C, C++, and the Unix shell)
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Shell-style comments:
# create an HTML form requesting # that the user confirm the action echo confirmationForm();
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C++ comments: // create an HTML form requesting
// that the user confirm the action echo confirmationForm();
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C comments: /* create an HTML form requesting
that the user confirm the action */ echo confirmationForm();
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Variable names always begin with a dollar sign ($)
and are case-sensitive
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Here are some valid variable names: $bill $head_count $MaximumForce
$I_HEART_PHP $_underscore $_int
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Here are some illegal variable names:
$not valid $| $3wa
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another of a different type
You can replace a variable’s value with another of a different type (known as type juggling) $what = “Fred”; $what = 35; $what = array(“Fred”, 35);
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You can reference the value of a variable whose name
is stored in another variable $foo = “bar”; $$foo = “baz”; // $bar = “baz”
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What variable contains 100?
$foo = ‘bar’; $$foo = ‘world’; $$$foo = 100;
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constant cannot change. Only scalar values can be constants
Once set, the value of a constant cannot change. Only scalar values (Booleans, integers, floats, and strings) can be constants
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Constants are set using the define() function:
define(‘PUBLISHER’, “O’Reilly”); echo PUBLISHER;
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Update: PHP 7 allows us to define array constants
define(‘NAME’, [‘One’,‘Two’,‘Three’]);
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You cannot give a variable, function, class, or constant
the same name as a keyword
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__CLASS__ and endforeach __DIR__ array() endif __FILE__ as endswitch __FUNCTION__ break endwhile __LINE__ echo eval() __METHOD__ else exit() __NAMESPACE__ elseif extends __TRAIT__ empty() final __halt_compiler() enddeclare insteadof abstract endfor interface
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isset() require_once default list() return die() namespace callable do new case for or catch foreach print class function private clone global protected const goto public continue if require declare implements
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include var include_once while instanceof xor static switch throw trait try unset() use
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In PHP, arithmetic operators are very similar to that in Java
$b = 3; var_dump($a + $b); // 13 var_dump($a - $b); // 7 var_dump($a * $b); // 30 var_dump($a / $b); // var_dump($a % $b); // 1 var_dump($a ** $b); // 1000 var_dump(-$a); // -10
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Assignment operators are also very similar
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But be careful! $a = ‘1’; $b = 2; $c = $a + b; $d = $a . $b;
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There are also incrementing and decrementing operators
$b--;
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Comparison operators are similar, too
var_dump(2 < 3); // true var_dump(3 < 3); // false var_dump(3 <= 3); // true var_dump(4 <= 3); // false var_dump(2 > 3); // false var_dump(3 >= 3); // true var_dump(3 > 3); // false
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And so are the logical operators
var_dump(true && true); var_dump(true && false); var_dump(true || false); var_dump(false || false); var_dump(!false);
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But there are the PHP 7’s new “spaceship” operator
var_dump(1 <=> 5); var_dump(1 <=> 1); var_dump(5 <=> 2);
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PHP 7 also introduces the new null coalesce operator
$uname = isset($_GET['uname']) ? $_GET['uname'] : 'guest'; var_dump($uname); $uname = $_GET['uname'] ?? 'guest'; $_GET['uname'] = 'admin';
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When comparing values, we need to be careful with type juggling
var_dump($a == $b); var_dump($a === $b); var_dump($a != $b); var_dump($a !== $b); var_dump($a == $c); var_dump($a <> $c);
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Strings are delimited by either single or double quotes ‘big dog’
“fat hog”
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Variables are interpolated within double quotes, while
within single quotes they are not
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Interpolation is the process of replacing variable names in the
string with the values of those variables
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$name = “Guido”; echo “Hi, $name”; echo ‘Hi, $name’; Hi, Guido Hi, $name
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The other way is to surround the variable being interpolated with curly braces
echo “You are the $nth person”; echo “You are the {$n}th person”; You are the 12th person
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What’s the output? $var = ‘world’; $$var = 100;
echo ‘Hello $var<br>’; echo “Hello $var<br>”; echo ‘Hello $world<br>’; echo “Hello $world<br>”;
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To test whether two strings are equal, use the == operator
if ($a == $b) { echo “a and b are equal” }
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Use the is_string() function
to test whether a value is a string if (is_string($x)) { // $x is a string }
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gets the length of a string
The strlen() function gets the length of a string $s = ‘FILKOM UB’; echo strlen($s); // 9
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The strtolower() function converts all characters in
a string to lowercase $s = ‘FILKOM UB’; echo strtolower($s); // filkom ub
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The strtoupper() function converts all characters in a string to uppercase
$s = ‘filkom ub’; echo strtoupper($s); // FILKOM UB
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The trim() function removes all blank spaces surrounding a string
$s = ‘ FILKOM UB ’; echo trim($s); // FILKOM UB
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To concatenate a string, use the dot operators
$s1 = ‘FILKOM ’; $s2 = ‘UB’; $s3 = $s1 . $s2; // FILKOM UB
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Use the is_bool() function to test whether a value is a Boolean or not
if (is_bool($x)) { // $x is a Boolean }
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Use unset() to remove a variable $name = “Fred”;
unset($name); // throws a PHP notice
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has been set to something,
To see if a variable has been set to something, use isset() $s1 = isset($name); // $s1 is false $name = “Fred”; $s2 = isset($name); // $s2 is true
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values all evaluate to false:
In PHP, the following values all evaluate to false: The keyword false The integer 0 The floating-point value 0.0 The empty string (“”) and the string “0” An array with zero elements An object with no values or functions The NULL value
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$val = “”; if ($val) { // this won’t be executed }
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bye.
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