Web programming - PHP Part I.

Web Programming PHP Part I. Krisztian Balog | University of
Stavanger

PHP - Originally stood for Personal Home Page - It
now stands for PHP: Hypertext Preprocessor - which is a recursive backronym - Used on ~40% of all websites - E.g., large part of Facebook’s front-end is written in PHP

Executed on the server - Client-server architecture Client Server HTTP
request HTTP response ﬁle’s extension must be .php # Web server knows from the extension # that it has to use a PHP interpreter: LoadModule php5_module "c:/php/php5apache2.dll" AddType application/x-httpd-php .php Internet

Local development - Need WAMP/MAMP running - You can also
use an online try-it editor for today’s exercises - E.g., http://phptester.net/ Both the client and the server run on the same machine. No internet connection needed. Client Server HTTP request HTTP response Your machine http://localhost refers to the web server running on your local machine

Files and editor - The PHP ﬁles need to be
placed under your www root folder - PhpStorm is being installed in the PC room - You can use Atom - https://atom.io/

Outline - Embedding and execution - Syntax - Types and
variables - Arrays - Objects

Embedding & execution

Mixing with HTML - Code embedded in between <?php …
?> - File must have .php extension! - In general, mixing HTML and PHP code is bad practice — use templating engines (coming later) <html> […] Today is: <?php echo date("Y-m-d H:i:s"); ?> […] </html>

Output to screen - We use the echo statement -
Has no return value - Can be used both with and without parentheses: echo or echo() - Marginally faster than print echo "something";

Exercise #0 https://github.com/kbalog/web-programming/tree/master/  exercises/php/basics

Syntax

General syntax - Very similar to C, and Perl (and
JavaScript) - Reserved words - function, if, this, echo, break, return, … - End lines with ; - Comments - // single line - /*  multi-line  */

Control statements - if if ($a > $b) { echo
"a is greater than b"; } else { echo "b is greater than a"; }

Control statements - switch switch ($color) { case "red": //
do something break; case "green": // do something else break; default: // default case }

Control statements - loops for ($i = 0; $i <
10; $i++) { echo $i; } $i = 0; while ($i < 10) { echo $i; $i++; }

Functions - Syntax function functionName() {  // code to be
executed  } - Note: function names are not case-sensitive - Arguments separated with a comma function functionName($arg1, $arg2) { - Arguments can have default values function functionName($arg1, $arg2=50) {

Functions (2) - Return value function add($x, $y) { return
$x+$y; }

Types & variables

Declaring variables - Always implicitly - PHP has no command
for declaring a variable - Start with $ - Variable is created the ﬁrst time it’s used $name = "John"; $age = 28; - Type is determined by the interpreter - Variable names are case-sensitive

Types - Integer - Float - String - Boolean -
Array - Object - null (reserved word)

Variable scope - declared outside a function => global scope
- declared within a function => local scope - global keyword is used to access a global variable within a function function myTest() {  global $x;  […]  }

Constants - Once deﬁned, cannot be changed or undeﬁned -
Constants are automatically global across the entire script - Convention is to use UPPERCASE for constants define("DB_SERVER", "localhost"); define("DB_USERNAME", "balog");

Operators  http://www.w3schools.com/php/php_operators.asp - Arithmetic operators - +, -, *, /,
%, ** - Assignment operators - =, +=, -=, *=, .=, … - Comparison operators - ==, <, >, !=, >=, <=, <>, … - Logical operators - &&, ||

Strings  http://www.w3schools.com/php/php_ref_string.asp - Both single and double quotes can be
used  "John" 'August' - Concatenation  $str = "two " . "words"; - Length  strlen("two"); // 3 - Interpreted strings — works only with " quotes!  $name = "John";   $str = "Hello $name"; 

- Substring  substr("Hello world!", 1, 2); // el - Searching
for substring  strpos("Hello world!", "world"); // 6 - Replacing text within a string  str_replace("world", "Dolly", "Hello world!"); // Hello Dolly! - Lowercasing/uppercasing  strtolower("Dolly"); // dolly  strtoupper("Dolly"); // DOLLY  Strings  http://www.w3schools.com/php/php_ref_string.asp

Exercises #1-#3 https://github.com/kbalog/web-programming/tree/master/  exercises/php/basics

Arrays

Types of arrays 1. Indexed arrays: Arrays with a numeric
index   $numbers = array(1, 2, 3, 4, 5); echo $numbers[0]; // 1 echo $numbers[4]; // 5  2. Associative arrays: Arrays with named keys   $colors = array( "red" => "#ff0000", "green" => "#00ff00", "blue" => "#0000ff" ); echo $colors["red"]; // #ff0000 echo $colors["blue"]; // #0000ff

Types of arrays (2) 3. Multidimensional arrays: Arrays containing one
or more arrays $marks = array( "Robert" => array( "math" => "A", "physics" => "B" ), "Sarah" => array( "math" => "C", "chemistry" => "B", "literature" => "A" ), ); echo $marks["Robert"]["math"]; // A echo $marks["Sarah"]["chemistry"]; // B

Working with indexed arrays - Iterating   $vect = array(3,
2, 4, 1);  for ($i = 0; $i < count($vect); $i++) { echo $vect[$i] . " "; } // Output: 3 2 4 1 - Sorting - From low to high: sort($vect); - From high to low: rsort($vect);

Associative arrays - Iterating   $arr = array( "lemon" =>
3, "orange" => 2, "banana" => 4, "apple" => 1 );   foreach ($arr as $key => $value) { echo "(" . $key . ": " . $value . ") "; } // Output: (lemon: 3) (orange: 2)   // (banana: 4) (apple: 1)

Associative arrays (2) - Sorting - By key - From
low to high: ksort($arr);   // apple => 1, banana => 4, lemon => 3, orange => 2 - From high to low: krsort($arr);  // orange => 2, lemon => 3, banana => 4,,apple => 1 - By value - From low to high: asort($arr);   // apple => 1, orange => 2, lemon => 3, banana => 4 - From high to low: arsort($arr);  // banana => 4, lemon => 3, orange => 2, apple => 1

More on arrays - See arrays.php on github - http://onlinephpguide.com/php-array-functions
- http://www.w3schools.com/php/php_arrays.asp

Exercises #4, #5 https://github.com/kbalog/web-programming/tree/master/  exercises/php/basics

Objects

Objects - Syntax class myClass { const CONSTANT = 'constant
value'; public $name; public $age; private $_id; function __construct($name, $age) { $this->name = $name; $this->age = $age; $this->_id = 123; } […] }

Objects - Syntax class Person { […] } - Member
variables and constants (i.e., properties) class Person { const CONSTANT = "beer"; public $name; public $age; private $_id;

Creating objects - Constructor function __construct($name, $age) { $this->name =
$name; $this->age = $age; $this->_id = 123; } - Creating a new object $c = new Person("John", 32);

Methods - Syntax: $obj->methodName($args);  class Person { […]  function getName()
{  return $this->name;  }    $c = new Person("John", 32);  echo $c->getName(); // John

Static methods - Syntax: ClassName::methodName($args);  class Person { […]  static
function saySomething() { echo self::CONSTANT; }    Person::saySomething(); // echos “beer”

Visibility (variables and methods) - public — can be accessed
everywhere - Methods declared without explicit visibility are public - Class constants are always public (cannot be made private or protected) - private — can only be accessed by the class that declared it - By convention, variables/methods are preﬁxed with _ - For example: private $_value; private function _dosomething($param) { … } - protected — an be accessed only within the class itself and by inherited classes

:: vs. ->, self vs. $this - If the variable
or method being referenced is declared as const or static, then you must use the :: operator, otherwise use -> - If you are accessing a const or static variable or method from within a class, then you must use the self-reference self - If you are accessing a variable or method from within a class that is not const or static, then you must use the self- referencing variable $this

date() function - date() function - Returns date/day/month/year/day-of-week/… as a
string - If you don’t specify a timestamp, the current date and time will be used - Use the mktime() function to get the Unix timestamp for a date - See - http://php.net/manual/en/function.date.php - http://www.w3schools.com/php/php_date.asp $d = mktime(11, 14, 54, 8, 12, 2014); echo date("Y-m-d h:i:s", $d); // 2014-08-12 11:14:54

More on Date/Time - DateTime class - Represents date and
time - You can do math on them, e.g., calculate difference - See http://php.net/manual/en/class.datetime.php - Calendar functions - Day of week, number of days in a month, etc. - See http://php.net/manual/en/ref.calendar.php

Remember - These two produce the same <h1>Days: <?php echo
$days; ?></h1> - and <?php echo"<h1>Days: ". $days; ."</h1>"; ?>

Handling input variables

HTTP requests - GET request - Variables are passed in
the URL - E.g., http://localhost/myscript.php?name=John&age=12 - Works both with links (<a href=…>) and forms - POST request - Variables are passed in the request body - Works only with forms

Form submission Client Server Internet http://…/formhandler.php <form action="formhandler.php" method="GET">

Form handling in PHP - Global variables $_GET, $_POST and
$_REQUEST contain the input variables as associative arrays - $_GET is when HTTP method GET is used - $_POST is when HTTP method POST is used - $_REQUEST is for both GET and POST methods - Avoid using $_REQUEST unless you know what you’re doing!

Example <form action="formhandler.php" method="GET"> <label>Name: <input type="text" name="name"></label><br /> <label>Age:
<input type="text" name="age"></label><br /> […] </form> echo $_GET['name']; // John  echo $_GET['age']; // 32 <form action="formhandler.php" method="POST"> <label>Name: <input type="text" name="name"></label><br /> <label>Age: <input type="text" name="age"></label><br /> […] </form> echo $_POST['name']; // John  echo $_POST['age']; // 32

Handling form input - Referencing $_GET['xxx'] or $_POST['xxx'] will raise
a NOTICE if variable xxx is not provided - echo $_GET['page']; - Notice: Undefined index: page in …/index.php

Handling form input (2) - Solution: use isset() to check
if $_GET['xxx'] (or $_POST['xxx']) is set $page = ""; if (isset($_GET['page'])) { $page = $_GET['page']; } echo $page; - A more compact solution: $page   = isset($_GET['page']) ? $_GET['page'] : "";

Separating PHP code to multiple files - <?php include "time.inc.php";
?> - Convention to use .inc.php extensions - Generally means that a file is to be included and does not make a standalone script in itself include vs. require - Included file is executed immediately!

include, require, require_once - include and require are identical, except
upon failure: - include will only produce a warning (E_WARNING) and the script will continue - require will produce a fatal error (E_COMPILE_ERROR) and stop the script - require_once will check if the ﬁle has already been included and, if so, will not require it again - Functions cannot be redeclared - To avoid errors on subsequent inclusion

PHP error levels  http://php.net/manual/en/errorfunc.constants.php - error_reporting() sets which errors are
shows - show all errors in dev environment Constant Description E_ERROR Fatal run-time errors, cannot be recovered. Execution of the script is halted. E_WARNING Run-time warnings (non-fatal errors). Execution of the script is not halted. E_PARSE Compile-time parse errors. E_NOTICE Run-time notices. The script encountered something that could be an error. E_ALL All errors and warnings

PHP error levels - error_reporting() sets which errors are shows
- show all errors in dev environment ini_set("display_errors", 1); error_reporting(E_ALL); - don’t show but log errors in production env. ini_set("display_errors", 0); ini_set("log_errors", 1); // Define where do you want the log to go ini_set("error_log", "syslog");

Remembering form input   (pseudo code) - Process input values
- If the form has been submitted - Check input values - If error - Display form with input values remembered - Else - Process form (conﬁrmation page, save to database, etc.) - Else - Display form for the ﬁrst time (i.e., empty form)

Exercise #12 https://github.com/kbalog/web-programming/tree/master/  exercises/php/basics

Exercise #12 skeleton // read in form values  $name =
get_value_post("name");  […]    // check if the form has been submitted  if ($submitted) {  // check for errors  $errors = array(); […]     if (count($errors) > 0) {  display_form($name, $email, $year, $month, $day, $sex, $terms, $errors);  }  else {  confirm($name, $email, $year, $month, $day, $sex);  }  }  else {  // display form for the first time  display_form();  }

References - Oﬃcial PHP documentation  http://php.net/docs.php - W3C PHP5 Tutorial 
http://www.w3schools.com/php/default.asp

Web programming - PHP Part I.

Web programming - PHP Part I.

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