LIS651 lecture 1 arrays functions & sessions

LIS651 lecture 1arrays functions & sessions

Thomas Krichel

2008-10-25

today

• geeky operators• more string functions• more number functions• arrays• the foreach() {} statement• functions• include() and require()• sessions

geeky increment/decrement

• ++ is an operator that adds one. The value of the resulting expression depends on the position of the operator$a=4;

print ++$a; // prints: 5

print $a; // prints: 5

$b=4;

print $b++; // prints 4

print $b; // prints 5

• -- works in the same way

geeky combined operators

• There are some combined operators that change a value and set it to the new one. For example $a+=$b ;

• is the same as $a=$a+$b;

• Same effect for -=, *=, /=, %=, and .=$a="I want ";

$b="Balitka 8";

$a.=$b;

print $a; // prints: "I want Baltika 8"

string functions

• There are a long list of string functions in the PHP reference manual. When you work with text, you should look at those string functions at

http://www.php.net/manual/en/ref.strings.php• Working with text is particularly important when

checking the input of users into your form. • I am looking at just a few of examples here. You

really need to read the reference to see what is available.

trim()• trim(string) removes the whitespace at the

beginning and the end of the string string. It returns the transformed string.$input=" Festbock ";

$output=trim($input);

print "|$output|"; // prints: |Festbock|

• whitespace is any of the following characters– the blank character– the newline– the carriage return– the tabulation character

strlen()

• strlen(string) returns the length of the string string.$zip=trim($_POST['zipcode']);

$zip_length=strlen($zip);

print $zip_length;

// hopefully, prints 5

strip_tags()

• strip_tags(string) removes HTML tags from the string string$input="<b>But</b>weiser";

print strip_tags($input); // prints: Butweiser

$in="<a href=\"http://porn.com\"><img src=\"http://porn.com/ad.gif\"/></a>";

print strip_tags($in); // prints nothing, hurray!

htmlspecialchars()

• htmlspecialchars(string) makes XML entities out of XML special characters in the string string. <,>,&, and " are transformed. It returns the transformed string.$in="What does the <div> element do?";

print htmlspecialchars($in);

// prints: What does the <div> element do?

• Using htmlspecialchars() is considered to be good security because it prevents injection of HTML and especially its <script> element.

substr()

• substr( string , start , offset) returns the substring of a string string starting at position start, with length offset.$string=“I like beer.”;

$sub=substr($string, 2, 4);

print $sub; // prints “like”

more number functions

• abs() calculates the absolute valueprint abs(-3) // prints: 3

print abs(3) // prints: 3

• max() and min() return maximum and minimum print min(2,3) // prints: 2

• rand( min , max ) returns a random integer between the integers min and max, included.

• The list of functions that use numbers is http://php.net/manual/en/ref.math.php

rand()

• rand( min , max ) returns a random integer between the integers min and max, included.

variable types

• Variables in PHP have types. You can check for typesis_numeric()

is_string()

is_int()

is_float()

• They all return a Boolean value.• They can be used to check the nature of a

variable.

arrays

• The variables we have looked at up until now are scalars. They only contain one piece of data.

• Arrays are variables that can contain more than one piece of data. – For example, a six pack in conveniently represented as

an array of cans of beer.– For another example, a class is a group of people,

each having a name, a social security number, etc.

numeric arrays• An numeric array has key value pairs where the

keys are numbers.$good_beers[0]="Baltika 8";

$good_beers[1]="Bruch Festbock";

• or as follows$lousy_beers=array("Miller Lite", "Sam Adams",

"Budweiser");

print $lousy_beers[0]; // prints: Miller Lite

print $lousy_beers[2]; // prints: Budweiser

keeping count in numeric arrays

• For numeric arrays, you can add members very simple without keeping track of number.$beers=array("Karlsberg", "Bruch") ;

$beers[]="Budweiser";

// $beer now has Karlberg, Bruch and Budweiser

print count($beers) ; // prints 3

string arrays

• Sometimes you need data structured by a string. For example for a price list. $price['Grosswald Export']=1.45;

$price['Bruch Festbock']=1.74;

// the array $price has strings as keys

• An equivalent way to declare this is $price=array('Grosswald Export' => 1.45, 'Bruch

Festbock' => 1.74);

array functions

• There is a very large number of array functions. They are described in the array function reference.

http://www.php.net/manual/en/ref.array.php• Now we are just looking at some examples.

count()

• count() returns the size of an array$price['Grosswald Export']=1.45;

$price['Bruch Festbock']=1.74;

$product_number=count($price);

print "We have $product_number products for you today.";

// prints: We have 2 products for you today.

unset()

• This can be used to unset an element$beers_drunk('Amstel' => 'good', 'Miller' =>'ok',

'Budweiser'=>'lousy');

unset($beers_drunk('Amstel');

• Now the array $beers_drunk only has two elements.

foreach() {} loop, numeric array• The foreach loop loops over arrays. You

use it as

foreach($array as $element).• The array $array is the array you are

looping through.• Each time you reach a new element, the

current element is placed in $element.

a foreach() example

$bottles=array('Amstel', 'Karlsberg', 'Sam Adams');

foreach($bottles as $beer) {print "Thomas has a $beer,\n";} // prints:// "Thomas has a Amstel, // Thomas has a Karlsberg,// Thomas has a Sam Adams,"

foreach() loop, string array• The foreach loop loops over arrays. You

use it as

foreach( $array as $key => $value ).• The array $array is the array you are

looping through.• Each time you reach a new element, the

current key is placed in $key and the value in $value.

another foreach() example

• Recall the $price string array.• Another example illustrates

print "<table caption=\"price list\">\n";

foreach ($price as $item => $euro_amount) {

print "<tr><td>$item</td>\n";

print "<td>€$euro_amount</td></tr>\n";

}

print "</table>";

• This prints the full price list. But it could also do the whole form. This is fabulous!

foreach() example from the form

• $_GET is an array. You can loop through it.

foreach($_GET as $control => $value) {

print “you set $control to $value<br/>\n”;

}

the well-aligned price table$l_r=array('left','right');

$count=0; // counter of elements printed

print "<table caption=\"price list\">\n";

foreach ($price as $item => $euro_amount) {

print "<tr><td align=\"$l_r[$count % 2]\"";

print "$item";

$count++;

print "</td>\n<td align=$l_r[$count % 2]\">

€$euro_amount</td></tr>\n";

$count++;

}

print "</table>\n";

// This produces something like

// <table caption="price list">

// <tr><td align="left">Grosswald Export</td>

// <td align="right">€1.45</td></tr>

// <tr><td align="left">Bruch Festbock</td>

// <td align="right"'>€1.74</td></tr>

// </table>

multiple arrays• Example

$products[0]['name']="Grosswald Pilsener";

$products[0]['price']=1.56;

$products[1]['name']="Grosswald Export";


$products[2]['name']="Bruch Landbier";


printing a debugging representation $a = array ('a' => 'apple', 'c' => array ('one', 'two'));

print_r ($a); // prints a debugging representation:Array

(

[a] => apple

[c] => Array

(

[0] => one

[1] => two

)

)

functions

• The PHP function reference is available on its web site http://php.net/quickref.php. It shows the impressive array of functions within PHP.

• But one of the strengths of PHP is that you can create your own functions as you please.

• If you recreate one of the built-in functions, your own function will have no effect.

simplest function

function beer_print {

print "beer\n";

}

beer_print() ; // prints: “beer” and newline

A more practical example

• Stephanie Rubino was an English teacher and objects to sentences likeYou have ordered 1 bottles of Grosswald Pils.

• Let us define a function rubino_print(). It will take three arguments– a number to check for plural or singular– a word for the singular– a word for the plural

a function and its arguments• declare the arguments to the function in

parenthesisfunction rubino_print ($number, $singular,$plural) {

if($number == 1) {

print "one $singular";

}

else {

print "$number $plural";

}

}

rubino_print(3,'woman','women'); // prints: “3 women”

default arguments

• Sometimes you want to allow a function to be called without giving all its arguments. You can do this by declaring a default value, using an equal sign in the function listfunction thomas_need($thing='beer') {

print "Thomas needs $thing.\n";

}

thomas_need(); // prints: “Thomas needs beer.”

thomas_need('vodka'); // prints: “Thomas needs vodka”.

rubino_print using common plurals function rubino_print ($num, $sing,$plur=1) { if($num == 1) {

print "one $sing";

}

elseif($plur ==1) {

print "$num $sing"."s";

}

else {

print "$num $plur";

}

}

rubino_print(6,'beer') // prints: “6 beers”

return value• Up until now we have just looked at the side

effect of a function. • "return" is a special command that returns a

value.• It takes the return value as a parameter

return $result;

• When return is used, the function is left. Example function good_beer () { return 'Festbock';}$beer=good_beer;print $beer ; // prints: “Festbock”.

rubino_print with return

function rubino_print ($number, $singular,$plural) {

if($number == 1) {

return "one $singular";

}

return "$number $plural";

}

$order=rubino_print(2,"beer","beers");

print "you ordered $order\n";

// prints: you ordered 2 beers.

utility function for database queriesfunction mysql_fetch_all($query) {

$r=@mysql_query($query);

if($err=mysql_error()) {

return $err;

}

if( mysql_num_rows($r) ) {

while($row=mysql_fetch_array($r)) {

$result[]=$row;

}

return $result;

}

}

usage example

my $query="SELECT * FROM my_table";

if(is_array($rows=mysql_fetch_all($query)) {

// do something

}

else { if (! is_null($rows)) {

die("Query failed!");}

}

visibility of variables• Variables used inside a function are not visible

from the outside. Example$beer="Karlsberg";

function yankeefy ($name='Sam Adams') {

$beer=$name;

}

yankeefy();

print $beer; // prints: Karlsberg

• The variable inside the function is something different than the variables outside.

accessing global variables.

• There are two ways to change a global variable, i.e. one that is defined in the main script.

• One is just to call it as $GLOBAL['name'] where name is the name of the global variable.function yankeefy ($name="Sam Adams") {

$GLOBALS['beer']="name";

}

• The other is to change it outside a function definition.

• Example in brewer_quiz.php

working with many source files

• Many times it is useful to split a PHP script into several files.

• PHP has two mechanisms.• require(file) requires the to be included. If the file

is not there, PHP exits with an error.• include(file) includes the file.

require() and include()

• Both assume that you leave PHP. Thus within your included file you can write simple HTML.

• If you want to include PHP in your included file, you have to surround it by <?php and ?>, just like in a PHP script.

• Here is an example to use include to build the basic web page.

top.html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html>

<head><title>$title</title>

<meta http-equiv="content-type" content="text/html; charset=UTF-8"/>

<link rel="stylesheet" type="text/css" href="main.css"/>

</head>

<body>

bottom.html

<p id="validator">

<a href="http://validator.w3.org/check?uri=referer"><img

style="border: 0pt"

src="http://wotan.liu.edu/valid-xhtml10.png"

alt="Valid XHTML 1.0!" height="31" width="88" /></a>

</p>

</body>

</html>

trouble

• $title in the top.html is not understood as the title. It reads as $title, which means "idiot" for your web user.

• Even if you replace $title with <?php $title ?>

$title is empty. The definition from the outer file is not seen in the included file.

• So you have to split into three files, and print the title in the main file. I leave that to you to figure out.

login.php & create_account.php

• Both require a database that has three fields– id which is an auto_increment int acting as a handle– username is the username of the account. it must be

unique and this is enforced by mySQL– password is a varchar(41) because the sha1 of the

password is stored. This is 40 chars long.

sessions

• You will recall that HTTP is a stateless protocol. Each request/response is self-contained.

• Statefulness is crucial in Web applications. Otherwise users have to authenticate every time they access a new page.

• Traditionally, one way to create statefulness is to use cookies.

• PHP uses cookies to create a concept of its own, sessions, that makes it all very easy.

cookies

• A cookie is a piece of attribute/value data. A server can send cookies as value of a HTTP header Set-Cookie:. Multiple headers may be sent.

• When the client visits the web site again, it will send the cookie back to the server with a HTTP header Cookie:

Set-Cookie• Set-Cookie: name=value; [expires= date;]

[path=path;] [domain= domain] [secure]• where

– name= is the variable name set in the cookie– value= is the variable's value– date= is a date when the cookie expires– path= restricts the cookie to be sent only when requests

to a path starting with path are made– domain= restricts the sending of the cookie to a certain

domain– secure restricts transmission to https

Cookies:

• The browser compares the request it wants to make with the URL and the domain that sent the cookie.

• If the path is not set the cookie will only be sent to a request with the originating URL.

• If the cookie matches the request a request header of the form

Cookie: name1=value1 ; name2=value2

is sent.

sessions

• Sessions are a feature of PHP. PHP remembers a session through a special cookie PHPSESSID.

• To activate the sessions, include session_start(); at the beginning of your script, before any printing has been done.

• One a session is active, you have a special super-global variable $_SESSION. Session data is stored in special files on wotan.

$_SESSION

• This is an array where you can read and set variables that you want to keep during the session.if($_SESSION[user_name]) {

print "welcome $_SESSION[user_name]";

}

else {

// show users login form

print login_form();

}

ending sessions

• At 9 and 39 past each hour, wotan deletes all session files that have not been changed for 24 minutes or more.

• If you want to remove a session yourself, you can call session_destroy() in your script.

• An example is in visit.php.

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Thank you for your attention!

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LIS651 lecture 1 arrays functions & sessions