How the Web Works: Lecture 3

$1 Million for building a movie recommendation engine.

Lecture 3 The Web and PHP

User Web Server

GET helloworld.com User Web Server

GET helloworld.com User Web Server <html> <head> <title> Hello </title>
</head> <body> World! </body> </html>

User Web Server

POST helloworld.com cmd: make me a sandwich User Web Server

POST helloworld.com cmd: make me a sandwich User Web Server
<html> <head> <title> Hello </title> </head> <body> World! </body> </html>

User Web Server

You Idiot! Is that all you can do? User Web
Server

You Idiot! Is that all you can do? User Web
Server <html> <head> <title> Make Your Own </title> </head> <body> @#$%#^%$&^&$ </body> </html>

Static Pages + Placeholders <html> <head> <title> <?php $title ?>
</title> </head> <body> <?php $text ?> </body> </html> Computed Results +

<html> <head> <title> Hello </title> </head> <body> World </body> </html>

GET index.html <html> <head> <title> Hello </title> </head> <body> World
</body> </html>

GET index.html Return HTML <html> <head> <title> Hello </title> </head>
<body> World </body> </html>

GET index.html Return HTML <html> <head> <title> Hello </title> </head>
<body> World </body> </html> STATIC

GET index.php <html> <head> <title> <?php $title ?> </title> </head>
<body> <?php $text ?> </body> </html>

<body> <?php $text ?> </body> </html> Interpreter <html> <head> <title> Hello </title> </head> <body> World </body> </html>

<body> <?php $text ?> </body> </html> Return HTML Interpreter <html> <head> <title> Hello </title> </head> <body> World </body> </html>

<body> <?php $text ?> </body> </html> Return HTML Interpreter <html> <head> <title> Hello </title> </head> <body> World </body> </html> Dynamic

Can I see the PHP?

How Is that Useful?

Step 1: Take Input

Step 1: Take Input Step 2: Compute Results

Step 1: Take Input Step 2: Compute Results Step 3:
Put results in template

Step 1: Take Input Step 2: Compute Results Step 3:
Put results in template Step 4: Spit out HTML

I can do that too!

Why PHP? ... so can Perl, Python, Java, Ruby, or
even C PHP is easy to learn Syntax similar to Java Most popular Lots of (open) code out there - ex. Wordpress.

Hello, World! <html> <head> <title>My Page</title> </head> <body> <?php print
"Hello, World"; ?> </body> </html>

Hello, World! <html> <head> <title>My Page</title> </head> <body> <?php print
"Hello, World"; ?> </body> </html> = <html> <head> <title>My Page</title> </head> <body> Hello, World </body> </html>

Ask Now or everything else will seem so pointless you’ll
want to shoot me with a nerf gun.

Syntax Party!

Syntax Overview Always between <?php and ?> End lines with
; Case Sensitive Syntax similar to Java Variables Weakly Typed!

Variables Dont need to declare Prefixed with $ No explicit
type! Assign with = operator No integer / floats Boolean true or false <?php $var = 23; print $var; $var = "Hello"; print $var; $c = 2; print $c/2; $b = true; ?>

Operators + - * / % == < > <=
>= String Concatenation (.) && || ! XOR <?php $a = 23; $b = 15; print $a + $b; $var = "Hello" . “World”; $c = true; $d = false; $a = $c || $d; ?>

Comments <?php /* Multiline Comment */ $var = 23; print
$var; // Single Line Comment $var = "Hello"; print $var; ?> C++ / Java Style Comments

String Quoting Strings can be “string” or ‘string’, char not
special. Single Quotes ‘ ‘ - printed literally Double quotes “ “ - can embed values <?php $lang = “PHP”; $string1 = “I like $lang”; $string2 = ‘I like $lang’; print $string1; print $string2; ?>

String Quoting Strings can be “string” or ‘string’, char not
special. Single Quotes ‘ ‘ - printed literally Double quotes “ “ - can embed values $string1: I like PHP $string2: I like $lang <?php $lang = “PHP”; $string1 = “I like $lang”; $string2 = ‘I like $lang’; print $string1; print $string2; ?>

Arrays Created with array() ... actually Hash Tables Indices dont
have to be numbers! Appending with $arr[] Similar to PERL <?php $arr = array(); $arr[32] = 23; // following appends to [33] $arr[] = 24 $arr = array(“foo”=>1, “bar”=>2); print $array[“foo”]; print $array[“bar”]; ?> http://php.net/manual/en/language.types.array.php

Arrays ... are a (potentially) many-one mapping between any types
foo bar baz A B C

Arrays ... are a (potentially) many-one mapping between any types
foo bar baz gorp A B C

$_GET Special Array! Params passed in URL $val = $_GET[‘key’]
<?php $n1 = $_GET[‘n1’]; $n2 = $_GET[‘n2’]; $sum = $n1 + $n2; print “sum is $sum”; ?>

$_POST Similar to $_GET POST parameters $val = $_POST[‘key’] Processing
Forms <?php $a = 23; $b = 15; print $a + $b; $var = "Hello" . “World”; $c = true; $d = false; $a = $c || $d; ?>

Demo 1 PHP Form Processing

Control Flow, Functions

If Similar to C++/Java Things that are false: false “”
0 NULL Everything Else True if ($color == “red”) { print “red”; } else if ($color = “blue”) { print “blue”; } else { print “no color”; }

For Similar to C++/Java | ‘while’ also available | foreach
favored for ($i = 0; $i < 10; $i++) { print $i; }

Foreach Iterates as key, value pair or just as values
Similar to Java’s for(int a : arr) $languages = array( ‘best’ => ‘php’, ‘worst’ => ‘brainf*ck’, ‘easy’ => ‘php’ ); // Iterate as key-value pair foreach ($languages as $adj => $lang) { print “The $adj language is $lang”; } // Iterate over values foreach ($languages as $lang) { print “One language is $lang”; }

Functions Keyword function No return types Take/not take arguments Overloading
function count($i, $max = 10) { while ( $i< $max) { print $i; } } function factorial($n) { if ($n == 0) return 0; return $n * factorial($n-1); }

Demo 2 Some Functions and Iteration

Cookies & Sessions

Cookies

GET index.php Cookies

GET index.php Return Cookie + HTML Cookies

Cookies Website can store info on user’s computer. ... in
small files called “Cookies” Set with setcookie() Access with $_COOKIE Happens in HTTP header, before any HTML setcookie ($name, $value, $expire) $new_value = $_COOKIE[$name]; http://php.net/manual/en/function.setcookie.php

Already Logged In

Already Logged In Submitted Login Form

Already Logged In Submitted Login Form Not Logged In, Show
Login Form

Sessions Also store user info. ... on server Across multiple
pages $_SESSION[‘key’] = ‘val’ Login / Shopping Carts Data can’t be tampered session_start(); if (isset($_SESSION[‘user’])) { print “Welcome Back!”; } else { // Get $name from form $_SESSION[‘user’] = $name; }

Already Logged In

Already Logged In Submitted Login Form

Already Logged In Submitted Login Form Not Logged In, Show
Login Form

Example 3 Login/Logout

Object Oriented

Classes Logical group of variables and functions “public” & “private”
supported Use the class keyword -> to access members

Inheritance

Using Classes

Useful Functions print_r($arr) : Prints arrays, useful in debugging require_once(‘lib.php’)
: Imports other PHP files header($data) : Sets HTTP headers (Google for more) isset($var) : Checks is variable has a value explode($delimiter, $string) : Splits string to array mail($to, $subject, $message) : Sends email! htmlspecialchars($string) : Preventing XSS Attacks

Resources CCCPHP http://sipb-iap.scripts.mit.edu/2009/cccphp/CCCPHP.pdf PHP.net Google “php ___”

Week 3 Week 4

Announcement Homework 1 isn’t out yet Involves HTML, PHP, MySQL
I haven’t coded it yet =P Minis are now Extra Credit 2 Minis = 1 Homework Minis can cover for Homeworks

Photo Credits http://upload.wikimedia.org/wikipedia/zh/e/ea/PHP-logo.png http://benewmark.com/lafayette/homework_title.gif http://www.google.com/intl/en_ALL/images/logo.gif http://blog.crowdspring.com/wp-content/uploads/2009/04/netﬂix-prize.png http://www.mccullagh.org/db9/1ds-16/world-space-party-2007.jpg http://blog.motane.lu/wp-content/uploads/2009/09/mysql-logo.png http://www.coincommunity.com/forum/uploaded/Jaobler/2008516_50DolStarNote.jpg

How the Web Works: Lecture 3

How the Web Works: Lecture 3

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