Web Programming Step by Step, 2nd Edition

Lecture 6: Intro to PHP

Reading: 5.1 - 5.2

Except where otherwise noted, the contents of this document are Copyright 2012 Marty Stepp, Jessica Miller, and Victoria Kirst. All rights reserved. Any redistribution, reproduction, transmission, or storage of part or all of the contents in any form is prohibited without the author's expressed written permission.

URLs and web servers

http://server/path/file

• usually when you type a URL in your browser:
  • your computer looks up the server's IP address using DNS
  • your browser connects to that IP address and requests the given file
  • the web server software (e.g. Apache) grabs that file from the server's local file system, and sends back its contents to you

• some URLs actually specify programs that the web server should run, and then send their output back to you as the result:

  https://webster.cs.washington.edu/cse190m/quote.php
  

  • the above URL tells the server webster.cs.washington.edu to run the program quote2.php and send back its output

Server-Side web programming

• server-side pages are programs written using one of many web programming languages/frameworks
  • examples: PHP, Java/JSP, Ruby on Rails, ASP.NET, Python, Perl
• the web server contains software that allows it to run those programs and send back their output
• each language/framework has its pros and cons
  • we use PHP for server-side programming in this textbook

What is PHP?

• PHP stands for "PHP Hypertext Preprocessor"
• a server-side scripting language
• used to make web pages dynamic:
  • provide different content depending on context
  • interface with other services: database, e-mail, etc
  • authenticate users
  • process form information
• PHP code can be embedded in XHTML code

Lifecycle of a PHP web request

• browser requests a .html file (static content): server just sends that file
• browser requests a .php file (dynamic content): server reads it, runs any script code inside it, then sends result across the network
  • script produces output that becomes the response sent back

Why PHP?

There are many other options for server-side languages: Ruby on Rails, JSP, ASP.NET, etc. Why choose PHP?

• free and open source: anyone can run a PHP-enabled server free of charge
• compatible: supported by most popular web servers
• simple: lots of built-in functionality; familiar syntax
• available: installed on UW's servers (Dante, Webster) and most commercial web hosts
• well-documented: type php.net/functionName in browser Address bar to get docs for any function

Hello, World!

The following contents could go into a file hello.php:

<?php
print "Hello, world!";
?>

• a block or file of PHP code begins with <?php and ends with ?>
• PHP statements, function declarations, etc. appear between these endpoints

Viewing PHP output

• you can't view your .php page on your local hard drive; you'll either see nothing or see the PHP source code
• if you upload the file to a PHP-enabled web server, requesting the .php file will run the program and send you back its output

Console output: print

print "text";

print "Hello, World!\n";
print "Escape \"chars\" are the SAME as in Java!\n";

print "You can have
line breaks in a string.";

print 'A string can use "single-quotes".  It\'s cool!';

• some PHP programmers use the equivalent echo instead of print

Arithmetic operators

• + - * / %
. ++ --
= += -= *= /= %= .=

• many operators auto-convert types: 5 + "7" is 12

Variables

$name = expression;

$user_name = "PinkHeartLuvr78";
$age = 16;
$drinking_age = $age + 5;
$this_class_rocks = TRUE;

• names are case sensitive; separate multiple words with _
• names always begin with $, on both declaration and usage
• implicitly declared by assignment (type is not written; a "loosely typed" language)

Types

• basic types: int, float, boolean, string, array, object, NULL
  • test what type a variable is with is_type functions, e.g. is_string
  • gettype function returns a variable's type as a string (not often needed)
• PHP converts between types automatically in many cases:
  • string → int auto-conversion on +      ("1" + 1 == 2)
  • int → float auto-conversion on /      (3 / 2 == 1.5)
• type-cast with (type):
  • $age = (int) "21";

Comments

# single-line comment

// single-line comment

/*
multi-line comment
*/

• like Java, but # is also allowed
  • a lot of PHP code uses # comments instead of //
  • we recommend # and will use it in our examples

for loop

for (initialization; condition; update) {
	statements;
}

for ($i = 0; $i < 10; $i++) {
	print "$i squared is " . $i * $i . ".\n";
}

if/else statement

if (condition) {
	statements;
} elseif (condition) {
	statements;
} else {
	statements;
}

• NOTE: although elseif keyword is much more common, else if is also supported

while loop (same as Java)

while (condition) {
	statements;
}

do {
	statements;
} while (condition);

• break and continue keywords also behave as in Java