Web Programming Step by Step

Lecture 6
Introduction to PHP

Reading: 5.1 - 5.3

Except where otherwise noted, the contents of this presentation are Copyright 2009 Marty Stepp and Jessica Miller.

The display property (4.4.4)

h2 { display: inline; background-color: yellow; }

• values: none, inline, block, run-in, compact, ...
• use sparingly, because it can radically alter the page layout

Displaying block elements as inline

<ul id="topmenu">
	<li>Item 1</li>
	<li>Item 2</li>
	<li>Item 3</li>
</ul>

#topmenu li {
	display: inline;
	border: 2px solid gray;
	margin-right: 1em;
}

• lists and other block elements can be displayed inline
  • flow left-to-right on same line
  • width is determined by content (block elements are 100% of page width)

The visibility property

p.secret {
	visibility: hidden;
}

• hidden elements will still take up space onscreen, but will not be shown
  • to make it not take up any space, set display to none instead
• can be used to show/hide dynamic HTML content on the page in response to events

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/quote2.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 as responses to web requests
• each language/framework has its pros and cons
  • we use PHP for server-side programming in this textbook

What is PHP? (5.1.2)

• 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 (5.1.1)

• 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

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 (5.2.2)

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

Variables (5.2.5)

$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
• always implicitly declared by assignment (type is not written)
• a loosely typed language (like JavaScript or Python)

Types (5.2.3)

• 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 +
  • int → float auto-conversion on /
• type-cast with (type):
  • $age = (int) "21";

Arithmetic operators (5.2.4)

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

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

Comments (5.2.7)

# 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

String type (5.2.6)

$favorite_food = "Ethiopian";
print $favorite_food[2];            # h

• zero-based indexing using bracket notation
• string concatenation operator is . (period), not +
  • 5 + "2 turtle doves" === 7
  • 5 . "2 turtle doves" === "52 turtle doves"
• can be specified with "" or ''

Interpreted strings

$age = 16;
print "You are " . $age . " years old.\n";
print "You are $age years old.\n";    # You are 16 years old.

• strings inside " " are interpreted
  • variables that appear inside them will have their values inserted into the string
• strings inside ' ' are not interpreted:

  print 'You are $age years old.\n';    # You are $age years old.\n
  

• if necessary to avoid ambiguity, can enclose variable in {}:

  print "Today is your $ageth birthday.\n";     # $ageth not found
  print "Today is your {$age}th birthday.\n";
  

for loop (same as Java) (5.2.9)

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

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

bool (Boolean) type (5.2.8)

$feels_like_summer = FALSE;
$php_is_rad = TRUE;

$student_count = 217;
$nonzero = (bool) $student_count;     # TRUE

• the following values are considered to be FALSE (all others are TRUE):
  • 0 and 0.0 (but NOT 0.00 or 0.000)
  • "", "0", and NULL (includes unset variables)
  • arrays with 0 elements
• can cast to boolean using (bool)
• FALSE prints as an empty string (no output); TRUE prints as a 1

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

Math operations

$a = 3;
$b = 4;
$c = sqrt(pow($a, 2) + pow($b, 2));

• the syntax for method calls, parameters, returns is the same as Java