Web Programming Step by Step

Lecture 6
Introduction to PHP

Reading: 5.1 - 5.3

5.1: Server-Side Basics

5.1: Server-Side Basics
5.2: PHP Basic Syntax
5.3: Embedded PHP
5.4: Advanced PHP Syntax

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? (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
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!";
?>

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

5.2: PHP Basic Syntax

5.1: Server-Side Basics
5.2: PHP Basic Syntax
5.3: Embedded PHP
5.4: Advanced PHP Syntax

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!';

Hello, World! Escape "chars" are the SAME as in Java! You can have line breaks in a string. A string can use "single-quotes". It's cool!

some PHP programmers use the equivalent echo instead of print

Arithmetic operators (5.2.4)

+ - * / % . ++ -- = += -= *= /= %= .=
many operators auto-convert types: 5 + "7" is 12

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
implicitly declared by assignment (type is not written; a "loosely typed" language)

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 + ("1" + 1 == 2)
- int → float auto-conversion on / (3 / 2 == 1.5)
type-cast with (type):
- $age = (int) "21";

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

`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";
}

`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

PHP syntax template

HTML content

	<?php
		PHP code
	?>

HTML content

	<?php
		PHP code
	?>

HTML content ...

any contents of a .php file between <?php and ?> are executed as PHP code
all other contents are output as pure HTML
can switch back and forth between HTML and PHP "modes"

Math operations

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

math functions
`abs`	`ceil`	`cos`	`floor`	`log`	`log10`	`max`
`min`	`pow`	`rand`	`round`	`sin`	`sqrt`	`tan`

math constants
`M_PI`	`M_E`	`M_LN2`

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

`int` and `float` types

$a = 7 / 2;               # float: 3.5
$b = (int) $a;            # int: 3
$c = round($a);           # float: 4.0
$d = "123";               # string: "123"
$e = (int) $d;            # int: 123

int for integers and float for reals
division between two int values can produce a float

`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" produces 7
- 5 . "2 turtle doves" produces "52 turtle doves"
can be specified with "" or ''

String interpolation (variable injection)

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

variables inside " " are interpolated (i.e., injected)
- variables' values will be inserted into the string at that position

variables inside ' ' are not interpolated:

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";

`String` functions

# index  0123456789012345
$name = "Stefanie Hatcher";
$length = strlen($name);              # 16
$cmp = strcmp($name, "Brian Le");     # > 0
$index = strpos($name, "e");          # 2
$first = substr($name, 9, 5);         # "Hatch"
$name = strtoupper($name);            # "STEFANIE HATCHER"

Name	Java Equivalent
`strlen`	`length`
`strpos`	`indexOf`
`substr`	`substring`
`strtolower`, `strtoupper`	`toLowerCase`, `toUpperCase`
`trim`	`trim`
`explode`, `implode`	`split`, `join`
`strcmp`	`compareTo`

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
- "", "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

TRUE and FALSE keywords are case insensitive

5.3: Embedded PHP

5.1: Server-Side Basics
5.2: PHP Basic Syntax
5.3: Embedded PHP
5.4: Advanced PHP Syntax

Printing HTML tags in PHP = bad style

<?php
print "<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.1//EN\"\n";
print " \"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd\">\n";
print "<html xmlns=\"http://www.w3.org/1999/xhtml\">\n";
print "  <head>\n";
print "    <title>Geneva's web page</title>\n";
...
for ($i = 1; $i <= 10; $i++) {
	print "<p> I can count to $i! </p>\n";
}
?>

printing HTML tags with print statements is bad style and error-prone:
- must quote the HTML and escape special characters, e.g. \"
but without print, how do we insert dynamic content into the page?

PHP expression blocks (5.3.2)

<?= expression ?>

<h2> The answer is <?= 6 * 7 ?> </h2>

The answer is 42

PHP expression block: evaluates and embeds an expression's value into HTML
<?= expr ?> is equivalent to <?php print expr; ?>

Expression block example

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
 "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
	<head><title>CSE 190 M: Embedded PHP</title></head>	
	<body>
		<?php for ($i = 99; $i >= 1; $i--) { ?>
			<p> <?= $i ?> bottles of beer on the wall, <br />
				  <?= $i ?> bottles of beer. <br />
				  Take one down, pass it around, <br />
				  <?= $i - 1 ?> bottles of beer on the wall. </p>
		<?php } ?>
	</body>
</html>

Common errors: unclosed braces, missing = sign

	<body>
		<p>Watch how high I can count:
			<?php for ($i = 1; $i <= 10; $i++) { ?>
				<? $i ?>
		</p>
	</body>
</html>

</body> and </html> above are inside the for loop, which is never closed
if you forget to close your braces, you'll see an error about 'unexpected $end'
if you forget = in <?=, the expression does not produce any output

Complex expression blocks

	<body>
		<?php for ($i = 1; $i <= 3; $i++) { ?>
			<h<?= $i ?>>This is a level <?= $i ?> heading.</h<?= $i ?>>
		<?php } ?>
	</body>

This is a level 1 heading.

This is a level 2 heading.

This is a level 3 heading.

expression blocks can even go inside HTML tags and attributes

Web Programming Step by Step, Lecture 6-B

Introduction to PHP