Web Programming Step by Step, 2nd Edition

Lecture 7: Embedded PHP

Reading: 5.3 - 5.5

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.

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"

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

$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 ''

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";
  

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"

bool (Boolean) type

$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

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

NULL

$name = "Victoria";
$name = NULL;
if (isset($name)) {
	print "This line isn't going to be reached.\n";
}

• a variable is NULL if
  • it has not been set to any value (undefined variables)
  • it has been assigned the constant NULL
  • it has been deleted using the unset function
• can test if a variable is NULL using the isset function
• NULL prints as an empty string (no output)

Arrays

$name = array();                         # create
$name = array(value0, value1, ..., valueN);

$name[index]                              # get element value
$name[index] = value;                      # set element value
$name[] = value;                          # append

$a = array();     # empty array (length 0)
$a[0] = 23;       # stores 23 at index 0 (length 1)
$a2 = array("some", "strings", "in", "an", "array");
$a2[] = "Ooh!";   # add string to end (at index 5)

• to append, use bracket notation without specifying an index
• element type is not specified; can mix types

Array functions

Array function example

$tas = array("MD", "BH", "KK", "HM", "JP");
for ($i = 0; $i < count($tas); $i++) {
	$tas[$i] = strtolower($tas[$i]);
}                                 # ("md", "bh", "kk", "hm", "jp")
$morgan = array_shift($tas);      # ("bh", "kk", "hm", "jp")
array_pop($tas);                  # ("bh", "kk", "hm")
array_push($tas, "ms");           # ("bh", "kk", "hm", "ms")
array_reverse($tas);              # ("ms", "hm", "kk", "bh")
sort($tas);                       # ("bh", "hm", "kk", "ms")
$best = array_slice($tas, 1, 2);  # ("hm", "kk")

• the array in PHP replaces many other collections in Java
  • list, stack, queue, set, map, ...

The foreach loop

foreach ($array as $variableName) {
	...
}

$stooges = array("Larry", "Moe", "Curly", "Shemp");
for ($i = 0; $i < count($stooges); $i++) {
	print "Moe slaps {$stooges[$i]}\n";
}
foreach ($stooges as $stooge) {
	print "Moe slaps $stooge\n";  # even himself!
}

• a convenient way to loop over each element of an array without indexes

Functions

function name(parameterName, ..., parameterName) {
	statements;
}

function bmi($weight, $height) {
	$result = 703 * $weight / $height / $height;
	return $result;
}

• parameter types and return types are not written
• a function with no return statements is implicitly "void"
• can be declared in any PHP block, at start/end/middle of code

Calling functions

name(expression, ..., expression);

$w = 163;  # pounds
$h = 70;   # inches
$my_bmi = bmi($w, $h);

• if the wrong number of parameters are passed, it's an error

Variable scope: global and local vars

$school = "UW";                   # global
...

function downgrade() {
	global $school;
	$suffix = "(Wisconsin)";        # local

	$school = "$school $suffix";
	print "$school\n";
}

• variables declared in a function are local to that function; others are global
• if a function wants to use a global variable, it must have a global statement
  • but don't abuse this; mostly you should use parameters

Default parameter values

function name(parameterName = value, ..., parameterName = value) {
	statements;
}

function print_separated($str, $separator = ", ") {
	if (strlen($str) > 0) {
		print $str[0];
		for ($i = 1; $i < strlen($str); $i++) {
			print $separator . $str[$i];
		}
	}
}

print_separated("hello");        # h, e, l, l, o
print_separated("hello", "-");   # h-e-l-l-o

• if no value is passed, the default will be used (defaults must come last)

Printing HTML tags in PHP = bad style

<?php
print "<!DOCTYPE html>\n";
print "<html>\n";
print "  <head>\n";
print "    <title>Geneva's web page</title>\n";
...
for ($i = 1; $i <= 10; $i++) {
	print "<p class=\"count\"> 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

<?= expression ?>

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

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

Expression block example

<!DOCTYPE html>
<html>
	<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>

• expression blocks can even go inside HTML tags and attributes