Web Programming Step by Step

Lecture 7
PHP Syntax

Reading: 5.2 - 5.4

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

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));

• 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

$favorite_food = $favorite_food . " cuisine";
print $favorite_food;               # Ethiopian cuisine

• zero-based indexing using bracket notation
• there is no char type; each letter is itself a String
• string concatenation operator is . (period), not +
  • 5 + "2 turtle doves" === 7
  • 5 . "2 turtle doves" === "52 turtle doves"
• can be specified with "" or ''

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"

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

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

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 (5.4.3)

$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 (5.4.4)

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

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. \"
  • best PHP style is to minimize print/echo statements in embedded PHP code
• 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>

• PHP expression block: a small piece of PHP that evaluates and embeds an expression's value into HTML
  • <?= expression ?> is equivalent to:

    <?php print expression; ?>
    

  • useful for embedding a small amount of PHP (a variable's or expression's value) in a large block of HTML without having to switch to "PHP-mode"

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>

• expression blocks can even go inside HTML tags and attributes