Php basics

Instruction Separation
• PHP requires instructions to be terminated with a semicolon at the end of
each statement.
• The closing tag of a block of PHP code automatically implies a semicolon;

<?php
echo 'This is a test';
?>

<?php echo 'This is a test' ?>

<?php echo 'We omitted the last closing tag';

Comments
<?php
echo 'This is a test'; // This is a one-line c++ style comment

/* This is a multi line comment
yet another line of comment */

echo 'This is yet another test';
echo 'One Final Test'; # This is a one-line shell-style comment

?>

Types
• Some types that PHP supports.
• Four scalar types:
– boolean
– integer
– float (floating-point number, aka double)
– string
• Two compound types:
– array
– object
• And finally three special types:
– resource
– NULL

<?php
$a_bool = TRUE; // a boolean
$a_str = "foo"; // a string
$a_str2 = 'foo'; // a string
$an_int = 12; // an integer
echo gettype($a_bool); // prints out: boolean
echo gettype($a_str); // prints out: string
// If this is an integer, increment it by four
if (is_int($an_int)) {
$an_int += 4;
}
// If $a_bool is a string, print it out
// (does not print out anything)
if (is_string($a_bool)) {
echo "String: $a_bool";
}
?>

Booleans
• A boolean expression expresses a truth value. Can be TRUE or FALSE
<?php
$foo = True; // assign the value TRUE to $foo
?>
<?php
// == is an operator which tests
// equality and returns a boolean
if ($action == "show_version") {
echo "The version is 1.23";
}

// this is not necessary...
if ($show_separators == TRUE) {
echo "<hr>n";
}

// ...because this can be used with exactly the same meaning:
if ($show_separators) {
echo "<hr>n";
}

Integers
• An integer is a number of the set Z = {..., -2, -1, 0, 1, 2, ...}.
• Integers can be specified in decimal (base 10), hexadecimal (base 16), octal
(base 8) or binary (base 2) notation, optionally preceded by a sign (- or +).
• To use octal notation, precede the number with a 0 (zero). To use
hexadecimal notation precede the number with 0x. To use binary notation
precede the number with 0b.
<?php
$a = 1234; // decimal number
$a = -123; // a negative number
$a = 0123; // octal number (equivalent to 83
decimal)
$a = 0x1A; // hexadecimal number (equivalent to 26
decimal)
?>

Strings
• A string is series of characters, where a character is the same as a byte.
• A string literal can be specified in four different ways:
– single quoted
– double quoted
– heredoc syntax
– nowdoc syntax (since PHP 5.3.0)

Single Quoted
<?php
echo 'this is a simple string';

echo 'You can also have embedded newlines in
strings this way as it is
okay to do';

// Outputs: Arnold once said: "I'll be back"
echo 'Arnold once said: "I'll be back"';

// Outputs: You deleted C:*.*?
echo 'You deleted C:*.*?';

// Outputs: You deleted C:*.*?
echo 'You deleted C:*.*?';

// Outputs: This will not expand: n a newline
echo 'This will not expand: n a newline';

// Outputs: Variables do not $expand $either
echo 'Variables do not $expand $either';
?>

Double Quoted
• The most important feature of double-quoted strings is the fact that variable
names will be expanded.
Heredoc
• A third way to delimit strings is the heredoc syntax: <<<. After this operator,
an identifier is provided, then a newline. The string itself follows, and then
the same identifier again to close the quotation.
• The closing identifier must begin in the first column of the line. Also, the
identifier must follow the same naming rules as any other label in PHP: it
must contain only alphanumeric characters and underscores, and must start
with a non-digit character or underscore.
Nowdoc
• A nowdoc is identified with the same <<< sequence used for heredocs, but
the identifier which follows is enclosed in single quotes, e.g. <<<'EOT'. All
the rules for heredoc identifiers also apply to nowdoc identifiers, especially
those regarding the appearance of the closing identifier.

Arrays
• An array in PHP is actually an ordered map.
• A map is a type that associates values to keys.
• This type is optimized for several different uses:
– Array
– list (vector)
– hash table (an implementation of a map)
– Dictionary
– Collection
– Stack
– Queue
• As array values can be other arrays, trees and multidimensional arrays
are also possible.

Specifying an Array
• An array can be created using the array() language construct.
• It takes any number of comma-separated key => value pairs as arguments.

array(
key => value,
key2 => value2,
key3 => value3,
...
)

Specifying an Array
• As of PHP 5.4 you can also use the short array syntax, which replaces
array() with [].
<?php
$array = array(
"foo" => "bar",
"bar" => "foo",
);
// as of PHP 5.4
$array = [
"foo" => "bar",
"bar" => "foo",
];
?>
• The key can either be an integer or a string. The value can be of any type.

Accessing array elements with square
bracket syntax
• Array elements can be accessed using the array[key] syntax.
<?php
$array = array(
"foo" => "bar",
42 => 24,
"multi" => array(
"dimensional" => array(
"array" => "foo"
)
)
);
var_dump($array["foo"]);
var_dump($array[42]);
var_dump($array["multi"]["dimensional"]["array"]);
?>

Creating/modifying with square bracket
syntax
• An existing array can be modified by explicitly setting values in it.
• This is done by assigning values to the array, specifying the key in brackets.
The key can also be omitted, resulting in an empty pair of brackets ([]).
$arr[key] = value;
$arr[] = value;
// key may be an integer or string
// value may be any value of any type
• To change a certain value, assign a new value to that element using its key.
• To remove a key/value pair, call the unset() function on it.

Objects
• Object Initialization
– To create a new object, use the new statement to instantiate a class:
<?php
class foo
{
    function do_foo()
    {
        echo "Doing foo.";
    }
}

$bar = new foo;
$bar->do_foo();
?>

Resources
• A resource is a special variable, holding a reference to an external resource.
Resources are created and used by special functions

Null
• The special NULL value represents a variable with no value.

Php basics

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