variables in php 1
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Variables in PHP
Variables in PHP
Variables in PHP are denoted by a dollar sign followed by the name of the variable. A variable name is case-sensitive. A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.
Example Usage of Variables
<html><head><title>Greetings</title></head><body><h1>Greetings</h1><p><?php $person = "Tom"; $Person = "Dick"; echo "Hello $person and $Person";?></p></body></html>
Data Types in PHPPHP supports eight primitive data typesThere are four scalar types
boolean integer floating-point number string
There are two structured types array object
There are two special data types resource NULL
The programmer does not specify the type of a variable
a variable’s type is determined from the context of its usage
Booleans
The boolean data type admits two values true (case-insensitive) false (case-insensitive)
Example usage$itIsRainingToday = true;$thePrinterIsBusy = True;$theQueueIsEmpty = FALSE;
IntegersIntegers can be specified in decimal, hexadecimal or octal notation, optionally preceded by a sign
In octal notation, the number must have a leading 0 In hexadecimal notation, the number must have a
leading 0x.
Examples $a = 1234; # decimal number $a = -123; # a negative number $a = 0123; # octal number (equivalent to 83
decimal) $a = 0x1B; # hexadecimal number (equivalent to 27
decimal)
The maximum size of an integer is platform-dependent, but usually it’s 32 bits signed – about 2,000,000,000PHP does not support unsigned integers.
Floating Point Numbers
These can be specified using any of these forms:
$a = 1.234; $a = 1.2e3; $a = 7E-10;
The maximum size of a float is platform-dependent, although most support a maximum of about 1.8e308 with a precision of roughly 14 decimal digits
Strings
A string literal can be specified in three different ways:
single quoted double quoted heredoc syntax
Double-quoted Strings
In double-quoted strings, variables are interpreted to their values, and various characters can be escaped
\n linefeed \r carriage return \t horizontal tab \\ backslash \$ dollar sign \” double quote \[0-7]{1,3} a character in octal notation \x[0-9A-Fa-f]{1,2} a character in hexadecimal notation
Single-quoted Strings
In single-quoted strings, single-quotes and backslashes must be escaped with a preceding backslashExample usage
echo 'this is a simple string';
echo 'You can embed newlines in strings, just like this.'; echo ‘Douglas MacArthur said "I\'ll be back” when leaving the Phillipines'; echo 'Are you sure you want to delete C:\\*.*?';
Heredoc Strings
Heredoc strings are like double-quoted strings without the double quotesA heredoc string is delimited as follows
The string is preceded by <<< followed by a label The string followed by a 2nd occurrence of the same label
Example usage $str = <<<EOD Example of string spanning multiple lines using heredoc syntax. EOD;
String-manipulation functions
PHP provides huge range of string-manipulation functions:
addcslashes -- Quote string with slashes in a C style addslashes -- Quote string with slashes bin2hex -- Convert binary data into hexadecimal representation chop -- Alias of rtrim() chr -- Return a specific character chunk_split -- Split a string into smaller chunks convert_cyr_string -- Convert from one Cyrillic character set to another count_chars -- Return information about characters used in a string crc32 -- Calculates the crc32 polynomial of a string crypt -- One-way string encryption (hashing) echo -- Output one or more strings explode -- Split a string into an array get_html_translation_table -- Returns the translation table used by
htmlspecialchars() and htmlentities()
get_meta_tags -- Extracts all meta tag content attributes from a file and returns an array
hebrev -- Convert logical Hebrew text to visual text hebrevc -- Convert logical Hebrew text to visual text with newline conversion htmlentities -- Convert all applicable characters to HTML entities htmlspecialchars -- Convert special characters to HTML entities implode – creates a string from array elements join -- Join array elements with a string levenshtein -- Calculate Levenshtein distance between two strings localeconv -- Get numeric formatting information ltrim -- Strip whitespace from the beginning of a string md5 -- Calculate the md5 hash of a string md5_file -- Calculates the md5 hash of a given filename metaphone -- Calculate the metaphone key of a string nl2br -- Inserts HTML line breaks before all newlines in a string ord -- Return ASCII value of character parse_str -- Parses the string into variables print -- Output a string printf -- Output a formatted string
quoted_printable_decode -- Convert a quoted-printable string to an 8 bit string quotemeta -- Quote meta characters str_rot13 -- Perform the rot13 transform on a string rtrim -- Strip whitespace from the end of a string sscanf -- Parses input from a string according to a format setlocale -- Set locale information similar_text -- Calculate the similarity between two strings soundex -- Calculate the soundex key of a string sprintf -- Return a formatted string strncasecmp -- Binary safe case-insensitive string comparison of the first n
characters strcasecmp -- Binary safe case-insensitive string comparison strchr -- Find the first occurrence of a character strcmp -- Binary safe string comparison strcoll -- Locale based string comparison strcspn -- Find length of initial segment not matching mask strip_tags -- Strip HTML and PHP tags from a string stripcslashes -- Un-quote string quoted with addcslashes() stripslashes -- Un-quote string quoted with addslashes()
stristr -- Case-insensitive strstr() strlen -- Get string length strnatcmp -- String comparisons using a "natural order" algorithm strnatcasecmp -- Case insensitive string comparisons using a "natural order"
algorithm strncmp -- Binary safe string comparison of the first n characters str_pad -- Pad a string to a certain length with another string strpos -- Find position of first occurrence of a string strrchr -- Find the last occurrence of a character in a string str_repeat -- Repeat a string strrev -- Reverse a string strrpos -- Find position of last occurrence of a char in a string strspn -- Find length of initial segment matching mask strstr -- Find first occurrence of a string strtok -- Tokenize string strtolower -- Make a string lowercase strtoupper -- Make a string uppercase str_replace -- Replace all occurrences of the search string with the replacement
string
strtr -- Translate certain characters substr -- Return part of a string substr_count -- Count the number of substring occurrences substr_replace -- Replace text within a portion of a string trim -- Strip whitespace from the beginning and end of a string ucfirst -- Make a string's first character uppercase ucwords -- Uppercase the first character of each word in a
string vprintf -- Output a formatted string vsprintf -- Return a formatted string wordwrap -- Wraps a string to a given number of characters
using a string break character. nl_langinfo -- Query language and locale information
Arrays
An array in PHP is a structure which maps keys (array element names) to values The keys can specified explicitly or they can be omittedIf keys are omited, integers starting with 0 are keysThe value mapped to a key can, itself, be an array, so we can have nested arrays
Specifying an array
A special function is used to specify arraysarray( )
Format of Usagearray( [key =>] value, … )
A key is either a string or a non-negative integerA value can be anything
Specifying an array (contd.)Format of associative array specification
$ages = array("Peter"=>32, "Quagmire"=>30, "Joe"=>34);
Here is another associative (hash) array:$ages['Peter'] = "32"; $ages['Quagmire'] = "30"; $ages['Joe'] = "34";
Implicit indices are integers, starting at 0 Here is an ordinary array (indexed by integers,
starting at 0):$places = array (“Cork”, “Dublin”, “Galway”);
Here is the same array written differently$places[0] = “Cork”;$places[1] = “Dublin”;$places[2] = “Galway”;
Specifying an array (contd.)
If an explicit integer index is followed by implicit indices, they follow on from the highest previous index Here is an array indexed by integers 1,
2, 3$places = array (1 => “Cork”, “Dublin”, “Galway”);
Here is an array indexed by integers 1, 5, 6
$places = array (5=> “Cork”, 1 => “Dublin”, “Galway”);
Specifying an array (contd.)
A two-dimensional hash array$parents = array ( “tom” => array (“father” => “bill”,
“mother”=>”mary”), “dave” => array(“father” => “tom”, “mother” => orla”));
echo "Is " . $parents['tom']['father'] . " a part of the family?";= bill
A two-dimensional ordinary array$heights = array ( array (10,20,30,40,50),
array(100,200));echo $heights[0][1] ; = 20echo $heights[1][1] ; = 200
Array Example 1
<html>
<head><title>Array Demo</title></head>
<body>
<h1>Array Demo</h1>
<p>
<?php
$capital = array ('France'=>'Paris','Ireland'=>'Dublin');
echo 'The capital of Ireland is ';
echo $capital['Ireland'];
?>
</p>
</body>
</html>
Array Example 2
<html><head><title>Array Demo</title></head><body><h1>Array Demo</h1><p><?php $capital = array ('France'=>'Paris', ‘Ireland'=>'Dublin'); echo "The various capitals are\n<ul>"; foreach ($capital as $city) { echo "<li>$city</li>"; }; echo "</ul>"?></p></body></html>
Array Example 3<html><head><title>Array Demo</title></head><body><h1>Array Demo</h1><p><?php $capital = array ('France'=>'Paris', 'Ireland'=>'Dublin'); echo "The various capitals are\n<ul>"; foreach ($capital as $country => $city) { echo "<li>The capital of $country is $city</li>"; }; echo "</ul>"?></p></body></html>
Array Example 4
<html><head><title>Details about Fred</title></head><body><h1>Details about Fred</h1><?php$ages = array ("Fred" => 2, "Tom"=> 45);$parents = array ("Fred" => array("father" => "Tom", "mother"=>"Mary"));print "<p> Fred's age is ";print $ages["Fred"];print ".</p>";print "<p>His father is ";print $parents["Fred"]["father"];print ".</p>";?></body></html>
Array-manupulation functions
PHP provides a huge set of array-manipulation functionsarray -- Create an array array_change_key_case -- Returns an array with all string keys lowercased or uppercasedarray_chunk -- Split an array into chunksarray_count_values -- Counts all the values of an arrayarray_diff -- Computes the difference of arraysarray_filter -- Filters elements of an array using a callback function array_flip -- Flip all the values of an arrayarray_fill -- Fill an array with valuesarray_intersect -- Computes the intersection of arraysarray_key_exists -- Checks if the given key or index exists in the arrayarray_keys -- Return all the keys of an arrayarray_map -- Applies the callback to the elements of the given arrays array_merge -- Merge two or more arraysarray_merge_recursive -- Merge two or more arrays recursivelyarray_multisort -- Sort multiple or multi-dimensional arraysarray_pad -- Pad array to the specified length with a value
array_pop -- Pop the element off the end of arrayarray_push -- Push one or more elements onto the end of array array_rand -- Pick one or more random entries out of an array array_reverse -- Return an array with elements in reverse order array_reduce -- Iteratively reduce the array to a single value using a callback function array_shift -- Shift an element off the beginning of array array_slice -- Extract a slice of the arrayarray_splice -- Remove a portion of the array and replace it with something else array_sum -- Calculate the sum of values in an array. array_unique -- Removes duplicate values from an arrayarray_unshift -- Prepend one or more elements to the beginning of array array_values -- Return all the values of an arrayarray_walk -- Apply a user function to every member of an array arsort -- Sort an array in reverse order and maintain index association asort -- Sort an array and maintain index associationcompact -- Create array containing variables and their values count -- Count elements in a variablecurrent -- Return the current element in an array
each -- Return the current key and value pair from an array and advance the array cursor end -- Set the internal pointer of an array to its last element extract -- Import variables into the current symbol table from an array in_array -- Return TRUE if a value exists in an arrayarray_search -- Searches the array for a given value and returns the corresponding key if successful key -- Fetch a key from an associative arraykrsort -- Sort an array by key in reverse orderksort -- Sort an array by keylist -- Assign variables as if they were an array natsort -- Sort an array using a "natural order" algorithm natcasesort -- Sort an array using a case insensitive "natural order" algorithm next -- Advance the internal array pointer of an array pos -- Get the current element from an arrayprev -- Rewind the internal array pointerrange -- Create an array containing a range of elements reset -- Set the internal pointer of an array to its first element
rsort -- Sort an array in reverse ordershuffle -- Shuffle an arraysizeof -- Get the number of elements in variablesort -- Sort an arrayuasort -- Sort an array with a user-defined comparison function and maintain index association uksort -- Sort an array by keys using a user-defined comparison function usort -- Sort an array by values using a user-defined comparison function
Objects and functionsPHP supports object-oriented programming
<?phpclass thingAMeBob {
function say_hello() {echo “Hello, World!";}
} $thing1 = new thingAMeBob; $thing1->say_hello();
?>
And functions<?php
function add($x,$y) { $total = $x + $y; return $total; }
echo "1 + 16 = " . add(1,16); ?>
The NULL data type
This data type contains only one valueNULL
It is case-insensitiveThis is a value which is returned when some expression has no valueExample
$capital = array ('France'=>'Paris', 'Ireland'=>'Dublin');$capitalOfEngland = $capital[‘England’];
In this case, $capitalOfEngland would get the value NULL
Automatic variables in PHP
One of the main benefits of PHP is that it provides lots of variables automaticallyConsider, for example, the .php file on the next slideIt produces the output on the following two slides when viewed by MSIE 6.0 and Netscape 2.0
Example usage of automatic PHP variable
<html><head><title>Your browser</title></head><body><h1>Your Browser</h1><p>You are using <?php echo $_ENV[HTTP_USER_AGENT]; ?>to view this page.</p></body></html>
Global arrays
PHP creates 6 global arrays that contain EGPCS (environment, get, post, cookies and server) informationPHP also creates a variable called $_REQUEST that contains all the information in the 6 global arraysPHP also creates a variable called $PHP_SELF that contains the name of the current script (relative to the doc root)
Global arrays
$_ENV – Contains the values of any environment variables, such as the browser version Eg: $_ENV[HTTP_USER_AGENT]
$_POST – The values of any variables posted to the request. Eg: $_POST[username]
$_GET – The values of any variables sent via the URL Eg: $_GET[username]
Global arrays
$_FILES – Contains information about any files submitted$_COOKIES – Contains any cookies submitted as name value pairs (see later lectures)$_SERVER – Contains useful information about the webserver
$_SERVER Keys[DOCUMENT_ROOT][HTTP_*][PHP_SELF][QUERY_STRING][REMOTE_ADDR][REQUEST_METHOD][REQUEST_URI][SCRIPT_FILENAME][SCRIPT_NAME][SERVER_NAME][SERVER_PORT][SERVER_PROTOCOL][SERVER_SOFTWARE] [COMSPEC][GATEWAY_INTERFACE][PATHEXT][PATH][REMOTE_PORT][SERVER_ADDR][SERVER_ADMIN][SERVER_SIGNATURE][SystemRoot][WINDIR]
Changing Data Type
PHP will, in some circumstances, change the type of a datum For example, it will treat a string of digits as
a number if it finds them in an arithmetic expression
PHP also supports type casting<?php $myInteger = 12; $myFloat = 1.3; $result = $myFloat + (float) $myInteger; echo $result ?>