Lecture 9Introduction to PHP

Presented ByDr. Shazzad Hosain

Asst. Prof. EECS, NSU

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Server-side Scripting

• Server-side Web-scripting is mostly about connecting web-sites to back-end servers such as databases.

• This enables two way communication:– Server to client: Web-pages can be

assembled from back-end server output;– Client to Server: Customer-entered

information can be acted upon.

See next page for data flow in server-side scripting.

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Server-side Scripting (cont’d)

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What do You Need?• Where to Start?

– Install an Apache server on a Windows or Linux machine. Or IIS on wndows.

– Install PHP on a Windows or Linux machine – Install MySQL on a Windows or Linux machine– Or, Install XAMPP/WAMP to get all-in-one solution

• PHP + MySQL– PHP combined with MySQL are Cross-platform

(means that you can develop in Windows and serve on a Unix platform), Open source, Compatible with leading web servers, Faster and Truly Portable.

Introduction to PHP

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PHP Tag Styles – The good…• XML Style:

<?php print “this is XML style”;

?>• Short Style:

<?print “this is ASP style”;

?>

• To use Short style the PHP you are using must have “short tags” enabled in its config file… this is almost always the case.

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Comments• Why do we go on about comments so much?• because without them, marking would hurt our heads.

<? //C style comment

#perl style comment

/* C++ multi line comment */

?>

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PHP is for Lazy People• You know that means you! Don’t need to work with types and

conversions.

• Basic data types– numbers (integers and real) – strings (Double-quoted "abc“ and single-quoted 'abc')– booleans (true,false )

• Dynamic typing– Don't have to declare types – Automatic conversion done

• all variables in PHP are denoted with a leading dollar sign ($);– variables have default values.

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Variables in action<?

$x = false;         // boolean type $x = true;

$x = 10;         // decimal $x = 1.45;         // Floating point $x = 0x1A;         // hexadecimal 

$x = "mmm\"oo'oo\n";     // mmm"oo'oo  and a new line $x = 'mmm"oo\'oo\n';     // string = mmm"oo'oo\n

$y = &$x         // Reference

$x[1] = 10         // array of decimals $x["name"] = “jimbo";    // associative array $x[2]["lala"] = "xx";    // a two dimensional array

?>

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Variables (cont’d)Assigning variables:

$pi = 3 + 0.14159 // approximately

Re-assigning variables:

$my_num_var = “it is not a number”;$my_num_var = 5;

Unassigned variables:• PHP ensures that variables have default values

(they can be printed unassigned).

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Variables (cont’d)• Checking assignment with IsSet:

$set_var = 0; //set_var has a value //never_set does not

if (IsSet($set_var)) print(“set_var has a value. <BR>”);

if (IsSet($never_set)) print(“never_set has a value. <BR>”);else print(“never_set has no value. <BR>”);

• If you use an unset variable, system will complain.

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Switching Modes

<? if(strstr($HTTP_USER_AGENT,"MSIE")) {

?><b>You are using Internet Explorer</b>

<? } else {

?><b>You are not using Internet Explorer</b>

<? }

?>

Here we have flicked back

to HTML again

Here we are in PHP-mode

Using the arrow-

question mark tag we can quickly

switch modes

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Variable Scope

• The 3 basic types of scope in PHP is:

– Global variables declared in a script are visible throughout that script, but not inside functions

– Variables used inside functions are local to the function

– Variables used inside functions that are declared as global refer to the global variable of the same name

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Operators• Arithmetic Operators: +, -, *, / , %, ++, --• Assignment Operators: =, +=, -=, *=, /=, %=

• Comparison Operators: ==, !=, >, <, >=, <= • Logical Operators: &&, ||, !• String Operators: . , .=

Example Is the same asx+=y x=x+yx-=y x=x-yx*=y x=x*yx/=y x=x/yx%=y x=x%y

$a = "Hello ";$b = $a . "World!"; //now $b contains "Hello World!"

$a = "Hello ";$a .= "World!";

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Output- echo

For printing to output we can use:• echo - to print a string as argument.

echo “This prints in the browser.”; or echo(“This prints in the browser.”); or echo “This prints”, “in the browser.”;

• Note that echo will also work with the string concatenation operator . as:

echo “This prints” . “in the browser.”; orecho(“This prints” . “in the” . “browser.”); but echo(“This causes a”, “PARSE ERROR!”);

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Output- print (cont’d)• print - is very similar to echo, with two important differences:

– can accept only one argument;– returns a value, which represents whether the print

statement succeeded;• returned value 1 means that printing was successful;• returned value 0 means that printing was unsuccessful.

– Example: print(“3.14159”); //print a string

print(3.14159); //print a number

– numbers are converted to strings before they are printed.

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Output (cont’d)

• variables and strings $animal = “Antelope”; $heads = 1; $legs = 4; print(“$animal has $heads head(s). <BR>”); print(“$animal has $legs leg(s). <BR>”);

Output Antelope has 1 head(s). Antelope has 4 leg(s).

• Use single quotes to print directories print(‘C:\newcode\myphp.php’);

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Output (cont’d)

• HTML and line breaks– C programmers be aware that the new line

character “\n” is not the same as “<BR>”;– \n prints a new line in the HTML code generated,

while <BR> prints a new line on the browser;– what is the HTML and browser output of the

statement: print(“Is this only \n\n one line? <BR>”);

(left as an exercise).

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Simple String functionschr - Return a specific character ord - Return ASCII value of charactersprintf - Return a formatted stringstrlen - Get string lengthstrpos - Find position of first occurrence of a

stringstrrev - Reverse a stringstrtolower - Make a string lowercasestrtoupper - Make a string uppercasestr_replace - Replace all occurrences of the search

string with the replacement string

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PHP Control Statements

• Just for the record what’s the same as C++/Java?

– For Loops– While Loops– If Statements– Break, Continue, Exit, Switch, etc.

• The main concepts which differ in syntax are:– Functions– Classes

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If – exists• You often need to check whether a variable

exists in PHP.

• There are two ways to do this…

if ($a){

print “\$a exists";

}else{

print “\$a exists"; }

if (!empty($a)){

print “\$a exists";}else{ print “\$a exists"; }

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Conditionals: if else<html><head></head><body>

<?php$d=date("D");if ($d =="Fri") echo "Have a nice weekend! <br/>"; else echo "Have a nice day! <br/>";

$x=10;if ($x==10){ echo "Hello<br />"; echo "Good morning<br />";}?></body></html>

if (condition)code to be executed if condition is true;elsecode to be executed if condition is false;

date() is a built-in function that can be called with many different parameters to return the date (and/or local time) in various formats

In this case we get a three letter string for the day of the week.

<html><head></head><body> <!–- switch-cond.php --><?php$x = rand(1,5); // random integerecho “x = $x <br/><br/>”;switch ($x){case 1: echo "Number 1"; break;case 2: echo "Number 2"; break;case 3: echo "Number 3"; break;default: echo "No number between 1 and 3";}?></body></html> 23

Conditionals: switch

switch (expression){case label1: code to be executed if expression = label1; break; case label2: code to be executed if expression = label2; break;default: code to be executed if expression is different from both label1 and label2;}

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Looping: while and do-whileCan loop depending on a condition

<html><head></head><body>

<?php $i=1;while($i <= 5){ echo "The number is $i <br />"; $i++;}?>

</body></html>

loops through a block of code if and as long as a specified condition is true

<html><head></head><body>

<?php $i=0;do{ $i++; echo "The number is $i <br />";}while($i <= 10);?>

</body></html>

loops through a block of code once, and then repeats the loop as long as a special condition is true

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Looping: for and foreachCan loop depending on a "counter"

<?phpfor ($i=1; $i<=5; $i++){ echo "Hello World!<br />";}?>

loops through a block of code a specified number of times

<?php$a_array = array(1, 2, 3, 4);foreach ($a_array as $value) { $value = $value * 2; echo “$value <br/> \n”;}?>

loops through a block of code for each element in an array

<?php $a_array=array("a","b","c");foreach($a_array as $key=>$value){ echo $key." = ".$value."\n";}?>

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PHP Functions• Functions in PHP are not case sensitive.• Be careful of this because variable naming is case sensitive

function my_function(){print “My function was called”;

}

• Functions can be created anywhere in your PHP code• However good style demands they should always be at the

top of your code

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Do what is neatest…<?

Function my_function(){

print “My function was called”;}

?>

<?Function my_function(){

?>My function was

called<?

}?>

IS IDENTICAL TO…

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Passing Parameters• As normal you don’t have to specify the types of your

parameters...• Be careful of this because variable naming is case

sensitive

function display_table($data){print “<TABLE>”;

for ($i=0; $i<sizeof($data); $i++) print “<TR><TD> $data[$i]

</TD></TR>”;

print “</TABLE>”;}

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Defaults & Passing by Reference• As with other languages you can set defaults. PHP requires that

you do specify the correct number of parameters in a call.

• Equally you don’t have to pass by value – an ampersand will mean the variable is passed by reference and so any changes to it are global:

function increment(&$value, $amount=1){$value = $value + $amount;

}

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Example…function larger($x, $y){if ($x > $y)

return $x;

if ($x < $y) return $y;

if ($x == $y) return “x and y have the same value”;

}

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Variable ScopeThe scope of a variable is the

context within which it is defined.

<?php$a = 1; /* global scope */ function Test(){ echo $a; /* reference to local scope variable */ } Test();?>

The scope is local within functions.

<?php$a = 1;$b = 2;function Sum(){ global $a, $b; $b = $a + $b;} Sum();echo $b;?>

global

refers to its global version.

<?phpfunction Test(){ static $a = 0; echo $a; $a++;}Test(); Test();Test(); ?>

static

does not lose its value.

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Arrays in PHP• Arrays in PHP are associative, i.e. values of elements are stored

in association with the key values, rather than a strict linear order.

/* Direct assignment: create array $state_loc, and assign location with key = ‘San Mateo’ equal to ‘California’ */

$state_loc[‘San Mateo’]= ‘California’;

//…later assign ‘California’ to $state

$state = state_loc[‘San Mateo’];

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Arrays (cont’d)

• The array() construct

$fruit_basket = array(‘apple’,‘banana’);

• which can also be written as:

$fruit_basket[1] = ‘apple’;$fruit_basket[2] = ‘banana’;

• or (almost) equivalent to:

$fruit_basket[] = ‘apple’; //here indices start$fruit_basket[] = ‘banana’; //from 0 (not 1).

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Arrays (cont’d)

• Specifying indices using array()

$fruit_basket = array(0 =>‘apple’, 1 =>‘banana’ );

• We could also write:

$fruit_basket = array(‘red’ =>‘apple’, ‘yellow’ =>‘banana’ );

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Arrays (cont’d)

• Multi-dimensional arrays as arrays with elements that are arrays themselves.

$basket[0][0] = ‘apple’; $basket[0][1] = ‘banana’; $basket[1][0] = ‘rose’; $basket[1][1] = ‘tulip’;

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Arrays (cont’d)• Alternatively:

$basket = array(0 => array(0 => ‘apple’, 1 => ‘banana’ ), 1 => array(0 => ‘rose’, 1 => ‘tulip’) ) );

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Arrays (cont’d)• Or, for a more meaningful version:

$basket = array(‘fruits’ => array(‘red’ => ‘apple’, ‘yellow’ => ‘banana’ ), ‘flowers’ => array(‘red’ => ‘rose’, ‘violet’ => ‘tulip’) ) );

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Arrays (cont’d)• The program:

$kind = ‘flower’;$colour = ‘red’;print(“You want a {$basket[$kind][$colour]}.”);

• Outputs:

You want a rose.

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The list() construct• the list() construct is the inverse of array(), since array()

packages its arguments into an array, and list() takes the array apart again into individual variable assignments.

$fruits = array(‘apple’, ‘banana’, ‘orange’);list($red, $yellow) = $fruits;print(“The $red is red and the $yellow isyellow.<BR>”);

• Output:

The apple is red and the banana is yellow.

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Merging Arrays• array_merge()

$fruits = array("apples", "oranges", "pears");

$vegetables = array("potatoes", “onions", "carrots");

$newarray = array_merge($fruits, $vegetables);

$howmany = count($newarray);

print "$howmany"; // will output 6 to the screen

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Accessing Array Elements

<?php

$vegetables = array("potatoes", “onions", "carrots");

for ($i=0; $i< count($vegetables); $i++){ print "$vegetables[$i]<br>\n"; }

?>

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each() function

$vegetables = array("potatoes", “onions", "carrots");

for ($i=0; $i< count($vegetables); $i++){ $Line = each($vegetables); print "$Line[key] is $Line[value]<br>\n"; }

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Array Functions (the boring ones)

count - Count elements in a variable sizeof - Get the number of elements in variable

array_pop - Pop the element off the end of array array_push - Push one or more elements onto the end of arrayarray_shift - Shift an element off the beginning of array

array_search - Searches the array for a given value and returns the corresponding key if successful

sort - Sort an array into numerical order

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…er.. The exciting ones?

array_reverse - Return an array with elements in reverse orderarray_flip - Flip all the values of an array keys become valuesarray_unique - Removes duplicate values from an array

array_values - Return all the values of an arrayarray_sum - Calculate the sum of values in an array.

extract – converts arrays to scalar variablesarray_rand - Pick 1 or more random entries from the arrayshuffle – randomly reorders the elements in an array

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Constants• A constant is an identifier (name) for a simple value. A constant is case-sensitive by default. • By convention, constant identifiers are always uppercase.

<?php // Valid constant names define("FOO", "something"); define(“MAX", 100); define(“PI", 3.14159); // Invalid constant names define("2FOO", "something");

You can access constants anywhere in your script without regard to scope.

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Exploding Strings

• Not a new firework but rather a way of breaking a string down and putting it into an array.

• And its useful, especially if you are doing anything with cookies.

$email = “info@cs.nsu.edu”;$email_array = explode(“@”, $email);$domains = explode(“.”, $email_array[0]);

• Implode() reverses the process.$domain[0] = “cs”

$domain[1] = “nsu”

$domain[2] = “edu”

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Changing Case• Most people who use your sites will be muppets. (although your sites for

HLL will probably only be viewed by members of staff so draw your own conclusions).

• Whatever you tell them to do, they won’t enter data in the format you want and this will matter. Login names are classic examples of this.

• Imagine someone types “aStOn VillA” into a field…

Strtoupper()

Strtolower()

Ucfirst()

Ucwords()

Turns string to uppercase

Turns string to lowercase

Capitalises first character

Capitalises every word

ASTON VILLA

aston villa

Aston villa

Aston Villa

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Problem Characters• Some characters cause you no end of problems.

– Specifically ‘ and “.

• For example if you have a field asking for a name and someone sends you back: Ronnie O’Sullivan, consider the following code:

Print ‘Welcome to the site $name’;

Print ‘Welcome to the site Ronnie O’Sullivan’;

We need a way of marking, or escaping these characters so that databases such as mysql can understand we meant a literal character.

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Adding Slashes• To do this escaping normally you just add a \ (backslash). This can be very

painful to do manually.

AddSlashes() a function to do it for you.StripSlashes() reverses the process.

• So if a user typed in:You said to me that “you don’t give guarantees”

• $userInput = AddSlashes($userInput)

You said to me that \“you don\’t give guarantees\”.

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Crypt• crypt() will encrypt a string that you give it.

• This is especially useful for encrypting items such as passwords.

• This then cannot be reversed – but you can encrypt another string that is entered and then compare it with the stored encrypted string.

• You should always encrypt your users access information if its privacy is essential.

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Time inside PHP• Time() -- gives you the current UNIX/Windows timestamp

• Returns the current time measured in the number of seconds since the Unix Epoch (January 1 1970 00:00:00 GMT).

• You find yourself using this all the time once you have a complicated site. Common examples are:

– Keeping track of login times– Time how long processes are taking

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Date()

• Time is very useful but not very pretty – who wants to know the number of seconds since the unix epoch !?

• Date() outputs the current time into whatever format you specify:

Print date(“jS F Y”); 25th April 2007Print date("F j, Y, g:i a"); April 25, 2007, 9:46 pmPrint date("H:i:s"); 09:46:17Print date("D M j G:i:s T") ; Fri Apr 25 9:46:17 GMT

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Formatting the DateA – morning or afternoonj – day of the monthD – day of the week as a three letter word (eg. Mon)F – month of the year as a full stringm – month of the year as a two digit numberG – hour of the dayI – minutes past the hourS – seconds past the minuteT – timezone you are in (eg. GMT)Y – year in 4-digit formatz – day of the year as a number (0-365)

• You can also add a UNIX timestamp as a second argument in the date() function – the formatted string will represent that time.

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Getting Time and Date

date() and time () formats a time or a date.<?php//Prints something like: Mondayecho date("l");

//Like: Monday 15th of January 2003 05:51:38 AMecho date("l dS of F Y h:i:s A");

//Like: Monday the 15th

echo date("l \t\h\e jS");?>

date() returns a string formatted according to the specified format.

*Here is more on date/time formats: http://uk.php.net/manual/en/function.date.php

<?php$nextWeek = time() + (7 * 24 * 60 * 60); // 7 days; 24 hours; 60 mins; 60secsecho 'Now: '. date('Y-m-d') ."\n";echo 'Next Week: '. date('Y-m-d', $nextWeek) ."\n";?>

time() returns current Unix timestamp