UFCEUS-20-2 : Web Programming

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Nov 4, 2013 (3 years and 9 months ago)

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UFCEUS
-
20
-
2 : Web Programming

Lecture 2

PHP (1) : Data Types, Control Structures, Data
Structures, String Handling &
Input/Output

Pre
-
amble (1) Web 1.0

Basic web 1.0 architecture & communication


Pre
-
amble (2) http request/response cycle


Pre
-
amble (3)
Web oriented 3
-
tier architecture

PHP script

Remote services

Web Server

(Apache, IIS)


Browser

(IE, Chrome,

FireFox,

Opera)


Desktop

(PC or MAC)

Database

Database

Server

SQL

HTTP

HTML

Web Service

tables

DHTML

vision

touch

voice

PHP Origins

Originally created by
Rasmus

Lerdorf

(born Greenland,
educated in Canada) around 1995


PHP originally abbreviated as ‘Personal Home Pages’, now
known as ‘PHP Hypertext
Pre
-
processor
’


Other key developers:
Zeev

Surashi

and
Andi

Gutmans

(Israel) responsible for PHP 3.0
-

a complete re
-
write of
the original PHP/F1 engine (1997)


PHP is Open Source software

First version PHP/FI released 1995

PHP 5.0 released July 2004

Current stable version is
5.4.6 (as of August 2012)

PHP version 5.2.4 current at UWE

PHP Version 6 due for release since late 2010 but ??




PHP as a scripting language



o
A scripting language is:

–
often evolved not designed

–
cross
-
platform since interpreter is easy to port

–
designed to support a specific task
–

PHP Web support

–
un
-
typed variables (but values are typed)

–
implicit variable declaration

–
implicit type conversion

–
stored only as script files

–
compiled on demand

–
may run on the server (PHP, Perl) or the client (
Javascript
)


o
What are the potential differences in programming using
an interpreted scripting language like PHP in place of a
compiled language (e.g. Java in JSP, .NET)?


o
Free format
-

white space is ignored

o
Statements are terminated by semi
-
colon ;

o
Statements grouped by { … }

o
Comments begin with // or a set of comments /* */

o
Assignment is ‘=’: $a=6

o
Relational operators are ,< , > == ( not a single equal)

o
Control structures include if (
cond
) {..} else { }, while (
cond
) { .. } ,
for(
startcond
; increment;
endcond
) { }

o
Arrays are accessed with [ ]
-

$x[4] is the 5th element of the array
$x
–

indexes start at 0

o
Associative Arrays (hash array in Perl, dictionary in Java) are
accessed in the same way: $y["
fred
"]

o
Functions are called with the name followed by arguments in a fixed
order enclosed in ( ) :
substr
("fred",0,2)

o
Case sensitive
-

$
fred

is a different variable to $FRED


C
-
like language

PHP Scripts

o
every PHP script is a collection of one or more
statements
; these
statements appear as a collection of names, numbers and special
symbols;


o
individual statements are terminated by a
semicolon

(;) and blocks
of statements are contained within
curly brackets

({ .. });


o
statements can be
simple

(e.g.
print

or
echo
) while others can be
grouped statements

(e.g. the
if { .. }
elseif

{ .. } else { .. }

block)


o
PHP can use
literal values

such as numbers and blocks of text
(e.g.
9

or
"some text"
) or give names to specific
expressions

(e.g.
variables, functions or classes)


o
operators are used to
join values
, usually one value to the left of
the operator and one to the right (e.g. 9 + 3 )


<!
DOCTYPE html>

<html>


<?
php


# declare a variable & assign it a value


$name =
"Popeye";

?>


<head>


<title>
PHP Simple Example
</title>

</head>


<body>


<p>
Welcome to PHP,
<?
php

echo
("$name");
?>
!
</p>

</body>


</html>

Simple PHP script example


s
ingle line comment, use # or //

v
ariable ($name) with value
assignment (‘Popeye’)

s
cripting delimiters

c
all to built
-
in ‘echo()’ function

v
iew script

run script

Data Types (1)


o
PHP has eight different data types
–

5 basic and 2
composite types and 1 resource type

o
The 5 basic data types are:

-
integers

: whole numbers in the range
-
2,147,483,648 to
+2,147,483,647 on 32
-
bit architecture. Can be octal (prefixed by
0), decimal and hexadecimal (prefixed by 0x)

-
floating
-
point

: real or doubles (decimal), can be written using
base 10 notation (e.g. 3900 == 3.9e3)

-
strings

: sequence of characters contained by single (‘..’) or
double ("..") quotes. Within double quotes variables are replaced
by their values (interpolated). Escape sequences are used to
include special characters within double quoted strings (e.g.
\
" to
include a double quote and
\
\

to include a backslash)

-
booleans

: the
boolean

data type evaluates to either true or
false (e.g. $a == $b will evaluate to true if both variables contain
the same value, false otherwise

-
null

: a special data type that stands for a lack of value. Often
used to initialize or reset variables.

Data Types (2)

o
arrays

: are a composite data type that collect values into a list. The values
of the array elements can be text, a number or even another array. Arrays
can be from 1 to any number of dimensions.


-

arrays are referenced using square [ .. ] brackets.


<?
php



$cities[0] = "London";



$cities[1] = "Bath";



$cities[2] = "Bristol";



print ("I live in $cities[2].<
br
/>
\
n");


?>


-

an array can be indexed using a string value for the index (called
associative array or hash) and are useful in situations where there is a need
to collect different types of data into one array. (e.g.
$
userInfo

["name"] =
"Kevin";

)


-

array elements containing other arrays are used to build multi
-
dimensional
arrays.


<?
php



$modules = array(


"ISD"=>array(


"Joe",




"Tim",




"Mary"


)


"ISDP"=>array(




"Bob",


"Tom",


"Sue"




)



);



print ($modules["ISD"][2]);


?>

Data Types (3)

o
objects

: are another composite data type fully supported by php.


-

php supports standard object
-
oriented (OO) methodologies and
techniques such as



inheritance

-

the ability to derive new classes from

existing ones and inherit or override their attributes and

methods.



encapsulation

-

the ability to hide data from users of the class

(the
public
,
protected

and
private

keywords.)



special methods

-

for instance, code that is automatically run

when a object is created (constructor) or destroyed

(destructor).



polymorphism

–

o
verloading a function so that a function call

will behave differently when passed variables of different type.



-

a good introducton to OO programming using php can be found at

http://www.slideshare.net/mgirouard/a
-
gentle
-
introduction
-
to
-
object
-
oriented
-
php/

o
resources

: are a data type that hold handles to external resources
such as open files or database connections.

Control statements are a means of executing blocks of code depending on one
or more conditions.

if (expression) {..}
: the simple if statement takes the following form
–


if (expression)


{



this

block gets executed if the expression evaluates to true


}


if (expression) {..} elseif (expression) {..} else {..}

: the compound if
statement takes the following form
–



if (expression1)


{



this block gets executed if expression1 is true


}


elseif (expression2)


{



this block gets executed if expression1 is false



and expression2 is true



}



else


{



this block gets executed if both expression1 and



expression2 are false


}


? operator

: acts as a shortened version of the if {..} statement. It takes the
followng form
-



conditional expression ? true expression : false expression;

Control Structures (1)

Control Structures (2)

switch (expression) {case expression .. case expression .. default}

: similar to the
if .. elseif .. else

structure where a single expression
is compared to a set of possible values and if a match is made, the
block following the match is executed. The
break

statement can be
used to jump out of a switch structure. A default expression can be
used to execute code if none of the expressions evaluates to true.

o
Loops
–

allow for the repetition of blocks of code until a
condition is met.

while (expression) {..}

: when first reached the expression is
evaluated and if true the block of code following the expression is
executed, otherwise the block is skipped. The
break

statement can
be used to break out of a while block. The
continue

statement can
be used to return control to the beginning of the block.

do {..} while (expression)

: is a way of delaying the decision to
execute a code block until the end.

for (initialization; continue; increment) {..}

: used to carry out a block
a code a specific number of times.

foreach (array as key=>value) {..}

: provides a formalized method for
iterating over arrays.



Control Structures (3)

exit
,
die

and
return

: the
exit

statement is used to stop
execution
–

it is useful when an error occurs and it could
be harmful to continue execution;


the
die

statement is similar to exit but can be followed by
an expression which is sent to the browser just before the
script is aborted, for instance


$
fp

=
fopen
("somefile.txt", "r") OR die("Could not open
file");


the
return

statement can be used within functions (see
following section) but can also be used with the
include

statement. If used within a script, it stops execution within
the current script and returns control to the script that
made a call to include. That is, when a
include

is used,
the included script may return prematurely.

PHP Data Structures (1)

arrays


-

arrays collect values into lists


-

individual items (elements) are accessed using an
index

which can be an integer or
a string


-

you can build arbitrarily complex data structures using arrays within arrays, that is,
a value within an array can hold another array (multidimensional array)



single dimension arrays


-

use square brackets [ ] to refer to an element


-

arrays are treated like normal variables
–

you can create it at the point of use
without having to declare anything first.




example: referencing array elements



<?
php



$teacher[0] = "
Prakash
";



$teacher[1] = "Paul";



$teacher[2] = "Dan";



$teacher[3] = "Chris";




echo ("$teacher[3] teaches DSA).<
br
/>");


?>










Output?

Note: if you leave out the

index number, php will

start at 0 and use consecutive

integers thereafter.


<?
php


$teacher[] =
"
Prakash
";


$teacher[] =
"Paul";


$teacher[] =
"Dan";


$teacher[] =
"Chris";



$
indexCount

= count ($teacher);



for ($index=0; $index < $
indexCount
; $index++) {


print
("Teacher
$index is $teacher[$index]. <
br
/>");


}


?>

PHP Data Structures (2)


example: counting and accessing values using a loop

arrays (cont.)

r
un script

<?
php


//create hash with data


$user["Name"] = "Leon Trotsky";


$user["Location"] = "
Coyoacan
, Mexico City";


$user["Occupation"] = "Revolutionary";



//loop over the values


foreach

($user as $key=>$value) {


print
("$
key is $value<
br
/>");


}

?>


PHP Data Structures (3)

arrays (cont.)



Associative Arrays (Hashes in Perl, HashMaps in Java)

r
un script


String Handling

o
String literals (constants) enclosed in double quotes " "
or single quotes ‘ ’

o
Within "", variables are replaced by their value:
–

called
variable interpolation
. "My name is $name, I think"

o
Within single quoted strings, interpolation doesn’t occur

o
Strings are concatenated (joined end to end) with the
dot operator "
key"."board
" == "keyboard"

o
Standard functions exist:
strlen
(),
substr
()
etc


o
Values of other types can be easily converted to and
from strings
–

numbers implicitly converted to strings in a
string context.

o
Regular expressions be used for complex pattern
matching.


Input / Output & Disk Access (1)

o
Reading and Writing to Files


Communicating with files follows the pattern of opening a stream to a
file, reading from or writing to it, and then closing the stream.



fopen
(..) : the
fopen

function opens a file for reading or writing. The
function expects the name of a file and a mode e.g.


fopen

("c:/temp/myfile.txt", "r");


which opens a file called myfile.txt in the directory "c:/temp" in the
"read" mode




File read/write modes :


r

reading only


w

write only, create if necessary, discard previous content


a

append to file, create if necessary, start writing at end


r+

reading and writing


w+

reading & writing, create if necessary, discard previous content


a+

reading & writing, create if necessary, start writing at end


Input / Output & Disk Access (2)

fclose (resource file)

: used to close a file.

feof (resource file)

: as a file is read, php keeps a pointer
to the last place in the file read; the feof function returns
true if the end of file is reached.

fgetcsv(resource file, integer length, string separator)

:
used for reading comma
-
separated data from a file. The
optional separator argument specifies the character to
separate fileds’ If left out, a comma is used.

fgets(resource file, integer length)

: returns a string that
reads from a file. It will attempt to read as many
characters
–

1 as specified by the length value. A
linebreak character is treated as a stopping point, as is
the end of the file.

fwrite(resource file, string data, integer length)

: writes a
string to a file. The length argument is optional and sets
the number of bytes to write.

the
exit()

and
die()

functions

o
both the
exit()

and
die()
statements

terminate the
execution of a script. The two statements are
equivalent.

o
a message can be output as the script is
terminated e.g.


$filename = '/path/to/data
-
file';

$file =
fopen
($filename, 'r')


or exit("unable to open file ($filename)");



PHP Books

Intermediate :

Nixon, Robin :
Learning PHP, MySQL, JavaScript and CSS: A Step
-
by
-
Step Guide to Creating Dynamic Websites

: O'Reilly Media, 2
nd

ed.,
2012

Ullman, Larry :
PHP and MySQL for Dynamic Web Sites: Visual
QuickPro Guide

: Peachpit Press, 4
th

ed., 2011

McLaughlin, Brett :
PHP & MySQL: The Missing Manual

: Pogue Press,
2011


Advanced :

Zandstra, Matt :
PHP Objects, Patterns and Practice
, Apress, 3rd ed.,
2010

Gogala, Mladen :
Pro PHP Programming

: Apress, 2011

Saray, Aaron :
Professional PHP Design Patterns

: Wrox, 2009


On
-
line Resources

-

php

home :
http://www.php.net

-
learning PHP :
php

@ w3 schools

-
code and examples :



php

extension & application library (pear) :



http://pear.php.net/



resource index :
http://php.resourceindex.com/



weberdev

:





http://www.weberdev.com/ArticlesSearch/Category/Begi
nner+Guides



phpexample

:
http://phpexamples.me/