PHP I

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PHP I
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• PHP, or PHP Hypertext Preprocessor is a
  server-side scripting language.
• Originally created in 1994 by Rasmus Lerdorf, to
  track users at his web site.
• Over the last few years, it has rapidly developed
  into a server-side scripting language, that fully
  supports (interacts) with a host of relational
  database systems (MySql in particular), thereby
  making it extremely useful for generating dynamic
  page content.
• Latest version is version 4, but 5 due to be
  released soon.
• In addition, PHP is an open source technology,
  that is freely available. It is estimated that
  over 6 million domains now use PHP.
• It is platform independent, with implementations
  for most Unix, Linux and Windows operating
  systems.

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• Shares some similarity with JavaScript in that it
  also allows you to embed programs (scripts)
  inside HTML code.
• The distinction is that JavaScript (and other
  client-side scripting languages) are interpreted
  by the browser, whilst PHP (and other server-side
  scripting languages) is processed by the web
  server.
• Once the script is processed, the result of the
  script (HTML in most cases) replaces the PHP
  code, and is returned to the client.
• Hence the browser sees standard HTML and displays
  it appropriately.
• As the script is processed by the server, the
  technology is aptly named server-side scripting
  language

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• Sample PHP code
• lthtmlgtltheadgtlttitlegtWelcome to the world of
  PHPlt/titlegtlt/headgt
• ltbodygt
• ltpgt
• lt?php
• echo(Welcome to the world of PHP, a convenient
  means of generating dynamic page content.)
• ?gt
• lt/pgt
• lt/bodygt
• lt/htmlgt
• Resultant HTML code
• lthtmlgtltheadgtlttitlegtWelcome to the world of
  PHPlt/titlegtlt/headgt
• ltbodygt
• ltpgt Welcome to the world of PHP, a convenient
  means of generating dynamic page content.lt/pgt
• lt/bodygt lt/htmlgt

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• Advantages of Server-side scripting
• There are no browser incompatibility issues, as
  the PHP code is interpreted entirely by the
  server.
• Access to server side resources such as data from
  a relational database. This is perhaps the most
  important benefit of PHP.
• Reduced load on the client JavaScript may
  significantly slow the display of a web page on
  low memory computers, as the browser has to
  process the JavaScript code. PHP code is entirely
  processed by the web server, hence this burden is
  passed to the server.
• Drawbacks of Server-side scripting
• Multiple server calls As PHP code is interpreted
  by the web server, each time a user interacts
  with the page, a call has to be made to the web
  server.
• Security issues Use of PHP could expose the web
  server, and lead to unwanted access to web server
  resources.

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• Basic Syntax
• PHP scripts begin with lt?PHP and end with ?gt
  delimiters
• Any code within these 2 delimiters is processed
  by the web server as PHP code. PHP code can be
  embedded directly anywhere within an HTML
  document.
• PHP files are stored with a .php extension.
• Syntactically, PHP is very similar to JavaScript,
  and supports similar constructs such as Arrays
  and Conditional statements.
• In addition, PHP comes with a lot of built-in
  functions, that enable you to perform all sorts
  of complex tasks such as sending emails, file
  upload, downloads, etc.
• Single line comments begin with //.
• Multiple line comments are enclosed between /
  and /
• //this is a single line comment.
• / this is a multi-line
• comment /

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• Variables and Operators
• Variables in PHP are declared with symbol.
• PHP is a loosely typed language, i.e. its
  variables can contain any type of data such as
  integers, strings, etc. They may also change
  types over its lifetime.
• testvariable Hello World
• testvariable 3
• In the above example, testvariable is initially
  initialized with a string value, and subsequently
  assigned an integer value.
• You may use the settype built-in function to
  explicitly convert the type. E.g.
  settype(testvariable, integer) converts the
  type of testvariable from string, to integer.
• The is the assignment operator, while is
  the equality operator.
• Several comparative, and arithmetic operators
  (similar) to those in JavaScript exist for
  performing comparisons, and for computations.

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• PHP automatically converts variable types when
  used for arithmetic computation. E.g
• lt?PHP
• testvariable20 students
• testvariabletestvariable 20.
• The above statement would evaluate to 40.
• Note that for implicit conversion from string to
  integer, the number value must come before other
  text in the string.
• Variable value substitution
• Variable values can be directly written into HTML
  code, e.g
• lthtmlgtltheadgtlttitlegtPHP Examplelt/titlegtlt/headgt
• ltbodygt
• ltpgt Hello
• lt?php testvariablePaul Smith
  echo(testvariable)
• lt/pgt
• lt/bodygt
• lt/htmlgt

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• Array Declaration
• In the simplest form, arrays are declared using
  the built-in array function, as shown below
• anarray array (1,ten,four)
• The above code creates an array called anarray,
  that has 3 values.
• As in JavaScript and other similar programming
  languages, array indices start at 0, i.e.
• anarray0 1, anarray1 ten and
  anarray2 four
• It is also possible to assign values to array
  elements with the index. E.g. anotherarray0
  ten
• If the index is not specified, an array element
  will be added after the last existing element of
  the array, i.e.
• anarray the fourth element.
• The above code automatically creates the 4th
  element of anarray.

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• PHP also supports the use of non-numeric arrays
  (associative arrays).
• E.g.
• birthdaysKevin 20-03-1982
• birthdaysJames 21-07-1984
• Associative arrays are particularly useful for
  accessing, and processing HTML form elements, as
  demonstrated later.
• Accessing values of array elements
• The array followed by its index (in square
  brackets) translates to the value of the element.
• Illustrating with the examples above,
• ltpgtlt?php echo(anarray1) ?gt would result
  in ltpgttenlt/pgt
• ltpgtKevins birthday is lt?php
  echo(birthdaysKevin) ?gt. would result in
  ltpgtKevins birthday is 20-03-1982.

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• User Interaction and Forms
• Server-side languages such as PHP are limited in
  their ability to interact with user input in the
  sense that a request has to be sent to the
  server, server processes the PHP code to
  dynamically generate an HTML response, and sends
  this back to the client.
• Hence user interaction involves back and forth
  server calls.
• Sending information to the web server
• The simplest method of sending information from a
  client, to the web server is by sending it along
  with the URL string as a query string.
• This is accomplished with the use of a ? symbol
  before the variable that is being passed. In the
  case of sending multiple variables, they are
  separated with an ampersand ()
• E.g lta hrefphp_script.php?firstnamePaulgtPaullt/
  agt

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• The previous example demonstrates a link to a PHP
  program called php_script.php.
• The name variable is passed to the script in URL
  of the link, as part of the page request.
• PHP automatically creates an associative array
  variable called _GET that contains any values
  passed in the URL query string.
• Hence the value of the name variable passed in
  the example would be accessed with
  _GETfirstname.
• Example
• php_script.php
• lt? php
• firstname _GETfirstname //a variable is
  assigned the value
• echo(Welcome to this website, firstname)
  //of firstname
• ?gt //
  sent in the URL query string.

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• Passing multiple variable values with the GET
  method
• lta hrefphp_script.php?fnamePaullnameSmithgtPa
  ul Smithlt/agt
• Within php_script.php, these values would be
  accessed as _GET(fname) and _GET(lname),
  respectively.
• Passing Values from Forms
• GET Method
• Similar to passing variables in URL query strings
  as demonstrated above.
• PHP generates a _GET array for each named form
  element, and they can then be easily accessed by
  the PHP program.
• Due to limitations in the number of characters
  that can be sent with the GET method, it is
  sometimes technically impossible to use this
  method to pass form data.

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• lthtmlgtltheadgtlttitlegtPassing form element values to
  PHPlt/titlegt
• lt/headgt
• ltbodygt
• ltform methodGET actionphp_script.phpgt
• ltinput typetext namefnamegtlt/inputgt
• ltinput typetext namelnamegtlt/inputgt
• ltinput typesubmitgt
• lt/formgt
• lt/bodygtlt/htmlgt
• When the above form is submitted, it will
  generate an URL query string similar to href in
  the link, in the last example.
• POST Method
• The information is invisibly passed, such that it
  does not form part of the URL .

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• This method enables you to send data containing
  large values, e.g textarea, to the web server.
• The variables passed are placed in another
  special array called _POST.
• Example Here the GET method is replaced with
  POST
• lthtmlgtltheadgtlttitlegtPassing form element values to
  PHPlt/titlegt
• lt/headgt
• ltbodygt
• ltform methodPOST actionphp_script.phpgt
• ltinput typetext namefnamegtlt/inputgt
• ltinput typetext namelnamegtlt/inputgt
• ltinput typesubmitgt
• lt/formgt
• lt/bodygtlt/htmlgt

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• The values in the form elements are accessed with
  the _POST array.
• The php_script.php would have to be modified as
  shown below
• php_script.php
• lt? php
• firstname _POSTfname
• lastname _POSTlname
• echo(Welcome to this website,ltbgt firstname
  lastname!lt/bgt)
• ?gt
• The _REQUEST array
• Contains all variables that appear in both _GET
  and _POST
• So youre no longer concerned about the method of
  the form.

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• Control Structures
• PHP, like other programming languages provides
  facilities that allow us to control the sequence
  of actions in a script.
• The if-else statement
• Most common control structure.
• Takes the general form
• if (condition)
• //statements to execute if
  condition is true
• else // statement to execute if
  condition is false
• The else statement is optional, i.e if there are
  no statements to execute if the condition is
  false, the else statement can be omitted.

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• E.g.
• name _REQUESTname
• if (name Paul)
• echo (Welcome to this web site, master
  creator!)
• else echo(Welcome to this website name)
• Multiple conditions
• In practice, you might want to combine more than
  one condition within the if construct.
• This is achieved with the use of the and
  operator () and the or operator (). The word
  and is a legal operator in PHP.
• E.g.
• fname _REQUESTfname
• lname _REQUESTlname
• if (fname Paul lname Smith)
  // the condition evaluates to
• echo (Welcome to this web site, master
  creator!) // true only if both
• else echo(Welcome to this website fname
  lname) //statements are true.

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• The While Loop
• Takes the form
• while (condition)
• / execute statements over and over as
  long as condition remains true /
• Useful when youre processing a list of objects,
  e.g array elements.
• E.g
• count 1
• while (count lt 10)
• echo(This is element count)
• count

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• The For Loop
• Takes the form
• for (initialize condition update)
• / statements to execute in iterations, as
  long as condition
• remains true after each update /
• The counter variable is initialized, its
  condition set, and its value updated in the first
  line of the For Loop.
• E.g.
• for (count 1 count lt 10 count)
• echo(This is element count)
• References
• Build Your Own Database Driven Website Using PHP
  MySQL. Kevin Yank. 2nd Ed. Chapter 3
• Deitel, Deitel Nieto Chapter 29.