LIS651 lecture 0 Introduction to PHP with primitive data types

1
LIS651 lecture 0Introduction to PHP with
primitive data types

• Thomas Krichel
• 2009-03-08

2
today

• Introduction to the course
• Introduction to PHP
• Using form data in PHP

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course resources

• Course home page is at http//wotan.liu.edu/home/k
  richel/courses/lis651p08a
• The course resource page http//wotan.liu.edu/home
  /krichel/courses/lis651
• The class mailing list https//lists.liu.edu/mailm
  an/listinfo/cwp-lis651-krichel
• Me.
• Send me email. Unless you request privacy, I
  answer to the class mailing list.
• Skype me at thomaskrichel. Get skype from
  skype.com.

4
today

• We introduce PHP. Understanding PHP is the most
  difficult aspect of the course.
• We look at how PHP can be used to show the data
  that we get from the form.
• You should think about what data to get and how
  to show it.
• Everybody will build an example form and then a
  PHP script to show it.
• Finally we build a new PHP script that contains
  the form. So instead of two files, we only have
  one.

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PHP introduction

• PHP is the PHP Hypertext Processor.
• It is a tool that allows for server-side
  scripting.
• Its predecessor is PHP/FI, Personal Home Page /
  Forms Interpreter.
• PHP/FI was released by Rasmus Lerdorf in 1995. It
  was written in Perl.
• PHP/FI version 2 was released in 1997. It was
  written in C.
• PHP version 5 is the current version.

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Apache and PHP

• When a file ends in .php, is not simply sent down
  the http connection like other files.
• Instead, apache sends the file to the PHP
  processor.
• It sends to the client whatever the PHP processor
  returns.
• The PHP processor is a module that lives inside
  Apache.

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PHP language

• PHP is an interpreted language.
• You write a series of statements.
• Apache hands these statements to the PHP
  interpreter.
• The interpreter executes these statements one by
  one.
• When it find an error, it stops running and
  signals the error.
• Compiled languages are different. They read the
  whole program before starting to execute it.

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try it out

• Remember we duplicate validated.html when
  creating a new new file.
• Right-click on validated.html, choose duplicate.
• You may be asked to supply your password again.
• You erase the contents of the dialog box that
  suggests a new file name and put your new file
  name in there.
• If it contains PHP code, it has to end in .php.

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first PHP script

• Create a file with the name info.php, and the
  following contents
• lt?php
• phpinfo()
• ?gt
• nothing else. This will create a test page that
  tells you everything PHP knows about. Look at
  some of the variables.

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comment on info.php

• In terms of XML, the "lt?php" until "?gt" part is
  called a processing instruction. It is a type of
  node that we did not encounter in LIS650.
• We can call any part of the file between "lt?php"
  and "?gt" a PHP part of the file.
• The XML file here contains just the processing
  instruction.

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output of phpinfo()?

• phpinfo() create a whole web page for you, that
  validates against a loose HTML specification.
• That page contains a lot of technical detail.
• The section we may be interested in is PHP
  Variables. It contains variables that we may be
  interested in. These are variables that PHP can
  understand
• from its environment
• from the client

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the magic of PHP

• The client never sees the PHP code. It only sees
  what the PHP processor has done with the code.
• You can write normal HTML code, and you can
  switch to writing PHP code pretty much at any
  stage.
• You can have several PHP parts.
• PHP parts can not be nested.
• The contents of the PHP part can be called a PHP
  script.

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statements

• Like a normal text is split into sentences, a PHP
  script is split into statements.
• A PHP script contains one or more statements.
• Each statements tells the interpreter something.
• Each statement is ended by a semicolon.
• In our first script there is only one statement.
• Each statement is ended with a semicolon!
• Think of a statement like a rule in CSS. But
  never forget the semicolon!

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expressions

• The stuff before the semicolon is called an
  expression.
• You can think of an expression as anything anyone
  may want to write in a computer program.
• So an expression is just a way to talk about
  stuff in a program in a more edifying way than
  just calling it stuff.

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functions

• phpinfo() is a function.
• Functions are one of the most fundamental
  concepts in computer programming.
• A function is an expression that does something
  to something else. The something else is in the
  parenthesis. It is called the argument of the
  function.
• The argument of phpinfo() is empty.

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second php script hello.php

• Normally we write HTML code and then we add PHP
  parts.
• Take validated.html, copy to hello.php
• make the body
• ltdivgt
• lt?php
• print("Hello, world!")
• ?gt
• lt/divgt
• Validate the resulting XHTML.

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comment on hello.php

• print() is also a function. print() prints its
  argument. Here the argument is a string. A string
  is a sequence of characters enclosed by single or
  double quotes.
• For print, the () can be omitted.
• You could have written three statements
• lt?php
• print "ltdivgt"
• print "Hello, world!"
• print "lt/divgt"
• ?gt

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good style

• Write each statement on a new line.
• Add plenty of comments. There are three styles of
  comments in a PHP program
• // the rest of the line is a comment
• the rest of a line is a comment
• / this is a comment /
• Only last style can be used over several lines.
• Do you recognize two of the commenting styles?

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another way to write hello.php

• lt?php
• greeting"Hello, world!"
• print "ltdivgtgreetinglt/divgt"
• ?gt
• Here greeting is a variable. The first statement
  assigns it the string value "Hello, world!". The
  second statement prints it out.
• This example is important because it illustrates
  the concept of a variable.
• The name of the variable is greeting.

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variable names

• Variable name must start with a letter or
  underscore. They can contain letters, digits and
  underscores. The following are examples of
  illegal names
• 2drunk
• bottle-content
• brewer_at_grosswald
• Variable names are case sensitive. I use
  lowercase only and add underscores in long names.
• The variable name "this" is reserved.
• It is good to give variables meaningful names.

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strings

• a piece of text in PHP is called a string.
• A string is often surrounded by single quotes.
• print 'I want beer'
• want'beer'
• print 'I want want' // prints I want want
• If you want to use the values of variables, use
  double quotes
• want'beer'
• print "I want want"
• // prints I want beer

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single and double quotes

• You can use single quotes to quote double quotes
• print 'She wrote "I want beer." and sighed.'
• // prints She wrote "I want beer." and sighed.
• and vice versa
• print "She wrote 'I want beer.' and sighed"
• // prints She wrote 'I want beer.' and sighed.
• Sometimes it is not obvious when to put single
  quotes, double quotes, and when to leave them
  out. If one thing does not work, try something
  else.

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the backslash escape

• The backslash is used to quote characters that
  otherwise are special.
• print 'Don\'t give me bad beer!'
• kind'bock'
• beer'Festbock'
• print "ltp class\"kind\"gtbeerlt/pgt"
• // prints ltp class"bock"gtFestbocklt/pgt
• The backslash itself is quoted as \\
• print "a \\ against beer consumption"
• // prints a \ against beer consumption

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more backslash escapes

• \n makes the newline character
• \r make the carriage return (no use in
  Unix)?
• \t makes the tab (seldomly used in
  HTML)?
• \ makes the dollar (used in the
  shop)?
• amount'1.50'
• print "you owe \amount per bottle."
• // prints you owe 1.50 per bottle.
• If the backslash was not there would be
  considered to be a variable.

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concatenation

• This is done with the . operator. It puts two
  strings together, the second one after the first
  one.
• cost'5.23'
• message'This costs ' . cost
• print message
• // prints This costs 5.23

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numbers

• Numbers are set without the use of quotes.
• You can , -, and / for the the basic
  calculations.
• There also is the modulus operator . It gives
  the remainder of the division of the first number
  by the second
• print 10 7 // prints 3
• Use parenthesis for complicated calculations
• pack2 (10 7)
• print "a pack pack" // prints a 6 pack

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geeky increment/decrement

• is an operator that adds one. The value of the
  resulting expression depends on the position of
  the operator
• a4
• print a // prints 5
• print a // prints 5
• b4
• print b // prints 4
• print b // prints 5
• -- works in the same way

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type conversion

• In some circumstance, PHP converts numbers to
  strings and back. It works like magic. It
  converts numbers to strings when required
• one_in_three1/3
• print one_in_three // prints 0.333333333333
• and numbers to
• string"1.500"
• number3string
• print number
• Sometimes it converts to Boolean!

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Boolean value

• Every expression in PHP has a Boolean value.
• It is either 'true' or 'false'.
• In certain situation, an expression is evaluated
  as a Boolean
• For example
• if(expression)
• expression1 or expression2

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what is truth?

• All strings are true except
• the empty string
• the string "0"
• All numbers are true except
• 0
• 0.0
• example
• a5-4-1 // a is false
• Note that variables that you have not assigned
  contents are false. This includes misspelled
  variables!!

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isset()?

• isset() is a function that returns true if a
  variable is set.
• Under strict coding rules, that are enforced by
  PHP running on wotan, the PHP processor will
  issue a notice when you use a variable that has
  not been set to a value.
• isset(variable) can be used to find out if the
  variable variable was set before using it.

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comparison operators

• Expressions that are evaluated in Boolean often
  use comparison operators.
• beer 'grosswald' // checks for equality
• Note difference from
• beer'grosswald' // this is always true
• Other comparisons are
• lt smaller than lt smaller or equal than
• gt larger than gt larger or equal than

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logical operators

• and is logical AND. or is logical OR.
• if(brand'Budweiser' or brand"Sam Adams")
• print "Commiserations for buying a lousy
  beer\n"
• where is the mistake in this piece of code?
• ! is Boolean NOT
• These can be combined. Use parenthesis
• if(((pints) gt 2 and (vehicle'car')) or
  ((pints gt 6) and (vehicle'bicycle')))
• print "order a cab!\n"

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if( condition )

• if( condition ) evaluates an expression condition
  as Boolean, and executes a block of code
  surrounded by curly brackets if the expression is
  true.
• if(drunk)
• print "Don't drive!\n"
• Note you don't need to indent the block as done
  above, but the way Thomas has done it there is
  pretty much standard, so do it in the same way.

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if( condition ) else

• if you have an if() you can add an else block of
  code to execute when the condition is false
• if(sober)
• print "You can drive\n"
• else
• print "Check if you are fit to drive\n"

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elseif( condition )

• You can build chain of conditions
• if(pints_drunk0)
• print "You are ok to drive\n"
• elseif(pints_drunklt3)
• print "Don't use the car, get on your bike\n"
• elseif(pints_drunklt6)
• print "Take a cab home\n"
• else print "Call the local hospital!\n"

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while( condition )

• while( condition ) executes a piece of code
  while the condition condition is true
• count0
• while(count lt 100)
• print "???? ??? ????? -- ?????? ??
  ?????!ltbr/gt"
• countcount1 don't forget to increment
  count!

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getting back to forms

• Forms deliver data to the server. The server can
  then process the data and deliver a response.
• If the server process uses PHP, each control is
  visible to PHP as a PHP variable. It can be read
  into the script.

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control name and PHP variable

• When the form is passed to the PHP script named
  with the action of the the ltformgt the controls
  are accessible as PHP variables.
• If name is the name of the control, and if the
  method is POST, the control is read as the
  variable _POST'name'.
• If name is the name of the control, and if the
  method is GET, the control is read as the
  variable _GET'name'.

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example

• HTML file greet.html has
• ltform action"greet.php" method"get"gtltpgt
• your last name ltinput type"text"
  name"lastname"/gtlt/pgtlt/formgt
• PHP file greet.php has
• lt?php
• print "Hello "
• print _GET'lastname'
• ?gt
• in addition to the usual HTML stuff.

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iterative form input

• When users start to use your site, the shit hits
  the fan. Users have many ways to do things wrong.
• Many times you will have to print the form again,
  with values already filled in.
• In such circumstance a static HTML file for the
  form is unsuitable.
• Therefore we need a PHP file that writes out the
  form and processes the form.

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check for submission

• We include a hidden element in the form to see if
  it was submitted
• ltinput type"hidden" name"submitted" value"1"/gt
• We start the script we check for submission
• if(_GET'submitted')
• // work on the data that was submitted
• else
• // print form

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master example greet.php

• lt?php
• if(_GET'submitted')
• name_GET'name'
• print "ltdivgtHello name!lt/divgt\n"
• else
• print "ltform action\"greet.php\"
  method\"get\"gt\n"
• print "ltdivgtltinput type\"hidden\" "
• print "name\"submitted\" value\"1\"
  /gtlt/divgt\n"
• print "ltpgtYour name ltinput type\"text\" "
• print "name\"name\" value\"name\" /gt"
• print "lt/pgtlt/formgt\n"
• ?gt

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PHP calling itself

• One cool thing to help with that is
• _SERVERPHP_SELF
• It gives the file name of your script in the
  form. As
• you change your script file name, you do not
  need to change the name of the form submitted.
• So in the previous slide, if you replace
• action\"greet.php\"
• with
• action\""._SERVER'PHP_SELF'."\"
• you can change the name of the PHP file. It will
  still find the itself as the PHP file.

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http//openlib.org/home/krichel

• Thank you for your attention!
• Please switch off computers when you are done!