Developing Web Applications

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Lecture 7 Introduction to PHP
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Today
Introduction to PHP

• PHP - Overview
• Variables Scope
• Output
• Variable types Boolean Strings
• String Functions Parsers
• Screening User Input/Output
• Maths functions
• Control and flow

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What is PHP?

• PHP stands for PHP Hypertext Preprocessor
• PHP is a server-side scripting language, which
  allows you to create dynamic Web pages
• PHP scripts are executed on the server
• PHP supports many databases (MySQL, Informix,
  Oracle, Sybase, Solid, PostgreSQL, Generic ODBC,
  etc.)
• PHP is an open source software
• PHP is free to download and use

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Why PHP?

• PHP runs on different platforms (Windows, Linux,
  Unix, etc.)
• PHP is compatible with almost all servers used
  today (Apache, IIS, etc.)
• PHP is FREE to download from the official PHP
  resource www.php.net
• PHP is easy to learn and runs efficiently on the
  server side

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What is a PHP File?

• PHP files can contain text, HTML tags and scripts
• PHP files are returned to the browser as plain
  HTML 
• PHP files have a file extension of ".php",
  ".php3", or ".phtml

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What do You Need?

• If your server supports PHP you don't need to do
  anything. Just create some .php files in your web
  directory, and the server will parse them for
  you. Because it is free, most web hosts offer PHP
  support.
• However, if your server does not support PHP, you
  must install PHP.
• Download PHP http//www.php.net/downloads.php
• Download MySQL http//www.mysql.com/downloads/ind
  ex.html
• Download Apache Server http//httpd.apache.org/do
  wnload.cgi

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Basic PHP Syntax

• PHP code is executed on the server, and the plain
  HTML result is sent to the browser.
• A PHP scripting block always starts with lt?php
  and ends with ?gt. A PHP scripting block can be
  placed anywhere in the document.
• A PHP file normally contains HTML tags, just like
  an HTML file, and some PHP scripting code.
• lthtmlgt ltbodygt lt?php echo "Hello World" ?gt
  lt/bodygt lt/htmlgt
• Each code line in PHP must end with a semicolon.
  The semicolon is a separator and is used to
  distinguish one statement from another.

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Basic PHP Syntax

• There are two basic statements to output text
  with PHP echo and print.
• Echo is not a function and does not return a
  value
• echo "ltpgtThis is a paragraph.lt/pgt"
• Print is a function and returns a value 1
  success, 0 failure
• print("ltpgtThis is a paragraph too.lt/pgt")
• Note The file must have the .php extension. If
  the file has a .html extension, the PHP code will
  not be executed.

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Comments in PHP

• In PHP, we use // to make a single-line comment
  or / and / to make a large comment block.
• lthtmlgt
• ltbodygt
• lt?php //This is a comment
• / This is a
• comment block /
• ?gt
• lt/bodygt
• lt/htmlgt

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Variables in PHP

• Variables are used for storing a values, like
  text strings, numbers or arrays.
• When a variable is set it can be used over and
  over again in your script
• All variables in PHP start with a sign symbol.
• The correct way of setting a variable in PHP
• var_name value
• If you forget the sign at the beginning of the
  variable it will not work.
• lt?php
• txt "Hello World!"
• number 16
• ?gt

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Variables in PHP

• PHP is a Loosely Typed Language
• In PHP a variable does not need to be declared
  before using it.
• PHP automatically converts the variable to the
  correct data type, depending on how they are set.
• In a strongly typed programming language, you
  have to declare (define) the type and name of the
  variable before using it.
• In PHP the variable is declared automatically
  when you use it.

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Variables in PHP

• Variable Naming Rules
• A variable name must start with a letter or an
  underscore "_"
• A variable name can only contain alpha-numeric
  characters and underscores (a-z, A-Z, 0-9, and _
  )
• A variable name should not contain spaces. If a
  variable name is more than one word, it should be
  separated with underscore (my_string), or with
  capitalization (myString)

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Variables in PHP Scope

• Scope refers to where within a script a variable
  has meaning or a value
• Mostly variables are available to you anywhere
  within your script.
• Note that variables inside a function are local
  to that function and cannot be accessed outside
  the function even if the function call and the
  called function are in the same script.
• The modifier global allows function variables to
  be accessed outside the function

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Variables in PHP types

• String
• Number
• Integer
• Real (float, decimal, double)
• Boolean
• TRUE / FALSE
• Array
• Object

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Variables in PHP examples

• Integer
• a 1234 // decimal number
• a -123 // a negative number
• a 0123 // octal number (equivalent to 83
  decimal)
• a 0x1A // hexadecimal number (equivalent to
  26 decimal)
• Floating Point Numbers
• a 1.234 a 1.2e3 a 7E-10
• Boolean
• foo True // assign the value TRUE to foo
• // is an operator which returns a boolean
• if (action
  "show_version")
• echo "The
  version is 1.23"
• // this is valid but
  not necessary
• if (show_separators
  TRUE)
• echo "lthrgt\n"
• // because you can
  simply type this
• if
  (show_separators)

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Variables in PHP examples cont.

• Strings (single or double quoted)
• echo 'this is a simple string'
• echo 'You can also have embedded newlines in
  strings, like this way.'
• echo 'Arnold once said "I\'ll be back"'
• // output ... "I'll
  be back"
• echo 'Are you sure you want to delete C\.?'
• // output ... delete
  C\.?
• Arrays
• error_descriptionsE_ERROR "A fatal error has
  occured"
• error_descriptionsE_WARNING "PHP issued a
  warning"
• error_descriptionsE_NOTICE "This is just an
  informal notice"
• The above statements are in fact the same as the
  following, if E_ERROR, E_WARNING and E_NOTICE are
  defined as constants
• error_descriptions1 "A fatal error has
  occured"
• error_descriptions2 "PHP issued a warning"
• error_descriptions8 "This is just an
  informal notice"

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Constants and Global Variables

• To define a constant
• define(PI, 3.1416)
• area PIradiusradius
• Global variables defined outside any function
• global var1, var2
• function xyz()
• localvarX var1

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Arrays in PHP

• An array can store one or more values in a single
  variable name.
• When working with PHP, sooner or later, you might
  want to create many similar variables.
• Instead of having many similar variables, you can
  store the data as elements in an array.
• Each element in the array has its own ID so that
  it can be easily accessed.
• There are three different kind of arrays
• Numeric array - An array with a numeric ID key
• Associative array - An array where each ID key is
  associated with a value
• Multidimensional array - An array containing one
  or more arrays

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Numeric Arrays

• A numeric array stores each element with a
  numeric ID key.
• There are different ways to create a numeric
  array.

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Numeric arrays

• Say that we have a list of marks out of 100 in a
  subject 95, 93, 56, 70, 65, 98
• array value 1 - 95
• array value 2 - 93
• array value 3 - 56
• array value 4 - 70
• array value 5 - 65
• array value 6 - 98
• marks array (95, 93, 56, 70, 65, 98)
  generates a numerically-indexed array
• marks0 95
• marks1 93
• marks2 56
• marks3 70
• marks4 65
• marks5 98

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Numeric arrays (cont)

• The following code also generates a
  numerically-indexed array, allocating the next
  index after the highest current index to the
  element.
• marks 95
• marks 93
• marks0 is 95 and marks1 is 93.
• Note that array index starts at 0 by default.
• You can skip indexes by allocating a specific
  index to a value -
• marks5 56
• marks 70
• will be allocate 70 to marks6. Therefore
  marks5 is 56 and marks6 is 70.

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Associative Arrays

• In an associative array, each ID key is a string
  which is associated with a value.
• When storing data about specific named values, a
  numerical array is not always the best way to do
  it.
• With associative arrays we can use the names as
  keys and assign values to them.

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Associative arrays

• Suppose we have a list of marks in a subject and
  we want to represent who got what mark
• Adrian 95, Matty 93, Lance 56, Stephen 70,
  Craig 65, Andy 98
• marks array ("Adrian"gt93, "Lance"gt56,
  "Stephen"gt70, "Craig"gt65,
  "Andy"gt98)
• Array marks maps a key to a value (or assign a
  value to a key)
• name is the key
• mark is the value

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List an associative array

• list() in conjunction with each() assigns the key
  and value of an array item into the variables
  key and value.
• The following code prints each key / value pair
  into a table. Note that value might itself be an
  array.
• reset(marks) //go to the beginning of the array
• echo "lttable border\"1\"gt"
• while (list(key, value) each(marks))
• echo "lttrgtlttdgtkeylt/tdgtlttdgtvaluelt/tdgtlt/trgt\n"
• echo "lt/tablegtlthrgt"

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List an associative array (cont)

• each() actually returns an array for each array
  item which includes the key and value with index
  0 mapped to the key and index 1 mapped to the
  value.
• reset(marks)
• while (row each(marks))
• echo "Mark for row0 is row1ltbr /gt"

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Multidimensional Arrays

• In a multidimensional array, each element in the
  main array can also be an array. And each element
  in the sub-array can be an array, and so on.
• families array
• (
• "Griffin"gtarray
• ( "Peter", "Lois", "Megan" ),
• "Quagmire"gtarray
• ( "Glenn" ),
• "Brown"gtarray
• ( "Cleveland", "Loretta", "Junior" )
• )

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Strings

• A string variable is used to store and manipulate
  a piece of text.
• After we create a string we can manipulate it. A
  string can be used directly in a function or it
  can be stored in a variable.
• We can manipulate strings by operators or
  functions.
• There is only one string operator in PHP -- the
  concatenation operator (.), which is used to put
  two string values together.
• lt?php
• txt1"Hello World"
• txt2"1234"
• echo txt1 . " " . txt2
• ?gt
• There are many functions to manipulate strings

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String functions

• strlen() used to find the length of a string.
• lt?php echo strlen("Hello world!") ?gt
• The length of a string is often used in loops or
  other functions, when it is important to know
  when the string ends. (i.e. in a loop, we would
  want to stop the loop after the last character in
  the string)
• strpos() used to search for a string or
  character within a string.
• If a match is found in the string, this function
  will return the position of the first match. If
  no match is found, it will return FALSE.
• lt?php
• echo strpos("Hello world!","world")
• ?gt

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String functions others

• boolean strcmp (str1, str2)
• boolean strcasecmp (str1, str2)
• boolean strstr (str1, str2)
• boolean stristr (str1, str2)
• int strlen(str)
• string substr (str, start_pos, len)

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String functions others (cont)

• string chop (str)
• string ltrim (str)
• string trim (str)
• string str_replace (old_txt, new_txt, text)
• string substr_replace (old_txt, new_txt, text)
  
• strtolower(str)
• strtoupper(str)
• ucfirst(str)
• ucwords(str)

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String functions formatting input/output

• addslashes(str)
• stripslashes(str)
• escapeshellcmd(str)
• strip_tags(str)
• htmlspecialchars(str)
• htmlentities(str)
• nl2br(str)

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PHP Operators

• Operators are used to operate on values.
• Arithmetic Operators
• - /
• --

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PHP Operators

• Assignment Operators
• -
• /
• .

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PHP Operators

• Comparison Operators
• !
• gt
• lt
• gt
• lt

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PHP Operators

• Logical Operators
• !

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Maths functions

• low_int floor (double)
• high_int ceil (double)
• nearest_int round (double)
• (nearest even number if exactly .5)
• positive abs (number)
• min min (n1, n2 , nn)
• max max (n1, n2 , nn)

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Control and flow

• if (expr1)
• elseif (expr2)
• else
• while (cond)
• do while (cond)
• switch (var)
• case a
• case b
• for (i 0 i lt expr i )
• foreach (array_expr as value)
• foreach (array_expr as keygtvalue)
• break
• continue

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If.. Then.. else

• if (a gt b) print "a is bigger than b"
• if (a gt b)
• print "a is
  bigger than b"
• b a
• if (a gt b)
• print "a is
  bigger than b"
• elseif (a b)
  
• print "a is
  equal to b"
• else
• print "a is
  smaller than b"

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While

• / example 1 /
• i 1
• while (i lt 10)
• print i /
  the printed value would be
• 
  i before the increment
• 
  (post-increment) /
• / example 2 - alternative notation to using
  the braces - and endwhile/
• i 1
• while (i lt 10)
• print i
• i
• endwhile

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For loops

• / example 1 similar to C syntax / for
  (i 1 i lt 10 i)
• print i
• / example 2 / for
  (i 1i)
• if (i gt 10)
  
• break
• print i
• / example 3 / i 1
• for ()
• if (i gt 10)
• break
• print i
• i
• / example 4 / for
  (i 1 i lt 10 print i, i)

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Foreach

• An easy way to iterate over arrays. There are two
  syntaxes -- the second is a minor but useful
  extension of the first
• foreach(array_expression as value)
• foreach(array_expression as key gt value)
• The following are functionally identical
• //example 1 //
• reset (arr)
• while (list(, value) each
  (arr))
• echo "Value valueltbrgt\n"
• //example 2 //
• foreach (arr as value)
• echo "Value valueltbrgt\n"

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Foreach cont.

• / foreach example 1 value only /
• a array (1, 2, 3, 17)
• foreach (a as v)
• print "Current value of \a v.\n"
• / foreach example 2 value (with key printed
  for illustration) /
• a array (1, 2, 3, 17)
• i 0 / for illustrative purposes only /
• foreach(a as v)
• print "\ai gt v.\n"
• i
• / foreach example 3 key and value /
• a array ( "one" gt 1, "two" gt 2, "three" gt
  3, "seventeen" gt 17 )
• foreach(a as k gt v)
• print "\ak gt v.\n"

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Break Continue

• break ends execution of the current for, foreach,
  while, do..while or switch structure.
• arr array ('one', 'two', 'three', 'four',
  'stop', 'five')
• while (list (key, val) each (arr))
• if (val 'stop')
• break / You could also write 'break
  1' here. /
• echo "valltbrgt\n"
• / note list() is a multiple assignment function
  the key and value returned by each() are assigned
  to key and value. key is not used in this
  example./
• continue is used within looping structures to
  skip the rest of the current loop iteration and
  continue execution at the beginning of the next
  iteration.

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Switch

• if (i 0) print "i equals 0"
• if (i 1) print "i equals 1"
• if (i 2) print "i equals 2"
• / this is equivalent /
• switch (i)
• case 0
• print "i equals 0"
• break
• case 1
• print "i equals 1"
• break
• case 2
• print "i equals 2"
• break

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require() and include()

• require() includes and evaluates a specific file.
• require() and include() are identical in every
  way except how they handle failure. include()
  produces a warning while require() results in a
  fatal error.
• lt?php
• require 'prepend.php'
• require somefile
• require ('somefile.txt')
• ?gt
• require_once() or include_once() should be used
  in cases where the same file might be included
  and evaluated more than once during a particular
  execution of a script, and you want to be sure
  that it is included exactly once to avoid
  problems with function redefinitions, variable
  value reassignments, etc.

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What we covered today

• Introduction to PHP
• Variables, constants, arrays and strings
• Control structures sequence, repetition and
  selection

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Next More advanced PHP