Variables in PHP

1
Variables in PHP

• Bryan Duggan

2
Variables in PHP

• Variables in PHP are denoted by a dollar sign
  followed by the name of the variable.
• A variable name is case-sensitive.
• A valid variable name starts with a letter or
  underscore, followed by any number of letters,
  numbers, or underscores.

3
Example Usage of Variables

• lthtmlgt
• ltheadgt
• lttitlegtGreetingslt/titlegt
• lt/headgt
• ltbodygt
• lth1gtGreetingslt/h1gt
• ltpgt
• lt?php person "Tom"
• Person "Dick"
• echo "Hello person and Person"
• ?gt
• lt/pgt
• lt/bodygt
• lt/htmlgt

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Data Types in PHP

• PHP supports eight primitive data types
• There are four scalar types
• boolean
• integer
• floating-point number
• string
• There are two structured types
• array
• object
• There are two special data types
• resource
• NULL
• The programmer does not specify the type of a
  variable
• a variables type is determined from the context
  of its usage

6
Booleans

• The boolean data type admits two values
• true (case-insensitive)
• false (case-insensitive)
• Example usage
• itIsRainingToday true
• thePrinterIsBusy True
• theQueueIsEmpty FALSE

7
Integers

• Integers can be specified in decimal, hexadecimal
  or octal notation, optionally preceded by a sign
  
• In octal notation, the number must have a leading
  0
• In hexadecimal notation, the number must have a
  leading 0x.
• Examples
• a 1234 decimal number
• a -123 a negative number
• a 0123 octal number (equivalent to
  83 decimal)
• a 0x1B hexadecimal number (equivalent
  to 27 decimal)
• The maximum size of an integer is
  platform-dependent, but usually its 32 bits
  signed about 2,000,000,000
• PHP does not support unsigned integers.

8
Floating Point Numbers

• These can be specified using any of these forms
• a 1.234
• a 1.2e3
• a 7E-10
• The maximum size of a float is platform-dependent,
  although most support a maximum of about 1.8e308
  with a precision of roughly 14 decimal digits

9
Strings

• A string literal can be specified in three
  different ways
• single quoted
• double quoted
• heredoc syntax

10
Single-quoted Strings

• In single-quoted strings, single-quotes and
  backslashes must be escaped with a preceding
  backslash
• Example usage
• echo 'this is a simple string'
• echo 'You can embed newlines in strings,
• just like this.'
• echo Douglas MacArthur said "I\'ll be back when
  leaving the Phillipines'
• echo 'Are you sure you want to delete C\\.?'

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Double-quoted Strings

• In double-quoted strings,
• variables are interpreted to their values, and
• various characters can be escaped
• \n linefeed
• \r carriage return
• \t horizontal tab
• \\ backslash
• \ dollar sign
• \ double quote
• \0-71,3 a character in octal notation
• \x0-9A-Fa-f1,2 a character in hexadecimal
  notation

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Heredoc Strings

• Heredoc strings are like double-quoted strings
  without the double quotes
• A heredoc string is delimited as follows
• The string is preceded by ltltlt followed by a label
• The string followed by a 2nd occurrence of the
  same label
• Example usage
• str ltltltEOD
• Example of string
• spanning multiple lines
• using heredoc syntax.
• EOD

13
String-manipulation functions

• PHP provides huge range of string-manipulation
  functions
• addcslashes -- Quote string with slashes in a C
  style
• addslashes -- Quote string with slashes
• bin2hex -- Convert binary data into hexadecimal
  representation
• chop -- Alias of rtrim()
• chr -- Return a specific character
• chunk_split -- Split a string into smaller chunks
• convert_cyr_string -- Convert from one Cyrillic
  character set to another
• count_chars -- Return information about
  characters used in a string
• crc32 -- Calculates the crc32 polynomial of a
  string
• crypt -- One-way string encryption (hashing)
• echo -- Output one or more strings
• explode -- Split a string by string
• get_html_translation_table -- Returns the
  translation table used by htmlspecialchars() and
  htmlentities()

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• get_meta_tags -- Extracts all meta tag content
  attributes from a file and returns an array
• hebrev -- Convert logical Hebrew text to visual
  text
• hebrevc -- Convert logical Hebrew text to visual
  text with newline conversion
• htmlentities -- Convert all applicable
  characters to HTML entities
• htmlspecialchars -- Convert special characters
  to HTML entities
• implode -- Join array elements with a string
• join -- Join array elements with a string
• levenshtein -- Calculate Levenshtein distance
  between two strings
• localeconv -- Get numeric formatting information
• ltrim -- Strip whitespace from the beginning of
  a string
• md5 -- Calculate the md5 hash of a string
• md5_file -- Calculates the md5 hash of a given
  filename
• metaphone -- Calculate the metaphone key of a
  string
• nl2br -- Inserts HTML line breaks before all
  newlines in a string
• ord -- Return ASCII value of character
• parse_str -- Parses the string into variables
• print -- Output a string
• printf -- Output a formatted string

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• quoted_printable_decode -- Convert a
  quoted-printable string to an 8 bit string
• quotemeta -- Quote meta characters
• str_rot13 -- Perform the rot13 transform on a
  string
• rtrim -- Strip whitespace from the end of a
  string
• sscanf -- Parses input from a string according
  to a format
• setlocale -- Set locale information
• similar_text -- Calculate the similarity between
  two strings
• soundex -- Calculate the soundex key of a string
• sprintf -- Return a formatted string
• strncasecmp -- Binary safe case-insensitive
  string comparison of the first n characters
• strcasecmp -- Binary safe case-insensitive
  string comparison
• strchr -- Find the first occurrence of a
  character
• strcmp -- Binary safe string comparison
• strcoll -- Locale based string comparison
• strcspn -- Find length of initial segment not
  matching mask
• strip_tags -- Strip HTML and PHP tags from a
  string
• stripcslashes -- Un-quote string quoted with
  addcslashes()
• stripslashes -- Un-quote string quoted with
  addslashes()

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• stristr -- Case-insensitive strstr()
• strlen -- Get string length
• strnatcmp -- String comparisons using a "natural
  order" algorithm
• strnatcasecmp -- Case insensitive string
  comparisons using a "natural order" algorithm
• strncmp -- Binary safe string comparison of the
  first n characters
• str_pad -- Pad a string to a certain length with
  another string
• strpos -- Find position of first occurrence of a
  string
• strrchr -- Find the last occurrence of a
  character in a string
• str_repeat -- Repeat a string
• strrev -- Reverse a string
• strrpos -- Find position of last occurrence of a
  char in a string
• strspn -- Find length of initial segment
  matching mask
• strstr -- Find first occurrence of a string
• strtok -- Tokenize string
• strtolower -- Make a string lowercase
• strtoupper -- Make a string uppercase
• str_replace -- Replace all occurrences of the
  search string with the replacement string

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• strtr -- Translate certain characters
• substr -- Return part of a string
• substr_count -- Count the number of substring
  occurrences
• substr_replace -- Replace text within a portion
  of a string
• trim -- Strip whitespace from the beginning and
  end of a string
• ucfirst -- Make a string's first character
  uppercase
• ucwords -- Uppercase the first character of each
  word in a string
• vprintf -- Output a formatted string
• vsprintf -- Return a formatted string
• wordwrap -- Wraps a string to a given number of
  characters using a string break character.
• nl_langinfo -- Query language and locale
  information

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Arrays

• An array in PHP is a structure which maps keys to
  values
• The keys can specified explicitly or they can be
  omitted
• If keys are omited, integers starting with 0 are
  keys
• The value mapped to a key can, itself, be an
  array, so we can have nested arrays

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Specifying an array

• A special function is used to specify arrays
• array( )
• Format of Usage
• array( key gt value, )
• A key is either a string or a non-negative
  integer
• A value can be anything

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Specifying an array (contd.)

• Format of array specification
• array( key gt value, ... )
• Here is a hash array
• mothers
• array (tom"gtmary", mick"gtann",
  bill"gtorla")
• Implicit indices are integers, starting at 0
• Here is an ordinary array (indexed by integers,
  starting at 0)
• places array (Cork, Dublin, Galway)

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Specifying an array (contd.)

• If an explicit integer index is followed by
  implicit indices, they follow on from the highest
  previous index
• Here is an array indexed by integers 1, 2, 3
• places array (1 gt Cork, Dublin,
  Galway)
• Here is an array indexed by integers 1, 5, 6
• places array (5gt Cork, 1 gt Dublin,
  Galway)

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Specifying an array (contd.)

• A two-dimensional hash array
• parents
• array ( tom gt array (father gt
  bill, mothergt mary),
• dave gt array(father gt
  tom, mother gt orla)
• )
• A two-dimensional ordinary array
• heights
• array ( array (10,20),
• array(100,200)
• )

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Array Example 1

• lthtmlgt
• ltheadgtlttitlegtArray Demolt/titlegtlt/headgt
• ltbodygt
• lth1gtArray Demolt/h1gt
• ltpgt
• lt?php
• capital array ('France'gt'Paris','Irelan
  d'gt'Dublin')
• echo 'The capital of Ireland is '
• echo capital'Ireland'
• ?gt
• lt/pgt
• lt/bodygt
• lt/htmlgt

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Array Example 2

• lthtmlgt
• ltheadgtlttitlegtArray Demolt/titlegtlt/headgt
• ltbodygt
• lth1gtArray Demolt/h1gt
• ltpgt
• lt?php
• capital array ('France'gt'Paris',
  Ireland'gt'Dublin')
• echo "The various capitals are\nltulgt"
• foreach (capital as city) echo
  "ltligtcitylt/ligt"
• echo "lt/ulgt"
• ?gt
• lt/pgt
• lt/bodygt
• lt/htmlgt

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Array Example 3

• lthtmlgt
• ltheadgtlttitlegtArray Demolt/titlegtlt/headgt
• ltbodygt
• lth1gtArray Demolt/h1gt
• ltpgt
• lt?php
• capital array ('France'gt'Paris',
  'Ireland'gt'Dublin')
• echo "The various capitals are\nltulgt"
• foreach (capital as country gt city)
• echo "ltligtThe capital of country
  is citylt/ligt"
• echo "lt/ulgt"
• ?gt
• lt/pgt
• lt/bodygt
• lt/htmlgt

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Array Example 4

• lthtmlgt
• ltheadgt
• lttitlegtDetails about Fredlt/titlegt
• lt/headgt
• ltbodygt
• lth1gtDetails about Fredlt/h1gt
• lt?php
• ages array ("Fred" gt 2, "Tom"gt 45)
• parents array ("Fred" gt array("father" gt
  "Tom", "mother"gt"Mary"))
• print "ltpgt Fred's age is "
• print ages"Fred"
• print ".lt/pgt"
• print "ltpgtHis father is "
• print parents"Fred""father"
• print ".lt/pgt"
• ?gt
• lt/bodygt
• lt/htmlgt

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Array-manupulation functions

• PHP provides a huge set of array-manipulation
  functions
• array -- Create an array
• array_change_key_case -- Returns an array with
  all string keys lowercased or uppercased
• array_chunk -- Split an array into chunks
• array_count_values -- Counts all the values of an
  array
• array_diff -- Computes the difference of arrays
• array_filter -- Filters elements of an array
  using a callback function
• array_flip -- Flip all the values of an array
• array_fill -- Fill an array with values
• array_intersect -- Computes the intersection of
  arrays
• array_key_exists -- Checks if the given key or
  index exists in the array
• array_keys -- Return all the keys of an array
• array_map -- Applies the callback to the
  elements of the given arrays
• array_merge -- Merge two or more arrays
• array_merge_recursive -- Merge two or more arrays
  recursively
• array_multisort -- Sort multiple or
  multi-dimensional arrays
• array_pad -- Pad array to the specified length
  with a value

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• array_pop -- Pop the element off the end of array
• array_push -- Push one or more elements onto the
  end of array
• array_rand -- Pick one or more random entries
  out of an array
• array_reverse -- Return an array with elements
  in reverse order
• array_reduce -- Iteratively reduce the array to
  a single value using a callback function
• array_shift -- Shift an element off the
  beginning of array
• array_slice -- Extract a slice of the array
• array_splice -- Remove a portion of the array
  and replace it with something else
• array_sum -- Calculate the sum of values in an
  array.
• array_unique -- Removes duplicate values from an
  array
• array_unshift -- Prepend one or more elements to
  the beginning of array
• array_values -- Return all the values of an array
• array_walk -- Apply a user function to every
  member of an array
• arsort -- Sort an array in reverse order and
  maintain index association
• asort -- Sort an array and maintain index
  association
• compact -- Create array containing variables and
  their values
• count -- Count elements in a variable
• current -- Return the current element in an array

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• each -- Return the current key and value pair
  from an array and advance the array cursor
• end -- Set the internal pointer of an array to
  its last element
• extract -- Import variables into the current
  symbol table from an array
• in_array -- Return TRUE if a value exists in an
  array
• array_search -- Searches the array for a given
  value and returns the corresponding key if
  successful
• key -- Fetch a key from an associative array
• krsort -- Sort an array by key in reverse order
• ksort -- Sort an array by key
• list -- Assign variables as if they were an
  array
• natsort -- Sort an array using a "natural order"
  algorithm
• natcasesort -- Sort an array using a case
  insensitive "natural order" algorithm
• next -- Advance the internal array pointer of an
  array
• pos -- Get the current element from an array
• prev -- Rewind the internal array pointer
• range -- Create an array containing a range of
  elements
• reset -- Set the internal pointer of an array to
  its first element

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• rsort -- Sort an array in reverse order
• shuffle -- Shuffle an array
• sizeof -- Get the number of elements in variable
• sort -- Sort an array
• uasort -- Sort an array with a user-defined
  comparison function and maintain index
  association
• uksort -- Sort an array by keys using a
  user-defined comparison function
• usort -- Sort an array by values using a
  user-defined comparison function

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Objects

• PHP supports object-oriented programming
• The subject is too big to cover here
• But heres an example
• lt?php
• class thingAMeBob
• function say_hello()
• echo Hello, World!"
• thing1 new thingAMeBob
• thing1-gtsay_hello()
• ?gt

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The NULL data type

• This data type contains only one value
• NULL
• It is case-insensitive
• This is a value which is returned when some
  expression has no value
• Example
• capital array ('France'gt'Paris',
  'Ireland'gt'Dublin')
• capitalOfEngland capitalEngland
• In this case, capitalOfEngland would get the
  value NULL

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Automatic variables in PHP

• One of the main benefits of PHP is that it
  provides lots of variables automatically
• Consider, for example, the .php file on the next
  slide
• It produces the output on the following two
  slides when viewed by MSIE 6.0 and Netscape 2.0

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Example usage of automatic PHP variable

• lthtmlgt
• ltheadgt
• lttitlegtYour browserlt/titlegt
• lt/headgt
• ltbodygt
• lth1gtYour Browserlt/h1gt
• ltpgt
• You are using
• lt?php echo _ENVHTTP_USER_AGENT ?gt
• to view this page.
• lt/pgt
• lt/bodygt
• lt/htmlgt

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Global arrays

• PHP creates 6 global arrays that contain EGPCS
  (environment, get, post, cookies and server)
  information
• PHP also creates a variable called _REQUEST that
  contains all the information in the 6 global
  arrays
• PHP also creates a variable called PHP_SELF that
  contains the name of the current script (relative
  to the doc root)

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Global arrays

• _ENV Contains the values of any environment
  variables, such as the browser version
• Eg _ENVHTTP_USER_AGENT
• _POST The values of any variables posted to
  the request.
• Eg _POSTusername
• _GET The values of any variables sent via the
  URL
• Eg _GETusername

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Global arrays

• _FILES Contains information about any files
  submitted
• _COOKIES Contains any cookies submitted as
  name value pairs (see later lectures)
• _SERVER Contains useful information about the
  webserver

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_SERVER Keys

• DOCUMENT_ROOTHTTP_PHP_SELFQUERY_STRING
  REMOTE_ADDRREQUEST_METHODREQUEST_URISCR
  IPT_FILENAMESCRIPT_NAMESERVER_NAMESERVER_
  PORTSERVER_PROTOCOLSERVER_SOFTWARE
  COMSPECGATEWAY_INTERFACEPATHEXTPATHR
  EMOTE_PORTSERVER_ADDRSERVER_ADMINSERVER_S
  IGNATURESystemRootWINDIR

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Changing Data Type

• PHP will, in some circumstances, change the type
  of a datum
• For example, it will treat a string of digits as
  a number if it finds in an arithmetic expression
• PHP also supports type casting
• lt?php myInteger 12
• myFloat 1.3
• result myFloat (float)
  myInteger
• echo result ?gt