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====== Introduction to PHP (Part 1) ======

**Supplementary Material**

Provided for Reference. This material is no longer taught on this module.

**Lecturer**: [[C.P.Jobling@Swansea.ac.uk|Dr Chris P. Jobling]].

An introduction to PHP, one of the most popular server-side scripting languages for web applications.





===== Introduction to PHP (Part 1) =====

PHP is rapidly becoming the favourite language for server-side web applications development. In this lecture we introduce the language and some of its features. To set PHP in context, you should study this lecture in conjunction with the [[eg-259:lecture5|Introduction to JavaScript]].

-----

Based on Chapter 12 of Robert W. Sebasta, //Programming the World-Wide Web//, 3rd Edition, Addison Wesley, 2006. and Chapter 12 of Chris Bates, //Web Programming: Building Internet Applications//, 3rd Edition, John Wiley, 2006.










===== Contents of this Lecture =====

//Introduction to PHP with examples//

    * [[eg-259:lecture16#origins_and_uses_of_php|Origins and Uses of PHP]]
    * [[eg-259:lecture16#overview_of_php|Overview of PHP]]
    * [[eg-259:lecture16#general_syntactic_characteristics|General Syntactic Characteristics]]
    * [[eg-259:lecture16#primitives_operations_and_expressions|Primitives, Operations, and Expressions]]
    * [[eg-259:lecture16#output|Output]]
    * [[eg-259:lecture16#control_statements|Control Statements]]

The [[eg-259:examples:php1#examples_from_lecture_16|Examples for PHP Part 1]].


===== Learning Outcomes =====

//At the end of this lecture you should be able to answer these questions//:

  - How does a web server determine whether a requested document includes PHP code 
  - What are the two modes of the PHP processor? 
  - What are the syntax and semantics of the include construct? 
  - Which parts of PHP are case sensitive and which are not? 
  - What are the four scalar types of PHP? 


===== Learning Outcomes (continued) =====

//At the end of this lecture you should be able to answer these questions//:

  - How can a variable be tested to determine whether it is bound 
  - How can you specify to the PHP processor that you want uses of unbound variables to be reported 
  - How many bytes are used to store a character in PHP? 
  - What are the differences between single- and double-quoted literal strings 




===== Learning Outcomes (continued) =====

//At the end of this lecture you should be able to answer these questions//:

  - If an integer expression appears in Boolean context, how is its Boolean value determined? 
  - What happens when an integer arithmetic operation results in a value that cannot be represented as an integer? 
  - If a variable stores a string, how can the character at a specific position in that string be referenced? 
  - What does the ''chop'' function do? 
  - What is a //coercion//? 


===== Learning Outcomes (continued) =====

//At the end of this lecture you should be able to answer these questions//:

  - What are the three ways the value of a variable can be explicitly coerced to a specific type 
  - How can the type of a variable be determined? 
  - If a string is compared with a number, what happens? 
  - What is the advantage of using the unique closing reserved words such as ''endwhile''? 



===== Origins and Uses of PHP =====

  * Developed by Rasmus Lerdorf in 1994 to allow him to track visitors to his Web site 
  * PHP is an acronym for //Personal Home Page//, or //PHP: Hypertext Preprocessor// 
  * PHP is an open-source product 
  * PHP is used for form handling, file processing, and database access 

===== Overview of PHP =====

  * PHP is a server-side scripting language whose scripts are embedded in HTML documents 
  * PHP is an alternative to CGI, ASP.NET, JSP, and Allaire's ColdFusion 
  * The PHP processor has two modes: copy (HTML) and interpret (PHP) 
  * PHP syntax is similar to that of JavaScript 
  * PHP is dynamically typed 
  * PHP is purely interpreted 


===== General Syntactic Characteristics =====

  * PHP code can be specified in an HTML document internally or externally:
    * Internally: ''<?php … ?>'' 
    * Externally: ''include ("myScript.inc")'' 
  * The file can contain both PHP and HTML 
  * If the file contains PHP, the PHP must be enclosed in tags ''<?php … ?>'', even if the include statement is already in ''<?php … ?>'' 
  * Every variable name begins with a ''$'' 




===== General Syntactic Characteristics (continued) =====

  * Three different kinds of comments (Java and Perl):
<code php>
    // JavaScript-like inline comment
    # perl-like inline comment
    /* Java-like block comment */
</code>
  * Compound statements are formed with braces
  * Compound statements are not blocks

----

//explanation//: a block is defined as code for which variables defined between braces (not function bodies), are local to the enclosing block. 
Java has this property but JavaScript and PHP do not. 

===== Primitives, Operations, and Expressions =====

  * [[eg-259:lecture16#variables|Variables]] 
  * [[eg-259:lecture16#primitive_types|Primitive Types]]
  * [[eg-259:lecture16#strings|Strings]]
  * [[eg-259:lecture16#booleans|Booleans]]
  * [[eg-259:lecture16#arithmetic_operators_and_expressions|Arithmetic Operators and Expressions]]
  * [[eg-259:lecture16#string_operations_and_functions|String Operations and Functions]]
  * [[eg-259:lecture16#scalar_type_conversions|Scalar Type Conversions]] 


===== Variables =====

  * There are no type declarations 
  * An unassigned (unbound) variable has the value ''NULL''
    * The ''unset'' function sets a variable to ''NULL'' 
    * The ''IsSet'' function is used to determine whether a variable is ''NULL'' 
  * ''error_reporting(15);'' -- prevents PHP from using unbound variables 
  * PHP has many predefined variables, including the environment variables of the host operating system 
  * You can get a list of the predefined variables by calling ''phpinfo()'' in a script 

===== Primitive Types =====

  * //There are eight primitive types//:
    * Four scalar types: ''boolean'', ''integer'', ''double'', and ''string'' 
    * Two compound types: ''array'' and ''object'' 
    * Two special types: ''resource'' and ''NULL'' 
  * //Integer// and //double// are like those of other languages 



===== Strings =====

  * Characters are single bytes
  * String literals are single or double quoted
  * //Single-quoted string literals//
    * Embedded variables are **not** interpolated 
    * Embedded escape sequences are **not** recognized 
  * //Double-quoted string literals//
    * Embedded variables **are** interpolated 
    * If there is a variable name in a double-quoted string but you don't want it interpolated, it must be escaped. 
    * Embedded escape sequences **are** recognized 
  * For both single- and double-quoted literal strings, embedded delimiters must be escaped

-----

<note>
**Characters are single bytes**: This means that, unlike HTML, PHP does not natively support Unicode characters. There are a pair of functions ''utf8_encode()'' and ''utf8_decode()'' which provide some Unicode support. There are implications of this if you want to develop PHP applications accessible in countries which do not use the //utf-8// character set.
</note>

===== Booleans =====

  * values are ''true'' and ''false'' (case insensitive) 
  * ''0'' and ''""'' and ''"0"'' are ''false''; other values are ''true'' 


===== Arithmetic Operators and Expressions =====

  * Usual C-based language operators 
  * If the result of integer division is not an integer, a double is returned 
  * Any integer operation that results in overflow produces a double 
  * The modulus operator coerces its operands to integer, if necessary 
  * When a double is rounded to an integer, the rounding is always towards zero 
  * //Arithmetic functions//
    * ''floor'', ''ceil'', ''round'', ''abs'', ''min'', ''max'', ''rand'', etc. 

===== String Operations and Functions =====

  * The only operator is period ''.'', for concatenation 
  * //Indexing// – ''$str[3]'' is the fourth character 
  * //Functions//:
    * ''strlen'', ''strcmp'', ''strpos'', ''substr'', as in C 
    * ''chop'' -- remove whitespace from the right end 
    * ''trim'' -- remove whitespace from both ends 
    * ''ltrim'' -- remove whitespace from the left end 
    * ''strtolower'', ''strtoupper'' -- convert case of string 



===== Scalar Type Conversions =====

  * //String to numeric//
    * If the string contains a period, an ''e'' or an ''E'', it is converted to double; otherwise to integer 
    * If the string does not begin with a sign or a digit, zero is used 
  * Explicit conversions – //casts//
    * e.g., ''(int)$total'' or ''intval($total)'' or ''settype($total, "integer")''
  * The type of a variable can be determined with ''gettype'' or ''is_type'':
<code php>
      gettype($total)  // may return "unknown"
      is_integer($total) // a predicate function
</code>


===== Output =====

  * Output from a PHP script is HTML that is sent to the browser
  * HTML is sent to the browser through standard output
  * There are three ways to produce output: ''echo'', ''print'', and ''printf''
    * ''echo'' and ''print'' take a string, but will coerce other values to strings:
<code php>
       echo "whatever";   # Only one parameter
       echo("first <br />", $sum)  # More than one
       print "Welcome to my site!";  # Only one
</code>

===== More Output =====

  * ''echo'' has a shorthand ''<?= ?>'' that makes it pleasanter to print the value of a PHP variable in //copy mode//:
<code html>
<p>Hello <?=$name?>, welcome to my site. It's <?=date("D M j Y")?> today.</p>
</code>
----
  * This shorthand should only be used for printing variables or with functions that return a string.
  * The short syntax only works with the [[http://uk2.php.net/manual/en/ini.core.php#ini.short-open-tag|short_open_tag]] configuration setting enabled (which it is in Ubuntu). 

===== Hello World (PHP) =====

  * PHP code is placed in the body of an HTML document
<code html>
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title> Trivial php example </title>
  </head>
  <body>
    <?php
      print "Welcome to my Web site!";
    ?>
  </body>
</html> 
</code>
















===== First PHP Example =====

A simple example to illustrate a PHP document: [[/eg-259/examples/lecture16/today.php|today.php]] ([[http://localhost/eg-259/examples/lecture16/today.php|today.php @ localhost]])

----

<code php>
<!DOCTYPE html>

<!-- today.php - A simple example to illustrate a PHP document -->
<html lang="en">
  <head> 
    <meta charset="utf-8" />
    <title> today.php &ndash; A simple example to illustrate a PHP document  </title>
  </head>
  <body>
    <p>
      <?php
        print "<b>Welcome to my home page <br /> <br />";
        print "Today is:</b> ";
        print date("l, F jS");
        print "<br />";
      ?>
    </p>
  </body>
</html>
</code>

Result:

{{eg-259:l16-today.png|Result of executing PHP script today.php}}

 

===== Control Expressions =====

  * Relational operators -- same as JavaScript, (including ''==='' and ''!=='') 
  * Boolean operators -- two sets, ''&&'' and ''and'', ''||'' and ''or''. 

===== Selection statements =====

  * ''if'', ''if-else'', ''elseif'' 
  * ''switch'' -- as in C 
  * The ''switch'' expression type must be integer, double, or string 

===== Looping constructs =====

  * ''while'' -- just like C 
  * ''do-while'' -- just like C 
  * ''for'' -- just like C 
  * ''foreach'' -- discussed later 

===== Other statements =====

  * ''break'' -- in any ''for'', ''foreach'', ''while'', ''do-while'', or ''switch'' 
  * ''continue'' -- in any loop 


===== Alternative componund delimiters =====

  * "syntax sugar" -- improves readability:
<code php>
    if (...) :
      ...
    endif;
</code>













===== Another Example =====

An example to illustrate loops and arithmetic: [[/eg-259/examples/lecture16/powers.php|powers.php]] ([[http://localhost/eg-259/examples/lecture16/powers.php|powers.php @ localhost)]]

----

  * Code:
<code php>
<!DOCTYPE html>

<!-- powers.php
     An example to illustrate loops and arithmetic
     -->
<html lang="en">
  <head> 
    <meta charset="utf-8">
    <title> powers.php &ndash An example to illustrate loops and arithmetic </title>
  </head>
  <body>
    <table border = "border">
      <caption> Powers table </caption>
      <tr>
        <th> Number </th>
        <th> Square Root </th>
        <th> Square </th>
        <th> Cube </th>
        <th> Quad </th>
      </tr>
      <?php
        for ($number = 10; $number <=20; $number++) {
          $root = sqrt($number);
          $square = pow($number, 2);
          $cube = pow($number, 3);
          $quad = pow($number, 4);
          print("<tr align = 'center'> <td> $number </td>");
          print("<td> $root </td> <td> $square </td>");
          print("<td> $cube </td> <td> $quad </td> </tr>");
        }
      ?>
    </table>
  </body>
</html>

</code>

  * Result

{{eg-259:l16-powers.png|Result of executing the powers.php script}}
 




===== Intermingling HTML and PHP =====

  * HTML can be intermingled with PHP script
<code php>
    <?php
      $a = 7;
      $b = 7;
      if ($a == $b) {
        $a = 3 * $a;
    ?>
    <br />
    At this point, $a and $b are
    equal <br />
    So, we change $a to three times $a
    <?php
      }
    ?> 
</code>

----

<note warning>
this is not necessarily a good idea! Notice how the end brace for the conditional is separated from the loop body by several unrelated HTML tags. This produces fragile code -- if the second set of PHP tags where removed, a syntax error would occur which might be difficult to track down.
</note>



===== Summary of This Lecture =====

//Introduction to PHP with examples//

    * [[eg-259:lecture16#origins_and_uses_of_php|Origins and Uses of PHP]]
    * [[eg-259:lecture16#overview_of_php|Overview of PHP]]
    * [[eg-259:lecture16#general_syntactic_characteristics|General Syntactic Characteristics]]
    * [[eg-259:lecture16#primitives_operations_and_expressions|Primitives, Operations, and Expressions]]
    * [[eg-259:lecture16#output|Output]]
    * [[eg-259:lecture16#control_statements|Control Statements]]

The [[eg-259:examples:php1#examples_from_lecture_16|Examples for PHP Part 1]].

===== Learning Outcomes =====

//At the end of this lecture you should be able to answer these questions//:

  - How Does a Web server determine whether a requested document includes PHP code 
  - What are the two modes of the PHP processor? 
  - What are the syntax and semantics of the include construct? 
  - Which parts of PHP are case sensitive and which are not? 
  - What are the four scalar types of PHP? 


===== Learning Outcomes (continued) =====

//At the end of this lecture you should be able to answer these questions//:

  - How can a variable be tested to determine whether it is bound 
  - How can you specify to the PHP processor that you want uses of unbound variables to be reported 
  - How many bytes are used to store a character in PHP? 
  - What are the differences between single- and double-quoted literal strings 




===== Learning Outcomes (continued) =====

//At the end of this lecture you should be able to answer these questions//:

  - If an integer expression appears in Boolean context, how is its Boolean value determined? 
  - What happens when an integer arithmetic operation results in a value that cannot be represented as an integer? 
  - If a variable stores a string, how can the character at a specific position in that string be referenced? 
  - What does the ''chop'' function do? 
  - What is a //coercion//? 


===== Learning Outcomes (continued) =====

//At the end of this lecture you should be able to answer these questions//:

  - What are the three ways the value of a variable can be explicitly coerced to a specific type 
  - How can the type of a variable be determined? 
  - If a string is compared with a number, what happens? 
  - What is the advantage of using the unique closing reserved words such as ''endwhile''? 









===== What's Next? =====

** Introduction to PHP (Part 2) **

//Further features of the PHP language//

  * [[eg-259:lecture17#arrays|Arrays]] 
  * [[eg-259:lecture17#functions|Functions]]
  * [[eg-259:lecture17#pattern_matching|Pattern Matching]]

[[eg-259:lecture15|Previous Lecture]] | [[eg-259:home]] | [[eg-259:lecture17|Next Lecture]]