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eg-259:lecture16 [2008/12/08 11:19] – eechriseg-259:lecture16 [2013/03/08 18:03] (current) – [Introduction to PHP (Part 1)] eechris
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 +~~SLIDESHOW~~
 +====== 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]]