~~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: '''' * Externally: ''include ("myScript.inc")'' * The file can contain both PHP and HTML * If the file contains PHP, the PHP must be enclosed in tags '''', even if the include statement is already in '''' * Every variable name begins with a ''$'' ===== General Syntactic Characteristics (continued) ===== * Three different kinds of comments (Java and Perl): // JavaScript-like inline comment # perl-like inline comment /* Java-like block comment */ * 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 ----- **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. ===== 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($total, "integer")'' * The type of a variable can be determined with ''gettype'' or ''is_type'': gettype($total) // may return "unknown" is_integer($total) // a predicate function ===== 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: echo "whatever"; # Only one parameter echo("first
", $sum) # More than one print "Welcome to my site!"; # Only one ===== More Output ===== * ''echo'' has a shorthand '''' that makes it pleasanter to print the value of a PHP variable in //copy mode//:

Hello , welcome to my site. It's today.

 ---- * 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 Trivial php example ===== 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]]) ---- today.php – A simple example to illustrate a PHP document

Welcome to my home page

"; print "Today is: "; print date("l, F jS"); print "
"; ?>

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: if (...) : ... endif; ===== 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: powers.php &ndash An example to illustrate loops and arithmetic "); print(""); print(""); } ?>
Powers table
Number Square Root Square Cube Quad
$number $root $square $cube $quad
* Result {{eg-259:l16-powers.png|Result of executing the powers.php script}} ===== Intermingling HTML and PHP ===== * HTML can be intermingled with PHP script
At this point, $a and $b are equal
So, we change $a to three times $a ---- 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. ===== 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]]