12. Server-Side Scripting with PHP

What We Will Cover Announcements Please silence all cell phones and pagers When class is over, please shut down your computer if it is on. Elucidations 12.1: Getting Started With PHP 12.1.1: Introduction to PHP 12.1.2: How PHP Web Applications Work 12.1.3: Creating PHP Documents 12.1.4: PHP Development Process 12.1.5: Components Needed for PHP Development 12.1.6: Summary Activity 12.1 12.2: Creating PHP Scripts 12.2.1: Working with the PHP Tag 12.2.2: Understanding Statements and Whitespace Rules 12.2.3: Comments in PHP 12.2.4: Importance of Proper Syntax 12.2.5: Summary Activity 12.2 12.3: Working with Variables and Data Types 12.3.1: Introduction to PHP Variables 12.3.2: Assigning a Value to a Variable 12.3.3: Writing a Variable Value to a Web Document 12.3.4: PHP Data Types 12.3.5: Summary 12.4: Arithmetic Using Operators and Functions 12.4.1: Using Arithmetic Operators 12.4.2: Mathematical Functions 12.4.3: Writing Complex Expressions 12.4.4: Summary Wrap Up Due Next: Final Project Report and Presentation (12/11/06) Elucidations Questions from last class? Specifying the Domain and Path Homework Questions? A11: Cookies (11/20/06) Quiz 10 (11/20/06) Homework Discussion Questions How many people have worked with cookies before? What did you use them for and why did you think they were an appropriate tool to accomplish what you needed to do? What practical uses can you envision for cookies beyond those discussed in the textbook? When passing data from one page to another, what are the advantages and disadvantages of cookies compared to appending data to a URL? Question About the Course Would you prefer to: Spend another hour in class each week and not post discussion topics Read the text and post discussions but not spend another hour in class? ^ top 12.1: Getting Started With PHP Objectives At the end of the lesson the student will be able to: Discuss how PHP pages are processed Create and run a simple PHP script Describe the development process for PHP Install the components needed to run PHP on a computer ^ top 12.1.1: Introduction to PHP PHP is a programming language that can run on a Web server PHP stands for "PHP Hypertext Processor" Running a programming language on a Web server provides several advantages: You can dynamically generate HTML and client-side scripts Processing is done in a known environment, unlike Javascript You can isolate common page elements in one file for inclusion in multiple pages You can connect to databases to take advantage of their power Many server-side programming languages exist, of which PHP is one of the most popular Brief History of PHP 1994 - Rasmus Lerdorf created PHP Used it to keep track of who was looking at his online resume 1995 - Other people started using PHP 1997 - About 50,000 users of PHP world-wide with many contributors 2000 - PHP 4 released 2002 - Most popular scripting language on the Web 2005 - PHP 5 released What Can PHP Do? Perform calculations Dynamically generate the HTML (and JavaScript) returned to the browser Create different content for different users Automatically send email Validate the data a user enters into forms Connect to databases to store and retrieve data Access and change files on the server Create server-side redirects Create sessions and track users across multiple Web pages of a site Generate GIF and PNG images dynamically Control online games ^ top 12.1.2: How PHP Web Applications Work Web applications are a set of Web pages generated in response to user requests Users typically interact with the Web application using a browser The browser contacts a Web server to request a Web page or other data When the browser requests a Web page that uses PHP several steps occur Many of these steps are invisible to the user User enters query (URL) into a browser (client) Browser connects to server and sends a request for a PHP file Web server receives the request, finds the file and reads it PHP scripting engine executes the PHP statements, usually returning HTML to the Web server Web server sends the results back to the client Results get sent over the Internet Browser receives results and displays them to the user ^ top 12.1.3: Creating PHP Documents To create PHP scripts for processing, you include the code to execute inside a pair of PHP tags: <?php ... ?> Where ... is the code to execute You can place the PHP tags and code directly inside the HTML of a Web page For example: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>Sample PHP Script</title> </head> <body> <p> <?php     print "Hello PHP World!"; ?> </p> </body> </html> Note how the PHP portion starts with a "<?php" tag and ends with "?>" Between these tags is a single PHP print statement Statements are the commands you give a computer in a program You can view this page by following the link: helloworld.php When you view the source of the Web page, notice that you do not see the PHP code The PHP engine on the server processed the PHP code and only returned what was printed Note that all PHP pages end with a suffix of .php This lets the Web server know to pass the page request to the PHP engine for processing ^ top 12.1.4: PHP Development Process Developing PHP-enhanced HTML documents consists of three steps Writing the PHP (and HTML) code Copying the coded files to the server Accessing the file on the server using a browser This process is repeated many times during development Writing Code You can use any text editor to create PHP code, just like you can for HTML For instance, we could enter the code in TextPad Some people like to use Web development tools to create HTML and PHP However, I do not recommend them when learning PHP because: Some tools write PHP code for you, which does not help you learn These are complex tools that themselves are difficult to learn Learning to use the tool can distract you from your goal of learning PHP I do recommend using development tools if you code professionally because: You can place components on the Web page more easily You can improve your productivity Copying Files to the Server If you have access to a Web server running PHP, you can copy your file to the server using FTP For instance, you can upload to WebHawks with CoreFTP See John Govsky's: How to Upload to Webhawks.org with CoreFTP Lite To access your pages on WebHawks use: http://webhawks.org/~yourusername/ Viewing the File You view a PHP-enhanced Web page using a browser In the browser's address bar, enter the Web address of the file Note: do NOT use the "Open File" command in your browser Remember that all PHP pages must be processed by a Web server Otherwise, the PHP code is not processed ^ top 12.1.5: Components Needed for PHP Development To develop PHP documents you need access to a Web server and a PHP engine While you ultimately want to publish your work on the Web, it is more convenient to develop your code on your own computer It turns out that installing a Web server and PHP on your own computer is simple and free For instructions, see How To Install PHP and MySQL Using localhost The name given to the server running on your computer is "localhost" The term localhost means the location of the system currently in use The localhost Web server is assigned the IP address 127.0.0.1 Thus you can access the local server using either the name localhost or the IP address For example, to access the PHP-enhanced Web page named helloworld.php in the root directory of your local server, you can use any of the following addresses: http://localhost/helloworld.php http://127.0.0.1/helloworld.php ^ top 12.1.6: Summary PHP is a programming language that can run on a Web server It was first developed by Rasmus Lerdorf in 1994 PHP files are stored on a web server When the user requests a PHP file, the web server asks PHP to answer the request The web server knows when to do this based on the file extension Thus, every PHP file must end in .php You must copy all PHP files to a location accessible by the web server To view the file, you use a browser to access the web server To make development easier, you can install the Web server and PHP engine on your own computer To access files using the Web server on your computer, you use the name localhost Check Yourself What is the difference between dynamic HTML and dynamic Web pages? What is a Web application? What does the Web server do with a page with a suffix of .php? How do you code a PHP tag? How do you view a PHP-enhanced Web page? What is wrong with using the File Open command for viewing a PHP-enhanced Web page? What software components do you need for developing PHP on your own computer? What is meant by the term "localhost"? ^ top Activity 12.1 In this exercise, we install PHP on the computers in the classroom. Specifications Install PHP by following the instructions in How To Install PHP and MySQL. If you have difficulty, ask another classmate or the instructor for help. Please keep track of any problems you have so we can discuss them. ^ top 12.2: Creating PHP Scripts Learner Outcomes At the end of the lesson the student will be able to: Code a PHP script tag Discuss PHP statements and whitespace rules Create comments in PHP Describe how to avoid common PHP syntax problems ^ top 12.2.1: Working with the PHP Tag Programmers commonly embed PHP scripts within HTML tags Only the output from PHP statements gets displayed in the page However, you can create HTML tags within the PHP as well The following script demonstrates both techniques <html> <head> <title>Generating HTML from PHP</title> </head> <body> <h1>Generating HTML from PHP</h1> <?php   print "<p>Generating HTML in PHP statements</p>";   print "</body></html>"; ?> We can save this file using a name like embedded.php The file name must follow the rules for a PHP file and end with .php Otherwise, the Web server will not send the file to the scripting engine If the above were saved as embedded.html, we would see very different output To save the file with localhost access on our classroom machines, we save to the directory: C:\Program Files\xampp\htdocs ^ top 12.2.2: Understanding Statements and Whitespace Rules Statements are the commands you give a computer in a program One of PHP's many statements is the print statement: print "Hello PHP World!"; Note that most statements end with a semicolon (;) However, a closing PHP tag (?>) implies a semicolon Thus, you do not need to use a semicolon to end the last PHP statement of a tag Besides using semicolons to end statements, there are other PHP rules you need to know PHP Ignores Most Extra White Space Whitespace is any sequence of non-printing characters like: Blank spaces Blank lines Tabs Like HTML, PHP ignores most occurrences of extra white space This means that you can add extra spaces in your code to make it easier to read Typically, you start statements on a new line If the statement get too long, then you wrap it to another line There are coding standards describing how to use whitespace to format your PHP code For more information, see: How To Document and Organize Your PHP Code ^ top 12.2.3: Comments in PHP You use comments to describe your code to people Comments are ignored when the script runs Using comments does not measurably slow down your code You should use comments in two cases: To describe the purpose of the script To describe particularly tricky lines of code Comments can start with two forward slash marks (//) These last from the slashes to the end of the line For example: <?php // This is a comment ?> You can add comments like these after a code statement, like: <?php print "A simple script"; //Output a line ?> Alternatively, you can create single-line comments using a pound sign (#): <?php print "A simple script"; #Output a line ?> Another easy way to make comments is: /* ... */ This style allows multi-line comments, such as: <?php /* This is a multiline comment */ ?> Also, this style allows all or part of a line to be commented: <?php /* here comes the code */ print "A simple script"; ?> ^ top 12.2.4: Importance of Proper Syntax Ideally, you will always write correct code In reality, there are often problems to correct Syntax errors happen when you write one or more PHP statements that are grammatically incorrect in the PHP language For example, notice the syntax of the following print statement: <?php print "The message to print"; ?> The message to print is enclosed in quotation marks If you forget one of the quotation marks, you get a syntax error You would then have code like the following: <?php print "The message to print; ?> When we run this, PHP reports an error Even though the error is on line 2, PHP incorrectly reports it on line 4 Sometimes your script does not contain errors on the line reported PHP can only approximate where the problem is located When you get an error, you need to edit the script, republish it and then view it again Several attempts may be needed to correct all the syntax errors Advice: start with something you know works and add to it in small steps Then when errors occur, you know they were due to the most recent changes Avoiding Common Syntax Problems End most PHP statements with a semicolon (;) Realize that PHP ignores extra whitespace Use quotation marks, parenthesis and brackets in pairs ^ top 12.2.5: Summary Statements are the commands you give a computer in a program You place PHP statements inside PHP tags like: <?php print "The message to print"; ?> To code PHP, you must use proper syntax Some of the rules you need to follow include: Most PHP statements end with a semicolon (;) Like HTML, PHP ignores most extra whitespace Also, PHP allows you to place comments within the code Check Yourself What is the syntax of a PHP tag? How do you separate statements in PHP? What is meant by the term "whitespace"? How do you code a multi-line comment? What are the three way of coding a single-line comment? What is wrong with the following PHP statement? <?php print "The message to print; ?> ^ top Exercise 12.2 In this exercise we look at how to create a PHP script file and view it in a web browser. Be prepared to answer the questions after the exercise. Specifications Save the following file using the name embedded.php in a directory that the Web server can access. If you installed XAMPP on Windows XP, the root directory of the Web server is: C:\Program Files\xampp\htdocs <html> <head> <title>Generating HTML from PHP</title> </head> <body> <h1>Generating HTML from PHP</h1> <?php print "<p>Generating HTML in PHP statements</p>"; print "</body></html>"; ?> Load the file using the URL for the localhost server. For instance, if you save in the root directory of the server, you would use the URL: http://localhost/embedded.php View the source of the Web page. Q1: When you view the source of the page, do you see any PHP code? Try adding PHP comments to your embedded.php file. Q2: Where in the file are you able to add PHP comments without the comments appearing in the source of the Web page? Create an error in the PHP script by removing one of the double-quote marks (") Q3: What error did PHP report?? Now load the file using the File Open menu of the browser. Q4: Does the output appear different than previously? View the source of the browser page. Q5: When you view the source of embedded.html, do you see the PHP code? Q6: How do you explain the difference? ^ top 12.3: Working with Variables and Data Types Objectives At the end of the lesson the student will be able to: Store and access data in PHP variables Recognize literal data values Display variable values in a Web document ^ top 12.3.1: Introduction to PHP Variables Recall that a variable is the name of a location in a computer's memory In this location you can store a single number, text string or logical value Values stored in a variable can change (vary) as the program runs Creating Variables When you create a variable, you tell the computer to reserve memory space To create a variable in PHP, you make up a name and start using the variable However, you have to follow certain rules when you make up a variable name The syntax for creating a variable: $variableName Where variableName is the name you make up For example: $userName Naming a Variable A variable name is a dollar sign ($) followed by letters, numbers, or underscore characters However, PHP has some limitations on variable names The first character of a variable name must always be a dollar sign ($) The second character must be a letter or an underscore ( _ ) Any of the following characters can be a: Letter Digit Underscore ( _ ) Note that variable names cannot contain any periods or spaces Also note that variable names cannot be a reserved keyword In addition, variable names are cAsE sEnSiTiVe! $id, $ID, $iD and $Id are all valid, but different, identifiers Check Yourself Which of the following are valid identifiers? $myHello2 $2myHello $My_HeLlO $my hello $a_very_long_variable_name_that_is_hard_to_read $hel-lo Programming Style: Variable Naming Conventions Professional programmers follow naming conventions when creating names Conventions are not required by PHP but make code easier to read One convention is to start variable names with a lowercase letter (after the dollar sign) Another is to use uppercase letters or underbars ('_') as word separators $myVar $my_var Another good practice is to choose names that describe the value that the variable stores For example: $counter is more descriptive than $c ^ top 12.3.2: Assigning a Value to a Variable To assign a value to a variable you use an equal (=) sign The syntax is: $variableName = value; For example: $userName = "eparrish"; Note the way that an assignment statement works PHP always assigns the value on the right-hand side of the equals sign to the variable on the left-hand side You cannot reverse the sides Here is another example of assigning values to variables: $num1 = 5; $num2 = 10; $num1 = $num2; This example uses two variables: $num1 and $num2 At the end of the three assignment statements, both variables have the value 10 ^ top 12.3.3: Writing a Variable Value to a Web Document So far we have used a print statement to output text and HTML tags You can also use a print statement to display a variable's value: print $myAge; You can include text with the variable to print: $myAge = 29; print "I am $myAge years old."; Executing the above will display: I am 29 years old. Note how you can display the value of a variable inside a double-quoted string A More Complicated Example What does the following display? <html> <head> <title>Variable Example</title> </head> <body> <?php   $firstNum = 12;   $secondNum = 356;   $temp = $firstNum;   $firstNum = $secondNum;   $secondNum = $temp;   print ("firstNum = $firstNum <br>           secondNum = $secondNum"); ?> </body> </html> Check yourself. ^ top 12.3.4: PHP Data Types Data type: the type of information stored in a variable or literal A data type is important because it tells a computer how to store and interpret the data PHP has four single-valued (a.k.a. scalar) data types: Boolean: either true or false Integer: any number without a decimal point, such as -1, 0 or 13 floating-point: any number with a decimal point, such as 3.14159 or -22.5 String: any group of text characters, such as "Hello" or 'So long' Note that you can use either single or double quote marks to surround a string Each data type allows you to use write literal values in your code Literal values are a sequence of characters in a form that you might normally write These literal values are useful for assigning values to variables such as: $truth = true; $myInt = 1; $myFloat = 1.234; $myString = "Hi mom!"; Check Yourself What is the data type for each of the following? false 0.33 -128 "$3.95" PHP is Weakly Typed Programmers refer to PHP as a weakly-typed language This is because variables are not strictly tied to specific data types For example, the following sequence is valid in PHP: $month = 11; $month = "November"; A PHP variable's data type always depends on how it is used Some other languages, in contrast, are strongly typed For instance, Java and C++ are strongly typed Strongly-typed languages force a programmer to explicitly identify a variable's data type ^ top 12.3.5: Summary In this section, we learned how to create and use variables When you create a variable, you tell the computer to reserve memory space To create a variable in PHP, you make up a name and start using the variable However, you have to follow certain rules when you make up a variable name The syntax for creating a variable: $variableName Where variableName is the name you make up You make up a name for each variable following the naming rules of PHP To assign a value to a variable, you use the syntax: $variableName = value; You can write the value of a variable to a web page using print For example: $myAge = 29; print "I am $myAge years old."; As shown in this example, you can display the value of a variable inside a double-quoted string We also discussed data types and how PHP deals with them Check Yourself How do you store data in a program? What are the four scalar data types supported by PHP? What code do you use to declare a variable named weekDay and assign it a value of "Friday"? ^ top Activity 12.3 Take one minute to read over the following Quick Quiz questions. We will discuss the questions in one minute. Quick Quiz PHP requires you to declare variables before you use them. True False AnswerFalse By setting the variable named "$name" to true, you have declared the variable type to be a _____Boolean type. Which of the variable declarations below passes a text value to the variable text1? text1 = 'Hello World' $text1 = "Hello World" var text1 = "Hello World" var $text1 = 'hello world' AnswerB ^ top 12.4: Arithmetic Using Operators and Functions Objectives At the end of the lesson the student will be able to: Work with arithmetic operators to construct expressions Make use of PHP functions ^ top 12.4.1: Using Arithmetic Operators You can perform simple arithmetic in PHP using operators An operator is a symbol that acts upon a variable or other data value PHP's operators are those used in most programming languages: + for addition - for subtraction * for multiplication / for division % for modulus (integer remainder) For instance, the following code uses two operators: $x + $y - 3 Combinations of operators, variables and other items are called arithmetic expressions An expression is part of a statement that produces a value We can use expressions to perform arithmetic and display the results print (3 + 4); // prints 7 You can use operators with variables as well: print $myAge + 1; Let us look at a complete example Example of Arithmetic What does the following display? <html> <head> <title>Counting Fruit</title> </head> <body> <?php   $apples = 12;   $oranges = 14;   $totalFruit = $apples + $oranges;   print "The total number of fruit is $totalFruit"; ?> </body> </html> Check yourself. Explanation of Code The relevant part is the PHP code First we create two variables and assign them values: $apples = 12; $oranges = 14; The next line adds the two variables and assigns the value to a new variable: $totalFruit = $apples + $oranges; Then the print statement displays the value of the $total_fruit variable: print "The total number of fruit is $totalFruit"; Showing that using PHP you can add apples and oranges ^ top 12.4.2: Mathematical Functions There are many common mathematical operations that are not provided by operators Instead, PHP provides the Mathematical Functions library Functions include: abs(), pow(), max(), min(), rand(), round(), sqrt(), log(), and trig functions The library also includes common math constants such as: M_PI (approximately 3.141592653) M_E (base of natural logarithms, approximately 2.71828182) If you need to handle big numbers you can use the BCMath Arbitrary Precision Mathematics Functions Arguments Most mathematical functions require you to send them one or more arguments An argument is an input value that functions use in processing Usually mathematical functions return a value based on the arguments Examples $value = pow(2, 3); // value gets int 8 print($value); $num = -2.0; $value = abs($num); // value gets float 2.0 print($value); Other Predefined PHP Functions PHP offers many libraries of predefined functions For a complete list see the Function Reference One of the main attractions of PHP is the large number of predefined functions you can make use of in your scripts ^ top 12.4.3: Writing Complex Expressions Can use many operators and functions in the same expression: $x = 1 + 2 * 3; What is the value of $x after this statement? The value of $x might be either 9 or 7 The correct answer depends on the order in which PHP applies the arithmetic operators The computer follows certain rules when evaluating an expression Precedence, Associativity and Other Arithmetic Rules Arithmetic operators are processed in a precedence order like in algebra: Functions Parenthesis: ( ) Multiplication, division, modulus: *, /, % Addition, subtraction: +, - Operators with the same precedence are evaluated from left to right You can use parenthesis to group expressions You can have parenthesis within parenthesis Innermost parenthesis evaluated first However, you cannot use parenthesis or dots to indicate multiplication Instead, you must always use the * operator Note that using parenthesis to specify and clarify operator precedence is a good idea Examples of Expressions Algebra Expression PHP Expression 2 (10 + 5) 2 * (10 + 5) 1 12.3 + 3 · 7.3 1 / (12.2 + 3 * 7.3) 10 - 7 3.3 + 9 · 1.6 (10 - 7) / (3.3 + 9 * 1.6) 2 · 42 2 * 4 * 4 ^ top 12.4.4: Summary You can perform arithmetic on numeric values: $num = $num + 2; PHP supports all the standard math operations: $a = 2; $b = 4; print $a + $b // Addition: Sum of $a and $b print $a - $b // Subtraction: Difference of $a and $b print $a * $b // Multiplication: Product of $a and $b print $a / $b // Division: Quotient of $a and $b print $a % $b // Modulus: Remainder of $a divided by $b When you want to perform more complicated math operations, you use mathematical functions: $value = pow($a, $b); print($value); You can use many operators and functions in the same expression: $average = ($a + $b) / 2; ^ top Wrap Up Due Next: Final Project Report and Presentation (12/11/06) ^ top Home | WebCT | Announcements | Schedule | Room Policies | Course Info Help | FAQ's | HowTo's | Links Last Updated: November 25 2006 @15:13:10