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Topics Introducing Three-Tier Architectures Introducing PHP

Basic Features Variables and Constants Expressions and Operators Type Conversion Conditions and Branches Loops Arrays User-Defined Functions Objects

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Introducing Three-Tier Architectures Most web database applications bring together

the Web and databases through three layers of application logic naming three-tier architecture: At the base of an application is the database tier,

consisting of the database management system that manages the database containing the data users create, delete, modify, and query.

Built on top of the database tier is the complex middle tier, which contains most of the application logic and communicates data between the other tiers.

On top is the client tier, usually web browser software that interacts with the application. Figure 1-1.

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Introducing Three-Tier Architectures

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Introducing Three-Tier Architectures Client Tier

The client tier in the three-tier architecture model is usually a web browser.

Web browser software:» Processes and displays HTML resources» Issues HTTP requests for resources» Processes HTTP responses

There are significant advantages to using a web browser as the thin-client layer» Easy deployment » Support on a wide range of platforms

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Introducing Three-Tier Architectures Middle Tier

In most three-tier web database systems, the majority of the application logic is in the middle tier.

» it drives the structure and content of the data displayed to the user

» it processes input from the user as it is formed into queries on the database to read or write data.

» It also adds state management to the HTTP protocol. » It integrates the Web with the database management

system.

the components of the middle tier are » a web server» a web scripting language» the scripting language engine

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Introducing Three-Tier Architectures The PHP scripting language is used as the

middle-tier scripting language. PHP has emerged as a component of many

medium- and large-scale web database applications.

there are many reasons that make PHP a good choice, including:

» PHP is open source, meaning it is entirely free. » One or more PHP scripts can be embedded into

static HTML files and this makes client-tier integration easy.

» Fast execution of scripts.» Platform and operating-system flexibility.» PHP is suited to complex systems development. It is

a fully featured programming language.

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Introducing Three-Tier Architectures

Database Tier The database tier is the base of a web database

application. In a three-tier architecture application, the

database tier manages the data. In many web database applications, data

management are provided by a RDBMS system,

and the data stored in a relational database. The MySQL RDBMS is used to manage data.

Like PHP, MySQL is open source software.88

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Introducing PHP PHP is similar to high-level languages such as

C, Perl, Pascal, FORTRAN, and Java, and programmers who have experience with any of these languages should have little trouble learning PHP.

The current version of PHP is PHP4, which we call PHP. The current release at the time of writing is 4.0.6.

PHP is a recursive acronym that stands for PHP: Hypertext Preprocessor.

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Introducing PHP PHP is a scripting language that's usually

embedded or combined with HTML and has many excellent libraries that provide fast, customized access to DBMSs.

It's an ideal tool for developing application logic in the middle tier of a three-tier application.Example 2.1

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http://SourceExample.2-1.PHP.htm/

http://OutputExample.2-1.PHP.htm/

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Basic Features several features of PHP:

The begin and end script tags are <?php and ?> or, more simply, just <? and ?>. The longer begin tag style <?php avoids conflicts with other processing instructions that can be used in HTML.

Other begin and end tag styles can also be configured, such as the HTML style that is used with JavaScript or other embedded scripts: <script language="PHP"> and </script>.

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Basic Features White space has no effect, except to aid readability

for the developer. For example, the script could have been written succinctly as <? php echo "Hello, world";?> with the same effect. Any mix of spaces, tabs, carriage returns, and so on in separating statements is allowed.

A PHP script is a series of statements, each terminated with a semicolon. Our simple example has only one statement: echo "Hello, world";.

A PHP script can be anywhere in a file and interleaved with any HTML fragment. While Example 2-1 contains only one script, there can be any number of PHP scripts in a file.

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Basic Features When a PHP script is run, the entire script including

the start and end script tags <?php and ?> is replaced with the output of the script.

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Basic Features The freedom to interleave any number of scripts

with HTML is one of the most powerful features of PHP.Example 2.2

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Basic Features Comments

// This is a one-line comment

# This is another one-line comment style

/* This is how you

can create a multi-line

comment */

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Basic Features Outputting data with echo and print

echo "Hello, world";

// print works just the same

print "Hello, world";

// numbers can be printed too

echo 123;

// So can the contents of variables

echo $outputString;

The difference between print and echo is that echo can output more than one argument:echo "Hello, ", "world";

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Basic Features There is also a shortcut that can output data. The

following very short script outputs the value of the variable $temp:<?=$temp; ?>

The print and echo statements are also often seen with parentheses:echo "hello";

// is the same as

echo ("hello");

Parentheses make no difference to the behavior of print. However, when they are used with echo, only one output parameter can be provided.

more complex output is printf

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Basic Features String literals

PHP can create double- and single-quoted string literals. If double quotation marks are needed as part of a string, the easiest approach is to switch to the single-quotation style:

echo 'This works';

echo "just like this.";

One of the convenient features of PHP is the ability to include the value of a variable in a string literal.

$number = 45;

$vehicle = "bus";

$message = "This $vehicle holds $number people";

// prints "This bus holds 45 people"

echo $message;

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Variables and Constants Variables

Variables in PHP are identified by a dollar sign followed by the variable name.

Variables don't need to be declared. they have no type until they are assigned a value.

$var = 15;

$var = "Sarah the Cat";

Variable names are case-sensitive in PHP, so $Variable, $variable, $VAriable, and $VARIABLE are all different variables.

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Variables and Constants Types

PHP has four scalar types:»Boolean$variable = false;$test = true

»Float$var2 = 6.0;$var3 = 1.12e3;

»Integer$var1 = 6;

»String$variable = "This is a string";

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Variables and Constants two compound types:

» Array» Object

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Variables and Constants Constants

define("pi", 3.14159);

echo pi;

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Expressions and Operators

// Assign a value to a variable$var = 1;

// Sum integers to produce an integer

$var = 4 + 7;

// Subtraction, multiplication, and division

// that might have a result that is a float or

// an integer, depending on the initial value of $var

$var = (($var - 5) * 2) / 3;

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Expressions and Operators// These all add 1 to $var

$var = $var + 1;

$var += 1;

$var++;

// And these all subtract 1 from $var

$var = $var - 1;

$var -= 1;

$var--;

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Expressions and Operators// Double a value

var = $var * 2;

$var *= 2;

// Halve a value

$var = $var / 2;

$var /= 2;

// These work with float types too

$var = 123.45 * 28.2;

String assignments and expressions are similar:

1352172

// Assign a string value to a variable

$var = "test string";

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Expressions and Operators// Concatenate two strings together

// to produce "test string"

$var = "test" . " string";

// Add a string to the end of another

// to produce "test string"

$var = "test";

$var = $var . " string";

// Here is a shortcut to add a string to

// the end of another

$var .= " test";

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Type Conversion PHP provides several mechanisms to allow

variables of one type to be considered as another type.

Variables can be explicitly converted to another type with the following functions:

string strval(mixed variable) integer intval(mixed variable) float floatval(mixed variable)

The function settype(mixed variable, string type) can explicitly set the type of variable to type, where type is again one of array, boolean, float, integer, object, or string.

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Type Conversion PHP supports type-casting in much the same way as C.

By placing the type name in parentheses in front of a variable, PHP converts the value to the desired type:(int) $var Cast to integer

(bool) $var Cast to Boolean

(float) $var, (double) $var or (real) $var Cast to float

(string) $var Cast to string

(array) $var Cast to array

(object) $var Cast to object

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Conditions and Branches if...else Statement

if ($var < 5)

echo "Variable is very small";

elseif ($var < 10)

echo "Variable is small";

elseif ($var < 20)

echo "Variable is big";

elseif ($var < 30)

echo "Variable is very big";

can use == <= >= inside expressions can use || && ! inside expressions

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Conditions and Branches switch Statement

switch ($menu)

{

case 1:

echo "You picked one";

break;

case 2:

echo "You picked two";

break;

default:

echo "You picked another option";

}

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Conditions and Branches Conditional Expressions

There is a new operator in PHP4, the is-identical operator ===. This isn't found in other languages and returns true only if the expression evaluates as equal and the arguments are of the same type.

// Returns true, since both are integers and equal

if (5 === 5)

echo "Same types and value";

// Returns false, since there are mixed types

// (5.0 is a float, and 5 is an integer)

if (5.0 === 5)

echo "This never prints!";

// The normal equality check would return true

if (5.0 == 5)

echo "This always prints";

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Loops While

$counter = 1;

while ($counter < 11)

{

echo $counter;

echo " ";

// Add one to $counter

$counter++;

}

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Loops do...while

$counter = 1;

do

{

echo $counter;

echo " ";

$counter++;

} while ($counter < 11);

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Loops for

for($counter=1; $counter<11; $counter++)

{

echo $counter;

echo " ";

}

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Loops Foreach

The foreach statement was introduced in PHP4 and provides a convenient way to iterate through the values of an array.

// Construct an array of integers

$lengths = array(0, 107, 202, 400, 475);

// Convert an array of centimeter lengths to inches

foreach($lengths as $cm)

{

$inch = (100 * $cm) / 2.45;

echo "$cm centimeters = $inch inches\n";

}

Example 2.3

Output

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Arrays Arrays in PHP are sophisticated and more

flexible than in many other high-level languages. An array is an ordered set of variables, in which

each variable is called an element. Arrays can be either numbered or associative,

which means that the elements of an array can be accessed by a numeric index or by a textual string, respectively.

In PHP, an array can hold scalar values—integers, Booleans, strings, or floats—or compound values —objects and even other arrays, and can hold values of different types.

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Arrays Creating Arrays

$numbers = array(5, 4, 3, 2, 1);

$words = array("Web", "Database", "Applications");

// Print the third element from the array

// of integers: 3

echo $numbers[2];

// Print the first element from the array

// of strings: "Web"

echo $words[0];

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Arrays Associative arrays

An associative array uses string indexes—or keys—to access values stored in the array. An associative array can be constructed using array( ).

$array = array("first"=>1, "second"=>2, "third"=>3);

// Echo out the second element: prints "2"

echo $array["second"];

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Arrays Heterogeneous arrays

The values that can be stored in a single PHP array don't have to be of the same type; PHP arrays can contain heterogeneous values.

$mixedBag = array("cat", 42, 8.5, false);

var_dump($mixedBag);

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Arrays Multidimensional arrays

PHP arrays can also hold other arrays creating multidimensional arrays.

Example 2.4

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Arrays Using foreach Loops with Arrays

The foreach statement was specifically introduced in PHP4 to make working with arrays easier.

// Construct an array of integers

$lengths = array(0, 107, 202, 400, 475);

// Convert an array of centimeter lengths to inches

foreach($lengths as $cm)

{

$inch = $cm / 2.54;

echo "$cm centimeters = $inch inches\n";

}

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Arrays Using Array Pointers

PHP maintains an internal index that points to the current element in the array.

$a = array("a", "b", "c", "d", "e", "f");

echo current($a ); // prints "a

// Array ( [1]=> a [value]=> a [0]=> 0 [key]=> 0 )

print_r each($a);

// Array ( [1]=> b [value]=> b [0]=> 1 [key]=> 1 )

print_r each($a);

// Array ( [1]=> c [value]=> c [0]=> 2 [key]=> 2 )

print_r each($a);

echo current($a ); // prints "d"

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Arrays Other functions that use the array's internal

pointer are: end( ) next( ) prev( ) reset( ) key( ) list( )

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Arrays Basic Array Functions

The count( ) function returns the number of elements in the array var:

integer count(mixed var)

The maximum and minimum values can be found from an array numbers with max( ) and min( ):

number max(array numbers)

number min(array numbers)

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Arrays Finding values in arrays with in_array( ) and

array_search( ) The in_array( ) function returns true if an array

haystack contains a specific value needle:boolean in_array(mixed needle, array haystack [,

boolean strict])

The array_search( ) function works the same way as the in_array( ) function, except the key of the matching value needle is returned rather than the Boolean value true:

mixed array_search(mixed needle, array haystack [, boolean strict])

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Arrays Reordering elements in arrays with

array_reverse( ) The array_reverse( ) function creates a new array

by reversing the elements from a source array:array array_reverse(array source [, bool

preserve_keys])

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Arrays Sorting Arrays

The simplest array-sorting functions are sort( ) and rsort( ), which rearrange the elements of the subject array in ascending and descending order.

sort(array subject [, integer sort_flag])

rsort(array subject [, integer sort_flag])

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User-Defined Functions Functions provide a way to group together

related statements into a cohesive block. For reusable code, a function saves duplicating

statements and makes maintenance of the code easier.

Example 2-6

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User-Defined Functionsfunction heading($text, $headingLevel)

{

switch ($headingLevel)

case 1:

$result = "<h1>" . ucwords($text) . "</h1>";

break;

case 2:


break;

default:

$result = "<p><b>" . ucfirst($text) . "</b>";

return($result);

}

$test = "user defined functions";

echo heading($test, 2);

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User-Defined Functions Variable Scope

Variables used inside a function are different from those used outside a function. The variables used inside the function are limited to the scope of the function.

function doublevalue($var)

{

$temp = $var * 2;

}

$variable = 5;

doublevalue($variable);

echo "\$temp is: $temp";

no value for $temp.

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User-Defined Functions If you want to use a value that is local to a

function elsewhere in a script, the easiest way to do so is to return the value of the variable.


{

$returnVar = $var * 2;

return($returnVar);

}

$variable = 5;

$temp = doublevalue($variable);


$temp is: 10

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User-Defined Functions Global variables

The global statement declares a variable within a function as being the same as the variable that is used outside of the function.

function doublevalue( )

{

global $temp;

$temp = $temp * 2;

}

$temp = 5;

doublevalue( );


$temp is: 10

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User-Defined Functions How Variables Are Passed to Functions

By default, variables are passed to functions by value, not by reference.


{

$var = $var * 2;

}

$variable = 5;


echo "\$variable is: $variable";

$variable is: 5

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User-Defined Functions An alternative to returning a result or using a

global variable is to pass a reference (using &$var in the declaration) to a variable as an argument to the function. This means that any changes to the variable within the function affect the original variable.

function doublevalue(&$var)

{

$var = $var * 2;

}

$variable = 5;


echo "\$variable is: $variable";

?>

$variable is: 10

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User-Defined Functions PHP allows functions to be defined with default

values for arguments. A default value is simply supplied in the argument list using the = sign.

function heading($text, $headingLevel = 2)

{

switch ($level)

case 1:


break;

case 2:


break;

default:

$result = "<p><b>" . ucfirst($text) . "</b>";

return($result);

}

$test = "user defined functions";

echo heading($test);

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Objects PHP has limited support for object-oriented

programming and allows programmers to define their own classes and create object instances of those classes.

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Objects Classes and Objects

A class defines a compound data structure made up of member variables and a set of functions that operate with the specific structure.

Example 2.7

To use the data structures and functions defined in a class, an instance of the class—an object— needs to be created.

objects are created using the new operator.$aCounter = new Counter;

Example 2.8

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Objects Inheritance

One of the powerful concepts in object-oriented programming is inheritance.

Inheritance allows a new class to be defined by extending the capabilities of an existing base class.

PHP allows a new class to be created by extending an existing class with the extends keyword.

Example 2.9

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Objects» The power of inheritance doesn't come from

simply reusing code. Objects created from the extended class can be used as if they were created from the existing base class. This ability to use an object as if it were an instance of the base class is known as polymorphism.

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