PHP

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PHP
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Topics
PHP
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
PHP
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
PHP

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Introducing Three-Tier Architectures
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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
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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
PHP
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
PHP
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
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
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 Output
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Basic Features
PHP
several features of PHP The begin and end script tags are lt?php and ?gt or, more simply, just lt? and ?gt. The longer begin tag style lt?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 ltscript language"PHP"gt and lt/scriptgt.
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Basic Features
PHP
White space has no effect, except to aid readability for the developer. For example, the script could have been written succinctly as lt? php echo "Hello, world"?gt 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
PHP
When a PHP script is run, the entire script including the start and end script tags lt?php and ?gt is replaced with the output of the script.
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Basic Features
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The freedom to interleave any number of scripts with HTML is one of the most powerful features of PHP. Example 2.2 Output
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Basic Features
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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
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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
PHP
There is also a shortcut that can output data. The following very short script outputs the value of the variable temp lt?temp ?gt 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
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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
PHP
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
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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
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two compound types Array Object
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Variables and Constants
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Constants define("pi", 3.14159) echo pi
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Expressions and Operators
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// 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
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// 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
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// 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
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// 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
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
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
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if...else Statement if (var lt 5) echo "Variable is very small" elseif (var lt 10) echo "Variable is small" elseif (var lt 20) echo "Variable is big" elseif (var lt 30) echo "Variable is very big" can use lt gt inside expressions can use ! inside expressions
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Conditions and Branches
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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
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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
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While counter 1 while (counter lt 11) echo counter echo " " // Add one to counter counter
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Loops
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do...while counter 1 do echo counter echo " " counter while (counter lt 11)
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Loops
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for for(counter1 counterlt11 counter) echo counter echo " "
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Loops
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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
PHP
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 valuesintegers, Booleans, strings, or floatsor compound values objects and even other arrays, and can hold values of different types.
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Arrays
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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 numbers2 // Print the first element from the array // of strings "Web" echo words0
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Arrays
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Associative arrays An associative array uses string indexesor keysto access values stored in the array. An associative array can be constructed using array( ). array array("first"gt1, "second"gt2, "third"gt3) // Echo out the second element prints "2" echo array"second"
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Arrays
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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
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Multidimensional arrays PHP arrays can also hold other arrays creating multidimensional arrays. Example 2.4
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Arrays
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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
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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 ( 1gt a valuegt a 0gt 0 keygt 0 ) print_r each(a) // Array ( 1gt b valuegt b 0gt 1 keygt 1 ) print_r each(a) // Array ( 1gt c valuegt c 0gt 2 keygt 2 ) print_r each(a) echo current(a ) // prints "d"
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Arrays
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Other functions that use the array's internal pointer are end( ) next( ) prev( ) reset( ) key( ) list( )
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Arrays
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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
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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
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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
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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
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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 Functions
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function heading(text, headingLevel) switch (headingLevel) case 1 result "lth1gt" . ucwords(text) . "lt/h1gt" break case 2 result "lth2gt" . ucwords(text) . "lt/h2gt" break default result "ltpgtltbgt" . ucfirst(text) . "lt/bgt" return(result) test "user defined functions" echo heading(test, 2)
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User-Defined Functions
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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
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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. function doublevalue(var) returnVar var 2 return(returnVar) variable 5 temp doublevalue(variable) echo "\temp is temp" temp is 10
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User-Defined Functions
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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( ) echo "\temp is temp" temp is 10
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User-Defined Functions
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How Variables Are Passed to Functions By default, variables are passed to functions by value, not by reference. function doublevalue(var) var var 2 variable 5 doublevalue(variable) echo "\variable is variable" variable is 5
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User-Defined Functions
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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 doublevalue(variable) echo "\variable is variable" ?gt variable is 10
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User-Defined Functions
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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 result "lth1gt" . ucwords(text) . "lt/h1gt" break case 2 result "lth2gt" . ucwords(text) . "lt/h2gt" break default result "ltpgtltbgt" . ucfirst(text) . "lt/bgt" return(result) test "user defined functions" echo heading(test)
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Objects
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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
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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 classan object needs to be created. objects are created using the new operator. aCounter new Counter Example 2.8
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Objects
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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
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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.