PHP –Writing Reusable Code 10 March 2006 Adina Crainiceanu IT420: Database Management and Organization

Goals Today  Writing Reusable code  External files  Functions

Typical Function Presentation  string date (string format [, int timestamp]) Return type Function name Parameter type Parameter name Optional parameter(s)

Calling a Function  $todayDate = date(“d F y”);  Note:  Function names are NOT case sensitive  Variable names are case senstive

Writing Reusable Code  Example: Typical page header: My Page Name  Type same code for every page?  What if want to change bgcolor?

Include files  Write code once and save it into a file  Include the file in every page  Example: header.php

Include example (cont)  index.php <?php $pageTitle = “Adina’s Page”; include (“header.php”); echo “Some content for my page”; ?>

Generated HTML Page Adina’s Page Some content for my page

Include Functions  include(string fileName)  Includes the content of fileName into current file  require(string fileName)  Like include()  Fatal error if fileName not found!  include_once(string fileName)  require_once(string fileName)

Class Exercise  Write the code for a footer in a file  Include it in index.php file, to obtain a well- formed HTML document

User-Defined Functions  Define functions to performs repetitive tasks  Examples:  Open a database connection and select a database  Display the elements of an array as a table  …

Define a Function  function my_function() { echo ‘This is printed by my function’; } Keyword to define a function Function name Function code

Calling the Function Result: This is printed by my function

Function Parameters  function my_function($text) { echo $text; }  Call: my_function(“Print this text”);  Result: Print this text

Optional Parameters  function my_function($text=“Default text”) { echo $text; }  Call: my_function(“Print this text”);  Result: Print this text  Call: my_function();  Result: Default text

Multiple Optional Parameters  function start_table($border, $cellspacing=2, $cellpadding=2){ echo “<table border = $border cellspacing = $cellspacing cellpadding = $cellpadding>”; }  start_table(1) equivalent start_table(1,2,2)  start_table(2,3) equivalent start_table(2,3,2)  start_table(2,3,4)  Parameter values filled in from left to right!

Return Values  function add_values($a, $b){ $result = $a + $b; return $result; }  Call: $added_val = add_values(4,5);  Result: $added_val has value 9

Class Exercise  Write a function is_leap to test whether a yar is a leap year or not  Return “Yes” if input parameter is leap year  Return “No” if input parameter is not a leap year

Variables Scope  Variables declared in functions are visible from declaration line to end of function – local variables  Variables declared outside functions are visible from declaration line to end of file, but not inside functions – global variables  Superglobal variables ($_POST, $_SERVER, …) are visible everywhere  Keyword global makes local variables global – not recommended

Variables Scope Example  function fn(){ $var = ‘content’; } fn(); echo $var;  Result?  Nothing is printed!

Variables Scope Example 2 $var = ‘content 1 ’; echo $var; function fn(){ echo $var; $var = ‘content 2 ’; echo $var } fn(); echo $var;  Result? content 1 content 2 content 1

Class Exercise  Write a function my_dbconnect to open a db connection and select a database  Input parameters:  db server name  user name – optional, default value “root”  password – optional, default value “”  database name  Return value:  FALSE if errors occurred  database connection if everything OK

Class Exercise  Write the PHP script to use my_dbconnect  Connect to localhost  Default user and password  Select database vp5fund