PHP

Multi pages forms are just as they sound, a single form spread across multiple pages. These are useful in terms of usability as it can break up an otherwise dauntingly big form into smaller chunks. It can also be useful if you want to process some of the results in order to determine what forms the user sees on later steps.

There are two ways in which it is possible to do this using PHP.

The first (and simplest) is just to cycle through the items submitted on a previous form and print them out as hidden fields. Our first page source code will look like this:

EAN13 barcodes are commonly used to label products in Europe. If you want to know more about how they work then please view the Wikipedia entry on European Article Numbers.

EAN13 barcodes are actually 12 digits long and are validated by using a check digit, which is placed at the end, making the code 13 digits long. The check digit is worked out by the following process:

If you are selling a system the last thing you want is for people to copy the system and pass it on for free. There are numerous ways to implement parts of the system that will stop this from happening.

By far the easiest is to create a section of code that is hidden, the removal of which will cause the application to fall over. It could even be as simple as a link back to your site so that even if you give you application away for free, you will always have that link present.

This method involves the use of a function called eval(), which takes PHP code as a string and interprets it to produce output. Here is an example that prints a link to #! code.

I have previously talked about Removing commas from the end of strings, but it is also possible to use the implode() function to do the same sort of thing.

implode() takes two parameters, the separator and the array, and returns a string with each array item separated with the separator. The following example shows how this function works.

$array = array(1,2,3,4,5,6);
$list = implode(',', $array);

The $list variable will now contain the string "1,2,3,4,5,6". However, things tend to become messy again when you have an array with empty items in it.

Net_Ping is a PHP wrapper for the ping program and provides a neat way pinging a host or checking if a site is up and running. To install it you just need to have pear installed. Once that is done you can do a search for PEAR Net_Ping by opening a terminal and typing:

> ping search ping

This will return the following:

Retrieving data...0%.MATCHED PACKAGES, CHANNEL PEAR.PHP.NET:
=======================================
PACKAGE           STABLE/(LATEST) LOCAL
Net_Ping          2.4.4 (stable)        Execute ping
Services_Pingback 0.2.2 (alpha)         A Pingback User-Agent class.

You can install Net_Ping by running the following:

> pear install Net_Ping

Which should produce the following output.

If you have a site with parts of it using SSL, but want to turn it off for mundane pages like the blog section then use the following code. This uses the $_SERVER['HTTPS'] variable to see if HTTPS is turned on, if it is then a header is issued and the page redirected.

if ($_SERVER['HTTPS'] == 'on') {
    $url = "http://" . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'];
    header('Location: ' . $url, true, 301);
    exit();
}

You can turn it back on again on your secure pages using the opposite.

if ($_SERVER['HTTPS'] != 'on') {
    $url = "https://" . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'];
    header('Location: ' . $url, true, 301);
    exit();
}

Don't include both of these scripts on the same page or you will break the site! Also, make sure that no headers have been issued before hand as this code can cause a "headers already issued" error.

Converting an array of information into a string is easy, but when you are doing this for insertion into a database having trailing commas is going to mess up your SQL statements.

Take the following example, which takes an array of values and converts them into a string of values. This practice is quite common in PHP database manipulation.

$values = array('one', 'two', 'three', 'four', 'five');
$string = '';
 
foreach ( $values as $val ) {
    $string .= '"'.$val.'", ';
}
 
echo $string; // prints "one", "two", "three", "four", "five",

Obviously we need to strip the trailing comma from the end of this string. To do this you can use the following function.

A prime number is a number which has exactly two distinct number divisors: 1 and itself. So if you take the number 11, it can only be divided to get a whole number if it is divided by 1 or 11. If any other number is used then a fraction is always found.

The following function uses a method called trial division to detect if a number is prime or not.

PHP TestFest 2009 is a series of events that you can go to and learn how to test PHP and make new friends and contacts in the PHP community.

One thing that concerned me was that writing these tests might require a in depth knowledge of C++ but this is not the case. Each test is just writing a few lines of PHP code (preferably no more than 10) which will have a known outcome. The tests will be run and the output compared to the expected outcome. For more information about writing tests please refer to the phpt test basics page from the PHP site.