Youth Tech's Online PHP Class: Lesson One
Introduction, Basic Format, Output [Chat:
7/12/02]
Hosted by YTCC Spark
Welcome to the first Lesson of Youth Tech's PHP Course. In this
lesson, we will introduce PHP, what it is/can be used for, describe the
basic format of ALL PHP pages, and talk about output functions.
What is PHP?
"PHP
is a widely-used general-purpose scripting language that is especially
suited for Web development and can be embedded into HTML." --
php.net
Essentially, PHP is an inline scripting language developed for use
with HTML. What that means is that PHP and HTML can be intertwined
with each other in a webpage. This means that not all of the
webpage must be generated by the PHP.
What can I use it for?
PHP is typically used to add dynamic content to a website. PHP
can be used to read/write files on the server, to access databases, to
include files from other sources, and to execute server-side
programs. It also provides the ability to solve more complex
problems than with HTML alone. It can also be used to just generate HTML
on the fly allowing maintenance of a page to be simplified.
Some tasks that can be almost entirely handled with PHP include:
- Shopping Carts
- User Authentication
- News Scripts
- File Upload Scripts
So what does PHP code look like?
First off, PHP is a lot like C and C++. It is an
object-oriented programming language, but with some twists.
Ordinarily, all pages that contain PHP code will end in the extension .php.
There are basically two ways to do a PHP page. All PHP pages are
variations on these two methods:
Method 1: Static with PHP Blurbs
<HTML>
<HEAD>
<TITLE>Page Title</TITLE>
</HEAD>
<BODY>
<!-- SOME HTML CODE HERE -->
<?PHP
// START PHP CODE
// SOME PHP CODE HERE!
// END PHP CODE
?>
<!-- SOME MORE HTML CODE -->
</BODY>
</HTML>
Method 2: Dynamic by Default
<?PHP
// START PHP CODE
// PHP CODE TO PRINT OUT A WHOLE PAGE
// END PHP CODE
?>
There are some cases where you MUST use method 2, but for most of our
work, you will be able to use whichever method you prefer.
NOTE: Comments begin with // in PHP and continue to the end of
the line.
NOTE: All lines of actual code MUST end with a ;. The
only exceptions will be shown later.
Two basic output functions.
The two basic output functions are print and echo. These
functions are used like this:
print "Hello World";
echo "Hello World";
Now, you might be wondering what the use of these two functions is if
they're the same. Well, there are really two differences.
Print will place a "newline character" at the end of each
print statement so that you don't manually have to print it out.
With echo, you really should use:
echo "Hello World\n";
The \n is the representation of a newline.
Echo can also accept multiple arguments, as in:
echo "Hello ", "World!", "\n";
You can use either a single quote (') or a double quote (")
unless what you are trying to print contains a variable or a special
character (like \n). More details on that in Lesson Two.
Questions from the Class
Q: Can't I use <? ?> instead of <?PHP ?> ?
A: Well, on some servers yes, on some no. I recommend
going on the side of caution and using the extra 3 letters. It
ensures compatibility on ANY server with PHP, and 3 characters is not
much. If you need to use lots of opening/closing tags and want to
type less, then I suggest a search/replace from "<?" to
"<?PHP".
Q: What does the mathematical symbol '%' do?
A: While it is technically known as the modulus operator, it
essentially is REMAINDER division. For example, 22%5=2, because
22/5=4, with a remainder of 2. 28%4=0, because 28/4=7 with no
remainder. Because you can't do division by 0, any number %0 is
also problematic. Programmers should try to avoid this in advance
and prevent it divide by 0 and mod 0.
Q: In some programming languages, the @ sign must be escaped.
("\@") Does PHP require this?
A: No, in fact, this could cause problems. My email
address would not be "ytccspark\@youthtech.com", but "ytccspark@youthtech.com".
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