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Huggles, sir?
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Lesson 00 - What is PHP?
Quote:
First, before getting into the specifics of PHP, let's begin with understanding how a web server and HTML works. When you type in a url and hit "enter" you are sending a request to the server to retrieve the document that you have specified. The web server looks at the url that you specify and looks for a matching document, finds it (or doesn't) grabs it, and sends it to you. Your web browser then parses (i.e. looks through) the data and displays it to you. Any change that is made to that HTML file will be viewable by you in the source, and so is considered "client-side." JavaScript is the same way -- the interpretation of the JavaScript is left up to your browser, and so is no work for the server at all, since it just hands the data over to you.
PHP is a bit different. When you request a PHP file, the web server grabs the file and then -- instead of just sending it on to you -- the server itself looks through the file and does the necessary logic (e.g. fetching information from a database, inserting dates, names, and other dynamic data) and then sends the results to your web browser. If you view the source of a PHP file you will only see HTML and JavaScript because all of the work that the PHP/web server does is "server-side." It is done before you ever see a thing.
-- to be continued --
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Below is a list of the contents of each lesson file. You should be able to copy/paste the lessons below into a text editor and save the file with a .php extension, and have it work. I will try to keep these as up-to-date as possible.
Lesson 01 - Comments
PHP Code:
<?
/* When you see text with a forward-slash and asterix before it, or two
forward slashes, that means that it is a 'comment', or just normal text
which is flagged to be ignored by the PHP engine. The slash-star method
is best for multiline comments, because you only need to put a slash-star
when you want the comment to start, and a star-slash when you want it to end. */
// This is the other form of comments, and in order to use them you
// need to have a double-slash at the beginning of each line. This is
// ideal for small one line comments like variable descriptions.
/* You will notice that this php file has nothing in it but comments. So, when run,
it will do absolutely nothing. */
/* Now, you may ask, if these are just comments, wtf are <? and ?> doing in here?
Those are the "php tags". Before PHP code starts, you put <? and after it ends,
you put ?>. It acts similarly to html tags like <table> and </table>. All php (including
comments) MUST be between the <? and ?> tags.
Because PHP is a server-side language, all of the stuff between <? and ?> is parsed
(looked at, executed) by the server before it ever gets to your web browser. So,
if you load this up with a web browser and try to "view source" you will see nothing
at all. The only part of a PHP program that the web browser will see it the output,
aka the results of the program. */
/* **** Task #1 ***
Try making your own comment in the space below, including whatever you like. Try
out both types of comments /* and // and check to make sure that none of this makes
it to the web browser!
Spacing is important in order to retain readability, so try to use four spaces, or
tabs in order to indent when you need to. */
?>
Lesson 02a - Variables
PHP Code:
<?
/* There are a few different kinds of variables in PHP. First off, variables are
the basis of any programming language, and are what gives a program the ability
to be dynamic. Variables of all types are denoted by a dollar sign ($) before
the name. So, $fruit is a variable named "fruit". What it contains, however,
is generally up to you.
In PHP you don't need to initialize variables -- if you refer to one, it is just..
"there". So, you need to be careful about spelling variables consistently and
not to make typos, because the PHP engine won't really warn you about it and it
can lead to some frustrating bug-hunting.
Let's start off with pre-defined variables. These are variables which PHP itself
sets every time that it looks through a php file. These are things like the
location of the file (02 - variables.php in this case), IP of the person who
is accessing the file, etc.
A simple example of setting a variable, is shown below:
*/
$greeting = "Hello";
/* You'll notice a few things about this statement which holds true to many things
about php. First, the variable is to the left of the = because you are setting
the value of it, to Hello. It's easy to understand why if you speak it out-
loud, "greeting equals Hello". Secondly, notice how Hello is in quotes?
This is because it is a string, not a numeric value (like the integer 2, or a
decimal like 3.14). All strings need to be surrounded by quotes when you echo
or manipulate them in any way. Lastly, notice the semi-colon at the end? For the
most part if you make a single statement you need a semi-colon after it to tell PHP
that you are done. Think of it as a period. Loops are an exception to this, but we
will get to those later.
Capitalization is very important in PHP. It is generally a good idea to have all
variables be entirely lowercase, and only use alphanumeric characters along with
underscores (_) if necessary. $greeting is not the same as $Greeting, so it is
important to remain consistent and watch the typos.
Now that we have set $greeting, let's do something with it: */
echo $greeting . " World!<br>";
/* Whoa, what kind of craziness is this, you ask? Let's take it one chunk at a time.
Firstly, "echo" is a command which will print out whatever is to the right of it, to
the output as long as it exists. So the first thing that will be echoed is "Hello".
The period is a concatination operator, which essentially means that it "joins" the
values to the left and right of it. So, we are joining the contents of the variable
greeting with the string " World!" (notice the space!) and printing it out. The end
result should print out "Hello World!" to your browser.
Another way to do this very same thing is to include the variable in the double-quotes
like below: */
echo "$greeting World!<br>";
/* This will also print out "Hello World!" just as the first example did. One thing that
you need to be careful about, however, is what kind of quotes that you use. Double
quotes will work fine in the above example, but if you use single quotes (''s) it will
instead print out "$greeting World!" -- this is because single quotes convert whatever
is inside them, to a string without parsing any potential variables.
*** TASK #1 ***
$SERVER_NAME is a predefined variable which contains the name of the server host (i.e.
www.seretogis.org) and can be used just like any other variable.
In the space below, change $greeting to something else (e.g. "Goodbye Cruel") and then
print out the following, where "www.x.org" is the $SERVER_NAME variable, and Hello is
your new greeting:
Hello World, from www.x.org! */
?>
Lesson 02b - Variables - Arrays
PHP Code:
<?
/* As valuable as singular variables are, arrays are priceless. An array is basically a
"stack" of different values, all assigned to different part (indexes) of one variable.
In order to keep each value separate from the other, they are assigned different numeric
indexes. By default, indexes start at 0 and work their way up. So, the first value that
you set to an array named $fruit would be referred to as $fruit[0]. I will create an array
and echo it's contents below:
*/
$fruit = array( "orange", "apple", "banana" );
echo $fruit[0] . "<br>"; // will echo "orange" and a newline
echo $fruit[1] . "<br>"; // will echo "apple" and a newline
echo $fruit[2] . "<br>"; // will echo "banana" and a newline
echo $fruit[43] . "<br>"; // will echo nothing but a newline, because index 43 is not set!
/* An array with numeric (number) indexes is known as a "numerically-indexed array". You can
also use words as an index, and that sort of array is referred to as a "hash" by perl veterans.
Logically, the two types of arrays work the same, but creating a hash and referring to its
contents works a little differently, as shown below:
*/
$person = array( "name" => "Bob",
"age" => 25,
"gender" => "male",
"human" => true );
echo $person['name'] . "<br>";
echo $person['age'] . "<br>";
echo $person['gender'] . "<br>";
/* As you see in the previous example, both types of arrays can contain a wide variety of data,
not just strings, but also integers, booleans (true/false), etc.
*** TASK #1 ***
In the space below, create a numerically-indexed array called $weekdays and set to it,
the names of each day of the week ("Monday", "Tuesday", etc). Then, echo out each one
with a <br> after it so that they show up in a nice list. */
?>
Lesson 03a - Loops - if/else
PHP Code:
<?
/* In the previous lesson you learned what variables are, and how to set and display
them. Now that you know how to do that, you will need to learn some basic logic
called "loops" to enable you to do much more powerful things with PHP.
The first "loop" we will deal with, is if/else. Let's use the variable $fruit
and take a look at it's contents.
*/
$fruit = "apple";
/* Now, $fruit is a variable so it is something that we can change at any time. Let's
add some logic to examine what $fruit is, and output something depending on its value.
*/
if ( $fruit == "orange" ) {
echo $fruit . " is a color!";
}
else {
echo $fruit . " is not orange!";
}
/* Let's examine this line-by-line:
1) if ( $fruit == "orange" ) {
This does two things. First, the part between the parenthesis "( )" is a
comparison. It means that $fruit must be equal to the string orange in order
for the next line to be executed. Be sure to notice that == is used instead
of =, this is because the two are very different things. = is used to set the
value of something, == is used to compare two values. == is also case-sensitive,
so orange is not == Orange or ORAnGe. If you wanted to check if something is
NOT equal to a value, use != instead of ==. If you want to see if a variable
exists at all, you could just type: "if ( $fruit ) {". And to check to see if
a variable does not exist? You guessed it: "if ( ! $fruit ) {"
Secondly, notice the left brace "{" -- this is important, as it means that it is
the beginning of code that is to be executed if the comparison is true. It is not
necessary if you only plan on executing one line of code, but if you have any more
than one line and don't use "{" and "}" your script will break.
2) echo $fruit . " is a color!";
This line is what is executed if the comparison in line 1 is true. The result
would this printed to the screen: orange is a color!
3) }
This is the counterpart to "{" -- it notifies PHP that the code to be executed is
over, and that it can move on to other things.
4) else {
This starts what code should be executed if the comparison is false. I.e. if the
value of $fruit is not the string orange.
5) }
This concludes the "else" section, and finishes up your if/else loop!
The else { } section itself is completely optional. If you ONLY want to do something if
a variable has a certain value, all other possibilities be damned, you can just use
lines one through three.
*/
echo "<br><br>";
/*
*** TASK #1 ***
Below, is an example of a broken "if/else" loop. Fix it and change the value of $fruit so
that you are sure that both the "if" and "else" blocks work! Refer to the if/else loop
above if you need help!
*/
$fruit = "celery";
if ( $fruit = celery ) {
echo "What? " . $fruit . " is not a fruit!";
else {
echo $fruit . " is quite fruity.";
{
?>
Lesson 03b - Loops - for/foreach
PHP Code:
<?
/* I hope that you remember how to work with arrays, because we will be using them quite
a bit in this lesson. If you don't, go through Lesson 02b again to refresh your memory.
The "for" loop is incredibly useful, and in this lesson you will just learn the most
common usage of it -- to loop through and print the contents of arrays. We begin!
*/
$fruit = array( "apple", "orange", "banana", "lemon", "lime" );
for ( $x = 0; $x < count( $fruit ); $x++ ) {
echo $fruit[$x] . "<br>\n";
}
/* Let's examine this line-by-line:
1) for ( $x = 0; $x < count( $fruit ); $x++ ) {
This may look a bit confusing, so we will break it up even further -- into the
three statements which it is composed of:
$x = 0;
This first expression is something which is executed only once, at the
beginning of the loop. This is a good spot to initialize an increment
variable (something that we will increment in order to move the loop
forward).
$x < count( $fruit );
Remember comparisons? This second expression is the comparison for the for
loop. count( ) is a function which will, literally, count the number of
entries in the fruit array. This way, if you go up and add peach to the
array, you won't have to change the comparison in your for statement,
because count( ) will know that you added a value.
$x++
The third and final part of the for loop is executed after each interation
of the loop, EVEN IF THE CONDITION IS NOT TRUE. This is a good place to
increment your increment variable, as we do here -- $x++ adds 1 to $x.
2) echo $fruit[$x] . "<br>\n";
This line is what is executed if the comparison in line 1 is true. Notice how $x
is between the [ ]? This is because we want a different value to be printed for
each iteration. On the first iteration, it will print out $fruit[0], on the second
it will print $fruit[1], and so on until the condition is no longer met (i.e. $x
becomes equal to the number of elements in the fruit array.
3) }
This is the counterpart to "{" -- it notifies PHP that the code to be executed is
over, and that it can move on to other things.
Next, the "foreach" loop! Be aware, a foreach loop works ONLY on arrays! If you give it
any other sort of variable, it will vomit all over your new shoes.
*/
foreach ( $fruit as $salad ) {
echo $salad . "<br>\n";
}
/* You already know the basics, so let's just example the first line this time.:
1) foreach ( $fruit as $salad ) {
The first expression "$fruit" is the name of the array that we want to loop through.
The "as" means that we are going to assign it to th second expression, $salad. If you
also want to know the key (the index of the array that you are dealing with in each
iteration of the loop) you can modify your foreach statement slightly to this:
foreach ( $fruit as $key => $salad )
Now, $salad is still the value of each entry in $fruit, but $key is the index/key
of that particular value.
That's all there really is to foreach -- it's very simple, no count( ) or $x++ or
anything like that to worry about -- it auto-increments and handles no comparison.
*/
echo "<br><br>";
/*
*** TASK #1 ***
In the space below, create an array named vegetable with at least four entries, and loop
through it and print out each value twice -- once using the "for" loop, and once using
the "foreach" loop.
*/
echo "<br><br>";
/*
*** TASK #2 ***
What?! A second task? Yes! Learning how to use for and foreach correctly is so important
that there is another task. Below, there is a broken for loop, and a broken foreach loop.
Fix them both so that they print out the values in $vegetable -- be sure to look over them
carefully, you never know what sort of simple error there could be! ;)
*/
for ( $x == 0; $x < count( vegetable ); $x++ )
echo $vegetable[x] . "<br>\n";
}
foreach ( $vetable as salad ) {
echo $salad "<br>\n";
}
?>
__________________
seretogis - sieg heil
perfect little dream the kind that hurts the most, forgot how it feels well almost
no one to blame always the same, open my eyes wake up in flames
Last edited by seretogis; 11-20-2003 at 01:50 AM..
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