Quakenet/#php Tutorial - Complete content

1. Welcome

This is the Quakenet/#php.de tutorial about php and mysql. It covers php5.

2. Requirements

You must meet some requirements before working with this tutorial.

1. As the php scripts generate html code you need to be able to write html code. Use a tutorial like http://www.w3schools.com/HTML/ to learn HTML if you are not familiar with it.

2. First, you need an editor for writing the php scripts. Since you wrote html code before, you could use the editor you are already using. However, you shouldn't use any WYSIWYG editors. Use editors with syntax highlightning instead. A list of common php editors can be found in our FAQ: "I'm looking for a good PHP-editor".

3. To actually test and run your php script you need some webspace with php support. There are enough free hosting services to test your php scripts. It's even possible to test your script on your local machine. Note that scripts may only work on your local machine, as they could try to access resources that may not be available on a remote host.

3. Layout of the tutorial

This tutorial is seperated into chapters. Each chapter contains several sections. The chapters are ordered in a linear fashion, so there is a strict order for reading the chapters in. It's really not recommended to skip a chapter (also see the warning at top of every page).

Sometimes, there are also excercises following a chapter. These are for testing your knowledge of the chapter. They usually contain knowledge questions and questions about implementing of php scripts.

A complete version of the tutorial can be found at total.html. This can be used to print the tutorial at once instead of printing each chapter. Note that this document is big.

4. Licence and download of the tutorial

We offer a download version of this tutorial with all HTML/CSS files and images.

download of tut.php-quake.net.en.tar.gz

This tutorial may of course be read from the url http://tut.php-quake.net/, and the download version can be used to read the tutorial offline. Also, the tutorial can be used for education in real life, for example at school or at college. However, the tutorial must be cited if it is used. The tutorial may be copied onto any storage medium for the pupil/students/employees. For the internet parts of the tutorial may be cited.

It is forbidden to make a copy of the tutorial (like a mirror). This applies to the online and offline version of the tutorial. If you want to mention the tutorial to your users, link to http://tut.php-quake.net/. If you have any further questions about the licence, ask an operator of the QuakeNet channel #php.

1. What is PHP and what does it?

PHP is the recursive backronym of PHP: Hypertext Preprocessor. The name indicates something is proceeded before some point. In this case all the php statements inside the file are proceeded before the server sends the file (or be more specific: the output of the php script) to the client. This is similar to the well known C preprocessor.

PHP is a module or programm installed on the webserver. Often other usefull programms like MySQL is installed. The following diagramm illustrate how it looks like.

Img.:Installed modules on the webserver

As shown in the diagramm php isn't related to the client or its browser in any way. This is the reason why you cannot control the client. Actions like starting Winamp are not possible.

Common usage of PHP is the processing of data given from a HTML form, that has been send to the webserver. As the php scripts running on the webserver they can access and work with any databases installed on the server (like MySQL as mentioned above). So you can easily write news scripts which reads the news stored in a database. The result of each php script is still plain html code. The browser doesn't recognized in any way the html code isn't generated by a php script. Of course the user see the extensions .php in the URL. However, neither the browser nor the client using it can access the php code you wrote inside the php file.

2. A request of a file seen by a client

If the client requests a file from a server the following happends.

Img.:Client send request to the server

In the viewpoint of the client he gets the answer of the server.

Img.:Client receives the response from the server

The client used only one connection to the server, however he get two seperated contents from the server.

1. First the client receives the so called headers. These headers describe the following content and contains several informations about the server. These data are normally hidden by the user but can be shown with browser extensions like Firebug. Headers looks like this:

   HTTP/1.1 200 OK
   Date: Mon, 26 Nov 2007 22:37:21 GMT
   Server: Apache
   Content-Type: text/html

   It's possible to change all these headers with php before they are send to the client. This also means it is possible to generate and send image data to the client if you set the proper content type like Content-Type: image/png.

2. After the headers there are the so called content. In most cases it containts the html code generated by the php script but can also be the binary data of an image.

You can change both parts with php as much you want, but there is one restriction. The headers must be send before you send the content. These happends automatically if you send the first part of the content. If you print some stuff with php you cannot change the headers. If you try this anyway you will get an error message like Cannot modify header information - headers already sent by (output started at ...).

3. Request of a file in the view of the server

If the server receives a request to a html file he just read the file from the hard disk and send it to the client.

Img.:Server receives the request from the client

As the server must send headers to the client he generate the headers from the files content. E.g. he check the file size and generate a Content-Length header. A complete list of headers may be look like this.

HTTP/1.1 200 OK
Date: Wed, 28 Nov 2007 16:34:05 GMT
Server: Apache
Last-Modified: Mon, 26 Nov 2007 23:24:33 GMT
ETag: "d9b8a-2301-43fdd444c0e40"
Accept-Ranges: bytes
Content-Length: 8961
Content-Type: text/html

If the headers are send the server sends the html code of the file and is finished with this request.

Img.:Server sends the response to the client

As the server hasn't much to do this request is handled very quickly. However, if the file is a php script the server has much more to do.

Img.:Server receives the request from the client

Now the server reads the content of the file. This is a similar to a normal html file.

Img.:Server reads the file contents

Now the processing of php must be followed. As the server itself don't understand php he uses the php interpreter. This interpreter reads and executes the statements inside the file accordingly to the rules of the programming language.

Img.:Server processed the php statements with the php interpreter

If the php interpreter finishes the webserver again get the two parts headers and content. These are send to the client back.

Img.:Server sends the response to the client

In point of view of the client nothing is changed. He doesn't even notice php is installed on the server and the requested file contained php code. But the user notice a performance lost if he access php files from a webserver. As php files must be parsed and executed by an php interpreter the server needs much more time (compared to a single html file) to send a response to the client.

1. Layout of a php file

PHP code can be used everywhere in html. To switch into php mode write the character sequence <?php. To leave the php mode again write ?>. Another way is to stop the php mode with the file ending. You can switch into php mode everywhere in your file, its even possible to use the whole file in php mode (file beginns with <?php and ends with ?>). The webserver only handle files as php scripts if the file got the .php extension. This is the default settings for webservers with php support, but can be changed by the admin of course.

A sample php script looks like this:

<?php
echo "Example of a php script\n";
?>

In this example the whole file is in php mode. But as mentioned above the php mode can be used only at possition where needed, too.

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xml:lang="en" lang="en">
    <head>
        <title>Hi all</title>
    </head>
    <body>
        <?php
        echo "<p>The php mode</p>\n";
        ?>
    </body>
</html>

Any text which is outside of php mode is send to the client without interpreted by php. But it can be controlled with a php construct like loops.

The second version isn't useable for changing the headers. With the first character (which doesn't belongs to <?php) which is send as content to the client (in this example the < from the line <?xml version="1.0" encoding="utf-8" ?>) the headers are also send to the client. So its impossible to change the headers with setcookie oder header anymore.

Using a xml declaration can be problematic in some cases. The xml declaration starts with <?xml which is not the same as <?php. But there exists a setting called short_open_tag which allowes you to enable php mode just with <?. This will interfere with the xml declaration if the setting is enabled as php tries to interprete the code xml version="1.0" encoding="utf-8" as php code. Since this isn't valid php code a error message is shown. To solve this problem you can echo the xml declaration with php. A easier way is to deactivate this setting.

2. Functions

To test php create a file with the following content.

<?php
phpinfo();
?>

Save this file as phpinfo.php and upload it to the webserver. If you open this file in your browser you can get two possible outputs.

1. You get an empty page. In this case the following must be checked.

   • The file must got the .php extension so the php interpreter loads this file.

   • The file contains valid php code.

   • The webserver supports php.

   • The file is loaded via http://. Beginners often try to open the file over an URL like file://C|/....

   In this case check the source code you get from the server. Depending on your browser you can see the source code at View -> Source. If you see your php code then the webserver doesn't support php.

2. In the more common case you see a lot of information about the installed php version. You can even check the configuration with phpinfo. This is the first location to check which php modules are installed and how the configuration settings are. Its important to check the php version, but also important to check settings like error_reporting and display_errors.

In this example you see how to use a function. Each function call starts with the function name, in this case its phpinfo. It is followed by an opening parenthese (. It is possible to supply parameters for the function. These parameters changes the processing of the function accordingly to the definition of the function in the manual. If a function accept more than one parameter the parameters are seperated by a comma (,). After all parameters (if any) the parameter list is closed by a closing parenthese ). These parentheses must be used even if no parameter are used (like in phpinfo();). Each statement in php must be terminated by a semicolon ;. A single function call like this one is a valid statement in php any must be terminated by semicolon.

<?php
name_of_function(parameter1,parameter2,...);
?>

Each part of a function call can be seperated by any number for spaces. To be more specific each part can be seperated by any number of whitespaces. These includes spaces but also includes newlines and tabs. The following function call are all equivalent.

<?php
name_of_function(parameter1,parameter2);
name_of_function(parameter1, parameter2);
name_of_function     (parameter1    ,parameter2)     ;
name_of_function(
    parameter1,
    parameter2);
name_of_function       (      parameter1      ,
    parameter2
)             ;
                      name_of_function        (parameter1,parameter2)         ;
?>

It depends on your own programm style which one is the best for you to read. In php there exists a standard called PEAR Coding Standard. You should use this standard to write and indent your code so you and any other php programmer can read and understand your code.

1. Output of strings

The main goal of php scripts, beside any programm logic behinds it, is to generate an output, e.g. a list of news. You use the language construct echo to print some text without leaving the php mode. Check the following example.

<?php
echo 'A text which is printed';
?>

You notice first the parentheses of the function are missing. But thats not an error as echo is not a function but a language construct. The manual explains this as follow:

echo() is not actually a function (it is a language construct), so you are not required to use parentheses with it.

The second thing you noticed is the text to print is written in two apostrophes '. This is the way (independent of echo) to create a string with the written content. This string is the parameter for the language construct echo and it uses it to print the string. If you upload this script to your webserver and runs it you get the following output.

A text which is printed

Now we add a second echo statement in your php script.

<?php
echo 'A text which is printed';
echo 'Another text which should be printed';
?>

If you test this script on your webserver you get the following output.

A text which is printedAnother text which should be printed

The second string is just printed after the first one. Nothing else is actually written in your php script. First a string is printed then a second string is printed. To actually get a newline in the output you can use the html tag <br/>.

2. Print html code

Html code or be more specific the special characters < and > can be used in string without any problems. This allowes you to add the html tag <br/> at the end of your first string.

<?php
echo 'A text which is printed<br/>';
echo 'Another text which should be printed';
?>

As expected you will get the following output.

A text which is printed
Another text which should be printed

If you check the source code in your browser you still see both strings in one line.

A text which is printed<br/>Another text which should be printed

3. Special characters in strings

If you add a apostrophe in your string you will get some problems as php recognize it as the end of your string, to early...

<?php
echo 'Dummy text ' with apostrophe';
echo 'Another text;
?>

As you see in this syntax highlighting php builds the string until the second apostrophe. To actually get a ' inside your string you can use double quoted string. These are strings build with quotes (") instead of apostrophes.

<?php
echo "Dummy text ' with apostrophe";
echo "Another text";
?>

Another way is to use escape sequences. In php strings the character \ is the escape character and is used to create such a escape sequence. In single quotes strings (strings with ' as delimiter) you can use the escape sequence \' to get a apostrophe into the string.

<?php
echo 'Dummy text \' with apostrohpe';
echo 'Another text';
?>

The same way can be used to get a quote inside a double quoted string.

<?php
echo "Dummy text \" with apostrohpe";
echo "Another text";
?>

But now a question is rised how to get a single \ inside your string as it start a escape sequence. The solution is to escape the escape character.

<?php
echo "Double quoted with \\ im text";
echo 'Single quoted with \\ im text';
?>

As it looks both single quoted and double quoted strings using the same functionality of escape sequences double quoted strings got more escape sequences. The following table shows the additional escape sequences which can be used in double quoted strings.

1. What are comments?

Text or lines in your php scripts which are ignored by the php interpreter are called comments. This is like the html comments with <!-- -->. With these you can (as the name implies it) write comments inside your script. These are used to add e.g. the authors name or the license into the php script without interfering the php interpreter.

2. Syntax of comments

There are 4 types of comments in php but we only use 3 of them. And from them two are almost the same. These comment types are seperated into two groups, the one line comments and the multi line comments

1. One line comments are comments which ends at the current line or at the ?>. These comments start with // (this is not the string escape sequence \\). The following text is marked as a comment and is ignored by the php interpreter.

   <?php
   echo 'Text'; // echo a string
   
   // Generate a second text
   echo 'Another text';
   
   // echo "I'm not printed as I am inside a comment";
   
   echo 'I am printed, althought I got // in the string';
   
   // comment running until the php end ?><?php echo "I'm not in the comment anymore"; ?>
   

   As you see not every charactersequence of // is treated as a comment, e.g. if it is used inside a string.

2. Multi line comments are comments which can be longer than one line. Instead of starting each line with a // a multi line comment starts with a single /* and stops with a */.

   <?php
   echo "Print something again";
   /* Some comments which
   use several
   lines
   until the ending */
   echo 'A normal php statement again';
   ?>
   

   For readability each comment can be written as you want, like indenting the lines.

   <?php
   echo "Print something again";
   /* Some comments which
      use several
      lines
      until the ending */
   echo 'A normal php statement again';
   ?>
   

   You can even exaggerate this to underline the comments.

   <?php
   /*************************
    * loading configuration *
    *************************/
   echo "config loaded";
   ?>
   

   For multi line comments you cannot use ?> to stop such a comment.

3. The third type are comments for PHPDoc. These are almost identically to multi line comments but uses /** as the start of the comment. However it must be appended by a whitespace (typically a newline).

   <?php
   /**
   A comment in PHPDoc style
   */
   echo "normal php code";
   ?>
   

   You may ask why there are almost two identically comment tyes. PHPDoc are special comments which are used to document special parts of your php script. These are used before selfwritten functions.

   <?php
   /**
    * Output a number.
    *
    * The following function outpus the given number.
    *
    * @param i The number to print.
    */
   function output_number($i) {
       // ...
   }
   ?>
   

   The syntax of such PHPdocs is defined by the phpDocumentor project. It's much the same as the Javadoc Tool with the same idea. Special programms (this mentioned PHPDoc) read this comments and generate html files for documentation. This way other php programmers can easily read the documentation to understand what the mentioned function (or class) is doing.

3. Commenting out

Besides writing developer notes into comments you also can do stuff which is called commenting out. During the development sometimes you want to disable some part of the script but without deleting the code. You can do this by putting the php code inside a comment. Check the following example.

<?php
do_this();
do_that();
and_this();
?>

If you dont want to call do_that() just put it inside a one line comment.

<?php
do_this();
//do_that();
and_this();
?>

For more than one lines you still can use multi line comments.

<?php
do_this();
/*
do_this();
and_this();
and_that();
and_now_this();
*/
and_again_that();
?>

There is a trick to active the commands in the comment again fast, instead of just deleting the /* and */. For this you must put the */ inside a one line comment with //.

<?php
do_this();
/*
do_this();
and_this();
and_that();
and_now_this();
//*/
and_again_that();
?>

To reactive the execution of the statements replace the /* with a //*.

<?php
do_this();
//*
do_this();
and_this();
and_that();
and_now_this();
//*/
and_again_that();
?>

Now you see the reason for the // before the */, otherwise you got invalid php code (and will get an parse error). Now you have 2 single one line comments. If you replace //* back to /* the statements are commented out again and you have one multi line comment.

As a multi line comment ends with */ its impossible to embed multi line comments inside multi line comments. This is not a problem as you normaly dont do this explicit. But it can happends if you comment out some code and some days later comment a wide area out.

<?php
do_this();
do_that();
/*
deactivated();
deactivated2();
*/
and_this();
and_that();
?>

Now we want so deactivate the code from do_that() to and_this(). You can try this with a multi line comment.

<?php
do_this();
/*
do_that();
/*
deactivated();
deactivated2();
*/
and_this();
*/
and_that();
?>

With this code php will stop the execution of the script. As you see in the syntax highlighting in this tutorial the outer comment isn't really an outer comment. For php the multi line comments start at line 3 and ends at line 8 (and not at line 10). In this case even the line and_this() gets executed. However, the whole script isn't run at all as the script results in a parse error in line 10.

1. What are variables?

Typically php scripts are generate the output dynamically. The php scripts itselfs (the contents of the files) are static however. So we need something which can be dynamic filled. For this there are so called variables. These are filled by the php script and can be reuse later in the script.

2. Syntax of variables

All variables in php starts with the dollar character $. After that the name of the variable starts with a letter or the underscore _. And after that the name can also use digits. Variables which begins with an underscore has some special meaning. For this reason the php developer shouldn't use own variables which start with an underscore.

<?php
$valid
$10_not_valid
?>

Variables are case-sensitive, so its important how you write your variables. The variable $foo is not the same as the variable $FOO. This is important as the superglobal variables like $_GET are not written as $_get.

3. Assignment operator

To fill a variable with a value you use the assignment operator =. The variable must be written on the left of the = character, the value to save must be written on the right.

<?php
$var = 'Content';
$123 = "not valid :(";
$some_variable = $another_variable;
?>

After we filled the variables with values we can use e.g. with echo

<?php
$email = 'foo@example.com';
echo 'Your email is: ';
echo $email;
?>

1. Concatenate of strings and variables

One operator of php is the concatenation operator which is written as a single dot (.). It is used to concatenate two expressions.

<?php
'John'.'Doe'; // generate a string "JohnDoe"
?>

It doesn't matter if you concat strings or variables. Even numbers can be concatenate.

<?php
'Foo'.'Bar';
'Bla'.$var;
$var1.$var2;
?>

In this examples the concatenations are calculated, however they are not used. As this is a valid expression itself it can be saved in a variable or printed directly with echo

<?php
$texts = 'Foo'.'Bar';
echo $some_variable.'String';
?>

The number of concatenations is unlimited, however php concatenate only 2 expressions together and use this result for the next concatenation.

<?php
$name = $surname.' '.$lastname;
// surname + one space + lastname
echo 'I am '.$name.', good morning.';
?>

It can be tricky to concatenate variables and strings if they contain single quotes and double quotes. There can be some errors if you use html code.

<?php
// you want a link <a href="index.php?section=XYZ">Link</a>, in this
// XYZ part should be filled with a variable
$var = 'XYZ';
echo '<a href="index.php?section='.$var.'">Link</a>';   // one valid solution
echo "<a href=\"index.php?section=\".$var.\">Link</a>";
// this would generate <a href="index.php?section=".XYZ.">Link</a> as the text, which is not what you want
echo '<a href="index.php?section=".$var.">Link</a>';
// this would generate <a href="index.php?section=".$var.">Link</a>, which is also not what you want
?>

Some may be get irritated to write something like .'" or maybe ."\" after variables. However after the concat operator you can write any string which may contain any escape sequences you want. To don't get irritated you first write the full html code and then add the variable with the concatenate operator.

<?php
echo '<a href="index.php?section=XYZ">Link</a>';
//                               ^^^
//                 replace with  '..'  (which is invalid atm.)
//                                 |
//                                 V
echo '<a href="index.php?section='..'">Link</a>';
//                                ^^
//                     insert the variable
//                                   |
//                                   V
echo '<a href="index.php?section='.$var.'">Link</a>';
?>

With sprintf you got some possibilities to fill a string with a variables content.

1. The datatype numbers

If you want to calculate with variables (be more specific: with its content) you must use a data type which is used for numbers. One lazy way is to write a number in string and calculate with these strings.

<?php
echo "5"+"9";
?>

This will generated 14 as expected. However php didn't calculated with numbers but with strings. This doesn't work normally (or what do you expected for "hello" + "xyz"?), but the automatically typecasting take place here. The strings are got casted to real numbers first. In php there exists two types, the integer and float numbers.

2. Integer numbers

Integer numbers are any whole numbers, they don't have any decimal places. E.g 5, 31 and 199 are integer numbers, but also -1, -10 and -44. In php you write numbers as they are, the php interpreter reads the sequence of digits as a number.

<?php
$var = 5;
$var2 = 31;
$var3 = -10;
?>

Its also possible to write integer numbers in hexadecimal or octal notation, if you know how to calculate them. For hexadecimal notation you use the prefix 0x, for octal notation the prefix 0 (normal integer numbers starts with the highest digit or are zero anyway).

<?php
$var = 0xFF; // hexadecimal (255), often use for protocols
$var2 = 0763; // octal (499), often used for chmod
$var3 = 0; // normal zero, it doesn't matter if hex-, oct- or decimal
?>

3. Float numbers

Float numbers are values with decimal places like 5.7, 12.25 or -4.07, but also 10.0, 3.1E-10 or 4.5e3.

<?php
$var = 5.7;
$var2 = 3.1E-10;
$var = .1;
?>

Float numbers can be easily recognized by the decimal point ., so you dont use the comma (,) for the decimal places. As the dot . is also used for string concatenation you must be very carefully if you concat float numbers with strings. Sometimes you must use parentheses.

<?php
echo 'Percent value:'.77.3.'%';   // won't work
echo 'Percent value:'.(77.3).'%'; // works
echo 'Percent value:'. 77.3 .'%'; // works, these spaces "helps" php to parse this line correct
?>

4. Memory usage of integers and floats

There may be a question why to use integer and float numbers as float numbers can do more. Both types use (basically) the same memory usage but use a different usage of it. Integer values are saved very easily. Imagine you save an integer value into a 64 bit field. One bit is reserved for the sign (more or less, check Two's complement). The remaining 63 bits are for the significations. A bit with the value 1 means the integer number got this mentioned signification. The sum of all results in the value of the integer number. These significations starts from 2^0 (1) and goes up to 2^62 (4611686018427387904). As an example the number 50 got the significations 32, 16 and 2. On bit level these are the bits 1, 4 and 5. These are put into a 64 bit field.

Img.:Bits set for the integer value 50 (simplyfied)

However, integer numbers are saved in the Two's complement.

Float numbers are saved in a different way. As we can save decimal places too we cannot use the same significations as for integer numbers. Float numbers are normally saved in the IEEE 754 format. For a 32 bit float number one bit is used for the sign, 8 bits for the exponent and 23 bits for the mantissa. The mantissa builds a number between around 0 and 1. On this value a base-2-exponentation is multiplied. This exponentation is build with the mentioned 8 bits. Depending on the choosen standard the mantissa is moved left (if the factor is big, like 2^50) or moved right (if the factor is small, like 2^-50). With the sign bit you get a complete number. So you cannot save any number with decimal places but only a specific number of digits of the number. But thats normally no problem as we use it all the time like giving the weight of something in 31.6 tons instead of 31.6346800235 tons.

1. Aritmetic operations

In PHP are 6 simple aritmetic operations. First these are the 4 basic aritmetic operations +, -, * and / (/ is the division as : is already used in php and / is used in any other programming language, too), and there is the unary operator - which negates a number and the operator % which calculate the remains of a division (20:7 = 2 remaining 6).

<?php
$a = 10;
$b = 6;
echo $a-$b;   // 4
echo $a+$b;   // 16
echo $a*$b;   // 60
echo $a/$b;   // float(1.66666666667)
echo -$a;     // -10, same as echo 0-$a;
echo $a%$b;   // 4 (6 fits one times in 10 with a remain of 4)
?>

For any complex calculaten there exists a lot of functions, to find in the manual at Mathematical Functions. Especially pow is such a function which calculates the exponentation. Beginners try to use ^ as the exponentation and fails as php use ^ for something different than the exponentation (it is used for a bitwise XOR operation).

<?php
$base = 5;
$exponent = 7;
echo $base^$exponent;        // echos 2, which is not what you want
echo pow($base, $exponent);  // echos 78125
?>

1. Datatype boolean

In PHP there is a datatype which may use only one single bit. So this datatype can only be used to save just two possible values 0 and 1. In the context of programming languages you normally speak of about true (for 1) and false (for 0). This datatype is used to say if something is true or something is false

PHP uses the codes true and false to get the corresponding boolean values. These codes are case-insensitive, however you normally write them in lowercase.

<?php
$var = true;
$var2 = false;
$var3 = TRUE;
$var4 = FaLsE;

$var5 = 'true'; // this is a 4 character long string with the content "true", its not
                // the boolean value true
?>

This datatype is use for control structurs. With these you control which programm code is executed and which not.

2. Control structures

You can control the programm flow with control structures. You can control with these if a programm block is executed or not. You can build such a control structure with the language construct if

<?php
if (expression) statement
?>

The expression is calulated and must return a value. This value is checked for equivalent agains true. If this is the case the following statement gets executed. If you want to control more than one statement with one if you must use curly brackets to put the statements together.

<?php
if (expression) {
    statement_1;
    statement_2;
    // ...
    statement_n;
}
?>

The expression to check can be build with several expression together if you use operations like and or !.

3. Alternative execution

If you write some code with an if statement you often wants to execute some code if the if statement is not executed. An example can be to show an admin menu if the login is valid otherwise show an error message. You can write such an alternative execution with the keyword else which must belong to a previous if statement.

<?php
if (login_valid) {
    // show admin menu
} else {
    // show error message
}
?>

You can also copy the if statement and negate the expression with !.

<?php
if (login_valid) {
    // show admin menu
}
if (!login_valid) {
    // show error message
}
?>

This is however inadvisable and its sometimes not even possible to write.

You even can extend such an if-else with elseif structurs. This is a block between the if and else block which also contains an expression to check.

<?php
if (condition) {
    // do this
} elseif (another_condition) {
    // do that
} else {
    // do at least this
}
?>

The elseif part is executed/checked if the previosly if check gets false. You can even write more than one elseif structures.

<?php
if (condition) {
    // do this
} elseif (another_condition) {
    // do that
} elseif (and_another_condition) {
    // and do this
} elseif (expression) {
    // php-code
} else {
    // do at least this
}
?>

The condition which is first true gets executed. If no condition at all is true the else part gets executed.

4. Errors you may get with if();

As an if () looks like a function call it isn't one. A semicolon at the end isn't not just useless, it also breaks the correct working of an if statement. Check the following example.

<?php
if (false); // <-- notice the ; at the end
    echo 'Foobar';
?>

Althought the condition is false the echo statement gets executed anyway. The if statement controls only the next statement of the next block written with curly brackets. But in this case its not the echo 'Foobar'; line but the single ; behind the if(). The code looks actually more like this:

<?php
if (false)
    ;
echo 'Foobar';
?>

Or be more clear:

<?php
if (false) {
    ;
}
echo 'Foobar';
?>

As you see the if statment just controls an empty statement, independent of the following echo statement.

1. The compare operator ==

To check two values for equal you use the == operator. On both sides of the operator are the values to check. These can be variables and a constant value. PHP compares these values and returns a boolean value, so the result is either false or true. This value can be used later like in control structures.

<?php
"john" == "doe";        // results in bool(false), but the result isn't used in any way
$check = "max" == $var;   // checks the content and saves true or false in $check
var_dump('foo' == 'bar'); // outputs bool(false) for debugging
?>

2. Other compare operators

Besides == there are other compare operators. For numbers there are several operators like <, <=, > and >= which checks the same as they are written.

<?php
$var = 5 < 7;     // is true
$var = 10 <= 10;  // is true
$var = 9 > 9;     // is false
?>

And there is the unequal operator != to check if two values are not the same.

<?php
$var = 10 != 10;  // false
$var = 0 != 1;    // true, as 0 is not 1
?>

As enhancement to the compare operators == and != there are two operators === and !==. These do not just check the values but also the types of the values to check. In this case the string "10" are not the same as the integer value 10 as they were with ==.

<?php
$var = 5 == "5";  // is true
$var = 5 === "5"; // is false, because int != string

$var = 'Max' == "Max";  // is true, althought they use single quote strings and double quote strings
$var = 'Max' === "Max"; // is also true, both string have the same content and are strings
?>

You need this to check for return values of functions which can return the boolean value false but can also return a value which may be something like false but aren't a boolean value (like the integer 0).

<?php
$var = false == 10; // false
$var = false ==  0; // true, althought the first one is boolean and the second one is a number

$var = false === 10; // as above, false
$var = false ===  0; // this time its false as int != boolean
?>

3. Assignment operator vs. compare operator

A common error is to use an assignment operator instead of an compare operator just because you miss a equal character =. The php scripts are technically valid but they do not do what they should do.

<?php
$check = $name == 'Max'; // Checks the value agains 'Max' and saves the (boolean) result in $check
$check = $name = 'Max';  // saves the value of 'Max' in $name and use this result (the assignment) as
                         // the new value for the variable $check (which will be also 'Max')
?>

That may be frustrated if you have this in an if statement. You want to check a value but actually overwrites the variable with a new value. To solve this common error (which happends always...) you should write the value to check agains always on the left of the compare operator.

<?php
"Max" == $name;
?>

With this code its impossible to miss a equal character =. If you miss it anyway you get an parse error which can be easily be fixed. But try to fix an error where you miss a = somewhere in your code.

<?php
$check = "Max" == $name; // checking and save true/false in $check
$check = $name = "Max";  // maybe not that what you want and hard to find
$check = "Max" = $name;  // not possible, results in an parse error (and then you know where and how to fix)
?>

1. Combinations of several conditions

Sometimes a condition is build with several sub-conditions. You can combine these atomic conditions together to get the condition you want. There are 7 combinations/functions how to combine two boolean values. These are 3 basic and 4 extended combinations. PHP have implemented 4 of them but all other combinations can be build with these 4 combinations.

2. AND combination

The AND combination is the easiest logical combination. The result of such a combination is true if and only if both values used for this operator are true. The language usage of and is the same like in You are permitted to play outside if you have done your homework AND have cleaned up your room. In PHP this combination can be used with the and operator.

<?php
$var = false and false;  // results false
$var = false and true;   // results false
$var = true  and false;  // results false
$var = true  and true;   // results true
$playing = $homework_done and $room_cleaned_up;
?>

The following truth table shows the result of the AND combination.

In digital eletronics there are special diagramms for these combinations. The AND combination is drawn as followed.

Img.:AND combination as electronic symbol

As you see the & character this must be an and combination. Left are the inputs A and B and right the output Q.

3. OR combination

A OR combination is the second combination which is implemented in PHP with the keyword or. The natural language usage isn't exactly the same as in a programming language. A pedestrian light is showing green if you press the one or the other button. But this sounds like the pedestrian light is only switching if only one button is pressed. Thats not true as the pedestrian light switchs also if both button are pressed at the same time. And that is how the OR combination is working. It returns true if one value or both value is true.

<?php
$var = false or false; // results false
$var = false or true;  // results true
$var = true  or false; // results true
$var = true  or true;  // results true

$show_green = $button1 or $button2;
?>

The truth table looks like this.

In digital eletronics the following graphic symbol is used.

Img.:OR combination as graphic symbol

If you add the values of the inputs together you see why the graphic symbol shows >=1.

4. NOT operator

The NOT operator is an operator which got only one input. In PHP this its implemented with the ! operator. The value to check must be written after this operator. The result of this operator is the negate of the given value. If you have a coin and it falls on heads it is not on tails.

<?php
$is_heads = !$is_tails;
?>

You have already saw this ! in the compare operators != and !==. So you can write these compare operators as followed.

<?php
$var = $x != $y;    // with !=
$var = !($x == $y); // with !(==) (parentheses are needed, otherwise only the $x variable gets negated).
?>

The truth table is a little bit shorter as you have only 1 input. Die Wahrheitstabelle fällt entsprechend kürzer aus.

In digital eletronics the following graphic symbol is used.

Img.:NOT operation as a graphic symbol

The important part is not the 1 but the little circle at the output line. This is the mentioned negation, in this case at the output of the graphic symbol. This circle can also used at the input line, too.

5. NAND combination

Besides the 3 basic combination the NAND is an extended combination. Its a combination build with and AND and a NOT. There doesn't exists such an operator in php but can be build with other operators.

<?php
$check = !($var1 and $var);    // AND -> NOT = NAND
$check = !$var1 and $var;      // its not an NAND as only $var1 gets negated
?>

In digital eletronics the following graphic symbol is used.

Img.:NAND combination as graphic symbol

You can see how the AND and NOT operator is build together to get a NAND combination.

6. NOR combination

The NOR combination is the next extended combination. Its like NAND but with OR instead of AND. As PHP dont have such an operator build in you must build it the same as for NAND.

<?php
$check = !($var1 or $var);    // OR -> NOT = NOR
$check = !$var1 or $var;      // not an NOR as it only negates $var1
?>

And in digital eletronics its the same as with NAND.

Img.:NOR operation as graphic symbol

The truth table looks as followed.

7. XOR combination

The third extended operation is the XOR combination. It works like OR but exactly one value must be true to get true.

<?php
$check = ($var1 and !$var2) or (!$var1 and $var2);
?>

As noone wants to write such a combination with the 3 basic combination PHP implements this combination with the xor operator. The x stands for exclusive.

<?php
$check = false xor false;  // false
$check = true  xor false;  // true
$check = false xor true;   // true
$check = true  xor true;   // false

$sex_valid = $is_male xor $is_female;
?>

In digital eletronics the following graphic symbol is used.

Img.:XOR operation as graphic symbol

The =1 shows that the sum of the inputs must be exactly 1 to get the result true.

8. XNOR combination

The XNOR operation is easy. Its just the negation of XOR.

<?php
$check = !(false xor false); // true
$check = !(false xor  true); // false
$check = !(true  xor false); // false
$check = !(true  xor true ); // true
?>

The graphic symbol looks as followed.

Img.:XNOR-Verknüpfung als Schaltzeichen

9. Rules for simplify a condition

In digital eletronics there are several rules to simplify a condition/combination. These can be also applied in php scripts.

<?php
$check = true  and $var; /* is the same as: */ $check = $var;  // the true is useless
$check = false and $var; /* is the same as: */ $check = false; // it is always false
$check = true  or  $var; /* is the same as: */ $check = true;  // it is always true
$check = false or  $var; /* is the same as: */ $check = $var;  // the false is useless
?>

And there is something like double negation

<?php
$check = !(!$check); // like 'minus times minus'
?>

Much important are the De Morgan's law. In some circumstances you can convert an AND into an OR and the other way round.

<?php
$check = !$var1 and !$var2;
$check = !($var1 or $var2); // the same

$check = !($var1 and $var2);
$check = !$var1 or !$var2;  // the same
?>

You exclude the negation and switch the combination. This can be used to increase the readability of your php scripts.

<?php
$skip = !(('.' != $var) and ('..' != $var));   // what do I check? both values shouldn't be two values? I dont get it...
$skip = !(!(('.' == $var) or ('..' == $var))); // resolve double negation
$skip = ('.' == $var) or ('..' == $var);       // okay, now I get it
?>

1. Switch statements

A switch statement is a special control structure. Instead of checking any condition or expression like an if statement a switch statement can only be used to compare a expression agains a list of other expressions. It uses internally the compare operator ==.

Such a switch statement can be create with the keyword switch. It is followed by an expression written in parentheses, typically a variable. After that the body of the switch statement is followed, which starts and ends with curly brackets ({ and }).

<?php
switch ($var) {
}
?>

Inside of the switch body you can add case lines. The php interpreter jumps to this line if the expression has the same value as the value behind the case keyword. After the case expression there must be placed a colon :.

<?php
switch ($var) {
case 5:   // jump here if 5 == $var
case "b": // jump here if "b" == $var
}
?>

This is like a goto command, however such a command dont exists in php. If php jumps to a case block he executes the php code standing there. If he find any other case lines php ignores them. This also means the block doesn't stop at the next case.

<?php
$var = 4;
switch ($var) {
case 0:
    echo "I am not executed";
case 4:
    echo "I get executed";
case 90:
    echo "But I get executed, too";
}
?>

If you dont want this add a break statement. This will quit the case part and jumps to the end of the switch statement.

<?php
$var = 4;
switch ($var) {
case 0:
    echo "I am not executed";
    break;
case 4:
    echo "I get executed";
    break;
case 90:
    break; // useless as you are already at the end
}
?>

If there is no matching case php jumps to the default: line, if there is one.

<?php
switch ($formaction) {
case 'delete':
    echo "Something gets deleted";
    break;
case 'save':
    echo "Something gets saved";
    break;
default:
    echo "Show something or do something if no case is matched";
    break;
case 'reload': // can be found and is NOT catched by the default line 
    echo "Something gets reloaded";
    break;
}
?>

It is possible to add a default: line everywhere but such a block should be only placed as the last of all case blocks. This will increased the readability of your scripts. First an expression is checked again every case line and if no case line is found the default: line is loaded. Its like an else part of an if statement.

1. Assignment operator

There are some assignment operators in php which changes the content of a variable depending of its current content.

<?php
$var = 5;

$var = $var + 10;

$var += 10;
?>

The second adds the value of the variable and a constant value together and saves it in the variable. The third statements instead adds the value right on the current value of the variable and saves it. You must not place any whitespaces between + and = as this is a predefined operator.

<?php
$var = 5;

$var += 10;  // correct
$var + = 10; // wrong, results in an parse error
?>

This abbreviation can be used for every number calculation operators, even with / and %. However you shouldn't divide by 0 (of course).

<?php
$var = 20;

$var +=4; // $var == 24
$var *=4; // $var == 96
$var -=4; // $var == 92
$var /=4; // $var == 23
$var %=4; // $var == 3  (23/4 = 5, remaining 3)

?>

This abbreviation can also be used for the concat operator . to append very fast new text to a variable.

<?php
$x = 5;

$string  = "Hi \n";
$string .= "You can add new text easily.\n";
$string .= 'test';
$string .= 'The variable have the value '.$x."\n";
?>

In the last line the expression on the right gets calculated first and then is appended to the variable.

2. In-/decrement

Often you want to change a variable by increasing or decreasing the value by 1. For this reason there are increment and decrement operators in php, similar to C.

<?php
$name = 10;

$name++;    // increase by 1

echo $name; // outputs 11
?>

Thats for increment, for decrement use the -- operator.

<?php
$name = 10;

$name--;    // decrease by 1

echo $name; // outputs 9
?>

There aren't such operators for multiplication of division, these wouldn't make any sense. These increment and decrement operators are often used for for loops.

1. Meaning of loops

Loops are for executing some part of code more than once. The body of the loops get executed with some different content of variables. Additional the number of iterations are controlled by an expression/condition. If the expression results to false the loop is stopped and the following php code gets execute. As an example news entries are read from a database. Such a loop prints a single news (with title, date, content,...). If there aren't any news left the loop quits and the following php code gets execute.

There are 4 types of loops, however we discuss only 3 of them. The forth type is explained in the chapter Arrays as that is a special loop for arrays. The other loops are while, do-while and for.

2. While loop

The while loop is the easiest loop type. It got a loop header with only one expression. This expression get evaluated before the next iteration and checked agains boolean. If the expression results true the loop body gets executed once. Then the next check of the expression takes place. If the expression results in false the loop is quitted and the following php code gets executed. As the expression is checked on every iteration the value must be get false at some point. If not you get an endless loop and the scripts is terminated by the webserver as the scripts runs for too long, as it cannot left the loop (default is 30 seconds).

A while loop is created with the keyword while. Then the expression to checked is followed in parentheses (()). After that a single statement or a block of statements with curly brackets is followed. As for one statements the curly brackets are not needed you should use always use curly brackets for readability.

<?php
while (CarIsDirty()) {
    CleanTheCar();
}
?>

There is no restriction how the expression is build (with and's, or's, function calls...), however it must return a value to check.

3. Do-while loop

A do-while loop got an expression to check like the while loop. However the expression is at the end of the loop body and gets checked at this location. As the loop body is before the loop header the loop gets executed at least one time, even if the expression shows false. Thats the different to a while loop. If you need a loop which must be iterated at least one time use a do-while loop. If you need a loop which can be iterated zero times use a while loop.

A do-while loop is created with the keyword do. After that the loop body is added (again it should be always written with curly brackets). After the loop body exists the while keyword, the expression to check (in parentheses) and it MUST followed by a semicolon. At a while loop the semicolon is not followed (as wrong as in if ();) but it MUST be written if you have a do-while loop.

<?php
do {
    connect();
    $data = getSomeData();
    disconnect();
} while ($data > 40);
?>

4. For loop

A for loop is like a while loop with an expression to check. However it got 2 additional statements. The first one is an statement which is executed once (automatically), the second one one is executed after each iteration.

A for loop is created with the for keyword. It is followed by 3 expressions, each of them seperated by a ;. The whole list is written in parentheses. After the loop header there is the normal loop body with statements.

<?php
for (start_statement; condition; iteration_statement) {
    // statements
}
?>

At the beginning the start_statement part get executed (once). Then the condition is checked like in a while loop. After one iteration before the condition is checked again the iteration_statement part is executed.

<?php
// outputs the number from 0 to 9 (for 10 the condition is false)
for ($i=0; $i<10; $i++) {
    echo $i."\n";
}
?>

5. When while and when for loops?

As the while loop and the for loop are very similar there may be the question when to use a while and when to use a for loop. It's even possible to convert a while loop into a for loop and the other way round.

<?php
while (condition) {
   statements;
}
// convert to for:
for (;condition;) {
   statements;
}
?>

<?php
for (start; cond; iter) {
    statements;
}
// convert to while:
start;
while (cond) {
    statements;
    iter;
}
?>

The number of iterations is not the reason to decide if you use a while or a for loop. However you use a for loop if you know the number of iterations. If you know it you can create at counting loop, which iterate from a value to an other value.

<?php
for ($i=0; $i<10; $i++) {
    // do something with $i ($i iterates from 0 to 9)
}
?>

You use a while loop if you don't know the number of iterations (even if you can calculate the iterations somehow in your script). As an example you can read the rows out of a database, but don't know how many there are (and you actually don't care).

<?php
while (ThereAreSomeRowsLeft()) {
    OutputTheNextRow();
}
?>

You can also read a files content which a while loop, although you can get the file size with filesize.

<?php
while (!FileEnds()) {
    ReadOneByte();
}
?>

6. Continue and Break

The flow of a loop can also changed with other statements. You can use return to quits a loop. However, return can be use almost everywhere and has nothing to do with loops. But there exists two statements specially for loops, continue and break.

• break - quits the current iteration and quits the loop itself. It is like the condition to check evaluates to false (which is maybe not the case).

  <?php
  while (...) {
  
  
      break; // --->
             //     |
             //     V
  }          // <---
  ?>
  

• continue - quits the current iteration and jumps to the end of the loop body, but is still inside the loop. For for loops the iteration statement gets executed (for the next iteration) and for do-while loops the condition expression get checked.

  <?php
  // this is not an endless loop like expected
  do {          //   < - - -
                //          | This way isn't used
                //          |
      continue; // --->  - -
                //     |
                //     V  Thats the way of continue;
                // <---
  } while(false);
  ?>
  

An if statement cannot be controlled this way as an if statement is not a loop. Programm code like if (...) { ..... break; .....} only works if this if statement is inside a loop and this break; actually controls the loop.

Both statements can be used with a number which indicates how many loops should be stopped/continued. The current loop is always the number 1 and is increased as much as you nested a loop inside an other loop. The statement break 1; is the same as break; (without a number).

<?php
$found = false;
for ($x=0; $x<100; $x++) {
    for ($y=0; $y<100; $y++) {
        for ($z=0; $z<100; $z++) {
            if (PixelColor($x, $y, $z) == 0xFFCCFF) {
                $found = true;
                break 3;
            }
        }
    }
}
?>

These nested loops get executed 100*100*100 times, that are 1 million iterations. If the execution of PixelColor(int, int, int) needs only 10 µs this code will run for 10 seconds. With break 3; we quit all 3 loops if we found the pixel we are looking for. However, if the pixel is not found we run 1 million iterations anyway.

1. Layout of arrays

Arrays are very important to php. Form data and URL variables are saved in arrays. Values from a database are saved in arrays. Everything what is something like a mathematic function can be build with arrays. Per defintion an array is an ordered list (does not mean they are sorted) of pairs which each pair got a key and a value. These keys must be only integer numbers or strings. However the values can be everything, even arrays. A single array value can be use like a variable.

2. Usage of arrays

Arrays can be created with the language construct array. The values of the array are given as parameters.

<?php
$arr = array("foo", "bar", "bla", 5.6, false, -10, "foo", "foo", "bar", "foo");
?>

This array got 10 values. The keys, sometime called indexes, are generated automatically, starting by 0 ascending. The first value gets the index 0 and the last one gets the index 9. This can be checked with var_dump.

array(10) {
  [0]=>
  string(3) "foo"
  [1]=>
  string(3) "bar"
  [2]=>
  string(3) "bla"
  [3]=>
  float(5.6)
  [4]=>
  bool(false)
  [5]=>
  int(-10)
  [6]=>
  string(3) "foo"
  [7]=>
  string(3) "foo"
  [8]=>
  string(3) "bar"
  [9]=>
  string(3) "foo"
}

To get such a field use the array and brackets for the index.

<?php
$arr = array("foo", "bar", "bla", 5.6, false, -10, "foo", "foo", "bar", "foo");
echo $arr[0]; // outputs foo
echo $arr[3]; // outputs 5.6
echo $arr[4]; // outputs nothing as the string representation of bool(false) is an empty string
var_dump($arr[4]); // outputs bool(false);
?>

As you see its possible to have same values in the array as they got different keys. So there are 4 array entries with the value foo at the indexes 0, 6, 7 and 9.

The value can be changed as you want if you replace the value with all the operators you know.

<?php
$arr = array("one", "two");
$arr[1] = "five";
?>

If there is already an array entry with the given index the old value will be overwritten. If there isn't such an array entry with the given index a new array entry is created with the given key and value. So its possible to create an empty array and fills it with keys and values later on.

<?php
$arr = array();
$arr[3] = "value";
$arr[9] = "another value";
var_dump($arr);
?>

The var_dump creates the following output.

array(2) {
  [3]=>
  string(4) "value"
  [9]=>
  string(13) "another value"
}

As you see we got an array of the size of 2 entries, with the indexes 3 and 9 and the values value and another value. As mentioned the array is not sorted but there are a lot of sorting functions to do so.

Instead of numbers you can use strings as keys.

<?php
$user = array();
$user['name'] = 'John Doe';
$user['age'] = 18;
$user['home'] = 'Somewhere';

echo 'My name is '.$user['name'].', I am '.$user['age'].' old and living in '.$user['home'].".\n";

var_dump($user);
?>

Die Ausgabe ist dabei wie folgt:

My name is John Doe, I am 18 old and living in Somewhere.
array(3) {
  ["name"]=>
  string(8) "John Doe"
  ["age"]=>
  int(18)
  ["home"]=>
  string(9) "Somewhere"
}

Arrays which use strings as indexes are called associative arrays. All other kind of arrays are called just arrays or nummeric arrays.

If you assign a value to an array entry without an index given (as in $arr[]) the key is automatically generated as the biggest index number +1, but at least the value 0.

<?php
$foo = array();
$foo[] = "value";   // Index 0 is used
$foo[] = "value";   // Index 1 is used, biggest index was 0
$foo[10] = "value"; // Index 10 is used as given
$foo[] = "value";   // Index 11 is used, biggest index was 10
var_dump($foo);

$foo = array();
$foo[-5] = "value"; // Index -5 is used as given
$foo[] = "value";   // Index 0 is used, biggest index was -5 but at least 0 is used
var_dump($foo);
?>

The following output is generated.

array(4) {
  [0]=>
  string(5) "value"
  [1]=>
  string(5) "value"
  [10]=>
  string(5) "value"
  [11]=>
  string(5) "value"
}
array(2) {
  [-5]=>
  string(5) "value"
  [0]=>
  string(5) "value"
}

The indexes can also be assigned during the array construct. Instead of writing the value you can pretend the value with x => where x is the index for the value.

<?php
$bar = array(5 => "bar", "foo");
// 2. value gets the index 6

$var = array(-10 => "abc", "xyz");
// 2. value gets the index 0

$var = array("name" => "John Doe", "foobar");
// 2. value gets the index 0
?>

To delete an array entry use the funktion unset.

<?php
$arr = array();
$arr[] = "foo";
$arr[] = "bar";
$arr[] = "xyz";

unset ($arr[1]); // the entry "bar"

var_dump($arr);
?>

The output shows the entry with the index 1 is deleted, however the indexes 0 and 2 still exists.

array(2) {
  [0]=>
  string(3) "foo"
  [2]=>
  string(3) "xyz"
}

You can even use the compare operators == and ===, and the + operator. To arrays are the same (==) if they match in the same array entries and are identically (===) if they got the array entries in the same order and of the same type.

<?php
var_dump(array("x", "y") == array(1 => "y", 0 => "x"));  // bool(true)
var_dump(array("x", "y") === array(1 => "y", 0 => "x")); // bool(false)
?>

You can merge array together with the + operator. Indexes which are already used are not overwritten. If you really want to merge all values together use a function like array_merge.

<?php
var_dump(array("x") + array("y"));
// an array with just one value 'x' as both temporary arrays use the same key 0

var_dump(array_merge(array("x"), array("y")));
// an array with both values 'x' and 'y'
?>

3. Foreach loop

For arrays there exists a special loop called foreach. You can use it to iterate over all array entries. A foreach loop starts with the keyword foreach. Then a opening parenthese is followed with the array or variable to iterate on. After that the keyword as is followed with a new variable. After you use the closing parenthese the loop body followes.

<?php
$a = array("foo", "bar", "bla");
foreach ($a as $value) {
    echo $value."\n";
}
// outputs the value of the array
?>

If you need also the keys for each iteration pretend before your new variable the code $var =>.

<?php
$user = array('name' => "John Doe",
              'age' => 18,
              'home' => 'Somewhere',
              10 => 100);
foreach ($user as $k => $v) {
    echo "Array value with the index '".$k."' got the contents: ".$v."\n";
}
?>

The indexes are used if you want to change the array inside the loop. The loop variables ($k and $v in the last example) are only copies of the origin array values. If you want to change a value in the array use the normal array[index] syntax.

1. So far so good

Now you have all basics of php learned. Sure, there are a lot of more to learn like OOP or references, not to mentioned about extensions like mysqli. However, this is a good point to check the stuff you learned in the chapters before. For this reason there are some questions you should answered before proceeding to the next chapters.

1. The php manual

On the official homepage of php you get besides the source code and downloads of php also the manual of php. It contains some basic information about php like installation and security but also a list of all functions which exists in php. These functions are grouped together in groups like String or MySQL.

2. Finding a function description

There are a lot of function descriptions in the manual, however you must find the right one for you. First you should check the whole function reference, specially in the function groups. A function which should sort an array would be found in the group Arrays, a function to change a text in a string would be found in the group Strings. In such a group there is a list of all functions which belongs to it. Each function got a short description what they do. As an example you will find inside the group Arrays the function sort with the short description Sort an array. A click on this function gets you the description.

The easiest way for beginners (and the most annoying way for any helpers or forum moderators) is to simply ask in a forum or chat.

<user> I have a problem, I have an array in php but the values aren't sorted in any way.
       How can I sort the array?
<helper> sort
<helper2> with usort
<helper3> do you know www.php.net?
<helber4> try it with sort()
You have ben kicked from #helpchannel by operator3 (sort(), and next time check the manual at www.php.net/manual)

In most cases its just a function name. There are several ways to get the function description out of the manual.

1. On the homepage there is a link documentation in the upper manual which gets you to the manual. As the manual is translated into several language you should alyways use the english version, as this is the most up to date version. Inside the english version is a chapter called Function Reference. As the function may be a function for array the function may be in the Arrays" section. At the bottom of this there is a sorted list of functions in this group. There you find the function sort with the description Sort an array. Click on it and you get to the detailed description.

2. On the homepage is an input field in the top right corner which allowes you to search on the homepage. It searchs in the function reference by default but can also be changed to search in the bug database or on the whole site. You can enter the function name inside the search and get the function description or a search result list with functions which sounds similar to the entered one.

3. The simpliest way is to open the url http://www.php.net/FUNCTIONNAME where FUNCTIONNAME is the function to search for. This call automatically starts the search and redirects you to the function description.

3. How to read a function description

As you may want to read the function description in your native language you should however read it in english to get the most up to date version of the description. This can be done by selecting English in the drop down list in the top of the page.

After the name of the function there is an expression which shows in which php version this function exists and a short description of the function.

Now the detailed function description is followed. It starts with the function signature. It contains the return value, name of the function and the parameter list. The return value shows what kind of data the function is returning. The value void means no value is returned. The parameter list shows which parameter can be used. Every parameter got the syntax type $name or type &$name. The type shows which type the parameter should be. There are some special types which doesn't exists in php like number for a float or int number. A list of all pseudo types can be found at Pseudo-types and variables used in this documenation. After the type there is the name of the parameter. This name is also used in the function description itself. If there is a & the parameter is used as a reference. If this is the case the parameter must be a variable (and cannot be a static value) and the function changes the content of the variable. Without the & just a copy of the parameter is send to the function. If a parameter is written in brackets the parameter is optional.

After the function signature there is the description about the function and its parameters. It use the same parameter names as in the parameter list above. These parameters are written in a monospace italic font. The detailed function description also contains some examples how to use the function and a detailed list of all parameters and how they work.

The return value is explained in a seperate section. For a return value of void this section is omitted, for a return value of mixed there is a lot of text which descripe which type is when returned by this function.

There is also a changelog which explaines which parameters are implemented since which php version and how a function worked before or after a given php version.

The most functions got cross references to other similar functions. Maybe you read a function description which is not exactly what you want but may find the right function in the cross reference.

At the end there are user comments for each function. These explain some hints how to use the function and provides you with a lot of examples and experiances.

4. Function description for sort()

As an example we explain the function description for sort. This function exists in the php versions php4 and php5 and according to the short description this function is used to sort an array.

The function signature explaines this function returns a boolean value, the first parameter must be an array and the second parameter must be an integer value, if given. Independent how the function works all following programm lines are possible.

<?php
$a = array(4, 6, 10, -4);
$ret = sort($a);
$ret = sort($a, 4);
$ret = sort($a, 0);
sort($a, -400);
sort($a, 9*30-5);
sort($a, $a[0]); // possible as $a[0] got the value int(4)
?>

The function description got a text which explaines what the function do. In this case it sorts the array ascending. Further it says it returns true if the array is sorted or false if there was an error.

Since the second parameter can be any integer value only some of them makes sense. The description explaines that you should use the values SORT_REGULAR, SORT_NUMERIC, SORT_STRING or SORT_LOCALE_STRING to get the given behavior of the function. It looks like these values are strings and the function should be called with sort($a, "SORT_NUMERIC");, but thats not true. First, the second parameter must be an integer, not a string. Second, parameters or values written in uppercase are normally constants in php. If you check the group Arrays again you see a list of predefined constants which got the mentioned constants above. So you can use this constants for your function call.

<?php
sort($a, SORT_STRING);
sort($a, SORT_NUMERIC);
?>

As cross references a list of other sort function is shown and after that the user comments finishes the function description.

1. Indent

To increase the readability of your php code you should indent your code in a proper way. As an example we got the following php code.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
function todo($str) {
for($i=0;$i<strlen($str);$i++) {
if("z" == $str[$i]) {
$str[$i]="1";
}else{
if("a" == $str[$i]) {
$str[$i]="2";
}else{
switch($str[$i])
case "b":case "c":
$str[$i]=1;
break;
case "c":
$str[$i]=0;
}
}
}
}
class Foobar {
private $bar;
public function __construct($a) {
$this->bar = $a;
}
public function replace_something() {
foreach($a as $value) {
if(is_string($value)) {
$value=todo($value);
}
}
}
}
$obj = new Foobar(array("x","z"));
$obj->replace_something();
?>

It doesn't matter what this code is doing. As you see this code isn't indented in any way. You can't easily follow which block begins and which blocks end. But this is necessary to understand any php script and fixing errors. So this chapter deals about how to indent your code.

It doesn't matter how you indent your code but it should be done. Here we use the PEAR Coding Standard. All rules there use the indent of 4 spaces and dont use any tabs. This must be changed maybe in your editor. Of course there are a lot of more indent systems, check http://en.wikipedia.org/wiki/Indent_style.

2. Indent of statements and function calls

At function calls the parameters are seperated with a single space (and the comma of course). This way you can easily check how many parameters a function have. If the parameters are very long you can even write them vertically.

<?php
$str = str_replace('Foobar', 'FOOBAR', $str); // spaces between parameters
$str = name_xyz('A really long parameter',
                'another parameter',
                false,
                array(1, 2, 4),
                "foobar"); // function call with 5 parameters, the fourth one is an array
?>

You can add spaces if they increase the readability.

<?php
$var     = "Text"; // <-- some spaces before the =
$longvar = "Text";
?>

3. If statements

At an if statement the body is indented by one level. The opening curly bracket is written after the if condition, seperated with a space. The closing curly brackets is written in a single line at the same level as the if statement. After the if keyword a space is added.

<?php
if (condition) {
    // statements
    foobar();
    barbli();
    xyz();
    $var = "x";
}
?>

If the if statement got an else or even an else if it is written after the closing curly bracket, again seperated with a space.

<?php
if (condition) {
    do_this();
} else if (condition2) {
    do_that();
} else {
    or_this();
}
?>

4. Loops

Loop bodys are indent by one level as for if statements. The opening curly bracket is written after the loop header, seperated with a space. The closing curly bracket is written in a single line on the same indent level as the loop keyword.

<?php
while (condition) {
    work();
}
?>

At for loops the different parts are seperated with spaces.

<?php
for ($i=0; $i<10; $i++) {
    work();
}
?>

Same style is used for do-while and foreach loops.

<?php
do {
    work();
} while (condition);

foreach ($array as $value) {
    work($value);
}
?>

5. Funktion definitions

Each function definition should always have a PHPDoc comment. This way every developer can read what the function is doing. The parameters are seperated with a space. The opening curly bracket is written after the parameter list (again seperated with a space). The closing curly bracket is written on a single line at the same indent level as the function keyword. The function body is indented by one level.

<?php
/**
 * PHPDoc for the funciton foobar
 */
function foobar($bar, $bla) {
    work($bar);
    work($bla);
}
?>

6. Indent of classes

Classes are indented in the same way. Each field and methods are seperated additionaly with an empty line. As for functions the classes should also have PHPDoc comments for each part of the class.

<?php
/**
 * PHPDoc about Foobar
 */
class Foobar {
    /**
     * PHPDoc about $xyz
     */
    private $xyz;

    /**
     * PHPDoc about XYZ()
     */
    public function XYZ() {
        work();
    }
}
?>

7. Indent a switch

Switch statements using the same style, however the case statements are written in the same indent level as the switch keyword.

<?php
switch ($var) {
case 'z':
    work();
    break;
case 'y':
    work();
default:
    work();
}
?>

8. Indent of the example above

We indent the example now. Here is the same example from above.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
function todo($str) {
for($i=0;$i<strlen($str);$i++) {
if("z" == $str[$i]) {
$str[$i]="1";
}else{
if("a" == $str[$i]) {
$str[$i]="2";
}else{
switch($str[$i])
case "b":case "c":
$str[$i]=1;
break;
case "c":
$str[$i]=0;
}
}
}
}
class Foobar {
private $bar;
public function __construct($a) {
$this->bar = $a;
}
public function replace_something() {
foreach($a as $value) {
if(is_string($value)) {
$value=todo($value);
}
}
}
}
$obj = new Foobar(array("x","z"));
$obj->replace_something();
?>

And now with proper indention.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

/**
 * PHPDoc about Todo
 */
function todo($str) {
    for($i=0; $i<strlen($str); $i++) {
        if ("z" == $str[$i]) {
            $str[$i]="1";
        } else {                      // maybe replace with an else-if to save
            if ("a" == $str[$i]) {    // one indent level
                $str[$i]="2";
            } else {
                switch ($str[$i]) {
                case "b":
                case "c":
                    $str[$i]=1;
                    break;
                case "c":
                    $str[$i]=0;
                }
            }
        }
    }
}

/**
 * PHPDoc about Foobar
 */
class Foobar {
    /**
     * PHPDoc about $bar
     */
    private $bar;

    /**
     * PHPDoc about the constructor
     */
    public function __construct($a) {
        $this->bar = $a;
    }

    /**
     * PHPDoc about replace_something()
     */
    public function replace_something() {
        foreach ($a as $value) {
            if (is_string($value)) {
                $value = todo($value);
            }
        }
    }
}

$obj = new Foobar(array("x","z"));
$obj->replace_something();
?>

1. Constants

Constants are values like variables but cannot be changed afterwards. Additional they cannot be used for every type as for variables. They can only use scalar values and the special value NULL. In difference to variables constants can be accessed everywhere in your php scripts, even inside functions. Constants are often used for settings and parameters like error_reporting.

2. Defining and usage of constants

You can define a constant with the function define. The first parameter is the name, the second parameter is the value of the constant.

<?php
define('SITE_NAME', 'My cool homepage');
?>

Constants uses the same name convention like variables (explude the dollar character $ of course). However constants are typically written in uppercase.

To access a constant simply use its name.

<?php
echo SITE_NAME;
// or like:
echo 'Welcome on '.SITE_NAME.'!';
// but not:
echo 'Welcomeon SITE_NAME!'; // won't find it as a constant, its a simple string 
?>

3. Usage of constants

Constants are used for predefined functions as parameters which may be only integers or as return values which may be only integers. These contants are predefined as got useable names. As an example the function getimagesize returns some information about an image. The type of the image (png, jpeg, gif, ...) is encoded as an integer. The value 1 is for gif and the value 4 is for png. To check agains the type you could write the following code.

<?php
if (1 == $imagetype) {
} else if (4 == $imagetype) {
}
?>

Instead of looking in the manual all the time what 1 and 4 means you should use the predefined constants instead.

<?php
if (IMAGETYPE_GIF == $imagetype) {
} else if (IMAGETYPE_PNG == $imagetype) {
}
?>

Everyone understand what these if statements are checking. This is also used for parameters. As an example the function error_reporting expect an integer. This integer encodes by the bits it is used which errors are shown and which not. A valid function call would be the following:

<?php
error_reporting(8191);
?>

However noone will knows what this value means. In this case you should use the E_* instead.

<?php
error_reporting(E_ALL | E_STRICT);
?>

Besides that the values of the constants can be changed for different php versions. The value of E_ALL is in php version 5.2.x 6143, but before this version it was 2047. If you use the value 2047 instead of the constants the same script may be run differently on an other php version. If you use the constants instead it runs the same all the time as the current php version knows the right value for E_ALL and use the proper integer value for this function.

1. Errors in your php script

Nobody is perfect, so you will get errors in your php script. For any developer this means you must find and fix the error. There are a lot of techniques which may help like the functions var_dump and debug_print_backtrace, even debugger support.

2. Showing the error messages

To fix an error the error must be find somehow. This can't be possible sometimes if the error messages aren't shown. Depending on the php installation and configuration only some kinds of error messages are shown. You can change the types to shown with the error_reporting function or the setting error_reporting in your php.ini file. To show all error messages set this value to E_ALL

<?php
error_reporting(E_ALL);
?>

There is a setting called display_errors which enables/disables error message at all. During developing this setting should be enabled, but during production this setting should be disabled for security reason. There isn't a predefined function for changing this setting so we must use the ini_set function instead.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
?>

As all error messages are shown we can fix them.

3. Syntax error

Syntax errors are the easiest errors to fix as they prevent from running the script at all. Before the php script is running the php interpreter transforms the php code into tokens.

<?php
/**
 * Start of the script
 */
$i = 10;
do {
    echo $i."\n";
    $i = floor($i/2);
} while ($i)
echo 'i is now '.$i;
?>

This php script is transformed in the following list of tokes. In php there is just a list but we use the same indent as the php code.

T_OPEN_TAG
T_DOC_COMMENT T_WHITESPACE
T_VARIABLE T_WHITESPACE = T_WHITESPACE T_LNUMBER ; T_WHITESPACE
T_DO T_WHITESPACE { T_WHITESPACE
    T_ECHO T_WHITESPACE T_VARIABLE . T_CONSTANT_ENCAPSED_STRING ; T_WHITESPACE
    T_VARIABLE T_WHITESPACE = T_WHITESPACE T_STRING ( T_VARIABLE / T_LNUMBER ) ; T_WHITESPACE
} T_WHITESPACE T_WHILE T_WHITESPACE ( T_VARIABLE ) T_WHITESPACE
T_ECHO T_WHITESPACE T_CONSTANT_ENCAPSED_STRING . T_VARIABLE ; T_WHITESPACE
T_CLOSE_TAG

For a better readability we delete all T_WHITESPACE tokens as they are ignored anyway. They come from all newlines and spaces inside your code.

T_OPEN_TAG
T_DOC_COMMENT
T_VARIABLE = T_LNUMBER ;
T_DO {
    T_ECHO T_VARIABLE . T_CONSTANT_ENCAPSED_STRING ;
    T_VARIABLE = T_STRING ( T_VARIABLE / T_LNUMBER ) ;
} T_WHILE ( T_VARIABLE )
T_ECHO T_CONSTANT_ENCAPSED_STRING . T_VARIABLE ; 
T_CLOSE_TAG

The php interpreter is calculating with this list of tokens. It checks if all tokes are at the correct location and if they fit together. The statement $i = 10; is translated into T_VARIABLE = T_LNUMBER ; (without any T_WHITESPACE tokens). PHP check if this is a valid statement, which is true for this example.

If we run our script we get the following error message.

Parse error: syntax error, unexpected T_ECHO, expecting ';' in FILENAME on line 10

The php interpreter don't like line 10, however it looks okay for us. The problem is at line 9 as the semicolon is missing after the do-while loop. The php interpreter read all tokens until that point and expect after the closing parenthese ) a semikolon (see expecting ';'). Now he finds first a T_WHITESPACE token (which is ignored anyway). But then it founds the T_ECHO token from echo. This is absolutly not expected (see unexpected T_ECHO) and stops which the execution of the script with a parse error. The list of expected tokens are truncated as they may be following more than one token. Listing all tokens wouldn't help at all. Programmers know how to code and they want to know whats wrong and not what may be right.

The line number mentioned only the line in which the error occurs, but may not the reason for the error. There are some places where you should search for the error.

• In most cases the error is one line above. Beginners often miss the semicolon. For the php interpreter the current statement isn't finished yet and he expect more code which normaly fails.

• In some cases the error is really in the given line number. You can write your whole php code in one line, but this will help noone...

• In rare cases the error is much more lines above. Sometimes you miss a string delimiter (' or ") and php reads the following php code as part of the string. He fails at this at the next beginning string delimiter (which is maybe a new string) or if he reaches the file end. Then you get an error message like Parse error: syntax error, unexpected $end in FILENAME on LASTLINE, although the last line is (the ?>) is not the reason for the error.

4. Understanding error messages

Beside syntax errors there can be of course normal errors like dividing by 0. The statement $x = $y / $a; is valid, however it can lead to an error message Warning: Division by Zero in FILE on LINE. All the error messages got the same layout. They begins with a classification of the error message. It can be a single notice but also a fatal error which stops the php script. However, all errors must be fixed. It doesn't help if you lower the error_reporting level, the error still exists.

After the classification the error message is followed. It descripe what happends or what didn't worked. These can only read with knowledge. An error Undefined index '0' is easy, but Warning: Cannot modify header information - headers already sent by (output started at FILE:LINE) in FILE on line LINE maybe not.

The mentioned filename shows where the error occured, but may be not the reason for the error (like a variable set in an other file). A common error is to fix the wrong file and watching how the error don't go away.

5. Finding semantic errors

If php shows an error message it is easy to find and fix them. But there are errors which cannot be find with php but still are errors. These semantic errors cannot be find by php as he is running the php code and don't think about it.

To check the flow of you php script you should use proper indent. If you indent your code you may resolve logical errors already. To check e.g. if an if statement is entered you should use echo or var_dump for debug lines.

<?php
echo 'before the if';
if (condition) {
    echo 'I am inside the if statement';
    do_this();
} else {
    echo 'I am inside the else';
    do_that();
}
echo 'after the if';
?>

If you get the output before the ifI am inside the ifstatementafter the if you first noticed you miss html newlines <br/> or php newlines with \n. But you also noticed the if statement is entered. If this isn't correct in your case you should check the condition, best with var_dump. You can check every variable with var_dump.

<?php
while ($i > $j) {
    var_dump($i, $j);
    do_this($i);
    do_that($j);
    $i += $j;
}
?>

This can also be used to output sql queries which are send to a database like MySQL.

<?php
var_dump($sql);
mysql_query($sql) or die(mysql_error());
?>

1. Putting php code in other files

If you start writing your php scripts they get longer and longer. If you write other php scripts which have the similar layout you get a new php script which gets longer and longer. It would make more sense if you can put this code somewhere else and just say load the code xyz. One way would be to put the code inside a function, but this must be written in the php script and the same function may be written and use in other php scripts, too. So its better to use include. This language construct is given a filenamen and the php script loads this file as php code.

2. Include

If you use the language construct include the following actions take place in background.

1. Leave the php modus (?>).

2. Load and execute the file.

3. Reenter php modus (<?php).

The execution is the same as the file contents is copy&pasted at the place where the include statement was.

<p>
    HTML Code in a file called <code>file.html</code>.
</p>

<?php
// content of a php file called index.php which is opened by an user

echo 'Before the include';

include 'file.html';

echo 'After the include';
?>

You will get the following html output.

Before the include<p>
    HTML Code in a file called <code>file.html</code>.
</p>
After the include

Now you see why include is leaving the php code. This way you can easily output html files. Internally it would looks like this.

<?php
// content of a php file called index.php which is opened by an user

echo 'Before the include';

?><p>
    HTML Code in a file called <code>file.html</code>.
</p>
<?php

echo 'After the include';
?>

That means if you want to load php files as php scripts you must still use <?php and ?> in your files.

<?php
// File: foobar.php
echo "A second line\n";
?>

<?php
// File: index.php, opened by an user
echo "First line\n";
include 'foobar.php';
echo "Third line\n";
?>

Generates the following output.

First line
A second line
Thrid line

PHP has done something like this.

<?php
// File: index.php, opened by an user
echo "First line\n";
?><?php
// File: foobar.php
echo "A second line\n";
?><?php
echo "Third line\n";
?>

If we delete this ?<>?php lines we see the complete php code we wants.

<?php
// File: index.php, opened by an user
echo "First line\n";
// File: foobar.php
echo "A second line\n";
echo "Third line\n";
?>

For this reason we also can use variables which are used in another file.

<?php
// File: config.php
$surname = 'John';
$lastname = 'Doe';
?>

<?php
// file: index.php, opened by the user
include 'config.php';

echo 'I am '.$surname.' '.$lastname.', welcome to my homepage';
?>

3. Include with directories

If you include a file inside a directory and this file also includes a file inside this directory php is looking at two positions for this file. The first position is relative to the file which wants to load the file. The second position is relative to the start script which is loaded in the browser. Here is an example how it works.

<?php
// index.php (opened by the user)
include 'inc/config.php';
echo 'My name is "'.$name.'"';
?>

<?php
// config.php (inside of the directory inc/)
include 'functions.php';
include 'variables.php';
echo "Config loaded\n";
?>

<?php
// functions.php (same directory as the file index.php)
function foobar() {
    // ...
}
echo "Functions loaded\n";
?>

<?php
// variables.php (inside of the directory inc/)
$name = 'John Doe';
echo "Variables loaded\n";
?>

The directory and files looks like followed.

index.php
functions.php
inc/config.php
inc/variables.php

If you open the index.php file you will get the following output.

Functions loaded
Variables loaded
Config loaded
My name is "John Doe"

It doesn't matter somehow where the files are which to load (in this case functions.php and inc/variables.php). Internally the following happends.

• At include 'functions.php'; the file functions.php is searched first in the directory where the config.php file is (in inc/). As it isn't found there it searches at the location of the start script. There is is the file and it gets loaded.

• At include 'variables.php'; the file is search first in the directory where the config.php file is (in inc/). There it finds the variable and loads it.

This can be a problem as there are two locations for searching a file (and even more with include_path). You can disable this if the path to the file starts with ./ or ../ (for the current and parent directory). If this is used the path is always relative to the start script and not relative to an other include anymore.

For developers this whole thing means that you you simply can use include without care about the paths where are other files are located or the current file is located. So you write just include 'variables.php'; instead of statements like include dirname(__FILE__).'/variables.php';.

4. Return value of include

Include files can use return like functions. This way you can use a include like a function and save the value in a variable.

<?php
// file.php
return "text";
?>

<?php
// index.php
$var = include 'file.php';
echo $var; // echoes 'text'
?>

The include returns the integer value 1 by default. This is a common error for beginners which try to load a php script with sth. like echo include 'news.php' and wonders where this stupid 1 at the end is coming from. So this hint: echo include '...'; doesn't make sense in most of the cases.

1. URL parameters

PHP scripts are run with inputs from the user. These inputs can be send to the scripts in 3 ways. One of them are the url parameters, also called GET variables. These are in the url and written after the path, seperated with a ?. Examples are http://www.example.com/file.php?section=news and http://www.example.com/dl.php?cat=5&id=3&view=false. An anchor (like #top in http://www.example.com/file.php#top) is not part of the GET variables and isn't send to the webserver at all.

2. Access the GET variables

All GET variables from the url are saved in the php array $_GET. This array is predefined and even exists if there aren't any GET variables. Additional this is a superglobal array which means it exists in all scopes and don't need to pass as parameters to functions. The name of a GET variable is the index/key of the array entry from $_GET. From the url http://www.example.com/file.php?section=news&site=show php creates the array entries 'section' => 'news' and 'site' => 'show'.

<?php
// opened with file.php?section=news
echo $_GET['section']; // outputs 'news'
?>

All values of GET variables are strings or arrays, even if they contain only digits. From ?var=false&ID=4 php creates the array entry with the string index var with the string value false (not bool(false)) and an array entry with the string index ID with the string 4 (not int(4)).

<?php
// if opend with file.php?var=false&ID=4
var_dump($_GET['var']); // outputs string(5) "false"
var_dump($_GET['ID']);  // outputs string(1) "4"
?>

If the name looks like an assignment to an array entry php evaluates it as this. From ?foo[4]=bar php creates the field $_GET['foo'][4] with the string bar. This is often used for forms, however all values are still arrays or strings.

3. Risks from external source

The $_GET array is only filled with values from the url. This also means if no value is added in the url no value with added to the $_GET array. This is something which must be checked inside your script. If you try to access an array field which doesn't exists you get an error message.

<?php
echo $_GET['not_defined'];
// Notice: Undefined index:  not_defined in FILE on line LINENUMBER
?>

To fix such an error you can of course change the error_reporting setting, but it is better to check if the index exists before reading from it. This can be done with the isset language construct.

<?php
if (isset($_GET['xyz'])) {
    echo "The GET variable 'xyz' exists and got the value '".$_GET['xyz']."'.";
} else {
    echo "There is no GET variable called 'xyz'.";
}
?>

Additional all variables are filled by the user, independent if the user clicked on a link or not. This means the content is not generated by the php script. This is a point of attack. For this reason you should never outputs a GET variable directly or treat them as right or valid. Whatever the user tries you should check the inputs first. If you expect a number like in ?show=news&newsid=5 you should always check the value first if it is really a number. For any inputs which get shown later should always be checked agains javascript code. This can be done with functions like htmlspecialchars.

1. 2 column layout

The sub sections of an internet page has often a similar layout. On the left there is a menu and in the center there is the content to show. This is realised with the include statement and a main file. Depending on a GET variable the main file selects the right php file to include.

The main file, often called index.php, is used to load the excluded html code with include or readfile or output its direct with echo

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

include 'header.html'; // doctype, <html> and the whole <head> tag
echo "    <body>\n";
include 'menu.html';

// load section

echo "    </body>\n";
echo "</html>\n";
?>

The header.html file contains everything about the html stuff and the menu.html shows the menu with all links to the sections.

2. Loading a section by a GET variable

As a GET variable should load the specific section we must think about how it is loaded. The first way to choose would be to use the GET variable directly at include.

<?php
if (isset($_GET['section'])) {
    include $_GET['section'];
} else {
    include 'news.php'; // loading the default part
}
?>

This way you can load the news with index.php?section=news.php or the guestbook with index.php?section=guestbook.php. But if you use this code this is the same as putting your login of your server on your homepage. A so called GET include allowes everyone to load every file. First you can load server files like index.php?section=/etc/passwd or index.php?section=/etc/apache2/ssl/server.key (if you got the proper rights). But be more dangerous it can load every php script. If someone opens index.php?section=http://www.example.com/evil_code.txt php loads the code from this url as php and executes it.

A better and more secure way is to restrict the files which can be loaded. There are several ways like restricting the directory or checking the file names. The best one is to use an array. The array use values for all valid filenames and string indexes to access them. This is called an Array include. This way you can specific with the GET variable which file to load.

<?php
$section = array();
$section['news'] = 'news.php';
$section['gb'] = 'guestbook.php';
$section['info'] = 'info.php';
?>

Depending on the GET variable we load the right file.

<?php
include $section[$_GET['section']];
?>

In this code we can get two index errors. First the user can open the url without a section variable. Second the user can try to load a section which doesn't exists. For both ways we use the isset statement before we include the file.

<?php
if (isset($_GET['section'], $section[$_GET['section']])) {
    include $section[$_GET['section']];
} else {
    include $section['news'];
}
?>

This can be used now in your index.php file.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

$section = array();
$section['news'] = 'news.php';
$section['gb'] = 'guestbook.php';
$section['info'] = 'info.php';

include 'header.html'; // doctype, <html> and the whole <head> tag
echo "    <body>\n";
include 'menu.html';

if (isset($_GET['section'], $section[$_GET['section']])) {
    include $section[$_GET['section']];
} else {
    include $section['news'];
}

echo "    </body>\n";
echo "</html>\n";
?>

A new section can easily added to the $section-Array.

1. What are forms?

Many internet pages provide areas which can be filled text or selections can be made. After that there is a button typically called Submit. These areas are called forms. These entered informations are send to a php script and this script use this values like adding a new user or news.

2. Forms in html documents

Forms are created with the <form> tag. The action attribute points to the url where the form is send to, in your case your php script. This script is opened with the entered data so the browser redirects to the php script.

You can specific with the method attribute how the data are send to the php script. If this value is get the data are send over the url, like a simple request to index.php?section=news. The values are added to url. As this can result in a long url its more common for forms to use the value post. With this value the form data is send hidden inside the HTTP request. The data itself are readable (they are not encrypted somehow) but are not visible to the user. So the form is e.g. just send to http://www.example.com/login.php but the form date are transmitted hidden.

3. Proceed in php

To access the form data in php you must give the form fields in your html code a name with the name attribute. Inside your php script the form data are saved in the superglobal arrays $_GET or $_POST, depending on which method is used. The index of the array field is the same as the name in the form field, the value is filled from the given form field.

The name of the form field can also be an array field. If the attribute name="foobar[5]" is used php will create a corresponding array field $_POST['foobar'][5]. If the index is omitted (name="foobar[]") an array field is created like $array[] = 'value';. This is used for checkboxes which will be stored in one array.

4. Text input fields

For one line input field you can use the html tag <input>. For simple text inputs use the attribute type="text", for passwords use type="password". Note that passwords are send not encrypted, the form field just shows * instead of the actually password. If you want multi line input fields use <textarea> instead.

<form action="script.php" method="post">
    <fieldset>
        <legend>Enter login</legend>
        <label>Username: <input type="text" name="Username" /></label>
        <label>Password: <input type="password" name="Pass" /></label>
        <input type="submit" name="formaction" value="Login" />
    </fieldset>
</form>

If you send this form php will get the folloing array fields.

<?php
$_POST['Username'] = /* input from the Username field */;
$_POST['Pass'] = /* input from the Pass field */;
$_POST['formaction'] = 'Login'; // set with the value="" attribute
?>

5. Drop-down lists

Drop-down lists are created with the <select> and <option> tags. You should add [] after the name of the drop-down list if you want to use the attribute multiple="multiple". This way all selected entries are saved in an array.

<form action="script.php" method="post">
    <fieldset>
        <legend>Form for Foobar</legend>
        <label>Name: <select name="Username">
            <option value="1">Blabli</option>
            <option value="4">Testuser</option>
        </select></label>
        <label>Rechte: <select name="Rights[]" multiple="multiple" size="5">
            <option value="1">News</option>
            <option value="2">Forum</option>
            <option value="3">Guestbook</option>
        </select></label>
        <input type="submit" name="formaction" value="Send" />
    </fieldset>
</form>

If you select the user Blabli and select the rights News and Guestbook the following array fields will be created.

<?php
$_POST['Username'] = "1";
$_POST['Rights'][] = "1";
$_POST['Rights'][] = "3";
$_POST['formaction'] = "Send";
?>

6. Radio and check boxes

For radio and check boxes you can use the <input> tag. Depends on what you want you must use type="radio" or type="checkbox". The checkboxes or radiobuttons which belongs together must habe the same name. For checkboxes the name should end with [] to get an array of all selected checkboxes.

<form action="script.php" method="post">
    <fieldset>
        <legend>Select pizza</legend>
        <fieldset>
            <legend>Size</legend>
            <label><input type="radio" name="Size" value="20" /> small</label>
            <label><input type="radio" name="Size" value="24" /> medium</label>
            <label><input type="radio" name="Size" value="30" /> big</label>
        </fieldset>
        <fieldset>
            <legend>Topping</legend>
            <label><input type="checkbox" name="Topping[]" value="salami" /> salami</label>
            <label><input type="checkbox" name="Topping[]" value="thunfish"> thunfish</label>
        </fieldset>
        <input type="submit" name="formaction" value="Order" />
    </fieldset>
</form>

If you order a medium pizza with salami and thunfish you will get the following array fields.

<?php
$_POST['Size'] = "24";
$_POST['Topping'][] = "salami";
$_POST['Topping'][] = "thunfish";
$_POST['formaction'] = "Order";
?>

If you dont specific a value for radio or check boxes the value will be on. If a check box is not selected its not send at all.

7. Trust noone

As like GET variables the form data is from external source. These can be filled with every value, even with javascript code. You must check the value inside your php script. Use the isset function to check if the form data exists.

<?php
if (!isset($_POST['name'], $_POST['password'])) {
    die ('Use only forms from the homepage.');
}
?>

The content can always be checked with string functions.

8. Magic Quotes

If you send text data from a form to a php script it can be possible that the data is changed automatically by your php script. The text A sample text with one ' and one " will be converted to A sample text with one \' and one \". This is called Magic Quotes. It was implemented to help beginners which want to save these values inside a database.

But this may be get annoying, at least if you get outputs like A sample text with one \\\\\\' and one \\\\\\". So we delete this backslashes with stripslashes if magic quotes is activated on your server.

<?php
if (get_magic_quotes_gpc()) {
    $in = array(&$_GET, &$_POST, &$_COOKIE);
    while (list($k,$v) = each($in)) {
        foreach ($v as $key => $val) {
            if (!is_array($val)) {
                $in[$k][$key] = stripslashes($val);
                continue;
            }
            $in[] =& $in[$k][$key];
        }
    }
    unset($in);
}
?>

You dont need to understand this code from http://talks.php.net/show/php-best-practices/26, it deletes all backslashes from $_GET, $_POST and $_COOKIE which are added throught magic quotes.

1. What is OOP?

OOP is the abbrevation for object-oriented programming and is a programming paradigm which programm code can be group together and creates a unit. This programm code is called a class which gets a name. From this class your can create an object. The simpliest description of an object is: an array with functions. Although this description doesn't mention everything about classes and objects its a easy way to understand what an objects is. Objects got some fields like an array got fields and they got functions (called methods) which deals with them. This knowledge is enough to work with classes and objects. If you want to create your own classes you will see the whole scope of classes like information hiding, inheritance, design pattern, ...

2. Create an object

To create an object from a class you must use the keyword new. It is followed by the name of the class.

<?php
$obj = new DateTime();
?>

This code creates a new DateTime object and saves inside the $obj variable a link to this created object. The variable doesn't save the object itself only a link to the object. We can check the object with var_dump.

<?php
$obj = new DateTime();
var_dump($obj);
?>

The output looks like this.

object(DateTime)#1 (0) {
}

If this object have public attributes they are shown like var_dump is used on an array. But the class DateTime has no public attributes.

3. Work with an object

If you have create an object you want to use it. This can be done with the -> operator. On the left is the variable which points to the object, on the right is the method or attribute which you want to call/access. As an example we call the format() method (date_format).

<?php
$obj = new DateTime();
echo $obj->format('H:i:s');
?>

Of course we could use date or strftime but we want to learn how to use classes and objects.

4. Constructors

If you create an object a special method is executed, the so called constructor. This method fills the internal attributes with default values. For the DateTime object it saves the timezone and the current time inside the object. Constructors are like normal methods and can have parameters. Yoou can check the function description for date_create to see what parameters are possible for the DateTime class.

<?php
$obj = new DateTime("-1 day");
?>

5. Destructors

Destructors are methods which are called by the php engine if the last reference/link to the object is deleted. As there is no possibility to access the object anymore there is no reason to hold it in the memory. PHP calls in this case the destructor which can do some shutdown statements like closing the connection to a database. After that the object is erased from the memory.

1. Layout of a mysql database

Whatever a php script is doing soon or later the php script must save the data somewhere. All variables are deleted after the script ends and are removed from the memory. It is possible to save these data in a file. The php script opens the file and reads or write to it as an user would edit an text file. If your create a guestbook with files as storage you can save it like this:

User|20. Jan 2008|Really good page
User2|11. Feb 2008|Hi Paul, how are you?
User3|13. Feb 2008|Cool page, visit my homepage too

Each row will be a guestbook entry and the character | is the delimiter for usernames, creation date and the text. The php script reads this file and use explode to get the three parts back.

For a relational database like MySQL a different approach is taken. The data are not saved in files but in tables. Each row in the table represents an entry. MySQL is using the following layout.

• First there exists the MySQL programm itself, its an application like everything else. It implements a login system to access the database.

• Inside this MySQL program are the databases. These are the workspaces for the users which logged into MySQL. Depending on the login only a subset of databases can be used. Typically each user have his own database. A costumer like usr_123456 got a database usr_123456 to use.

• Inside one database are the tables, which can be added, changed or deleted. At the beginning this area is empty and the user must create the tables. This can be done with a administration programm or application like phpMyAdmin. This is a common webinterface for working with MySQL databases. Each table got a list of columnnames and types and some additional objects like primary key or indexes.

• Inside the tables are the rows. Each row combine one column of the table with a value. As an example a row combines the column Username with the value Foobar and the column Birthday with the value 1.1.1980. A second row will assign the values UserBar and 2.4.1975 to these columns, but both rows are in the same table. This will look like this.

  Example of the table

  Username	Birthday
  Foobar	1.1.1980
  UserBar	2.4.1975

To you a MySQL database in php you need 4 values. You get them from the administrator of your webserver.

1. Host - This is the address to the server where mysql is installed. It can be any IP or host like db23.example.com but is often the same computer as the webserver is running. In this case the host is localhost

2. Username - The username to login.

3. Password - The password to login.

4. Database - The database to work with. A webapplication always use only one database.

1. Layout of tables in MySQL

In MySQL the data is saved in tables as rows. To identify a table all tables have a name. Additional all tables have a list of columns with names and types. A table news can have a column added with the type DATETIME. Each value added to the column added must be of type DATETIME.

2. Types for columns

MySQL supports a lot of column types. From this list you choose the right one for your colum. A number should be saved in an INT field and a long text should be saved in a TEXT field. A complete list of column types can be found in the mysql manual at Chapter 9. Data Types. Here is a short list of common column types.

• INT - This column type is used for integer values. Rows often got an column for identification with the name like ID. Such columns also have attributes like PRIMAR KEY (each ID is unique) and AUTO_INCREMENT (the next ID is created automatically).

• VARCHAR(n) - This type is used for short strings. The parameter n sets the maximum size of the string. You use this type for saving short strings like usernames or email addresses.

• DATETIME - Is used to save a time value with the full date. For a news script this type is used to save when a news entry was written.

• TEXT - This is used for longer strings like news texts.

3. Create a MySQL table

You create a table with the sql command CREATE TABLE. It is followed by the table name to create. You cannot use any MySQL keywords as table names. After that a opening parenthese followes and the list of columns. Each column entry is seperated with a comma. Each column entry is build with the name, the type and optional additional options like NOT NULL, PRIMARY KEY and AUTO_INCREMENT. Each sql command must be terminated with a semicolon. An example sql query looks like this.

CREATE TABLE news (
    id INT AUTO_INCREMENT PRIMARY KEY,
    author VARCHAR(30) NOT NULL,
    title VARCHAR(50) NOT NULL,
    content TEXT NOT NULL,
    added DATETIME NOT NULL
);

Note this is a sql query. You cannot use this as php code. To send a query (like this one) to the database you must use functions like mysql_query or mysqli_query.

The NOT NULL options can be used if a value must be added to this column. This create will create the following table.

As the table is recently created there aren't any rows yet.

Be careful of the case sensitivity of table and column names. The MySQL manual deals with problems about case sensitivity.

Each table within a database corresponds to at least one file within the database directory (and possibly more, depending on the storage engine). Triggers also correspond to files. Consequently, the case sensitivity of the underlying operating system plays a part in the case sensitivity of database and table names. This means database, table, and trigger names are not case sensitive in Windows, but are case sensitive in most varieties of Unix.

For this reason the mysql manual advise to use a consistent convention throught your whole application.

[...] To avoid problems caused by such differences, it is best to adopt a consistent convention, such as always creating and referring to databases and tables using lowercase names. This convention is recommended for maximum portability and ease of use.

1. Add a row

After we created the tables with the colums we want to add new rows into the table. This can be done with the INSERT INTO command. After the INSERT INTO keyword you add the table name which you want to fill. After the name there is a list of columns for which you want supplie values. This list is written in parenthese and seperated by commas. If a column is not written there mysql will save a defaut value in this column for the new row. As an example an INT column have the default value 0. After the column names there is the keyword VALUES. Now all values are followed, also seperated with commas and written in parentheses. As in php strings must be written in quotes.

As an example we add a row without any values.

INSERT INTO
    news()
VALUES
    ();

This create add a new row into the news table.

As you see the id column gets the value 1 automatically. The values for author, title and content are always an empty string. And the added column got the (invalid) time 0000-00-00 00:00:00. As an example we add a real row.

INSERT INTO
    news(author, title, content, added)
VALUES
    ("Me",
     "My first news",
     "I am testing how rows are added to mysql",
    NOW());

You see we only used 4 of 5 columns as the id column got its value by AUTO_INCREMENT. Additional the column added got the value NOW(). This is a mysql function which returns the current time and date. This value is saved in the added column. If the query is executed the table may look like this.

This table got 2 rows now.

1. Output a value

As we filled the tables with rows we want to read them out. This can be done with the SELECT command. It got a huge list of parameters. Howevery, whatever the SELECT query is calculating and doing the result is always a table, also called result set. This result set got columns and rows like the tables have and can have even 0 rows. Each column got a name to access the specific column.

As an simple example we outputs simple values without using any tables. We use the SELECT keyword to start the query. It is followed by the values we want to read, seperated with commas. These can be static values but also function calls.

SELECT NOW(), "Foobar", 6;

This query returns a result set with 3 columns and 1 row.

As you see we have the columns NOW(), Foobar and 6. You also see we got only one row and the value of NOW() is the current time and date.

The column names are the same as the expressions in the SELECT query. To use other names use the AS ... keyword.

SELECT NOW() AS current_time, "Foobar" AS username, 6 AS level;

This is important if you want to read from two tables at the same time but got columns with the same name in both tables (like the id columns).

2. Indent the SELECT query

As SELECT queries are very long its common to use a proper indent for them. The values for a mysql keyword are indented by one level.

SELECT NOW() AS current_time, "Foobar" AS username, 6 AS level;

This will become the following query.

SELECT
    NOW() AS current_time,
    "Foobar" AS username,
    6 AS level;

This way you can easily see how many columns the result set will have.

1. SELECT on tables

As we can read single values we try to read data from a table. We extend the SELECT query by the FROM ... keyword. The ... part is the table we want to read. If we have select a table this way we can use the column names in the SELECT part. So the syntax is SELECT columns FROM table. As an example we reads the columns id, author and title from our news table.

SELECT
    author,
    id,
    title
FROM
    news;

We get the following result set.

We see we got a result set with 3 columns and 2 rows. This is okay as the table got 2 rows and in the SELECT part we selected 3 columns. We also see the first row got empty values but thats also okay as the row itself just got only empty values. The order of the columns can be changed (we read id after author), but it doesn't matter as we read them in php by their name rather by their position.

1. MySQLi

To get back to php: we wants to access the database via php. As we cannot simply write the sql query inside the php code we need something to access the mysql database. We use the mysqli extension in the OOP style.

The mysqli extension provide us with some classes to work with mysql. First we use the MySQLi class. We login into the database with the constructor.

<?php
$db = new mysqli('localhost', 'username', 'password', 'database');
?>

If no connection could be established an warning is generated. We suppress this error with a @ before the new operator. This way no error messages from this line are shown. This doesn't mean you should write @ everywhere. Its just the error message which isn't show, the error still exists. Accordingly to the manual we should use mysqli_connect_errno to check if the connection is established. If this function returns 0 the connection is established, otherwise the mysqli_connect_error tells us why not.

<?php
$db = @new mysqli('localhost', 'username', 'password', 'database');
if (mysqli_connect_errno()) {
    die ('Could not open a mysql connection: '.mysqli_connect_error().'('.mysqli_connect_errno().')');
}
?>

As we got our MySQLi object now we can work with it. We use the query() method (MySQLi::query) to send a query, but we can also use prepare() (MySQLi::prepare) to create complex queries. The parameter is always a sql query which you want to send to the database. If you use a SELECT query an MySQLi_Result object is returned.

<?php
$db = @new mysqli('localhost', 'username', 'password', 'database');
if (mysqli_connect_errno()) {
    die ('Could not open a mysql connection: '.mysqli_connect_error().'('.mysqli_connect_errno().')');
}
$sql = 'SELECT
    title,
    added
FROM
    news';
$result = $db->query($sql);
?>

As every query can fail we always check for errors. You can check the return value of query(). If it is false there is an error and the error message is saved in the error field of the MySQLi object.

<?php
$db = @new mysqli('localhost', 'username', 'password', 'database');
if (mysqli_connect_errno()) {
    die ('Could not open a mysql connection: '.mysqli_connect_error().'('.mysqli_connect_errno().')');
}
$sql = 'SELECT
    title,
    added
FROM
    news';
$result = $db->query($sql);
if (!$result) {
    die ('Something is wrong with the query: '.$db->error);
}
var_dump($db, $result);    
?>

We check what kind of errors we have with the var_dump function.

object(mysqli)#1 (0) {
}
object(mysqli_result)#2 (0) {
}

The first one is our MySQLi object, the second one is the created MySQLi_Result object we are now working with. We show first how big the result set is. The number of rows is saved in the num_rows field. (MySQLi_Result::num_rows).

<?php
$db = @new mysqli('localhost', 'username', 'password', 'database');
if (mysqli_connect_errno()) {
    die ('Could not open a mysql connection: '.mysqli_connect_error().'('.mysqli_connect_errno().')');
}
$sql = 'SELECT
    title,
    added
FROM
    news';
$result = $db->query($sql);
if (!$result) {
    die ('Something is wrong with the query: '.$db->error);
}
echo 'The result set got '.$result->num_rows." rows<br />\n";
?>

In our case we have 2 rows in our table. To access one row we use the fetch_assoc() method (MySQLi_Result::fetch_assoc). This method returns an array which contains all data from a row. Each call of fetch_assoc() returns the next row. If the end of the result set is reached this method returns NULL.

<?php
$db = @new mysqli('localhost', 'username', 'password', 'database');
if (mysqli_connect_errno()) {
    die ('Could not open a mysql connection: '.mysqli_connect_error().'('.mysqli_connect_errno().')');
}
$sql = 'SELECT
    title,
    added
FROM
    news';
$result = $db->query($sql);
if (!$result) {
    die ('Something is wrong with the query: '.$db->error);
}
echo 'The result set got '.$result->num_rows." rows<br />\n";
var_dump($result->fetch_assoc());
var_dump($result->fetch_assoc());
var_dump($result->fetch_assoc());
var_dump($result->fetch_assoc());
?>

This code creates the following output:

The result set got 2 rows<br />
array(2) {
  ["title"]=>
  string(0) ""
  ["added"]=>
  string(19) "0000-00-00 00:00:00"
}
array(2) {
  ["title"]=>
  string(16) "My first news"
  ["added"]=>
  string(19) "2008-08-17 14:02:08"
}
NULL
NULL

As you see the first to calls returns the rows from the result set. After then the method returns only NULL values. This allowes you to use fetch_assoc() in a while loop.

<?php
$db = @new mysqli('localhost', 'username', 'password', 'database');
if (mysqli_connect_errno()) {
    die ('Could not open a mysql connection: '.mysqli_connect_error().'('.mysqli_connect_errno().')');
}
$sql = 'SELECT
    title,
    added
FROM
    news';
$result = $db->query($sql);
if (!$result) {
    die ('Something is wrong with the query: '.$db->error);
}
echo 'The result set got '.$result->num_rows." rows<br />\n";
while ($row = $result->fetch_assoc()) {  // NULL is equivalent to false
    // $row is now the array with the values.
    echo 'The news "'.$row['title'].'" was written at "'.$row['added']."\"<br />\n";
}
?>

If we output all rows we can close the result set with close() (MySQLi_Result::close).

<?php
$db = @new mysqli('localhost', 'username', 'password', 'database');
if (mysqli_connect_errno()) {
    die ('Could not open a mysql connection: '.mysqli_connect_error().'('.mysqli_connect_errno().')');
}
$sql = 'SELECT
    title,
    added
FROM
    news';
$result = $db->query($sql);
if (!$result) {
    die ('Something is wrong with the query: '.$db->error);
}
echo 'The result set got '.$result->num_rows." rows<br />\n";
while ($row = $result->fetch_assoc()) {  // NULL is equivalent to false
    // $row is now the array with the values.
    echo 'The news "'.$row['title'].'" was written at "'.$row['added']."\"<br />\n";
}
unset($result); // you can delete the variable with unset() as it isn't needed anymore.
?>

If you want you can close the connection to the database with the close() method (MySQLi::close) but this happends at the end of your script anyway.

1. Writing your own news script

Our news script should be easy and prints the html code just quick'n'dirty. It will be implemented and shouldn't be loaded with include in other areas.

2. Layout of the mysql table

We delete the old table with phpMyAdmin or with DROP TABLE news;. Now we think about the columns we need.

• id - A column for identify a news. This column got the type INT and get the attributes UNSIGNED, NOT NULL, AUTO_INCREMENT and PRIMARY KEY.

• title - This column got the title of the news and its type is VARCHAR(100), 100 chars should be enought. As you must supply a title it got the attribute NOT NULL.

• added - The time when the news was added, so it must be got the type DATETIME with the attribute NOT NULL. Note that we cannot use the name date as it is a reserved keyword in mysql (for the column type DATE).

• content - This column got the real news text. As text might be a better then TEXT is already a mysql keyword and shouldn't be used as column name. We set the type of this column to TEXT as we might want to add a longer news text. Again we use the NOT NULL attribute.

Note these NOT NULL doesn't prevent you from entering an empty string, it only prevents you from enter a empty value at all (these NULL values). This table can be created with phpMyAdmin or with the following sql query.

CREATE TABLE news (
    id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
    title VARCHAR(100) NOT NULL,
    added DATETIME NOT NULL,
    content TEXT NOT NULL 
);

It looks like the old table but we want to start from the beginning.

3. The news script

Now we begin our news script. As always we increase the error reporing level to get all error messages.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
?>

Then we open the connection to mysql.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

// change to your login
$db = @new MySQLi('localhost', 'username', 'pass', 'dbname');
if (mysqli_connect_errno()) {
    die ('Could not create a connection to the database: '.mysqli_connect_error());
}
?>

And now lets go. First we echo some html header stuff. We write them in a new file and load them with include.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

// change to your login
$db = @new MySQLi('localhost', 'username', 'pass', 'dbname');
if (mysqli_connect_errno()) {
    die ('Could not create a connection to the database: '.mysqli_connect_error());
}
include 'header.html'; // DOCTYPE, <html>, <head>, and the starting <body> tag
?>

Now we send our sql query and output the result with a loop.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

// change to your login
$db = @new MySQLi('localhost', 'username', 'pass', 'dbname');
if (mysqli_connect_errno()) {
    die ('Could not create a connection to the database: '.mysqli_connect_error());
}
include 'header.html'; // DOCTYPE, <html>, <head>, and the starting <body> tag
$sql = 'SELECT
            title,
            added,
            content
        FROM
            news
        ORDER BY
            added DESC';
// "ORDER BY" to sort the news by the date, descending
$result = $db->query($sql);
if (!$result) {
    die ('Query failed, query was: '.$sql."<br />\nError message: ".$db->error);
}
if (!$result->num_rows) {
    echo '<p class="info">There are no news.</p>';
} else {
    while ($row = $result->fetch_assoc()) {
        echo '<h1>'.$row['title']."</h1>\n";
        echo '<h2>'.$row['added']."</h2>\n";
        echo '<p>'.$row['content']."</p>\n";
}
?>

And at the end we output the html footer with include.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

// change to your login
$db = @new MySQLi('localhost', 'username', 'pass', 'dbname');
if (mysqli_connect_errno()) {
    die ('Could not create a connection to the database: '.mysqli_connect_error());
}
include 'header.html'; // DOCTYPE, <html>, <head>, and the starting <body> tag
$sql = 'SELECT
            title,
            added,
            content
        FROM
            news
        ORDER BY
            added DESC';
// "ORDER BY" to sort the news by the date, descending
$result = $db->query($sql);
if (!$result) {
    die ('Query failed, query was: '.$sql."<br />\nError message: ".$db->error);
}
if (!$result->num_rows) {
    echo '<p class="info">There are no news.</p>';
} else {
    while ($row = $result->fetch_assoc()) {
        echo '<h1>'.$row['title']."</h1>\n";
        echo '<h2>'.$row['added']."</h2>\n";
        echo '<p>'.$row['content']."</p>\n";
}
include 'footer.html'; // </body>, </html> and maybe some copyright notes
?>

Now we have written our news script.

4. Downside of the news script

At the moment we can only add new databases if we work at the database directly. This can be done as always with phpMyAdmin. We just click on Insert and enters the new data. The id column should be empty as this value is generated automatically by AUTO_INCREMENT. At the added select the function NOW() from the drop-down list. As you see this is a very rudimentary without any user interactions like news comments, but as written at the top it is an easy and simple news script.

1. Writing an own guestbook

A guestbook is similar to a newsscript but the entries are from the users, not from the administrator. But this also result in problems as the user can enter any text they want. And then you have content in your guestbook you don't want to have. For this reason every user input must be checked, also for spam.

2. Layout of the mysql tables

We use a similar table as the news table. It got 4 columns.

1. id - The normal identification column with the type INT.

2. added - The time when the entry was added. Type is DATETIME.

3. author - The name of the user who added the entry. A VARCHAR(50) should be enought.

4. content - The text of the entry. Type is TEXT.

The sql query looks like this.

CREATE TABLE guestbook (
    id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
    author VARCHAR(50) NOT NULL,
    added DATETIME NOT NULL,
    content TEXT NOT NULL
);

You can add this table with phpMyAdmin of course.

3. Layout of the php scripts

The php script as two objectives. First, it must fetch the rows from the database and show them. Second, it must process the values from a form to add them in mysql. We can differ it by checking the value of $_SERVER['REQUEST_METHOD']. If the file is opened by a POST request (like a form) we save the form values to the database, for all other request types (which include the GET request) we show the guestbook and a form for adding new guestbook entries.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

if ('POST' == $_SERVER['REQUEST_METHOD']) {
    // code for adding new entries in the database
} else {
    // code for showing the guestbook and the form
}
?>

As we use the mysql we create a connection to the database. And we load some html stuff with include or even better with readfile.

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

$db = @new mysqli('localhost', 'username', 'password', 'database');
if (mysqli_connect_errno()) {
    die('Could not create a connection to the database: '.mysqli_connect_error().'('.mysqli_connect_errno().')');
}

readfile('header.html'); // contains the <body> tag

if ('POST' == $_SERVER['REQUEST_METHOD']) {
    // code for adding new entries in the database
} else {
    // code for showing the guestbook and the form
}

readfile('footer.html');
?>