Learning PHP

Here are some more friendly PHP tutorials.

• A Gentle Introduction to PHP by Bob Brown.
• eFishDesign Coding Tutorials by Eric Fisher.

What is PHP

PHP is a C like language. PHP is called a server side language, because it is executed by a server, never by a browser. The output of the PHP code is sent, as html code, from the server to the browser.

Why use PHP?

1. A server side language, such as PHP, is essential to deal with input from forms. Forms can greatly increase the interactivity of your site.
2. PHP lets you communicate with databases on your web server.
3. PHP can help you avoid writing repetitious html code:
   • For example, if there is a bit of code you want in each of your web pages (such as a title, or a menu), it can be included with a single line PHP statement.
   • PHP programs can be inserted anywhere in your html file to generate html code, that would be time consuming to write. Thus my table of browser safe colors was written in PHP.

What do you need to use PHP?

1. You can install a server, and PHP on your computer. This is a good option, if you can do it, because it allows you to error check your files, and run them without the bother of uploading them to a web site.
2. You can use your web hosting server. Whether this is a good option depends on your web hosting server.
   1. You need a server that outputs PHP parsing errors. Otherwise you will see nothing but a blank page whenever you make a PHP syntax error.
   2. It is a great convenience if you choose a server that provides you with cPanel. cPanel allows you to modify your files while they are uploaded. It is available at low cost from some web hosting services.

What is a PHP file?

How do you execute a PHP file?

1. With an anchor tag. You can call a PHP file with an anchor tag, just as you can call an html file.

       <a href="test.php">Click here. </a>

2. With a form. You can set your PHP file as the action attribute of a form. When the form is submitted, the PHP file will be executed.

       <form method="POST" action="test.php">
       <input type="submit">
       </form>

Information about your PHP Build

One of the first programs you should run is the following:

<?php 
 phpinfo(); 
?>

php_info

<?php          ?> 

<?php
// This is a comment.
but this is not.

/* This is 
   a 
   comment, too.  */
?>

NULL, Empty, Set and Unset Variables

When you need to determine whether a variable has been given a value -- for instance, in checking form input -- the best thing to do is to see php.net's type comparison tables.

gettype()

if (  ){    }
else{  };

for ($i=0;$i<5;$i++){
  statements;
};

foreach($array as $var){ 
  echo($var);
}

foreach ($array as $key => $value){
echo"$key  $value ";
}

while ( ){ 

 };

do {  } while ( );

Arrays

<?php
$a=array(key1=>value1,key2=>value2); 
?>

Watch what print_r does with an array.

<?php
 $a=array('a'=>'apple', 'b' => 'banana', 'c' => array ('x', 'y', z'));
 print_r ($a);
?>

Array ( [a] => apple [b] => banana [c] => Array ( [0] => x [1] => y [2] => z ) ) 

To find the number of items in an array, you can use the sizeof function; sizeof() is an alias for count(). You can't use sizeof() on a string. It will return 1.

<?php
 $a=array('a'=>'apple', 'b' => 'banana', 'c' => array ('x', 'y', z'));
 $l=sizeof($a)
 echo"$l";
?>

Multidimensional Arrays

Evidently multidimensional arrays are arrays of arrays.

Array elements can be referred to as:

$x[$i][$j]

However, references to multidimensional arrays can be ambiguous. Thus the code:

echo"$x[$i][$j]";

will only yield something such as:

Array[0]

The request was interpreted as a request to echo $x[$i] which is an array, followed by [$j].

To refer to an element of a multidimensional array unambiguously, you can enclose it in curly braces.

echo {$x[$i][$j]};

Strings in PHP

When strings are placed within double quotes, variables within the string are evaluated.

However, when a string is placed within single quotes, the string is taken literally. Variable names rather than variables are printed out.

String Functions

Using PHP Functions

Using PHP to add Text to Files

The require() function causes the contents of a file to be inserted as that point. The inserted file can be either a PHP file or an html file.

<?php 
 require("test.php"); 
?>

<?php 
 require("foot.htm"); 
?>

Defining PHP Functions

Example:

<?php 
function state($x){
 if ($x=='S') return 'Solid';
 else if($x=='L') return 'Liquid';
 else if ($x=='G') return 'Gas';
}
?>

Functions can return an array output. The array is declared and filled within the function, and the array variable is returned.

<?php 
function Colors($h){
$dml=array(3,'dark','medium','light');
return $dml;
}
?>

Math Constants and Functions

These constants and functions have been available since PHP v 4.

Accessing Files and Directories on the Server

The function scandir('directoryName') returns an array, each term of which consists of one file in the directory.

<?php 
$directory="/usr/local/";
echo "Contents of Directory $directory<br>";
$folder=scandir($directory); 
 foreach($folder as $var){ 
  echo($var);
  echo'<br>';
}
?>

Files may be opened and read with the file('filename') function. The result is an array, each item of which corresponds to one line of the file.

<?php 
echo"Contents of file freetype-config using file() function<br>";
$content=file("/usr/bin/freetype-config");
 foreach($content as $var){ 
  echo($var);
  echo'<br>';
}
?>

Output

The echo statement sends text and html tags to the browser. Echo is not a function. These echo statements are correct:

<?php
echo "<h5>One enchanted evening</h5>"; 
echo $x;
echo($x);        //When () used, only one variable is accepted.
echo $x, $y, $z; //Variables must be sep'd by commas
echo $row[0]."  ".$row[1]."  ".$row[2 ]."<br>";
?>

If you want to send a quotation mark to the browser, you must send it as \"

The print() function accepts only one argument, and returns true or false.

The print_r() function accepts strings, integers, floats, arrays. If given an array, the keys and values of the array will be printed. One caveat: print_r() will move the array pointer to the end of the array. You can use reset() to bring it back to beginning.

Note: In versions of PHP before 4.0.4, print_r() would continue forever if given an array or object that contains a direct or indirect reference to itself. An example is print_r($GLOBALS).

Formatted Output using the printf() and sprintf() functions

The functions, printf() and sprintf(), are identical except for one point. The printf() function writes the code to the document, while sprintf() writes it to a string variable.

The first argument of printf() is a string which directs formatting. The succeeding arguments are data to be printed within the string.

The data can be integers, floating point numbers, strings, or boolean variables.

The format string can contain any sort of explanatory text, but the feature which directs formatting is a set of "conversion specifications". We'll call these "specs" for short. There should be one "spec" for each datum.

Each "spec" has two functions:

• It shows where in the format string to place the datum. It does this by its position within the string.
• It shows how to format the datum.

Each "spec" must have at least two characters: it begins with a % sign and ends with a type specifier. In between may be more characters which further direct the formatting. First let's look at type specifiers, since they are essential.

Need some examples here

try monkeys octal binary, hex scientific, decimal

Next let's look at format modifiers, which go between the % and the type specifier. If they are used they must be in the order shown in the table below.

Example with leading zeros

How to include a % in the format string.

Here output was rounded to 1 decimal point:

$out_bmi=sprintf('%0.1f', $_bmi);

Peter Kantor describes and compares the different PHP output commands in PHP Client Side.

Documentation on sprintf() can be found at php.net

Using PHP to Generate non Html Files

Images and image files can be generated with php. This is explained in the section on PHP Image Functions