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What You Should Already Know
Before you continue you should have a basic understanding of the following:
- HTML / XHTML
- Some scripting knowledge
If you want to study these subjects first, find the tutorials on our HTML Help Page.
What is PHP?
- PHP stands for PHP: Hypertext Preprocessor
- PHP is a server-side scripting language, like ASP
- PHP scripts are executed on the server
- PHP supports many databases (MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, Generic ODBC, etc.)
- PHP is an open source software (OSS)
- PHP is free to download and use
What is a PHP File?
- PHP files may contain text, HTML tags and scripts
- PHP files are returned to the browser as plain HTML
- PHP files have a file extension of ".php", ".php3", or ".phtml"
What is MySQL?
- MySQL is a database server
- MySQL is ideal for both small and large applications
- MySQL supports standard SQL
- MySQL compiles on a number of platforms
- MySQL is free to download and use
PHP + MySQL
- PHP combined with MySQL are cross-platform (means that you can develop in Windows and serve on a Unix platform)
Why PHP?
- PHP runs on different platforms (Windows, Linux, Unix, etc.)
- PHP is compatible with almost all servers used today (Apache, IIS, etc.)
- PHP is FREE to download from the official PHP resource: www.php.net
- PHP is easy to learn and runs efficiently on the server side
Where to Start?
- Install an Apache server on a Windows or Linux machine
- Install PHP on a Windows or Linux machine
- Install MySQL on a Windows or Linux machine
- A variable name must start with a letter or an underscore "_"
- A variable name can only contain alpha-numeric characters and underscores (a-Z, 0-9, and _ )
- A variable name should not contain spaces. If a variable name is more than one word, it should be separated with underscore ($my_string), or with capitalization ($myString)
- A single expression (most often a variable) is evaluated once
- The value of the expression is compared with the values for each case in the structure
- If there is a match, the code associated with that case is executed
- After a code is executed, break is used to stop the code from running into the next case
- The default statement is used if none of the cases are true
- Numeric array - An array with a numeric ID key
- Associative array - An array where each ID key is associated with a value
- Multidimensional array - An array containing one or more arrays
- while - loops through a block of code if and as long as a specified condition is true
- do...while - loops through a block of code once, and then repeats the loop as long as a special condition is true
- for - loops through a block of code a specified number of times
- foreach - loops through a block of code for each element in an array
- All functions start with the word "function()"
- Name the function - It should be possible to understand what the function does by its name. The name can start with a letter or underscore (not a number)
- Add a "{" - The function code starts after the opening curly brace
- Insert the function code
- Add a "}" - The function is finished by a closing curly brace
- Variables sent with HTTP POST are not shown in the URL
- Variables have no length limit
Basic PHP Syntax
A PHP scripting block always starts with <?php and ends with ?>. A PHP scripting block can be placed anywhere in the document.
On servers with shorthand support enabled you can start a scripting block with <? and end with ?>.
However, for maximum compatibility, we recommend that you use the standard form (<?php) rather than the shorthand form.
A PHP file normally contains HTML tags, just like an HTML file, and some PHP scripting code.
Below, we have an example of a simple PHP script which sends the text "Hello World" to the browser:
Each code line in PHP must end with a semicolon. The semicolon is a separator and is used to distinguish one set of instructions from another.
There are two basic statements to output text with PHP: echo and print. In the example above we have used the echo statement to output the text "Hello World".
Comments in PHP
In PHP, we use // to make a single-line comment or /* and */ to make a large comment block.
Variables in PHP
Variables are used for storing a values, like text strings, numbers or arrays.
When a variable is set it can be used over and over again in your script
All variables in PHP start with a $ sign symbol.
The correct way of setting a variable in PHP:
$var_name = value; |
New PHP programmers often forget the $ sign at the beginning of the variable. In that case it will not work.
Let's try creating a variable with a string, and a variable with a number:
<?php $txt = "Hello World!"; $number = 16; ?> |
PHP is a Loosely Typed Language
In PHP a variable does not need to be declared before being set.
In the example above, you see that you do not have to tell PHP which data type the variable is.
PHP automatically converts the variable to the correct data type, depending on how they are set.
In a strongly typed programming language, you have to declare (define) the type and name of the variable before using it.
In PHP the variable is declared automatically when you use it.
Strings in PHP
String variables are used for values that contains character strings.
In this tutorial we are going to look at some of the most common functions and operators used to manipulate strings in PHP.
After we create a string we can manipulate it. A string can be used directly in a function or it can be stored in a variable.
Below, the PHP script assigns the string "Hello World" to a string variable called $txt:
<?php $txt="Hello World"; echo $txt; ?> |
The output of the code above will be:
Hello World |
Now, lets try to use some different functions and operators to manipulate our string.
Variable Naming Rules
The Concatenation Operator
There is only one string operator in PHP.
The concatenation operator (.) is used to put two string values together.
To concatenate two variables together, use the dot (.) operator:
<?php $txt1="Hello World"; $txt2="1234"; echo $txt1 . " " . $txt2; ?> |
The output of the code above will be:
Hello World 1234 |
If we look at the code above you see that we used the concatenation operator two times. This is because we had to insert a third string.
Between the two string variables we added a string with a single character,
an empty space, to separate the two variables.
Using the strlen() function
The strlen() function is used to find the length of a string.
Let's find the length of our string "Hello world!":
<?php
echo strlen("Hello world!");
?>
|
The output of the code above will be:
12 |
The length of a string is often used in loops or other functions, when it is important to know when the string ends. (i.e. in a loop, we would want to stop the loop after the last character in the string)
Using the strpos() function
The strpos() function is used to search for a string or character within a string.
If a match is found in the string, this function will return the position of the first match. If no match is found, it will return FALSE.
Let's see if we can find the string "world" in our string:
<?php
echo strpos("Hello world!","world");
?>
|
The output of the code above will be:
6 |
As you see the position of the string "world" in our string is position 6. The reason that it is 6, and not 7, is that the first position in the string is 0, and not 1.
PHP Operators
This section lists the different operators used in PHP.
Arithmetic Operators
| Operator | Description | Example | Result |
|---|---|---|---|
| + | Addition | x=2 x+2 |
4 |
| - | Subtraction | x=2 5-x |
3 |
| * | Multiplication | x=4 x*5 |
20 |
| / | Division | 15/5 5/2 |
3 2.5 |
| % | Modulus (division remainder) | 5%2 10%8 10%2 |
1 2 0 |
| ++ | Increment | x=5 x++ |
x=6 |
| -- | Decrement | x=5 x-- |
x=4 |
Assignment Operators
| Operator | Example | Is The Same As |
|---|---|---|
| = | x=y | x=y |
| += | x+=y | x=x+y |
| -= | x-=y | x=x-y |
| *= | x*=y | x=x*y |
| /= | x/=y | x=x/y |
| .= | x.=y | x=x.y |
| %= | x%=y | x=x%y |
Comparison Operators
| Operator | Description | Example |
|---|---|---|
| == | is equal to | 5==8 returns false |
| != | is not equal | 5!=8 returns true |
| > | is greater than | 5>8 returns false |
| < | is less than | 5<8 returns true |
| >= | is greater than or equal to | 5>=8 returns false |
| <= | is less than or equal to | 5<=8 returns true |
Logical Operators
| Operator | Description | Example |
|---|---|---|
| && | and | x=6 y=3 (x < 10 && y > 1) returns true |
| || | or | x=6 y=3 (x==5 || y==5) returns false |
| ! | not | x=6 y=3 !(x==y) returns true |
The If...Else Statement
If you want to execute some code if a condition is true and another code if a condition is false, use the if....else statement.
Syntax
if (condition) code to be executed if condition is true; else code to be executed if condition is false; |
Example
The following example will output "Have a nice weekend!" if the current day is Friday, otherwise it will output "Have a nice day!":
<html> <body> <?php
$d=date("D");
if ($d=="Fri")
echo "Have a nice weekend!";
else
echo "Have a nice day!";
?>
</body> </html> |
If more than one line should be executed if a condition is true/false, the lines should be enclosed within curly braces:
<html> <body> <?php
$d=date("D");
if ($d=="Fri")
{
echo "Hello!<br />";
echo "Have a nice weekend!";
echo "See you on Monday!";
}
?>
</body> </html> |
The ElseIf Statement
If you want to execute some code if one of several conditions are true use the elseif statement
Syntax
if (condition) code to be executed if condition is true; elseif (condition) code to be executed if condition is true; else code to be executed if condition is false; |
Example
The following example will output "Have a nice weekend!" if the current day is Friday, and "Have a nice Sunday!" if the current day is Sunday. Otherwise it will output "Have a nice day!":
<html> <body> <?php
$d=date("D");
if ($d=="Fri")
echo "Have a nice weekend!";
elseif ($d=="Sun")
echo "Have a nice Sunday!";
else
echo "Have a nice day!";
?>
</body> </html> |
The Switch Statement
If you want to select one of many blocks of code to be executed, use the Switch statement.
The switch statement is used to avoid long blocks of if..elseif..else code.
Syntax
switch (expression)
{
case label1:
code to be executed if expression = label1;
break;
case label2:
code to be executed if expression = label2;
break;
default:
code to be executed
if expression is different
from both label1 and label2;
}
|
Example
This is how it works:
<html> <body> <?php
switch ($x)
{
case 1:
echo "Number 1";
break;
case 2:
echo "Number 2";
break;
case 3:
echo "Number 3";
break;
default:
echo "No number between 1 and 3";
}
?>
</body> </html> |
What is an array?
When working with PHP, sooner or later, you might want to create many similar variables.
Instead of having many similar variables, you can store the data as elements in an array.
Each element in the array has its own ID so that it can be easily accessed.
There are three different kind of arrays:
Numeric Arrays
A numeric array stores each element with a numeric ID key.
There are different ways to create a numeric array.
Example 1
In this example the ID key is automatically assigned:
$names = array("Peter","Quagmire","Joe");
|
Example 2
In this example we assign the ID key manually:
$names[0] = "Peter"; $names[1] = "Quagmire"; $names[2] = "Joe"; |
The ID keys can be used in a script:
<?php $names[0] = "Peter"; $names[1] = "Quagmire"; $names[2] = "Joe"; echo $names[1] . " and " . $names[2] . " are ". $names[0] . "'s neighbors"; ?> |
The code above will output:
Quagmire and Joe are Peter's neighbors |
Associative Arrays
An associative array, each ID key is associated with a value.
When storing data about specific named values, a numerical array is not always the best way to do it.
With associative arrays we can use the values as keys and assign values to them.
Example 1
In this example we use an array to assign ages to the different persons:
$ages = array("Peter"=>32, "Quagmire"=>30, "Joe"=>34);
|
Example 2
This example is the same as example 1, but shows a different way of creating the array:
$ages['Peter'] = "32"; $ages['Quagmire'] = "30"; $ages['Joe'] = "34"; |
The ID keys can be used in a script:
<?php $ages['Peter'] = "32"; $ages['Quagmire'] = "30"; $ages['Joe'] = "34"; echo "Peter is " . $ages['Peter'] . " years old."; ?> |
The code above will output:
Peter is 32 years old. |
Multidimensional Arrays
In a multidimensional array, each element in the main array can also be an array. And each element in the sub-array can be an array, and so on.
Example
In this example we create a multidimensional array, with automatically assigned ID keys:
$families = array ( "Griffin"=>array ( "Peter", "Lois", "Megan" ), "Quagmire"=>array ( "Glenn" ), "Brown"=>array ( "Cleveland", "Loretta", "Junior" ) ); |
The array above would look like this if written to the output:
Array ( [Griffin] => Array ( [0] => Peter [1] => Lois [2] => Megan ) [Quagmire] => Array ( [0] => Glenn ) [Brown] => Array ( [0] => Cleveland [1] => Loretta [2] => Junior ) ) |
Example 2
Lets try displaying a single value from the array above:
echo "Is " . $families['Griffin'][2] . " a part of the Griffin family?"; |
The code above will output:
Is Megan a part of the Griffin family? |
Looping
Very often when you write code, you want the same block of code to run a number of times. You can use looping statements in your code to perform this.
In PHP we have the following looping statements:
The while Statement
The while statement will execute a block of code if and as long as a condition is true.
Syntax
while (condition) code to be executed; |
Example
The following example demonstrates a loop that will continue to run as long as the variable i is less than, or equal to 5. i will increase by 1 each time the loop runs:
<html> <body> <?php
$i=1;
while($i<=5)
{
echo "The number is " . $i . "<br />";
$i++;
}
?>
</body> </html> |
The do...while Statement
The do...while statement will execute a block of code at least once - it then will repeat the loop as long as a condition is true.
Syntax
do
{
code to be executed;
}
while (condition);
|
Example
The following example will increment the value of i at least once, and it will continue incrementing the variable i as long as it has a value of less than 5:
<html> <body> <?php
$i=0;
do
{
$i++;
echo "The number is " . $i . "<br />";
}
while ($i<5);
?>
</body> </html> |
The for Statement
The for statement is used when you know how many times you want to execute a statement or a list of statements.
Syntax
for (initialization; condition; increment)
{
code to be executed;
}
|
Note: The for statement has three parameters. The first parameter initializes variables, the second parameter holds the condition, and the third parameter contains the increments required to implement the loop. If more than one variable is included in the initialization or the increment parameter, they should be separated by commas. The condition must evaluate to true or false.
Example
The following example prints the text "Hello World!" five times:
<html> <body> <?php
for ($i=1; $i<=5; $i++)
{
echo "Hello World!<br />";
}
?>
</body> </html> |
The foreach Statement
The foreach statement is used to loop through arrays.
For every loop, the value of the current array element is assigned to $value (and the array pointer is moved by one) - so on the next loop, you'll be looking at the next element.
Syntax
foreach (array as value)
{
code to be executed;
}
|
Example
The following example demonstrates a loop that will print the values of the given array:
<html> <body> <?php
$arr=array("one", "two", "three");
foreach ($arr as $value)
{
echo "Value: " . $value . "<br />";
}
?>
</body> </html> |
Create a PHP Function
A function is a block of code that can be executed whenever we need it.
Creating PHP functions:
Example
A simple function that writes my name when it is called:
<html> <body> <?php
function writeMyName()
{
echo "Kai Jim Refsnes";
}
writeMyName(); ?> </body> </html> |
Use a PHP Function
Now we will use the function in a PHP script:
<html> <body> <?php
function writeMyName()
{
echo "Kai Jim Refsnes";
}
echo "Hello world!<br />"; echo "My name is "; writeMyName(); echo ".<br />That's right, "; writeMyName(); echo " is my name."; ?> </body> </html> |
The output of the code above will be:
Hello world! My name is Kai Jim Refsnes. That's right, Kai Jim Refsnes is my name. |
PHP Functions - Adding parameters
Our first function (writeMyName()) is a very simple function. It only writes a static string.
To add more functionality to a function, we can add parameters. A parameter is just like a variable.
You may have noticed the parentheses after the function name, like: writeMyName(). The parameters are specified inside the parentheses.
Example 1
The following example will write different first names, but the same last name:
<html> <body> <?php
function writeMyName($fname)
{
echo $fname . " Refsnes.<br />";
}
echo "My name is ";
writeMyName("Kai Jim");
echo "My name is ";
writeMyName("Hege");
echo "My name is ";
writeMyName("Stale");
?>
</body> </html> |
The output of the code above will be:
My name is Kai Jim Refsnes. My name is Hege Refsnes. My name is Stale Refsnes. |
Example 2
The following function has two parameters:
<html> <body> <?php
function writeMyName($fname,$punctuation)
{
echo $fname . " Refsnes" . $punctuation . "<br />";
}
echo "My name is ";
writeMyName("Kai Jim",".");
echo "My name is ";
writeMyName("Hege","!");
echo "My name is ";
writeMyName("Ståle","...");
?>
</body> </html> |
The output of the code above will be:
My name is Kai Jim Refsnes. My name is Hege Refsnes! My name is Ståle Refsnes... |
PHP Functions - Return values
Functions can also be used to return values.
Example
<html> <body> <?php
function add($x,$y)
{
$total = $x + $y;
return $total;
}
echo "1 + 16 = " . add(1,16); ?> </body> </html> |
The output of the code above will be:
1 + 16 = 17 |
PHP Form Handling
The most important thing to notice when dealing with HTML forms and PHP is that any form element in an HTML page will automatically be available to your PHP scripts.
Form example:
<html> <body> <form action="welcome.php" method="post"> Name: <input type="text" name="name" /> Age: <input type="text" name="age" /> <input type="submit" /> </form> </body> </html> |
The example HTML page above contains two input fields and a submit button. When the user fills in this form and click on the submit button, the form data is sent to the "welcome.php" file.
The "welcome.php" file looks like this:
<html> <body> Welcome <?php echo $_POST["name"]; ?>.<br /> You are <?php echo $_POST["age"]; ?> years old. </body> </html> |
A sample output of the above script may be:
Welcome John. You are 28 years old. |
The PHP $_GET and $_POST variables will be explained in the next chapters.
Form Validation
User input should be validated whenever possible. Client side validation is faster, and will reduce server load.
However, any site that gets enough traffic to worry about server resources, may also need to worry about site security. You should always use server side validation if the form accesses a database.
A good way to validate a form on the server is to post the form to itself, instead of jumping to a different page. The user will then get the error messages on the same page as the form. This makes it easier to discover the error.
The $_GET Variable
The $_GET variable is an array of variable names and values sent by the HTTP GET method.
The $_GET variable is used to collect values from a form with method="get". Information sent from a form with the GET method is visible to everyone (it will be displayed in the browser's address bar) and it has limits on the amount of information to send (max. 100 characters).
Example
<form action="welcome.php" method="get"> Name: <input type="text" name="name" /> Age: <input type="text" name="age" /> <input type="submit" /> </form> |
When the user clicks the "Submit" button, the URL sent could look something like this:
http://www.offerithere.com/welcome.php?name=Peter&age=37 |
The "welcome.php" file can now use the $_GET variable to catch the form data (notice that the names of the form fields will automatically be the ID keys in the $_GET array):
Welcome <?php echo $_GET["name"]; ?>.<br /> You are <?php echo $_GET["age"]; ?> years old! |
Why use $_GET?
Note: When using the $_GET variable all variable names and values are displayed in the URL. So this method should not be used when sending passwords or other sensitive information! However, because the variables are displayed in the URL, it is possible to bookmark the page. This can be useful in some cases.
Note: The HTTP GET method is not suitable on large variable values; the value cannot exceed 100 characters.
The $_REQUEST Variable
The PHP $_REQUEST variable contains the contents of both $_GET, $_POST, and $_COOKIE.
The PHP $_REQUEST variable can be used to get the result from form data sent with both the GET and POST methods.
Example
Welcome <?php echo $_REQUEST["name"]; ?>.<br /> You are <?php echo $_REQUEST["age"]; ?> years old! |
The $_POST Variable
The $_POST variable is an array of variable names and values sent by the HTTP POST method.
The $_POST variable is used to collect values from a form with method="post". Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.
Example
<form action="welcome.php" method="post"> Enter your name: <input type="text" name="name" /> Enter your age: <input type="text" name="age" /> <input type="submit" /> </form> |
When the user clicks the "Submit" button, the URL will not contain any form data, and will look something like this:
http://www.offerithere.com/welcome.php |
The "welcome.php" file can now use the $_POST variable to catch the form data (notice that the names of the form fields will automatically be the ID keys in the $_POST array):
Welcome <?php echo $_POST["name"]; ?>.<br /> You are <?php echo $_POST["age"]; ?> years old! |
Why use $_POST?
However, because the variables are not displayed in the URL, it is not possible to bookmark the page.
The $_REQUEST Variable
The PHP $_REQUEST variable contains the contents of both $_GET, $_POST, and $_COOKIE.
The PHP $_REQUEST variable can be used to get the result from form data sent with both the GET and POST methods.
Example
Welcome <?php echo $_REQUEST["name"]; ?>.<br /> You are <?php echo $_REQUEST["age"]; ?> years old! |
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