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Wednesday, 21 August 2013
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Friday, 24 May 2013
PHP If...Else Statements
Conditional statements are used to perform different actions based on different conditions.
PHP Conditional Statements
Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this.In PHP we have the following conditional statements:
- if statement - executes some code only if a specified condition is true
- if...else statement - executes some code if a condition is true and another code if the condition is false
- if...else if....else statement - selects one of several blocks of code to be executed
- switch statement - selects one of many blocks of code to be executed
PHP - The if Statement
The if statement is used to execute some code only if a specified condition is true.Syntax
if (condition)
{
code to be executed if condition is true;
}
{
code to be executed if condition is true;
}
Example
<?php
$t=date("H");
if ($t<"20")
{
echo "Have a good day!";
}
?>
$t=date("H");
if ($t<"20")
{
echo "Have a good day!";
}
?>
PHP - The if...else Statement
Use the if....else statement to execute some code if a condition is true and another code if the condition is false.Syntax
if (condition)
{
code to be executed if condition is true;
}
else
{
code to be executed if condition is false;
}
{
code to be executed if condition is true;
}
else
{
code to be executed if condition is false;
}
Example
<?php
$t=date("H");
if ($t<"20")
{
echo "Have a good day!";
}
else
{
echo "Have a good night!";
}
?>
$t=date("H");
if ($t<"20")
{
echo "Have a good day!";
}
else
{
echo "Have a good night!";
}
?>
PHP Operators
The assignment operator = is used to assign values to variables in PHP.
The arithmetic operator + is used to add values together in PHP.
| Operator | Name | Description | Example | Result |
|---|---|---|---|---|
| x + y | Addition | Sum of x and y | 2 + 2 | 4 |
| x - y | Subtraction | Difference of x and y | 5 - 2 | 3 |
| x * y | Multiplication | Product of x and y | 5 * 2 | 10 |
| x / y | Division | Quotient of x and y | 15 / 5 | 3 |
| x % y | Modulus | Remainder of x divided by y | 5 % 2 10 % 8 10 % 2 |
1 2 0 |
| - x | Negation | Opposite of x | - 2 | |
| a . b | Concatenation | Concatenate two strings | "Hi" . "Ha" | HiHa |
PHP Assignment Operators
The basic assignment operator in PHP is "=". It means that the left operand gets set to the value of the expression on the right. That is, the value of "$x = 5" is 5.| Assignment | Same as... | Description |
|---|---|---|
| x = y | x = y | The left operand gets set to the value of the expression on the right |
| x += y | x = x + y | Addition |
| x -= y | x = x - y | Subtraction |
| x *= y | x = x * y | Multiplication |
| x /= y | x = x / y | Division |
| x %= y | x = x % y | Modulus |
| a .= b | a = a . b | Concatenate two strings |
PHP Incrementing/Decrementing Operators
| Operator | Name | Description |
|---|---|---|
| ++ x | Pre-increment | Increments x by one, then returns x |
| x ++ | Post-increment | Returns x, then increments x by one |
| -- x | Pre-decrement | Decrements x by one, then returns x |
| x -- | Post-decrement | Returns x, then decrements x by one |
PHP Comparison Operators
Comparison operators allows you to compare two values:| Operator | Name | Description | Example |
|---|---|---|---|
| x == y | Equal | True if x is equal to y | 5==8 returns false |
| x === y | Identical | True if x is equal to y, and they are of same type | 5==="5" returns false |
| x != y | Not equal | True if x is not equal to y | 5!=8 returns true |
| x <> y | Not equal | True if x is not equal to y | 5<>8 returns true |
| x !== y | Not identical | True if x is not equal to y, or they are not of same type | 5!=="5" returns true |
| x > y | Greater than | True if x is greater than y | 5>8 returns false |
| x < y | Less than | True if x is less than y | 5<8 returns true |
| x >= y | Greater than or equal to | True if x is greater than or equal to y | 5>=8 returns false |
| x <= y | Less than or equal to | True if x is less than or equal to y | 5<=8 returns true |
PHP Logical Operators
| Operator | Name | Description | Example |
|---|---|---|---|
| x and y | And | True if both x and y are true | x=6 y=3 (x < 10 and y > 1) returns true |
| x or y | Or | True if either or both x and y are true | x=6 y=3 (x==6 or y==5) returns true |
| x xor y | Xor | True if either x or y is true, but not both | x=6 y=3 (x==6 xor y==3) returns false |
| x && y | And | True if both x and y are true | x=6 y=3 (x < 10 && y > 1) returns true |
| x || y | Or | True if either or both x and y are true | x=6 y=3 (x==5 || y==5) returns false |
| ! x | Not | True if x is not true | x=6 y=3 !(x==y) returns true |
PHP Array Operators
| Operator | Name | Description |
|---|---|---|
| x + y | Union | Union of x and y |
| x == y | Equality | True if x and y have the same key/value pairs |
| x === y | Identity | True if x and y have the same key/value pairs in the same order and are of the same type |
| x != y | Inequality | True if x is not equal to y |
| x <> y | Inequality | True if x is not equal to y |
| x !== y | Non-identity | True if x is not identical to y |
PHP String Variables
A string variable is used to store and manipulate text.
String Variables in PHP
String variables are used for values that contain characters.After we have created a string variable we can manipulate it. A string can be used directly in a function or it can be stored in a variable.
In the example below, we create a string variable called txt, then we assign the text "Hello world!" to it. Then we write the value of the txt variable to the output:
Example
<?php
$txt="Hello world!";
echo $txt;
?>
$txt="Hello world!";
echo $txt;
?>
 |
Note: When you assign a text value to a variable, remember to put single or double quotes around the value. |
|---|
The PHP Concatenation Operator
There is only one string operator in PHP.The concatenation operator (.) is used to join two string values together.
The example below shows how to concatenate two string variables together:
Example
<?php
$txt1="Hello world!";
$txt2="What a nice day!";
echo $txt1 . " " . $txt2;
?>
$txt1="Hello world!";
$txt2="What a nice day!";
echo $txt1 . " " . $txt2;
?>
The output of the code above will be: Hello world! What a nice day!
Tip: In the code above we have used the concatenation operator two times. This is because we wanted to insert a white space between the two strings.
The strlen() function returns the length of a string, in characters.
The example below returns the length of the string "Hello world!":
Tip: In the code above we have used the concatenation operator two times. This is because we wanted to insert a white space between the two strings.
The PHP strlen() function
Sometimes it is useful to know the length of a string value.The strlen() function returns the length of a string, in characters.
The example below returns the length of the string "Hello world!":
Example
<?php
echo strlen("Hello world!");
?>
echo strlen("Hello world!");
?>
The output of the code above will be: 12
Tip: strlen() is often used in loops or other functions, when it is important to know when a string ends. (i.e. in a loop, we might want to stop the loop after the last character in a string).
If a match is found, it will return the character position of the first match. If no match is found, it will return FALSE.
The example below searches for the text "world" in the string "Hello world!":
Tip: strlen() is often used in loops or other functions, when it is important to know when a string ends. (i.e. in a loop, we might want to stop the loop after the last character in a string).
The PHP strpos() function
The strpos() function is used to search for a character or a specific text within a string.If a match is found, it will return the character position of the first match. If no match is found, it will return FALSE.
The example below searches for the text "world" in the string "Hello world!":
Example
<?php
echo strpos("Hello world!","world");
?>
echo strpos("Hello world!","world");
?>
The output of the code above will be: 6.
Tip: The position of the string "world" in the example above is 6. The reason that it is 6 (and not 7), is that the first character position in the string is 0, and not 1.
The PHP string reference contains description and example of use, for each function!
Tip: The position of the string "world" in the example above is 6. The reason that it is 6 (and not 7), is that the first character position in the string is 0, and not 1.
Complete PHP String Reference
For a complete reference of all string functions, go to our complete PHP String Reference.The PHP string reference contains description and example of use, for each function!
PHP Variables
Variables are "containers" for storing information:
Example
<?php
$x=5;
$y=6;
$z=$x+$y;
echo $z;
?>
$x=5;
$y=6;
$z=$x+$y;
echo $z;
?>
Much Like Algebra
x=5y=6
z=x+y
In algebra we use letters (like x) to hold values (like 5).
From the expression z=x+y above, we can calculate the value of z to be 11.
In PHP these letters are called variables.
|
Think of variables as containers for storing data. |
|---|
PHP Variables
As with algebra, PHP variables can be used to hold values (x=5) or expressions (z=x+y).Variable can have short names (like x and y) or more descriptive names (age, carname, totalvolume).
Rules for PHP variables:
- A variable starts with the $ sign, followed by the name of the variable
- A variable name must begin with a letter or the underscore character
- A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
- A variable name should not contain spaces
- Variable names are case sensitive ($y and $Y are two different variables)
|
Both PHP statements and PHP variables are case-sensitive. |
|---|
Creating (Declaring) PHP Variables
PHP has no command for declaring a variable.A variable is created the moment you first assign a value to it:
$txt="Hello world!";
$x=5;
$x=5;
Note: When you assign a text value to a variable, put quotes around the value.
PHP is a Loosely Typed Language
In the example above, notice that we did not have to tell PHP which data type the variable is.PHP automatically converts the variable to the correct data type, depending on its value.
In a strongly typed programming language, we will have to declare (define) the type and name of the variable before using it.
PHP Variable Scopes
The scope of a variable is the part of the script where the variable can be referenced/used.PHP has four different variable scopes:
- local
- global
- static
- parameter
Local Scope
A variable declared within a PHP function is local and can only be accessed within that function:Example
<?php
$x=5; // global scope
function myTest()
{
echo $x; // local scope
}
myTest();
?>
$x=5; // global scope
function myTest()
{
echo $x; // local scope
}
myTest();
?>
The script above will not produce any output because the echo statement
refers to the local scope variable $x, which has not been assigned a value within this scope.
You can have local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared.
Local variables are deleted as soon as the function is completed.
Global variables can be accessed from any part of the script, EXCEPT from within a function.
To access a global variable from within a function, use the global keyword:
You can have local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared.
Local variables are deleted as soon as the function is completed.
Global Scope
A variable that is defined outside of any function, has a global scope.Global variables can be accessed from any part of the script, EXCEPT from within a function.
To access a global variable from within a function, use the global keyword:
Example
<?php
$x=5; // global scope
$y=10; // global scope
function myTest()
{
global $x,$y;
$y=$x+$y;
}
myTest();
echo $y; // outputs 15
?>
$x=5; // global scope
$y=10; // global scope
function myTest()
{
global $x,$y;
$y=$x+$y;
}
myTest();
echo $y; // outputs 15
?>
PHP also stores all global variables in an array called $GLOBALS[index].
The index holds the name of the variable. This array is also accessible from
within functions and can be used to update global variables directly.
The example above can be rewritten like this:
To do this, use the static keyword when you first declare the variable:
The example above can be rewritten like this:
Example
<?php
$x=5;
$y=10;
function myTest()
{
$GLOBALS['y']=$GLOBALS['x']+$GLOBALS['y'];
}
myTest();
echo $y;
?>
$x=5;
$y=10;
function myTest()
{
$GLOBALS['y']=$GLOBALS['x']+$GLOBALS['y'];
}
myTest();
echo $y;
?>
Static Scope
When a function is completed, all of its variables are normally deleted. However, sometimes you want a local variable to not be deleted.To do this, use the static keyword when you first declare the variable:
Example
<?php
function myTest()
{
static $x=0;
echo $x;
$x++;
}
myTest();
myTest();
myTest();
?>
function myTest()
{
static $x=0;
echo $x;
$x++;
}
myTest();
myTest();
myTest();
?>
PHP Syntax
The PHP script is executed on the server, and the plain HTML result
is sent back to the browser.
Basic PHP Syntax
A PHP script can be placed anywhere in the document.A PHP script starts with <?php and ends with ?>:
<?php
// PHP code goes here
?>
// PHP code goes here
?>
A PHP file normally contains HTML tags, and some PHP scripting code.
Below, we have an example of a simple PHP file, with a PHP script that sends the text "Hello World!" back to the browser:
Example
<!DOCTYPE html>
<html>
<body>
<h1>My first PHP page</h1>
<?php
echo "Hello World!";
?>
</body>
</html>
<html>
<body>
<h1>My first PHP page</h1>
<?php
echo "Hello World!";
?>
</body>
</html>
Comments in PHP
Example
<!DOCTYPE html>
<html>
<body>
<?php
//This is a PHP comment line
/*
This is
a PHP comment
block
*/
?>
</body>
</html>
<html>
<body>
<?php
//This is a PHP comment line
/*
This is
a PHP comment
block
*/
?>
</body>
</html>
PHP Installation
What Do I Need?
To start using PHP, you can:- Find a web host with PHP and MySQL support
- Install a web server on your own PC, and then install PHP and MySQL
Use a Web Host With PHP Support
If your server has activated support for PHP you do not need to do anything.Just create some .php files, place them in your web directory, and the server will automatically parse them for you.
You do not need to compile anything or install any extra tools.
Because PHP is free, most web hosts offer PHP support.
Set Up PHP on Your Own PC
However, if your server does not support PHP, you must:- install a web server
- install PHP
- install a database, such as MySQL
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PHP Tutorial
PHP is a server scripting language, and is a powerful tool for making dynamic and interactive Web pages.PHP is a widely-used, free, and efficient alternative to competitors such as Microsoft's ASP.
Easy Learning with "Show PHP"
Our "Show PHP" tool makes it easy to learn PHP, it shows both the PHP source code and the HTML output of the code.Example
<!DOCTYPE html>
<html>
<body>
<?php
echo "My first PHP script!";
?>
</body>
</html>
PHP code is executed on the server.
What You Should Already Know
Before you continue you should have a basic understanding of the following:- HTML
- JavaScript
What is PHP?
- PHP stands for PHP: Hypertext Preprocessor
- PHP is a widely-used, open source scripting language
- PHP scripts are executed on the server
- PHP is free to download and use
|
PHP is simple for beginners. PHP also offers many advanced features for professional programmers. |
|---|
What is a PHP File?
- PHP files can contain text, HTML, JavaScript code, and PHP code
- PHP code are executed on the server, and the result is returned to the browser as plain HTML
- PHP files have a default file extension of ".php"
What Can PHP Do?
- PHP can generate dynamic page content
- PHP can create, open, read, write, and close files on the server
- PHP can collect form data
- PHP can send and receive cookies
- PHP can add, delete, modify data in your database
- PHP can restrict users to access some pages on your website
- PHP can encrypt data
Why PHP?
- PHP runs on different platforms (Windows, Linux, Unix, Mac OS X, etc.)
- PHP is compatible with almost all servers used today (Apache, IIS, etc.)
- PHP has support for a wide range of databases
- PHP is free. Download it from the official PHP resource: www.php.net
- PHP is easy to learn and runs efficiently on the server side
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