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WEB TECHNOLOGIESUnit 1-PHP
The PHP Hypertext Preprocessor (PHP) is a programming language that allows web developers to
create dynamic content that interacts with databases. PHP is basically used for developing web based
software applications.
PHP is a recursive acronym for "PHP: Hypertext Preprocessor".
PHP is a server side scripting language that is embedded in HTML. It is used to manage dynamic
content, databases, session tracking, even build entire e-commerce sites.
Common uses of PHP
PHP performs system functions, i.e. from files on a system it can create, open, read, write, and close
them.
PHP can handle forms, i.e. gather data from files, save data to a file, thru email you can send data,
return data to the user.
You add, delete, modify elements within your database thru PHP.
Access cookies variables and set cookies.
Using PHP, you can restrict users to access some pages of your website.
It can encrypt data.
Declaring Variables
In PHP, a variable starts with the $ sign, followed by the name of the variable:
<?php
$txt = "Hello world!";
$x = 5;
$y = 10.5;
?>
After the execution of the statements above, the variable $txt will hold the value Hello
world!, the variable $x will hold the value 5, and the variable $y will hold the value 10.5.
PHP Variables
A variable can have a short name (like x and y) or a more descriptive name (age, carname,
total_volume).
Rules for PHP variables:
A variable starts with the $ sign, followed by the name of the variable
A variable name must start with a letter or the underscore character
A variable name cannot start with a number
A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _)
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Variable names are case-sensitive ($age and $AGE are two different variables).
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 other
languages such as C, C++, and Java, the programmer must declare the name and type of the variable
before using it.
PHP Variables Scope
In PHP, variables can be declared anywhere in the script.
The scope of a variable is the part of the script where the variable can be referenced/used.
PHP has three different variable scopes:
local
global
static
Global And Local Scope
A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a
function:
<?php
$x = 5; // global scope
function myTest() {
// using x inside this function will generate an error
echo "<p>Variable x inside function is: $x</p>";
}
myTest();
echo "<p>Variable x outside function is: $x</p>";
?>
A variable declared within a function has a LOCAL SCOPE and can only be accessed within that
function:
<?php
function myTest() {
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$x = 5; // local scope
echo "<p>Variable x inside function is: $x</p>";
}
myTest();
// using x outside the function will generate an error
echo "<p>Variable x outside function is: $x</p>";
?>
PHP Data Types
Variables can store data of different types, and different data types can do different things.
PHP supports the following data types:
String
Integer
Float (floating point numbers - also called double)
Boolean
Array
Object
NULL
Resource
PHP String
A string is a sequence of characters, like "Hello world!".
A string can be any text inside quotes. You can use single or double quotes:
<?php
$x = "Hello world!";
$y = 'Hello world!';
echo $x;
echo "<br>";
echo $y;
?>
PHP Integer
An integer is a whole number (without decimals). It is a number between -2,147,483,648 and
+2,147,483,647.
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Rules for integers:
An integer must have at least one digit (0-9)
An integer cannot contain comma or blanks
An integer must not have a decimal point
An integer can be either positive or negative
Integers can be specified in three formats: decimal (10-based), hexadecimal (16-based -
prefixed with 0x) or octal (8-based - prefixed with 0)
In the following example $x is an integer. The PHP var_dump() function returns the data type and
value:
<?php
$x = 5985;
var_dump($x);
?>
PHP Float
A float (floating point number) is a number with a decimal point or a number in exponential form.
In the following example $x is a float. The PHP var_dump() function returns the data type and value:
<?php
$x = 10.365;
var_dump($x);
?>
PHP Boolean
A Boolean represents two possible states: TRUE or FALSE.
$x = true;
$y = false;
PHP Array
An array stores multiple values in one single variable.
In the following example $cars is an array. The PHP var_dump() function returns the data type and
value:
<?php
$cars = array("Volvo","BMW","Toyota");
var_dump($cars);
?>
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