PHP

PHP – Variables

A variable is simply a container that’s used to store both numeric and non-numeric information. And just as with any container, you can move it from  place to place, add stuff to it, or empty it out on the floor in a pile and fill it with something completely different.
PHP has some simple rules for naming variables. Every variable name must be preceded with dollar($) symbol and must begin with a letter or underscore character, optionally followed by more letters, numbers, or underscore character. Common punctuation characters, such as commas, quotation marks, or periods, are not permitted variable names; neither are spaces. So, for example, $root, $_num and $query are all valid variable names, while $58%, $1day, and email are all invalid variable names.
Assigning Values to Variables
Assigning value to a variables in PHP is quite easy: use the equality(=) symbol, which also happens to be PHP’s assignment operator. This assigns the value on the right side of the equation to the variable on the left.
To use a variable in a script, simply call it by name in an expression and PHP will replace it with its value when the script is executed. Here’s an example:

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”
“DTD/xhtml1-transitional.dtd”>
<html xmlns=http://www.w3.org/1999/xhtml  xml:lang=”en” lang=”en”>
<head><title/></head>
<body>
<?php
// assign value to variable
$name= ’Anuj’;
?>
<h2> Welcome to<? Php echo $name; ?>’s Blog!</h2>
</body>
</html>

In this example, the variables $name is assigned the value ‘Simon’. The echo statement is then used to print the value of this variable to the Web page.
You can also assign a variable the value of another variable, or the result of calculation.
The following example demonstrates both these situations:

<?php
//assign value to variable
$now=2008;
// assign value to another variable
$currentYear = $now;
//perform calculation
$lastYear = $currentYear-1;
//output: ‘2007 has ended. Welcome to 2008!’
echo “$lastYear has ended.  Welcome to $currentYear”;
?>

Destroying Variables
To destroy a variable, pass the variable to PHP’s aptly named unset() function, as in the following example:

<?php
//assign value to variable
$car = ‘Porsche’
//print variable value
//output: ‘Before unset(), my car is a Porsche’
Echo “Before unset(), my car is a $car”;
//destroy variable
unset($car);
//print variable vale
//this will generate an ‘undefined variable’ error
//output: ‘After unset(), my car is a’
echo “After unset(), my car is a $car;
?>

Inspecting Variable Content
PHP offers the var_dump() function, which accepts a variable and X-ray it for you.
Here’s example:

<?php
//define variables
$name = ‘Fiona’;
$age = 28;
//display variable contents
var_dump($name);
var_dump($age);
?>

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