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PHP variables

Variables are exactly as their name suggests: variable. If a quantity is not a variable (cannot - or should not - change), then it is a constant (always the same).

To define a constant:

define('LANG', 'english');
echo LANG; //Note: the definition requires quotes, but the use does not

To define a variable in PHP, use a dollar sign ($). e.g. the variable which is the name of a customer being called from a database of many hundreds of customers could be defined as: $name

Concatenation

Variables can be defined (or redefined) at any point in a script. They can also be added together: for example, the full name of a customer could take the two parts of the name and combine them: $fullname = $firstname.$lastname

A problem with this example is that the two name parts will have no space between them. The following example demonstrates how concatenation may be used to include non-variable elements, such as a space or a line break (<br />), into a variable:

<?php

$firstname = 'Fred';

$lastname = 'McGurty';

$fullname = $firstname.$lastname;

echo $fullname;

$fullname = $firstname.' '.$lastname;

echo $fullname;

$fullname = $lastname.', '.$firstname;

echo $fullname;

?>

The output of this code is FredMcGurty, Fred McGurty, and McGurty, Fred

Variable names

Variables are case sensitive and can include the underscore. These variable names: \$Customer, \$customer and \$_customer, are all valid and refer to different stored values.

Variable names may include numbers, but the first character after the dollar sign (\$) must be a letter or an underscore (_). $variable1 and $_variable1 are valid, but $1variable is not.

For clarity, a common technique to make variable names with multiple words more readable is to use the 'camelCase'. Instead of making a variable for 'my next great idea' $mynextgreatidea, we use the camel case to make it more legible: $myNextGreatIdea

Assignment Operator =

The equals sign (=) is used to assign a value to a variable. If the variable does not exist, the assignment also creates a new variable with this name. If the variable exists and has a previous value, the assignment replaces the previous value with the new value in the assignment statement. For example:

<?php

$newVariable = '42';

echo $newVariable;

?>

The output will be 42

<?php

$oldVariable = '42';

$oldVariable = '21';

$newVariable = $oldVariable;


?>

The $oldVariable value (42) is replaced by the new value (21). In this example, a new variable is then created and given the same value as the old variable.

Now, examine the difference between these two echo statements:

<?php

echo 'The value stored in the newly created variable $newVariable is '.$newVariable;

echo "The value stored in the newly created variable $newVariable is ".$newVariable;


?>

The outputs are:
The value stored in the newly created variable $newVariable is 21.

Content © Andrew Bone. All rights reserved. Created : October 14, 2015 Last updated :March 5, 2016

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