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:
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:
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:
The output of this code is
Fred McGurty, and
Variables are case sensitive and can include the underscore. These variable names:
\$_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 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:
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:
The output will be
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
The outputs are:
The value stored in the newly created variable $newVariable is 21.
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