A variable is simply a data item that may take on more than one value during the runtime of a program. There! That was the Google definition incase you were looking.
Before we dive into variables we need to understand what values can be set to a variable. These values include, but not limited to:
Variable Rule #1
Variables are represented by a dollar sign followed by the name of the variable. (example: $variable_name)
Variable Rule #2
The variable name is case-sensitive.
Variable Rule #3
A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.
Variable Rule #4
The variable $this is a special variable that can't be assigned.
The following is an example of assigning basic values to variables.
<?php //Null $null_variable = null; //Booleans $boolean_true = true; $boolean_false = false; //Integers $integer1 = 1; $integer2 = 2; $integer3 = 3; //Floats $float1 = 9.99; $float2 = 3.1415926535897932384626433832795028841971693993; //Strings $string1 = "PHP is Awesome"; $string2 = 'Strings can be enclosed with single or double quotes'; //Arrays $array1 = array('red','green','blue'); $array2 = array( 'red'=>1, 'green'=>2, 'blue'=>3 ); ?>
I think that you can see the pattern. Try not to focus on the differences such as:
- Why can strings be enclosed with single or double quotes?
- Why do the two array examples look so different?
Focus more on the format of how variables are assigned. The variable starts with a dollar sign ("$"), and the the value setter is initiated by the equal sign ("=").
Predefined variables are an important feature in PHP. There is a lot to cover here so I will defer to the knowledge base at www.php.net. Check out the resources on the section that covers the predefined variables.