The main way to store information in the middle of a PHP program is by using a variable. Here are the most important things to know about variables in PHP.
- All variables in PHP are denoted with a dollar sign ($varname).
- The value of a variable is the value of its most assigned.
- All the variables are assigned with the = operator, with the variable on the left-hand side and the expression to be evaluated on the right.
- Variables in PHP do not have intrinsic types - a variable does not know in advance whether it will be used to store a number or a string of characters.
- Variables used before they are assigned have default values.
- PHP does a good job of automatically converting types from one to another when necessary.
- PHP variables are Perl-like.
PHP has a total of eight data types which we use to construct our variables:
- Integers: are whole numbers, without a decimal point, like 4195.
- Doubles: are floating-point numbers, like 3.14159 or 49.1.
- Booleans: have only two possible values either true or false.
- NULL: is a special type that only has one value: NULL.
- Strings: are sequences of characters, like 'PHP supports string operations.'
- Arrays: are named and indexed collections of other values.
- Objects: are instances of programmer-defined classes, which can package up both other kinds of values and functions that are specific to the class.
- Resources: are special variables that hold references to resources external to PHP (such as database connections).
The first five are simple types, and the next two (arrays and objects) are compound - the compound types can package up other arbitrary values of arbitrary type, whereas the simple types cannot.
