Variables are created by assigning a value to them.

All variable names are preceded by $   (note: $i, $i++, $++i)

The type of a variable is that of the last assigned value.

Check/set variable type via gettype/settype functions.

Convert variable value via casting   (e.g. (int), (string), ...)

Default value of unassigned variable is   null   (distinguished constant)
(if unset variable used, get 0 or "" or false, depending on context)