5.0. Introduction

Along with conditional logic, variables are the core of what makes computer programs powerful and flexible. If you think of a variable as a bucket with a name that holds a value, PHP lets you have plain old buckets, buckets that contain the name of other buckets, buckets with numbers or strings in them, buckets holding arrays of other buckets, buckets full of objects, and just about any other variation on that analogy you can think of.

A variable is either set or unset. A variable with any value assigned to it, true or false, empty or nonempty, is set. The function isset(  ) returns true when passed a variable that’s set. To turn a variable that’s set into one that’s unset, call unset(  ) on the variable or assign null to the variable. Scalars, arrays, and objects can all be passed to unset(  ). You can also pass unset(  ) multiple variables to unset them all: