declaration of an external variable
Declares the variables x, y and z external ie wherever they are known and reported. Other variables are local ie unknown
to the outside and lost output function, unless they are declared static, in which case they retain their values.
Given the function:
a(); /* executes the function a */
$x; /* prints external variable x */
prints (1.0 2.0 3.0 4.0 5.0)