Animated Horizontal Lines

Animate horizontal lines. To achieve this we use "variables" for the first time. A variable is like a box where we can store a value and reuse this same value multiple times in our program.

A horizontal line has a starting and an ending point, and both are at the same distance from the top border of the screen. To make sure both points are at the same distance from the top (both have the same Y value), we use twice a variable that contains our Y value.

