To draw a square with side length 100, we write in the editor:

to square

repeat 4 [forward 100 right 90]

end

repeat 4 [forward 100 right 90]

end

We just have to modify this procedure by doing:

- We add :c at the end of the definition line. This indicates that the procedure is now waiting for an argument called :c
- We replace the side length 100 by the variable name :c

We obtain

to square :c

repeat 4 [forward :c right 90]

end

repeat 4 [forward :c right 90]

end

Therefore, if we write: square 100 square 50 square 30 square 20 square 10