  We study one dimensional (1D) carbon ribbons with the armchair edges and the
zigzag carbon nanotubes and their counterparts with finite length (0D) in the
framework of the H\"{u}ckel model. We prove that a 1D carbon ribbon is metallic
if its width (the number of carbon rings) is equal to $2+3n$. We show that the
dispersion law (electron band energy) of a 1D metallic ribbon or a 1D metallic
carbon nanotube has a universal {\it sin-}like dependence at the Fermi energy
which is independent of its width. We find that in case of metallic graphene
ribbons of finite length (rectangular graphene macromolecules) or nanotubes of
finite length the discrete energy spectrum in the vicinity of $\varepsilon=0$
(Fermi energy) can be obtained exactly by selecting levels from the same
dispersion law. In case of a semiconducting graphene macromolecule or a
semiconducting nanotube of finite length the positions of energy levels around
the energy gap can be approximated with a good accuracy. The electron spectrum
of 0D carbon structures often include additional states at energy
$\varepsilon=0$, which are localized on zigzag edges and do not contribute to
the volume conductivity.
