How to assign oxidation number of sulfur in thiocyanate anion?

Recently I was trying to solve a redox chemical equation:

$\ce{CuSCN + KIO3 + HCl <=> CuSO4 + KCl + HCN + ICI + H2O}$

The equation is in principle simple to solve; 1 element (I) is reduced and 2 elements (Cu, S) get oxidized. Number of exchanged electrons in both cases must be the same. However my problem is that I don't know how to assign the oxidation number to sulfur in a thiocyanate anion.

Later I solved the equation using matrix method and via obtained reaction coefficients ($4,7,14,4,7,4,7,5$) concluded that oxidation state of sulfur in thiocyanate is zero. Result is very surprising, because oxidation number zero in heteroatomic molecules is not common.

My questions are: how to assign the oxidation number in such cases? How is it possible that oxidation number of an atom bound to a more eletropositive atom is zero?

• If you assume that carbon isn't reduced that you'll get such result, but it's wrong assumption. – Mithoron Mar 3 '16 at 20:04
• Thanks for the idea! Only now oxidation states in relation to atom's valency make more sense. In $SCN^{-}$ I assigned oxidation states as S=-2, C=4, N=-3 and in $CN^{-}$ as C=2, N=-3 – Rok Narobe Mar 3 '16 at 20:39