Based on oxidation number consideration, explain why carbon monoxide is a flammable but carbon dioxide is not

Carbon in carbon monoxide has oxidation number +2 and can be oxidized to oxidation number +4 (carbon(IV) oxide) in reaction with oxygen:
2CO + O₂ → 2CO₂.
Carbon has maximal oxidation number in carbon(IV) oxide and cannot be more oxidized (increase of oxidation number), carbon with oxydation number +4 cannot lose electrons to molecule of oxygen.