In addition to the fact that it can form up to 4 bonds with other carbon atoms or with atoms of other elements, carbon is also unique in that it can bond with itself either as a straight chain or as a ring with possible in either case.

Four bonds

Explanation:

A carbon atom completes its octet (eight electrons in the outermost shell) only when it shares its valence electrons with other atoms. Hence, a carbon atom forms four covalent bonds by sharing valence electrons with other atoms. This is known as tetravalency of carbon established by August Kekule.

Whether carbon is in a straight chain,branched chain or cyclic structure, it always maintains its tetra valency, that it, it always forms four bonds at a time.