The food smells good: "good" is a subject complement here, and it's an adjective.
He became a physicist: "physicist" is a subject complement, and it's a noun.
An example of an object would be:
He scored a goal (scored what? - a goal): a direct object.
I gave him a tip: "him" (to whom?) is an indirect object. "a tip" (what?) is a direct object.
Student or Learner