This sentence is grammatically classified as complex, as it is made up of an independent clause and a dependent clause. I is a pronoun, and also the subject of the independent clause, am is a verb, hungry is an adjective modifying I, so is a subordinate conjunction, introducing the dependent clause, I is the subject of the dependent clause, and a pronoun, think is a verb, I'll is a contraction of I and will, which are a pronoun and verb respectively, have is a verb, some is an adjective modifying yogurt, and yogurt is a noun, and, as it happens, the only noun in the sentence.
