An interrogative sentence is a type of sentence that asks a question, as opposed to sentences that make a statement, deliver a command, or express an exclamation. Importantly, an interrogative sentence ends with a question mark.
An exclamatory sentence is a type of main clause that expresses strong feelings in the form of an exclamation, as opposed to sentences that make a statement (declarative sentences), express commands (imperative sentences), or ask a question (interrogatory sentences).
A declarative sentence states a fact. This word can be used to describe any action or speech that makes a statement. Declarative sentences are the opposite of questions. Known as a "mood" in the grammar world, you can also use declarative to describe other things that make a definite statement.
An imperative sentence is a type of sentence that gives instructions or advice, and expresses a command, an order, a direction, or a request. It is also known as a jussive or a directive. Depending upon its delivery, an imperative sentence may end with an exclamation mark or a period.
While i'm not entirely sure, (which is why I put the definitions to help you understand more incase im wrong.) I feel like "This summer is going by too fast" is a exclamatory sentence while "Summer is incomplete without a beach trip" is possibly a imperative sentence. Correct me if i'm wrong though.