need 作為實(shí)義動詞（也叫行為動詞）時,后面接另一個動詞,用不定式,need to do,表示“需要做某事”,其否定形式是 don't/doesn't need to do.例如：I need to clean my room.（我需要打掃我的房間.）否定句為 I don't need to clean my room.
need 作為情態(tài)動詞,只用于否定句或疑問句,不用于肯定句,此時 need 后面直接跟動詞原形.例如：I needn't clean my room.（我不需要打掃我的房間.）Need I clean my room?
相信你能看出以上兩者的區(qū)別.don't need come 就是一個錯誤的結(jié)構(gòu).
此外,need doing 表示“需要被做.”,等于 need to be done.例如：My room need cleaning.= My room need to be cleaned.（我的房間需要被打掃.）那如果答案有needn't come 可以選嗎？needn't come = don't need to come，兩個都正確。