std::queue & std::priority_queue

std::queue<T> is the first-in, first-out (FIFO) sibling of std::stack: items go in at the back, come out from the front, and the order is preserved. std::priority_queue<T> looks similar from the outside but reorders elements internally so the largest one is always next out. Both are container adapters from <queue>, both have a deliberately small interface, and both follow the same top()-then-pop() pattern you saw with std::stack in the previous chapter.