In tests this value is converted to the boolean false. It is often used as a sentinel indicating the end of a linked data structure. See Queues . A queue is used in simulations and operating systems when items have to be stored and their order preserved. A type of container that stores data in a particular order and uses this sequence to access them.
Sequential containers have a front and back element and a size .
You can push and pop items into or from a sequential container. A Stack is useful when something has to be stored while we do something else that might involve saving some more data and so on. The data is retrieved in the reverse order to which it is inserted. See Stacks . The Standard Template Library.