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Queues

Queues are declared as an "abstract" class. They are currently implemented in any of three ways.

VQueue
implement fixed sized Queues via arrays.
XPQueue
implement dynamically-sized Queues via XPlexes.
SLQueue
implement dynamically-size Queues via linked lists.

All possess the same capabilities; they differ only in constructors. VQueue constructors require a fixed maximum capacity argument. XPQueue constructors optionally take a chunk size argument. SLQueue constructors take no argument.

Assume the declaration of a base element x.

Queue q; or Queue q(int capacity);
declares a queue.
q.empty()
returns true if queue q is empty.
q.full()
returns true if queue q is full. XPQueues and SLQueues are never full.
q.length()
returns the current number of elements in the queue.
q.enq(x)
enqueues x on queue q.
x = q.deq()
dequeues and returns the front of queue
q.front()
returns a reference to the front of queue.
q.del_front()
dequeues, but does not return the front of queue
q.clear()
removes all elements from the queue.

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