Unified Computers & Programming, Spring 2006
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III. Overview
This System Problem is a departure from the C&P work you have done in the past.
While you are typically asked to create the programs, this one will ask you to
modify and add sections to existing code. For this SPL you will be pulling
together many of the C&P lessons. Your program will parse/read a file for
information, store this information in a priority queue, and then dynamically draw
how the pointers are being manipulated in the queue to make this all possible. The
final result should be similar to “test_queue.exe”.
First, what is a priority queue? As you should know, a queue is a method of
dynamically storing information using pointers. By definition, a queue is
supposed to be FIFO (First In, First Out). A priority queue is a little different. You
give the element a value when it is Enqueued. Upon Dequeue, the element in the
queue with the smallest or largest associated value is returned. Our priority queue
will return the element with minimum associated value current in the queue.
In the two files you are expected to modify: “priority_queue.adb” and
“test_queue.adb” you will find comments “--Fill in here as needed.” These
are locations that may need code. Since one of the skills tested in this SPL is code
reuse, read the comments in the given code or associated .ads file! You will
find that most of the .adb files are poorly commented, while the .ads files are
richly commented. This is typical of most programming languages, the
specification file or header file is has more explanations.
The procedures in “priority_queue.adb” that require modification are:
1. MakeEmpty
2. Enqueue – Sort the element into the queue using whatever sort you like.
3. Dequeue – No Sorting, just return the head element
A few words on “priority_queue.adb”
The record types that will form the nodes/elements of the queue have
already been defined and can be found in “priority_queue.ads.”
The general structure of the priority queue is depicted in Figure 1. The
Queue Type holds the basic information you need to know about the
Queue, the size and where its Head and Tail are. The Nodes form the
backbone of the Queue. Each Node has a pointer linking it to the next
Node (which should have a greater Value). Each Node also has a data
Element which gives the (X, Y) coordinates at which each Node should be
drawn in the window. The Tail pointer points to the last Node in the
Queue, which has no pointer to any other Node.
ToDo:
! Modify these procedures so that they act as described in
“priority_queue.ads”. (Hint: Look at the “Linked_List” package
on the Unified C&P Website Extra Material, Lecture C5 for
implementation ideas).
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