This section will document any updates applied to the project since original release:

• revision #: <description> (datestring)

In this project, resume our conceptual journey and explore another data structure: stacks.

A stack is considered one of the most important data structures, along with queues (next week's project) and trees. And it is largely because of how often we find them playing out in nature or our day-to-day lives.

The word “stack” is defined as:

• (generically): a pile of objects, typically one that is neatly arranged
• (computing): a set of storage locations that store data in such a way that the most recently stored item is the first to be retrieved

Additionally, when viewing it as a verb (an action), we also find some positive computing application (bolded) in a less reputable cardplaying usage:

• shuffle or arrange (a deck of cards) dishonestly so as to gain an unfair advantage

Or, to distill it out:

• arrange so as to gain advantage

Combining with our previous definitions, we have:

• a set of storage locations that are arranged in such a way so as to give us an advantage- the most recently stored item (the last to be placed onto the stack) is the first to be retrieved.

So, how does all this list and node stuff play into our stack implementation?

Well, we're going to build the stack ON TOP OF lists (which are composed of nodes).

Therefore, a stack is a data structure that stores its data in a list (which consists of nodes), and we apply various rules/restrictions on our access of that list data.

The concept of restricting access is a very important one- which we did with our list as well (limiting our access to the list through the use of append(), insert(), and obtain() versus manipulating the next/prev pointers manually all the time). By limiting how we access the data, we give ourselves certain algorithmic advantages:

• error reduction: if have a small set of operations that can do one thing, and do their one thing extremely well (insert(), append(), and obtain() again, for instance), we can then rely on them to do the low-level grunt work, freeing us up to accomplish higher level tasks (such as sorting or swapping), or even things like determining if a word is a palindrome.
• performance: by restricting our available choices, the edge cases we have to check for are reduced, and in ideal situations, the average case moves closer to the best case.

It is common to think of a stack as a vertical object, much like a pile of papers that need to be processed (or a pile of anything we need to work with).

Although we've commonly viewed lists horizontally (from left to right), there is absolutely nothing requiring this positional orientation.

Similarly, stacks possess no mandatory orientation, but we do usually visualize them as vertical entities, largely because that's how the piles of paper that accumulate on our desks tend to grow.

The stack data structure presents certain advantages that encourages its use in solving problems (why do we stack a bunch of papers all in the same place to create piles? Why is that more advantageous than giving each one its own unique desk space?), and we accomplish that by its compositional definition:

• a stack has a top, basically a node pointer that constantly points to the top node in the stack (equivalent to the underlying list's start or end pointer– you can decide which one you want to use).
• to put an item on the stack, we push it there. So one of the functions we'll be implementing is push(), which will take the node we wish to place on the given stack, and push will handle all the necessary coordination with its underlying list.
• to get an item off of the stack, we pop it. In our pop() function, we grab the top node off the stack (this also translates into a set of list-level transactions that our pop() function will handle for us).

These qualities cause the stack to be described as a LIFO (or FILO) structure:

• LIFO: Last In First Out
• FILO: First In Last Out

And that describes what is conceptually going on– if we can ONLY access our data through one location (the top), the data most immediately available to us is that which we most recently placed there (hence the last one we pushed in would be the first one we get back when popping it).

This concept is very important, and being aware of it can be of significant strategic importance when going about solving problems (and seeing its pattern proliferate in nature).

With that said, the existence of top, along with the core push() and pop() functions defines the minimal necessary requiments to interface with a stack. Sometimes we'll see additional actions sneak in. While these may be commonly associated with stacks, they should not be confused as core requiments of a stack:

• peek: the ability to gain access to the top node without removing it from the stack
• is the stack empty?: the ability to query the stack and determine if it is empty or non-empty (or perhaps if non-empty, how full is it?)

There

For this project, we're going to be re-implementing MOST of the previous node and list functions. There have been a few changes, namely:

1

#ifndef _NODE_H
#define _NODE_H
 
#include <stdlib.h>
 
struct node {
        char         data;
        struct node *prev;
        struct node *next;
};
typedef struct node Node;
 
Node *mknode(char  );     // allocate new node containing value
Node *rmnode(Node *);     // deallocate node
Node *cpnode(Node *);     // duplicate node
 
#endif

There is an addition of a “prev” node pointer, to allow connections to our previous neighbors.

The node value element has been renamed to “data”, just to make sure you understand what is going on code-wise.

1

#ifndef _LIST_H
#define _LIST_H
 
#include "node.h"                       // list relies on node to work
 
struct list {
    Node *start;                        // pointer to start of list
    Node *end;                          // pointer to end of list
};
typedef struct list List;               // because we deserve nice things
 
List *mklist(void  );                   // create/allocate new list struct
List *cplist(List *);                   // copy (duplicate) list
List *rmlist(List *);                   // remove all nodes from list
 
List *insert (List *, Node *, Node *);  // add node before given node
List *append (List *, Node *, Node *);  // add node after given node
List *obtain (List *, Node **       );  // obtain/disconnect node from list
 
void  display(List *, int);             // display list according to mode
 
Node *findnode(List *, int);            // locate node containing value
List *sortlist(List *, int);            // sort list (according to mode)
 
List *swapnode(List *, Node *, Node *); // swap positions of given nodes in list
 
#endif

The following changes have taken place:

• qty has been removed from the list; any code you wrote that is based on it will need to be implemented a different way (do NOT recreate the conditions to continue relying on a count, you will lose credit if you do so).
• getpos()/setpos() are no longer present. In many ways their functionality is no longer needed with the doubly-linked nature of the list.
• searchlist() has been renamed to findnode() (aesthetic change, to keep function names at 8 characters or less).
• displayf()/displayb() are gone, and previous functionality will be merged into one universal display() function.

In src/node/, you will find skeletons of what was previously there, ready for you to re-implement.

In src/list/, you will find the same- skeletons of the above prototyped functions, hollowed out in anticipation of being made operational.

Figure out what is going on, the connections, and make sure you understand it.

As ALL source files are now skeletons, no sample code has been given. This is intended to be a fresh implementation. While you may reference old code, do not rely on it- try your hand at implementing the functionality from scratch (the more you do this from scratch, the more it will help you).

In testing/list/unit/, you will find these new files:

• unit-append.c - unit test for append() library function
• unit-insert.c - unit test for insert() library function
• unit-swapnode.c - unit test for swapnode() library function
• unit-sortlist.c - unit test for sortlist() library function
• unit-display.c - unit test for display() library function

Additional unit tests will be provided via dll0 project updates.

There are also corresponding verify-FUNCTION.sh scripts that will output a “MATCH”/“MISMATCH” to confirm overall conformance with the pertinent list functionality.

These are complete runnable programs (when compiled, and linked against the list library, which is all handled for you by the Makefile system in place).

Of particular importance, I want you to take a close look at:

• the source code to each of these unit tests
  • the purpose of these programs is to validate the correct functionality of the respective library functions
  • follow the logic
  • make sure you understand what is going on
  • ask questions to get clarification!
• the output from these programs once compiled and ran
  • analyze the output
  • make sure you understand what is going on
  • ask questions to get clarification!

To be successful in this project, the following criteria must be met:

• Project must be submit on time, by the posted deadline.
  • Late submissions will lose 25% credit per day, with the submission window closing on the 4th day following the deadline.
• All code must compile cleanly (no warnings or errors)
  • all requested functions must be implemented in the related library
  • all requested functionality must conform to stated requirements (either on this project page or in comment banner in source code files themselves).
• Executed programs must display in a manner similar to provided output
  • output formatted, where applicable, must match that of project requirements
• Processing must be correct based on input given and output requested
• Output must be correct (i.e. the list visualization, where applicable) based on values input
• Code must be nicely and consistently indented (you may use the indent tool)
• Code must be commented
  • Any “to be implemented” comments MUST be removed
    • these “to be implemented” comments, if still present at evaluation time, will result in points being deducted.
  • Sufficient comments explaining the point of provided logic MUST be present
• Track/version the source code in a repository
• Submit a copy of your source code to me using the submit tool (make submit will do this) by the deadline.