Abstract

In this programming assignment, you will use linked lists to represent strings. You will implement functions that manipulate these linked lists to transmute the strings they represent. In doing so, you will master the craft of linked list manipulation! By completing this assignment, you will also gain experience with file I/O in C and processing command line arguments.

1. Overview

1.1. Array Representation of Strings in C

We have seen that strings in C are simply char arrays that use the null terminator (the character \0) to mark the end of a string. For example, the word dwindle is represented as follows:

d w i n d l e \0 x f

Notice the unused portion of the array may contain garbage data.

1.2. A Linked List Representation of Strings

In this assignment, we will use linked lists to represent strings. Each node will contain a single

character of the string. The null terminator ('\0) will not be afforded its own node in the linked list.

Instead, we will know that we have reached the end of a string when we encounter a NULL pointer.

For example, the word dwindle is represented as follows:

d --> w --> i --> n --> d --> l --> e --> NULL

The bulk of this assignment will involve writing functions to transmute these so-called listy strings.

1.3. ListyString and ListyNode Structs (ListyString.h)

For your linked lists, you must use the structs we have specified in ListyString.h without any

modifications. You must #include this header file from ListyString.c like so:

#include "ListyString.h"

The node struct you will use for your linked lists is defined in ListyString.h as follows:

typedef struct ListyNode

{

char data; // Each node holds a single character.

struct ListyNode *next; // Pointer to next node in linked list.

} ListyNode;

Additionally, there is a ListyString struct that you will use to store the head of each linked list string, along with the length of that list:

typedef struct ListyString

{

struct ListyNode *head; // Pointer to head of string's linked list.

int length; // Length of this string / linked list.

} ListyString;

2. Input Files

In this assignment, you will have to open and process an input file. When we run your program, we will use a command line argument to specify the name of the input file that your program will read. We will always provide a single command line argument after the name of the executable file when running your program at the command line. For example:

./a.out input01.txt

The first line of the input file will always be a single string that contains at least 1 character and no more than 1023 characters, and no spaces. The first thing you should do when processing an input file is to read in that string and convert it to a ListyString (i.e., a linked list string). That will become your working string, and you will manipulate it according to the remaining commands in the input file.

Each of the remaining lines in the file will correspond to one of the following string manipulation commands, which you will apply to your working string in order to achieve the desired output for your program:

Command Description

@ key str In your working string, replace all instances of key with str.

+ str Concatenate str to the end of your working string.

- key Delete all instances of key (if any) from your working string.

~ Reverse the working string.

? Print the number of characters in the working string.

! Print the working string.

Important note: For the first three commands listed in this table, key is always a single character, and str is a string. Both key and str are guaranteed to contain alphanumeric characters only (A-Z, a-z, and 0-9). Not counting the need for a null terminator ('\0), str can range from 1 to 1023 characters (inclusively). So, with the null terminator, you might need up to 1024 characters to store str as a char array when reading from the input file.

Another important note: If one of the above commands modifies your working string, you should also ensure that the length member of that ListyString struct gets updated. For more concrete examples of how these commands work, see the attached input/output files and check out the function descriptions below in Section 3, Function Requirements (page 4).

3. Function Requirements

In the source file you submit, ListyString.c, you must implement the following functions. You may implement any auxiliary functions you need to make these work, as well. Please be sure the spelling, capitalization, and return types of your functions match these prototypes exactly.

Important note: The input file specification in Section 2, Input Files, gives certain restrictions on the strings youll have to process from those input files. Namely, strings in the input file are limited to 1023 characters and are always alphanumeric strings with no spaces or other non-alphanumeric characters. Those restrictions are designed to make your processInputFile() function more manageable, and only apply when reading from an input file. Those restrictions do not apply when we call your functions in unit testing. For example, we could pass the string Hello, world! to your createListyString() function when we call it manually during unit testing.

int main(int argc, char **argv);

Description: You have to write a main() function for this program. It should only do the following three things: (1) capture the name of an input file (passed as a command line argument), (2) call the processInputFile() function (passing it the name of the input file to be processed), and (3) return zero.

Returns: 0 (zero).

int processInputFile(char *filename);

Description: Read and process the input file (whose name is specified by the string filename) according to the description above in Section 2, Input Files. To perform the string manipulations described in that section, you should call the corresponding required functions listed below. In the event that a bad filename is passed to this function (i.e., the specified file does not exist), this function should simply return 1 without producing any output.

Output: This function should only produce output if the input file has ? and/or ! commands. For details, see Section 2 (Input Files), or refer to the input/output files included with this assignment. Note that this function should not produce any output if the input file does not exist.

Returns: If the specified input file does not exist, return 1. Otherwise, return 0.

ListyString *createListyString(char *str);

Description: Convert str to a ListyString by first dynamically allocating a new ListyString struct, and then converting str to a linked list string whose head node will be stored inside that ListyString struct. Be sure to update the length member of your new ListyString, as well.

Special Considerations: str may contain any number of characters, and it may contain nonalphanumeric characters. If str is NULL or an empty string (), simply return a new ListyString whose head is initialized to NULL and whose length is initialized to zero.

Runtime Requirement: This should be an O(k) function, where k is the length of str.

Returns: A pointer to the new ListyString. Ideally, this function would return NULL if any calls to malloc() failed, but I do not intend to test your code in an environment where malloc() would fail, so you are not required to check whether malloc() returns NULL.

ListyString *destroyListyString(ListyString *listy);

Description: Free any dynamically allocated memory associated with the ListyString and return NULL. Be sure to avoid segmentation faults in the event that listy or listy->head are NULL.

Returns: NULL.

ListyString *cloneListyString(ListyString *listy);

Description: Using dynamic memory allocation, create and return a new copy of listy. Note that you should create an entirely new copy of the linked list contained within listy. (That is, you should not just set your new ListyStrings head pointer equal to listyhead.) The exception here is that if listy->head is equal to NULL, you should indeed create a new ListyStruct whose head member is initialized to NULL and whose length member is initialized to zero. If listy is NULL, this function should simply return NULL.

Runtime Requirement: The runtime of this function should be no worse than O(n), where n is the length of the ListyString.

Returns: A pointer to the new ListyString. If the listy pointer passed to this function is NULL, simply return NULL.

void replaceChar(ListyString *listy, char key, char *str);

Description: This function takes a ListyString (listy) and replaces all instances of a certain character (key) with the specified string (str). If str is NULL or the empty string (), this function simply removes all instances of key from the linked list. If key does not occur anywhere in the linked list, the list remains unchanged. If listy is NULL, or if listy->head is NULL, simply return.

Important Note: Be sure to update the length member of the ListyString as appropriate.

Runtime Requirement: The runtime of this function should be no worse than O(n + km), where n is the length of the ListyString, k is the number of times key occurs in the ListyString, and m is the length of str.

Returns: Nothing. This is a void function.

void reverseListyString(ListyString *listy);

Description: Reverse the linked list contained within listy. Be careful to guard against segfaults in the cases where listy is NULL or listy->head is NULL.

Runtime Consideration: Ideally, this function should be O(n), where n is the length of the ListyString. Note that if you repeatedly remove the head of listys linked list and insert it at the tail of a new linked list using a slow tail insertion function, that could devolve into an O(n2) approach to solving this problem.

Returns: Nothing. This is a void function.

ListyString *listyCat(ListyString *listy, char *str);

Description: Concatenate str to the end of the linked list string inside listy. If str is either NULL or the empty string (), then listy should remain unchanged. Be sure to update the length member of listy as appropriate.

Special Considerations: If listy is NULL and str is a non-empty string, then this function should create a new ListyString that represents the string str. If listy is NULL and str is NULL, this function should simply return NULL. If listy is NULL and str is a non-NULL empty string (), then this function should return a ListyString whose head member has been initialized to NULL and whose length member has been initialized to zero.

Runtime Requirement: The runtime of this function must be no worse than O(n+m), where n is the length of listy and m is the length of str.

Returns: If this function caused the creation of a new ListyString, return a pointer to that new ListyString. If one of the special considerations above requires that a NULL pointer be returned, then do so. Otherwise, return listy.

int listyCmp(ListyString *listy1, ListyString *listy2);

Description: Compare the two ListyStrings. Return 0 (zero) if they represent equivalent strings. Otherwise, return any non-zero integer of your choosing. Note that the following are not considered equivalent: (1) a NULL ListyString pointer and (2) a non-NULL ListyString pointer in which the head member is set to NULL (or, equivalently, the length member is set to zero). For the purposes of this particular function, (2) represents an empty string, but (1) does not. Two NULL pointers are considered equivalent, and two empty strings are considered equivalent, but a NULL pointer is not equivalent to an empty string.

Runtime Requirement: The runtime of this function must be no worse than O(n+m), where n is the length of listy1 and m is the length of listy2.

Returns: 0 (zero) if the ListyStrings represent equivalent strings; otherwise, return any integer other than zero.

int listyLength(ListyString *listy);

Description: Return the length of the ListyString (i.e., the length of listys linked list).

Runtime Requirement: The runtime of this function must be O(1).

Returns: The length of the string (i.e., the length of the linked list contained within listy). If listy is NULL, return -1. If listy is non-NULL, but listy->head is NULL, return zero.

void printListyString(ListyString *listy);

Description: Print the string stored in listy, followed by a newline character, . If listy is NULL, or if listy represents an empty string, simply print (empty string) (without the quotes), follow by a newline character, .

Returns: Nothing. This is a void function.

ListyString.h File:

#ifndef __LISTY_STRING_H

#define __LISTY_STRING_H

typedef struct ListyNode

{

// Each node holds a single character.

char data;

// Pointer to next node in linked list.

struct ListyNode *next;

} ListyNode;

typedef struct ListyString

{

// Head of the linked list representing this string.

ListyNode *head;

// Length of this linked list.

int length;

} ListyString;

// The following line is modified automatically by the test-all.sh script to

// enable and disable unit testing. Uncomment the following line if you are

// compiling your code with one of the unit tests (testcase06.c through

// testcase31.c) provided with the assignment.

//#define main __hidden_main__

// Functional Prototypes

int processInputFile(char *filename);

ListyString *createListyString(char *str);

ListyString *destroyListyString(ListyString *listy);

ListyString *cloneListyString(ListyString *listy);

void replaceChar(ListyString *listy, char key, char *str);

void reverseListyString(ListyString *listy);

ListyString *listyCat(ListyString *listy, char *str);

int listyCmp(ListyString *listy1, ListyString *listy2);

int listyLength(ListyString *listy);

void printListyString(ListyString *listy);

double difficultyRating(void);

double hoursSpent(void);

#endif