ex11_04.c

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/* Exercise 11.4 Using a structure to record the count of occurrences of a word. */
/*
  This program defines a structure that stores a word and the count of its occurrences.
  The structures are stored as they are created in a linked list. If you wanted the
  output in alphabetical order, you could insert the structures in the list to ensure
  that the list was ordered. Alternatively you could sort the list.
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

#define MAX_WORD_LENGTH    31
#define MAX_TEXT_LENGTH 10000

/* Structure defining a count of the occurrences of a given word */
struct WordCounter
{
  char *word;
  int word_count;
  struct WordCounter *pNext;                        /* Pointer to the next word counter in the list */
};

/* Function prototypes */
void addWord(char *pWord);                          /* Adds a word to the list or updates exisiting word */
bool is_separator(char ch);                         /* Tests for a separator character */
void show(struct WordCounter *pWordcounter);        /* Outputs a word and its count of occurrences */
struct WordCounter* createWordCounter(char *word);  /* Creates a new WordCounter structure */

/* Global variables */
struct WordCounter *pStart = NULL;                  /* Pointer to first word counter in the list */


int main(void)
{
  char text[MAX_TEXT_LENGTH];           /* Stores input text         */
  char buffer[MAX_WORD_LENGTH];         /* Buffer to hold a word     */
  size_t i = 0;                         /* Index to text             */
  int len = 0 ;                         /* Word length               */
  struct WordCounter *pCounter = NULL;  /* Pointer to a word counter */

  /* Read the text from the keyboard */
  printf("Enter the text:\n");
  gets(text);

  /* Extract the words from the text  */
  while(text[i] != '\0')
  {
    /* Skip over separators */
    while(is_separator(text[i]))
      ++i;

    /* It is either the end of the string or the start of a word    */
    /* As long as it is not the string terminator copy the character */
    len = 0;              /* Reset character count    */
    while((!is_separator(text[i])) && (text[i] != '\0'))
      buffer[len++] = text[i++];
    if(len>0)               /* Check we have some characters in the word */
    {
      buffer[len] = '\0';   /* We reached the end of a word so add terminator */
      addWord(buffer);      /* Add the word to the list */
    }
  }

  /* List the words and their counts */
  pCounter = pStart;
  while(pCounter)
  {
    show(pCounter);
    pCounter = pCounter->pNext;
  }
  printf("\n");

  /* Free the memory that we allocated */
  pCounter = pStart;
  while(pCounter)
  {
    free(pCounter->word);        /* Free space for the word */
    pStart = pCounter;           /* Save address of current */
    pCounter = pCounter->pNext;  /* Move to next counter    */
    free(pStart);                /* Free space for current  */
  }
  return 0;
}

/* Returns true if the argument is a separator character and false otherwise */
bool is_separator(char ch)
{
  /* Separators are space, comma, colon, semicolon, double quote, question mark, exclamation, and period */
  static char separators[] = { ' ' , ',',':' , '\"', '?' , '!' , '.'};

  for(int i = 0 ; i<sizeof separators ; i++)
  {
    if(ch == separators[i])
      return true;
  }

  return false;
}

void show(struct WordCounter *pWordcounter)
{
  /* output the word left-justified in a fixed field width followed by the count */
  printf("\n%-30s   %5d", pWordcounter->word,pWordcounter->word_count);
}

void addWord(char *word)
{
  struct WordCounter *pCounter = NULL;
  struct WordCounter *pLast = NULL;

  if(!pStart)
  {
    pStart = createWordCounter(word);
    return;
  }

  /* If the word is in the list, increment its count */
  pCounter = pStart;
  while(pCounter)
  {
    if(strcmp(word, pCounter->word) == 0)
    {
      ++pCounter->word_count;
      return;
    }
    pLast = pCounter;            /* Save address of last in case we need it */
    pCounter = pCounter->pNext;  /* Move pointer to next in the list        */
  }

  /* If we get to here it's not in the list - so add it */
  pLast->pNext = createWordCounter(word);
}

/* Create and returns a new WordCounter object for the argument */
struct WordCounter* createWordCounter(char *word)
{
  struct WordCounter *pCounter = NULL;
  pCounter = (struct WordCounter*)malloc(sizeof(struct WordCounter));
  pCounter->word = (char*)malloc(strlen(word)+1);
  strcpy(pCounter->word, word);
  pCounter->word_count = 1;
  pCounter->pNext = NULL;
  return pCounter;
}