K and R C, Solution to Exercise 6-4:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
Write a C Program that prints the distinct words in its input sorted into decreasing order of frequency of occurrence. Precede each word by its count. Read more about C Programming Language .

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#include<stdio.h>
#include<ctype.h>

#define MAXWORD 100
#define NDISTINCT 1000

struct tnode(
  char *word;
int count;
struct tnode *addtree(struct tnode *, char *);
int getword(char *, int);
void sortlist(void);
void treestore(struct tnode *);
struct tnode *list[DISTINCT];
int ntn = 0;

/* print distinct words sorted in decreasing order of freq.*/
main()
{
 struct tnode *root;
 char word[MAXWORD]
           int i;

 root = NULL;
 while(getword(word, MAXWORD) != EOF)
  if(isalpha(word[0]))
   root = addtree(root, word);
 treestore(root);
 sortlist();
 for(i = 0;i < ntn; i++)
  printf("%2d:%20sn",list[i]->count,list[i]->word);
 return 0;
}

//getword: get next word or character from input
int getword(char *word, int lim)
{
 int c, d, comment(void), getch(void);
 void ungetch(int);
 char *w = word;
 while(isspace(c = getch()))
  ;
 if(c !=EOF)
  *w++ = c;
 if(isalpha(c) || c == '-' || c == '#'){
  for(; --lim > 0; w++)
   if(!isalnum(*w = getch()) && *w != '-') {
    ungetch(*w);
    break;
   }
 }
 else if(c == ''' || c == '\'){
  for( ; --lim > 0; w++)
   if(((*w = getch()) == '\')
     *++w = getch();
   else if(*w == c) {
    w++;
    break;
   }else if(*w == EOF)
    break;
 }else if(c == '/')
  if((d = getch()) == '*')
   c = comment();
  else
   ungetch(d);
 *w = '';
 return c;
}


//comment: skip over comment and return a character
int comment()
{
 int c;
 while((c = getch()) != EOF)
  if(c == '*')
   if((c = getch()) == '/')
    break;
   else
    ungetch(c);
 return c;
}

//TREESTORE:STORE IN LIST[] POINTERS TO TREE NODES

void treestore(struct tnode *p)
{
 if(p != NULL) {
  treestore(p->left);
  if(ntn < NDISTINCT)
   list[ntn++] = p;
  treestore(p->right);
 }
}

//sortlist: sort list of pointers to tree nodes
void sortlist()
{
 int gap, i,j;
 struct tnode *temp;

 for(gap = ntn/2;gap > 0;gap /= 2)
  for(i = gap; i < ntn;i++)
   for(j = i - gap;j >= 0;j -= gap) {
    if((list[j]->count) >= (list[j+gap]->count))
     break;
    temp = list[j];
    list[j] = list[j+gap];
    list[j+gap] = temp;
   }
}

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