Figure 9.14  Two Orderings of One List Using an Array of Pointers
/*
 *  Maintains two orderings of a list of applicants:  the original
 *  ordering of the data, and an alphabetical ordering accessed through an
 *  array of pointers.
 */

#include <stdio.h>
#define STRSIZ 30  /*  maximum string length */
#define MAXAPP 50  /*  maximum number of applications accepted */

int alpha_first(char *list[], int min_sub, int max_sub);
void select_sort_str(char *list[], int n);

int
main(void)
{
      char  applicants[MAXAPP][STRSIZ]; /* list of applicants in the
order in which they applied	*/
      char *alpha[MAXAPP];              /* list of pointers to
applicants	*/
      int   num_app,                    /* actual number of applicants	*/
	    i;
      char  one_char;

      /*  Gets applicant list	*/
      printf("Enter number of applicants (0 . . %d)\n> ", MAXAPP);
      scanf("%d", &num_app);
      do    /* skips rest of line after number */
    	  scanf("%c", &one_char);
      while (one_char != '\n');

      printf("Enter names of applicants on separate lines\n");
      printf("in the order in which they applied\n");
      for  (i = 0;  i < num_app; ++i)
    	  gets(applicants[i]);

      /*  Fills array of pointers and sorts	*/
      for  (i = 0;  i < num_app;  ++i)
   	  alpha[i] = applicants[i];  /* copies ONLY address */
      select_sort_str(alpha, num_app);

      /*  Displays both lists	*/
      printf("\n\n%-30s%5c%-30s\n\n", "Application Order", ' ', "Alphabetical Order");
      for  (i = 0;  i < num_app;  ++i)
	     printf("%-30s%5c%-30s\n", applicants[i], ' ', alpha[i]);

      return(0);
}

/*
 *  Finds the index of the string that comes first alphabetically in
 *  elements min_sub..max_sub of list
 *  Pre:  list[min_sub] through list[max_sub] are of uniform case;
 *         max_sub >= min_sub
 */
int
alpha_first(char *list[],    	/* input - array of pointers to strings  	*/
	    int   min_sub,	/* input - minimum and maximum subscripts	*/
	    int   max_sub)	/*   of portion of list to consider     	*/
{
      int first, i;

      first = min_sub;
      for  (i = min_sub + 1;  i <= max_sub;  ++i)
          if (strcmp(list[i], list[first]) < 0)
                first = i;

      return (first);
}

/*
 *  Orders the pointers in array list so they access strings
 *  in alphabetical order
 *  Pre:  first n elements of list reference strings of uniform case;
 *        n >= 0
 */
void
select_sort_str(char *list[], /* input/output - array of pointers being
				 ordered to access strings alphabetically */
		int   n)      /* input - number of elements to sort       */
{

      int   fill,         /* index of element to contain next string in order */
	    index_of_min; /* index of next string in order */
      char *temp;

      for  (fill = 0;  fill < n - 1;  ++fill) {
          index_of_min = alpha_first(list, fill, n - 1);

          if (index_of_min != fill) {
                temp = list[index_of_min];
                list[index_of_min] = list[fill];
                list[fill] = temp;
          }
      }
}

Enter number of applicants (0 . . 50)
> 5
Enter names of applicants on separate lines
in the order in which they applied
SADDLER, MARGARET
INGRAM, RICHARD
FAATZ, SUSAN
GONZALES, LORI
KEITH, CHARLES

Application Order                  Alphabetical Order

SADDLER, MARGARET                  FAATZ, SUSAN
INGRAM, RICHARD                    GONZALES, LORI
FAATZ, SUSAN                       INGRAM, RICHARD
GONZALES, LORI                     KEITH, CHARLES
KEITH, CHARLES                     SADDLER, MARGARET