program11_05.c

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/* Program 11.5 Daisy chaining the horses both ways */
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>

int main(void)
{
  struct horse                        /* Structure declaration       */
  {
    int age;
    int height;
    char name[20];
    char father[20];
    char mother[20];
    struct horse *next;             /* Pointer to next structure     */
    struct horse *previous;         /* Pointer to previous structure */
  };

  struct horse *first = NULL;         /* Pointer to first horse      */
  struct horse *current = NULL;       /* Pointer to current horse    */
  struct horse *last = NULL;          /* Pointer to previous horse   */

  char test = '\0';                   /* Test value for ending input */

  for( ; ; )
  {
    printf("\nDo you want to enter details of a%s horse (Y or N)? ",
                                        first == NULL?"nother " : "");
    scanf(" %c", &test );
    if(tolower(test) == 'n')
      break;

    /* Allocate memory for each new horse structure */
    current = (struct horse*)malloc(sizeof(struct horse));

    if( first == NULL )
    {
      first = current;                /* Set pointer to first horse  */
     current->previous = NULL;
    }
    else
    {
      last->next = current;    /* Set next address for previous horse */
      current->previous = last; /* Previous address for current horse */
    }

    printf("\nEnter the name of the horse: ");
    scanf("%s", current -> name );    /* Read the horse's name   */

    printf("\nHow old is %s? ", current -> name);
    scanf("%d", &current -> age);     /* Read the horse's age    */

    printf("\nHow high is %s ( in hands )? ", current -> name);
    scanf("%d", &current -> height);  /* Read the horse's height */

    printf("\nWho is %s's father? ", current -> name);
    scanf("%s", current -> father);   /* Get the father's name   */

    printf("\nWho is %s's mother? ", current -> name);
    scanf("%s", current -> mother);   /* Get the mother's name   */

    current -> next = NULL;      /* In case it's the last horse..*/
    last = current;              /* Save address of last horse   */
  }

  /* Now tell them what we know. */
  while(current != NULL)         /* Output horse data in reverse order */
  {
    printf("\n\n%s is %d years old, %d hands high,",
               current->name, current->age, current->height);
    printf(" and has %s and %s as parents.", current->father,
                                            current->mother);
    last = current;       /* Save pointer to enable memory to be freed */
    current = current->previous; /* current points to previous in list */
    free(last);                 /* Free memory for the horse we output */
  }
  return 0;
}