Hi all !!!
Thankyou all for helping me in my time of dispair
(especially to those who gave tips and web sites).
I have now finished.
Yay!
For those who are curious (& for those who are
interested in seeing an example), the (properly
working) program's as follows.
Thanks again,
Kelly.
/*
Purpose:
To implement a LINKED LIST using
dynamic memory allocation
...where an item of the list is used
to store a person's identification
number, first name, surname, and age.
Files:
main.c
list.c
list.h
people.dta
*/
/*************** main.c **************/
#include <stdio.h>
#include "list.h"
extern void initialise(struct list *);
extern int empty(struct list *);
extern struct item * search(struct list *, int);
extern struct item * insert(struct list *, struct person);
extern int delete(struct list *, int);
extern void print(struct list *);
main()
{
FILE *peoplefile;
char transaction;
int id;
struct list l;
struct item *d;
struct person p;
if((peoplefile = fopen("people.dta", "r")) == NULL)
{
printf("Error: 'fopen' failed\n");
exit(1);
Quote:
}
initialise(&l);
while(fscanf(peoplefile, "%c %d", &transaction, &id) != EOF)
{
switch(transaction)
{
case 'd':
if(delete(&l, id))
{
print(&l);
}
else
printf("Error: Delete failed\n");
break;
case 'i':
d = search(&l, id);
if(d == NULL)
{
fscanf(peoplefile, "%s %s %i",
p.firstname,
p.surname,
&p.age);
p.id = id;
insert(&l, p);
}
else
printf("Error: Duplicate ID\n");
print(&l);
break;
default:
printf("Error: Invalid Transaction '%c'\n",
transaction);
exit(1);
}
/* gets rid of the rest of the line and \n, if any */
fscanf(peoplefile, "%*[^\n]");
fscanf(peoplefile, "%*c");
Quote:
}
fclose(peoplefile);
Quote:
}
/*************** list.c **************/
#include <stdio.h>
#include "list.h"
void initialise(struct list *);
int empty(struct list *);
int delete(struct list *, int);
struct item * search(struct list *, int);
struct item * insert(struct list *, struct person);
void print(struct list *);
void print_list(struct item *);
void initialise(struct list *list)
{
list->head = NULL;
list->tail = NULL;
Quote:
}
int empty(struct list *list)
{
if(list->head == list->tail)
return(1);
else
return(0);
Quote:
}
struct item * insert(struct list *list, struct person person)
{
struct item *temp, *i;
temp = (struct item *)malloc(sizeof(struct item));
temp->data = person;
temp->next = NULL;
if(list->head == NULL)
{
list->head = temp;
list->tail = temp;
return;
Quote:
}
i = list->tail;
i->next = temp;
list->tail = temp;
Quote:
}
int delete(struct list *list, int id)
{
struct item *x, *y, *temp;
if(empty(list))
{
printf("Error: Cannot delete, list is empty\n");
return(0);
Quote:
}
x = list->head;
y = x->next;
while(y != NULL)
{
if(x->data.id == id)
{
temp = x;
x = x->next;
list->head = x;
free(temp);
return(1);
}
if(y->data.id == id)
{
temp = y;
if(y->next == NULL)
{
x->next = NULL;
list->tail = x;
free(temp);
return(1);
}
if(y->next != NULL)
{
x->next = y->next;
free(temp);
return(1);
}
}
x = y;
y = y->next;
Quote:
}
}
struct item * search(struct list *list, int id)
{
struct item *y;
y = list->head;
while(y != NULL)
{
if(id == y->data.id)
return(y);
y = y->next;
Quote:
}
return(NULL);
Quote:
}
void print(struct list *list)
{
print_list(list->head);
printf("\n");
Quote:
}
void print_list(struct item *item)
{
if(item == NULL)
return;
printf("(%i %c %s %i) ",
item->data.id,
item->data.firstname[0],
item->data.surname,
item->data.age);
print_list(item->next);
Quote:
}
/*************** list.h **************/
#define FIRSTNAME_SIZE 20
#define SURNAME_SIZE 30
struct person
{
int id;
char fi
rstname[FIRSTNAME_SIZE];
char surname[SURNAME_SIZE];
int age
;
Quote:
};
struct item
{
struct person data;
struct item *next;
Quote:
};
struct list
{
struct item *head;
struct item *tail;
Quote:
};
/*************** people.dta **************/
i 111 Angela Adams 19
i 222 Erin Burns 21
i 333 John Smith 20
i 334 John Smith 22
i 444 Bill Yard 20
i 111 Lizz Ard 22
i 123 Anne Telope 17
d 111
d 334
d 123
i 234 Jack Aroo 18
i 345 Jill Aroo 19
Linked List using dynamic memory allocation (URGENT request for example)