circular linked list and insert at end function in C - c

Question

I am trying to create a circular linked list in C.
But I haven't understood quite well the linked lists.
Well the program gets an int to a function called list_end_ptr which initialises the circular linked list and creates nodes for the int.
Then another function (insert_at_end) puts new nodes on at the end of the initialized list and returns the last node.
A 3rd function prints the linked list (print_list) by getting the end node and printing first the first entered name and finishes with the last.
The idea is to have only an end node and work only with this, but I can't make it work. I have managed to make it partially work, when I print the data are printed in reverse order of the name entry (from last entered to the first).
Any idea?
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#define SIZE 10
#define NUM_PER_LINE 3
typedef struct node
{
char name[SIZE]; /* SIZE-1 χαρακτήρες και το '\0' */
struct node * next;
} CListNode;
void get_name(char *a);
void print_list(CListNode *end_ptr);
CListNode *initiate(int n);
CListNode *insert_at_end(CListNode *end_ptr, char *a);
int main(void) {
CListNode *list_end_ptr;
int n=6;
list_end_ptr=initiate(n);
print_list(list_end_ptr);
return 0;
}
void get_name(char *a)
{
char format[10];
sprintf(format, "%%%ds", SIZE-1);
scanf(format, a);
}
CListNode *insert_at_end(CListNode *end_ptr, char *a)
{
CListNode *temp, *head=NULL;
head=end_ptr->next;
temp=(CListNode *) malloc(sizeof(CListNode));
end_ptr->next=temp;
strcpy(temp->name, a);
temp->next=head;
return temp;
}
CListNode *initiate(int n) {
CListNode *end, *first=NULL;
int i;
char new_name;
end=(CListNode *) malloc(sizeof(CListNode));
if (end==0) {
printf("Allocation error...\n");
exit(0); }
end->next=end;
for (i=0; i<n; i++) {
if (i<1) {
printf("Enter the name of the %d person: ", i+1);
get_name(&new_name);
strcpy(end->name, &new_name);
first=end;
}
else
{
printf("Enter the name of the %d person: ", i+1);
get_name(&new_name);
insert_at_end(end, &new_name);
}
}
return end;
}
void print_list(CListNode *end_ptr)
{
int i=1;
CListNode *str_ptr;
if (end_ptr == NULL)
printf("\n List is empty");
else
{
str_ptr = end_ptr->next;
while (str_ptr != end_ptr)
{
printf("%s \t", str_ptr->name);
str_ptr = str_ptr->next;
if (i%NUM_PER_LINE==0) {
printf("\n");
}
i++;
}
printf("%s\n", str_ptr->name);
}
}

Answer 1

My friend you are not updating the end pointer for condition i>0.The very first node you create is very much right but when you code starts executing the else part of for loop, the end pointer is not manipulated correctly. Here is the corrected version of the code you have given
For the else part of for loop of the initiate function
else
{
printf("Enter the name of the %d person: ", i+1);
get_name(&new_name);
ptr=insert_at_end(first,end, &new_name);/*insert_at_end returns temp*/
end=ptr;
}
The insert at end function returns temp so that end pointer can be updated.
For the insert_at_end function just replace the line
head=end_ptr->next;
with
head=first;
Of course, you would have to pass the first pointer in call of the function as well.
So in short,you had almost done the job right and with minute modifications like:
insert_at_end function returned value should be put into a pointer which in turn is used to update end.
We end up with correct code.
Do not forget to update the prototype of function insert_at_end.It should be
CListNode *insert_at_end(CListNode *first,CListNode *end_ptr, char *a);

Answer 2

Generally, inserting at the end of a singly-linked list (which is what you have) is a matter of iterating through the next pointer until you get to a NULL value, and then create a node, and adjust the previous last node's next pointer to point to the new node.
The code includes <strings.h> but that should be <string.h>.
Also, where your current code has strcpy you should probably instead use strdup or strncpy to make sure you don't overrun your allocated SIZE for name.
There are a number of problems with this code, but this should get you started:
CListNode *initiate(int n) {
CListNode *end, *first;
int i;
char new_name[SIZE];
end = first = malloc(sizeof(*first));
if (first == NULL) {
printf("Allocation error...\n");
exit(0);
}
for (i=0; i<n; i++) {
printf("Enter the name of the %d person: ", i+1);
get_name(new_name);
insert_at_end(end, new_name);
}
return end;
}