Why does this linked-list ordered insert segfault? - c

Question

I am working on a program that inserts into a linked-list in sorted order, but it keeps seg faulting, and I can't figure out why. I suspect it has something to do with the pointers, but I can't tell as these are still a little bit confusing to me at this point in my programming career. Also, I must keep the insert prototype the same. I can't change the node parameter into a double pointer. Thanks!
#include <stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include<conio.h>
typedef struct node {
int data;
struct node *next;
};
int main ()
{
struct node* first;
int temp,x,y;
struct node *create (struct node *first);
first = NULL;
void display (struct node *first);
printf ("\n\nCreating a Linked List\n");
printf ("\nEnter Element: ");
scanf ("%d", &x);
y=x;
while(y>0)
{
scanf ("%d", &x);
insert_sorted_linked_list(first,x);
y--;
}
printf ("\nThe list after creation is: ");
display (first);
printf ("\nThe sorted list is: ");
display (first);
return(0);
} /*END OF MAIN*/
insert_sorted_linked_list(struct node* head, int val)
{
struct node* pCur;
struct node* pNew = (struct node*) (malloc(sizeof(struct node)));
pNew -> data = val;
pNew ->next = NULL;
pCur = head;
if( pCur->data == NULL )
{
head->data = pNew->data;
head->next = NULL;
}
else if (pNew->data < pCur->data)
{
pNew ->next = pCur ;
head = pNew;
}
}
void display (struct node *first)
{ struct node *save; /*OR sort *save */
if (first == NULL)
printf ("\nList is empty");
else
{ save = first;
while (save != NULL)
{ printf ("-> %d ", save->data);
save = save->next;
}
getch();
}
return;
}
EDIT: Changed main to int. The debugger doesn't like the lines:
struct node* pNew = (struct node*) (malloc(sizeof(struct node)));
if( pCur->data == NULL )
Not sure what is wrong though.
EDIT 2:
I decided i wasn't going to get it working the original way he ask for it before tomorrow morning, so I went a modified version posted here. That one didn't seg fault, but it turns out there was a logic error as well.
#include <stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include<conio.h>
typedef struct s
{
int data;
struct s *next;
}node;
void insert_sorted_linked_list(node **head, int val);
void display (node **first);
void freeList(node **first);
int main ()
{
node* first;
int x,y;
first = NULL;
printf ("\n\nCreating a Linked List\n");
printf ("\nEnter number of elements: ");
scanf ("%d", &x);
y=x;
while(y>0)
{
scanf ("%d", &x);
insert_sorted_linked_list(&first,x);
y--;
}
printf ("\nThe sorted list is: ");
display (&first);
freeList(&first);
return 0;
}
void insert_sorted_linked_list(node **head, int val)
{
node* pCur;
node* pNew = (node*) (malloc(sizeof(node)));
pNew->data = val;
pNew->next = NULL;
pCur = (*head);
if( pCur == NULL )
{
(*head) = pNew;
}
else if(pNew->data < pCur->data)
{
pNew->next = pCur;
(*head) = pNew;
}
else
{
while(pCur->next!=NULL && pNew->data > pCur->next->data)
pCur = pCur->next;
pNew->next = pCur->next;
pCur->next = pNew;
}
}
void display (node **first)
{
node *lisprint; /*OR sort *lisprint */
if (*first == NULL)
printf ("\nList is empty");
else
{
lisprint = *first;
while (lisprint != NULL)
{
printf ("-> %d ", lisprint->data);
lisprint = lisprint->next;
}
getch();
}
} /*END OF FUNCTION DISPLAY*/
void freeList(node **first)
{
node *i;
i = *first;
while(i !=NULL)
{
(*first) = (*first)->next;
free(i);
i = *first;
}
}
Thanks!

Answer 1

Please properly format your code! It was a pain in the a** just to see where the error was!
As it is,
/*PROGRAM TO CREATE & THEN DISPLAY THE LINKED LIST IN SORTED FORM*/
#include <stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include<conio.h>
typedef struct s
{
int data;
struct s *next;
}node;
/* your declaration for typedef was incorrect. We use typedef in C for structures so that we do not have to repeat struct s everytime. Using typedef, we can write node as we do in c++ */
void insert_sorted_linked_list(node **head, int val); /* do not need to return anything, as well as see the parameter. When we want to change a pointer, we pass the address to the pointer, as it results in passing by value */
void display (node **first); /* same here and below */
void freeList(node **first); /* if you don't do this, memory leak!!! */
int main ()
{
node* first; /*OR sort *first,*list,*pass */
int temp,x,y;
first = NULL; /*OR sort *create() */
printf ("\n\nCreating a Linked List\n");
printf ("\nEnter number of elements: "); /* specify what you want the user to enter */
scanf ("%d", &x);
y=x;
while(y>0)
{
scanf ("%d", &x);
insert_sorted_linked_list(&first,x); /*CALLING CREATE FUNCTION, notice the &first*/
y--;
}
printf ("\nThe list after creation is: ");
display (&first);
printf ("\nThe sorted list is: ");
display (&first);
freeList(&first);
return 0;
} /*END OF MAIN*/
void insert_sorted_linked_list(node **head, int val)
{
node* pCur;
node* pNew = (node*) (malloc(sizeof(node)));
pNew->data = val;
pNew->next = NULL;
pCur = (*head);
if( pCur == NULL )
{
(*head) = pNew;
}
else if (pNew->data < pCur->data)
{
pNew->next = pCur ;
(*head) = pNew;
}
}
/*DISPLAY FUNCTION*/
void display (node **first)
{
node *save; /*OR sort *save */
if (*first == NULL)
printf ("\nList is empty");
else
{
save = *first;
while (save != NULL)
{
printf ("-> %d ", save->data);
save = save->next;
}
getch();
}
} /*END OF FUNCTION DISPLAY*/
void freeList(node **first)
{
node *i;
i = *first;
while(i !=NULL)
{
(*first) = (*first)->next;
free(i);
i = *first;
}
}