Thread: problem with linked list

Code:

#include<stdio.h>
#include<stdlib.h>
struct node{
    int data;
    struct node *next;
};
int main()
{
    struct node *start,*ptr;
    int n,i,data;
    printf("Enter the number of elements  in the linked list: ");
    scanf("%d",&n);
    ptr=start;
     ptr= (struct node *)malloc(sizeof(struct node));
    printf("Enter the element 1: ");
    scanf("%d",&ptr->data);
    ptr=ptr->next;
    for(i=2;i<=n;i++)
    {
        printf("Enter the element %d: ",i);
             ptr= (struct node *)malloc(sizeof(struct node));


        scanf("%d",&ptr->data);
        ptr=ptr->next;
    }

ptr->next=NULL;
ptr=start;
while(ptr!=NULL)
{
    printf("%d->",ptr->data);

printf("NULL");
}

]

Did you have a specific question?

Line 13 doesn't store the head of the list (which isn't created yet), so you lose the list as soon as you start changing "ptr".

Line 17, what value does "ptr->next" have?

In fact, everything you do with the pointers seems backwards.

You assign "start" to "ptr", perhaps thinking that "start" will point to the same thing as "ptr" when you allocate memory afterwards. This is incorrect. You should allocate memory for the head ("start"), and then assign this value to "ptr". "start" represents the head, so you need to make sure this value isn't changed or you lose the list. You can use "ptr" to move about or modify the list as needed.

Additionally, you advance "ptr" to "ptr->next" before it is given a value (line 17), then try to allocate memory for it. This is also incorrect. You need to allocate memory for a node, and assign that value to "ptr->next".

I stopped reviewing the code at line 17. It seems you have fundamental misunderstandings on the concepts related to linked lists. I would advise you go back to your learning materials on the subject.

Also, you shouldn't cast "malloc()": http://faq.cprogramming.com/cgi-bin/...&id=1043284351

Your program is just one big plate of spaghetti. Split program to little, obvious pieces. For example:

Code:

typedef struct node node;

node* new_node(node* const previous, const int new_data)
{
    node* new = malloc(sizeof(node));
    new->data = new_data;
    new->next = previous->next;
    previous->next = new;
    return new;
}