Question

I was implementing a linked list with 3 elements using structs. It was working fine before I introduced the function to calculate the number of elements in the linked list Linked_list. Following is the code for the program in C.

C

#include <stdlib.h>
#include <stdio.h>

struct node{
    int data;
    struct node* next;
};

struct node* Linked_list();

int Length();

int main()
{
    int length;
    Linked_list();
    length = Length();
    printf("%d", length);
}

struct node* Linked_list() {
    struct node* head = NULL;
    struct node* second = NULL;
    struct node* third = NULL;

    head = malloc(sizeof(struct node));
    second = malloc(sizeof(struct node));
    third = malloc(sizeof(struct node));

    head->data = 1;
    head->next = second;

    second->data = 2;
    second->next = third;

    third->data = 3;
    third->next = NULL;

    printf("%d %d", head->data, second->data);
}

int Length(struct node* head){
    struct node* current = head;
    int count = 0;

    while(current!=NULL)
    {
        count++;
        current = current->next;
    }
    return count;
}

Answer 1

You are declaring and calling Length() as it had no parameters length = Length();

But when you define it it does have one parameter:

int Length(struct node* head)

This is legal, but what happens is that the actual function doesn’t get a head parameter to work with and that is why it crashes.

You should return head from Linked_list() (which is not currently returning anything) and feed that to Length().

struct node* Linked_list() {
    ....

    printf("%d %d", head->data, second->data);
    return  head;
}

And then on main:

struct node* head = Linked_list();
length = Length(head);

There might be other problems though.