Singly Linked List: newNode function doesn't point to next Node

Question

I am currently experimenting with singly-linked-list in C. I have written a newNode function to create a Node and a printNodes function to print out all nodes - it looks like this:

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

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

void printNodes(struct Node *current_node)
{
  while(current_node != NULL)
  {
    printf("Node is: %d\n", current_node->data);
    current_node = current_node->next;
  }
}

int main()
{
  int number_1 = 2;
  int number_2 = 3;
  int number_3 = 4;

  struct Node *head;
  struct Node *second;
  struct Node *third;

  head = (struct Node*)malloc(sizeof(struct Node));  
  second = (struct Node*)malloc(sizeof(struct Node)); 
  third = (struct Node*)malloc(sizeof(struct Node));

  head->data = number_1;      
  head->next = second; 

  second->data = number_2;      
  second->next = third; 

  third->data = number_3;     
  third->next = NULL; 

  printNodes(head);

}

output is correctly:

Node is: 2
Node is: 3 
Node is: 4

Now I wanted to write a function newNode which is used to create a new node, I changed my code to this:

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

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

struct Node *newNode(int number_x, struct Node *nextnode)
{
    struct Node *tmp_node;

    tmp_node = malloc(sizeof(struct Node));
    tmp_node->data = malloc(sizeof(struct Node));
    tmp_node->data = number_x;
    tmp_node->next = nextnode;

    return tmp_node;
}   

void printNodes(struct Node *current_node)
{
    while(current_node != NULL)
    {
        printf("Node is: %d\n", current_node->data);
        current_node = current_node->next;
    }
}

int main()
{
    int number_1 = 2;
    int number_2 = 3;
    int number_3 = 4;

    struct Node *head;
    struct Node *second;
    struct Node *third;

    head = newNode(number_1, second);
    second = newNode(number_2, third);
    third = newNode(number_3, NULL);

    printNodes(head);

}

After compiling I first get this warning message:

test.c:16:20: warning: incompatible pointer to integer conversion 
assigning to 'int' from 'void *' [-Wint-conversion]
tmp_node->data = malloc(sizeof(struct Node));
               ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~

And the output looks like this:

Node is: 2

It only shows the Node head, I guess there is something wrong with next pointing (e.g. head->next = second), but what is wrong? I am unable to solve this.

Thanks

Answer 1

Here

tmp_node->data = malloc(sizeof(struct Node)); /* remove this statement */

data is a member of struct Node & that's a integer, for this separately you don't have to allocate memory. you have already allocated for complete structure here

tmp_node = malloc(sizeof(struct Node)); /* this is enough */

Also here

head = newNode(number_1, second);

what is second ? It should be initialized with NULL like

struct Node *second = NULL;

then only in newNode() function tmp_node->next assigned with correct value

tmp_node->next = nextnode; /* now nextnode contains NULL, that's correct */

Or you can make it like below

head = newNode(number_1, NULL);
second = newNode(number_2, head);
third = newNode(number_3, second);

and then while calling printNodes() pass the third instead of head. For e.g

printNodes(third);

Sample code :

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

struct Node *newNode(int number_x, struct Node *nextnode) {
    struct Node *tmp_node;
    tmp_node = malloc(sizeof(struct Node));
    tmp_node->data = number_x;
    tmp_node->next = nextnode;
    return tmp_node;
}

void printNodes(struct Node *current_node) {
    while(current_node != NULL) {
        printf("Node is: %d\n", current_node->data);
        current_node = current_node->next;
    }
}

int main(void) {
    int number_1 = 2;
    int number_2 = 3;
    int number_3 = 4;

    struct Node *head = NULL;
    struct Node *second = NULL;
    struct Node *third = NULL;

    head = newNode(number_1, NULL);
    second = newNode(number_2, head);
    third = newNode(number_3, second);
    printNodes(third);
        return 0;
}