incompatible pointer type in c pointers - c

Question

#include<stdio.h>
#include<stdlib.h>
struct node {
int data;
struct node *next;
};
int insert (struct node *head, int data);
int print (struct node *head);
int main()
{
struct node *head;
head = NULL;
// printf("%d\n",head);
insert(&head,5);
insert(&head,4);
insert(&head,6);
print(&head);
print(&head);
print(&head);
}
int insert(struct node *head,int data) {
if(head == NULL) {
head = malloc(sizeof(struct node));
head->next = NULL;
head->data = data;
// printf("%d\n",data);
}
else {
struct node *tmp = head;
if(tmp->next!=NULL) {
tmp = tmp->next;
}
tmp->next = malloc(sizeof(struct node));
tmp->next->next = NULL;
tmp->next->data = data;
// printf("%d\n",data);
}
}
int print (struct node *head) {
printf("hello entered here\n");
struct node *tmp = head;
if (head == NULL) {
printf("entered null\n");
return;
}
while (tmp != NULL) {
if (tmp->next == NULL) {
printf("%0d", tmp->data);
} else {
printf("%0d -> ", tmp->data);
}
tmp = tmp->next;
}
printf("\n");
}
I got the following warning when i compile it
In function main:
insert.c:16: warning: passing argument 1 of insert from incompatible pointer type
insert.c:17: warning: passing argument 1 of insert from incompatible pointer type
insert.c:18: warning: passing argument 1 of insert from incompatible pointer type
insert.c:19: warning: passing argument 1 of print from incompatible pointer type
insert.c:20: warning: passing argument 1 of print from incompatible pointer type
insert.c:21: warning: passing argument 1 of print from incompatible pointer type
When i run it i will get following output
hello entered here
0 -> 5 -> 6
hello entered here
0 -> 5 -> 6
hello entered here
0 -> 5 -> 6
Please help me remove this warnings.
And can u also help me add a function to remove the node in C
What is the mistake I am doing?
Should i pass **head to the function?

Answer 1

Currently the functions print() and insert() expects to struct node* whereas you pass struct node **. If you want to pass a copy then drop the & in your function calls in your code.
If you want to modify the pointer head pass a pointer to pointer and modify the parameters accordingly:
#include<stdio.h>
#include<stdlib.h>
struct node {
int data;
struct node *next;
};
int insert (struct node **head, int data);
int print (struct node **head);
int main()
{
struct node *head;
head = NULL;
// printf("%d\n",head);
insert(&head,5);
insert(&head,4);
insert(&head,6);
print(&head);
print(&head);
print(&head);
}
int insert(struct node **head,int data){
if(*head == NULL){
*head = malloc(sizeof(struct node));
(*head)->next = NULL;
(*head)->data = data;
// printf("%d\n",data);
}
else {
struct node *tmp = *head;
if(tmp->next!=NULL){
tmp = tmp->next;
}
tmp->next = malloc(sizeof(struct node));
tmp->next->next = NULL;
tmp->next->data = data;
// printf("%d\n",data);
}
}
int print (struct node **head) {
printf("hello entered here\n");
struct node *tmp = *head;
if (*head == NULL) {
printf("entered null\n");
return;
}
while (tmp != NULL) {
if (tmp->next == NULL) {
printf("%0d", tmp->data);
} else {
printf("%0d -> ", tmp->data);
}
tmp = tmp->next;
}
printf("\n");
}

Answer 2

Your insert() smells - too complicated. This is some sort of OO actually.
Here is my way, direct typed:
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
// class node_t
typedef struct __node_s *node_t; // Mind the pointer here.
struct __node_s {
int data;
node_t next;
};
node_t node_init(void); // Constructor.
void node_append(node_t, int);
void node_drop_last(node_t);
void node_print(node_t);
void node_fini(node_t); // Destructor.
// end class node_t
int main(void)
{
node_t head = node_init();
node_append(head, 5);
node_append(head, 4);
node_append(head, 6);
node_print(head);
node_drop_last(head);
node_print(head);
node_fini(head);
head = NULL;
return 0;
}
node_t node_init(void)
{
node_t node = malloc(sizeof(struct __node_s));
assert(node);
memset(node, 0, sizeof(struct __node_s));
return node;
}
void node_insert(node_t head, int data)
{
node_t last = head, new = node_init();
for (; last->next; last = last->next);
new->data = data;
last->next = new;
}
void node_drop_last(node_t head)
{
node_t last = head;
if (!head->next)
return;
for (; last->next->next; last - last->next);
node_fini(last->next);
last->next = NULL;
}
void node_print(node_t head)
{
for (node_t this = head->next; this; this = this->next)
{
printf("%d", this->data);
if (this->next)
putchar(' '); // A lot faster!
}
putchar('\n');
}
void node_fini(node_t head)
{
if (head->next)
{
node_fini(head->next);
head->next = NULL;
}
free(head);
}