Why is (null) being printed in my c code? - c

Question

I am trying to add strings to a linked list but I have a problem with (null) being printed. Anyone who can help me?
The best I could do is narrow it down to this being the problem:
struct node *head = malloc(sizeof(struct node));
struct node *ptr = malloc(sizeof(struct node));
Here is the code:
#include <stdio.h>
#include <stdlib.h>
struct node {
char *data;
struct node *link;
};
struct node *add_begin(char *d, struct node *head) {
struct node *ptr = malloc(sizeof(struct node));
ptr->data = d;
ptr->link = head;
return ptr;
}
void add_end(struct node *point, char *data) {
struct node *temp = malloc(sizeof(struct node));
temp->data = data;
temp->link = NULL;
while (point->link != NULL) {
point = point->link;
}
point->link = temp;
}
int main() {
struct node *head = malloc(sizeof(struct node));
struct node *ptr = malloc(sizeof(struct node));
head->link = ptr;
char *data = "Chocolate Cake";
head = add_begin(data, head);
add_end(ptr, data);
while (head != NULL) {
printf("%s \n", head->data);
head = head->link;
}
}
Output:
Chocolate Cake
(null)
(null)
Chocolate Cake

Answer 1

The problem is you allocate dummy nodes, which are uninitialized and happen to have null pointers as data and link. The list should be initially empty, ie: head should be a null pointer.
Note that add_end should also return the head pointer in case an empty list was passed. Passing the arguments in the same order to both functions is highly recommended.
Here is a modified version:
#include <stdio.h>
#include <stdlib.h>
struct node {
char *data;
struct node *link;
};
struct node *add_begin(struct node *head, char *data) {
struct node *ptr = malloc(sizeof(*ptr));
ptr->data = data;
ptr->link = head;
return ptr;
}
struct node *add_end(struct node *head, char *data) {
struct node *ptr = malloc(sizeof(*ptr));
ptr->data = data;
ptr->link = NULL;
if (head == NULL) {
return ptr;
} else {
struct node *temp = head;
while (temp->link != NULL) {
temp = temp->link;
}
temp->link = ptr;
return head;
}
}
int main() {
struct node *head = NULL;
char *data = "Chocolate Cake";
head = add_begin(head, data);
head = add_end(head, data);
for (struct node *ptr = head; ptr; ptr = ptr->link) {
printf("%s\n", ptr->data);
}
return 0;
}
Output:
Chocolate Cake
Chocolate Cake