C Linked List Add Item at the End - c

Question

I'm writing a program that adds a node at the end of an existing linked list.
The problem is that it doesn't seem to assign to the variable nr of struct node of the last element of the linked list the hard coded value 7.
Here is the code:
#include<stdio.h>
#include<stdlib.h>
struct node {
int nr;
struct node *next;
};
void addNodes(struct node **head, int n);
void displayList(struct node *head);
void addItemLast(struct node *head);
int main() {
struct node* head = NULL;
int n;
printf("Introduceti numarul de noduri: ");
scanf("%d", &n);
addNodes(&head, n);
displayList(head);
addItemLast(head);
displayList(head);
return 0;
}
void addNodes(struct node **head, int n) {
*head = (struct node*)malloc(sizeof(struct node));
struct node *current = *head;
printf("\nIntroduceti %d noduri:\n", n);
for(int i = 0; i < n; i++) {
printf("Element %d = ", i+1);
scanf("%d", &(current -> nr));
current->next = (struct node*)malloc(sizeof(struct node));
current = current->next;
}
current->next = NULL;
}
void displayList(struct node *head) {
struct node *current = head;
int i = 1;
printf("\nElementele introduse sunt:\n");
while(current->next != NULL) {
printf("Elementul %d = %d\n", i, current->nr);
current = current->next;
i++;
}
}
void addItemLast(struct node *head) {
struct node *temp = head, *last;
last = (struct node*)malloc(sizeof(struct node));
if(last == NULL) {
printf("\nMemory cannot be allocated!\n");
} else {
last->nr = 7;
last->next = NULL;
while(1) {
if(temp->next == NULL) {
temp->next = last;
break;
}
temp = temp->next;
}
}
}
The last function, addItemLast(), doesn't work as expected.
This is the output:
Introduceti numarul de noduri: 3
Introduceti 3 noduri:
Element 1 = 1
Element 2 = 2
Element 3 = 3
Elementele introduse sunt:
Elementul 1 = 1
Elementul 2 = 2
Elementul 3 = 3
After the function with the problem runs, I get this output:
Elementele introduse sunt:
Elementul 1 = 1
Elementul 2 = 2
Elementul 3 = 3
Elementul 4 = 13383248
Element 4 does not contain the hard coded value 7, but instead has a garbage value and I can't figure out why.

Answer 1

Your implemenation of addNodes is incorrect, suppose I enter n = 2 , 3 nodes are created but only twice scanf function is called, so as result you have garbage value in some node (nr is not set).
Reimplement it (it works if addItemLast function is properly implemented) :
void addNodes(struct node **head, int n){
printf("\nIntroduceti %d noduri:\n", n);
for(int i = 0; i < n; i++){
struct node* last = addItemLast(*head);
if (*head == NULL)
*head = last;
printf("Element %d = ", i);
scanf("%d", &(last -> nr));
}
}
You need to change addItemLast to handle case when you want to call this function but head is NULL (without testing this case your program crashes while calling addItemLast for empty List):
struct node* addItemLast(struct node *head){
struct node *temp = head, *last;
last = (struct node*)malloc(sizeof(struct node));
if (head == NULL) // <---------
{
last->nr = 7;
last->next = NULL;
return last;
}
if(last == NULL){
printf("\nMemory cannot be allocated!\n");
}else{
last->nr = 7;
last->next = NULL;
while(1){
if(temp->next == NULL){
temp->next = last;
break;
}
temp = temp->next;
}
}
return last;
}
and finally function to display list should be:
void displayList(struct node *head){
struct node *current = head;
int i = 1;
printf("\nElementele introduse sunt:\n");
while(current != NULL){ // <---------
printf("Elementul %d = %d\n", i, current->nr);
current = current->next;
i++;
}
}

Answer 2

You do not have to check if current->next != NULL when accessing the element of current.
Change your while loop to:
while(current != NULL){
printf("Elementul %d = %d\n", i, current->nr);
current = current->next;
i++;
}