Linked list not adding node until second iteration - c

Question

I'm working on a FIFO page replacement algorithm and have it almost working. My code uses scanf() to read in a page number then it adds that item to a linked list, up to 16 pages. However, if the page already exists in the lined list, it does not add the page to this list again. There are three page frames (slots). Everything works properly, but, it does not add that item to the list until scanf() reads another integer to add to the list. I am utterly confused.
#include<stdio.h>
#include<stdlib.h>
typedef struct node {
int num;
struct node * next;
} node_t;
void print_list(node_t * head) {
node_t * current = head;
while (current != NULL) {
printf("%d\n", current->num);
current = current->next;
}
}
int fault(node_t * head, int check) {
node_t * current = head;
while(current->next != NULL){
if(current->num == check)
return 0;
current = current->next;
}
return 1;
}
void addNode(node_t * head, int num) {
node_t * current = head;
while (current->next != NULL) {
current = current->next;
}
/* now we can add a new variable */
current->next = malloc(sizeof(node_t));
current->next->num = num;
current->next->next = NULL;
}
int pop(node_t ** head) {
int retnum = -1;
node_t * nextNode = NULL;
if (*head == NULL) {
return -1;
}
nextNode = (*head)->next;
retnum = (*head)->num;
free(*head);
*head = nextNode;
return retnum;
}
///////////////////////////////////////////////////////
int main(){
int num;
int faults = 0;
int n = 0;
int j = 0;
node_t * head = malloc(sizeof(node_t));
if (head == NULL) {
return 1;
}
head->num = -1;
printf("Input page number up to 16 pages. Enter 'q' to quit.\n");
for(j=0;j<16;j++){
if(scanf("%d\n",&num) == 1) {
if (fault(head, num) == 1 && n < 3) {
n++;
faults++;
addNode(head, num);
}
else if (fault(head, num) == 1 && n >= 3) {
pop(&head);
addNode(head,num);
faults++;
}
}
else{
int c = getchar();
if( c == 'q' ){
break;
}
}
if (n == 1 && faults == 1)
pop(&head);
printf("\nPage Table:\n");
print_list(head);
printf("\nInput page number: \n");
}
printf("Number of page faults: %d\n", faults);
}
I ran it through gdb and it doesn't even call the addNode function until the second integer has been scanned.
(And yes I know scanf is garbage, I just didn't want to bother learning how to do something else)
Thanks for the help!

Answer 1

Your code:
if(scanf("%d\n",&num) == 1) {
should be :
if(scanf("%d",&num) == 1) {
And head needs to be initialized.
node_t * head = malloc(sizeof(node_t));
if (head == NULL) {
return 1;
}
head->next = NULL;