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

struct node {
   int value;
   struct node *next;
};

struct node *front;

void add_to_back(int v);
void remove_from_front();
void print_list();

int main() {
   int value;
   while (1) {
      printf("Enter a number: ");
      int rtn = scanf("%d", &value);
      if (rtn != 1) 
         break;
      else
         add_to_back(value);
   }

   print_list();

   remove_from_front();
   print_list();

   remove_from_front();
   print_list();
 
   remove_from_front();
   print_list();

   return 0;
}

void add_to_back(int v)
{
   struct node *new_node;
   new_node = (struct node *) malloc(sizeof(struct node));
   if (new_node == NULL) {
      printf("Error: malloc failed in add_to_back\n");
      exit(EXIT_FAILURE);
   }
   new_node->value = v;

   if (front == NULL) {
      front = new_node; //special case, empty list
   } else {
      struct node *cur;
      for (cur = front; cur->next != NULL; cur = cur->next) {
         ; //traverse list
      }
      cur->next = new_node;
   }
}
 
void remove_from_front()
{
   if (front == NULL)
      return; //empty list

   struct node *cur = front;
   front = front->next;
   cur->next = NULL;
   
   free(cur);
}

void print_list() 
{
   struct node *cur;
   for (cur = front; cur != NULL; cur = cur->next) {
      printf("%d ", cur->value);
   }
   printf("\n");
}