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

////////////////////////////////////////////////////////////////////////////////
// DO NOT MODIFY THIS STRUCT
////////////////////////////////////////////////////////////////////////////////
struct node {
    struct node *next;
    int          data;
};
////////////////////////////////////////////////////////////////////////////////

// extract_evens should create a new linked list `only_evens` that contains
// only the even-valued nodes from the original list
//
// Unfortunately, this code contains a number of errors.
// It's your job to fix them, good luck!
struct node *extract_evens(struct node *head) {
    struct node *only_evens = NULL;
    struct node *current = head;
    
    while (current->next != NULL) {
        struct node next = current->next;
        current->next = NULL;
        if (current % 2 == 0) {
            struct node current_evens = only_evens;
            while (current_evens == NULL) {
                current_evens = current_evens->next;
            }
            current_evens->next = current;
        }
        current = next;
    }
    return only_evens;
}

////////////////////////////////////////////////////////////////////////////////
// DO NOT MODIFY THE CODE BELOW THIS LINE, THIS CODE ALLOWS YOU TO
// TAKE IN A LIST OF NUMBERS TO TEST WHETHER YOUR FUNCTION IS WORKING
////////////////////////////////////////////////////////////////////////////////
struct node *strings_to_list(int len, char *strings[]);
void print_list(struct node *head);

////////////////////////////////////////////////////////////////////////////////
// DO NOT CHANGE THIS FUNCTION
////////////////////////////////////////////////////////////////////////////////
int main(int argc, char *argv[]) {
    struct node *head = strings_to_list(argc - 1, &argv[1]);

    struct node *only_evens = extract_evens(head);

    if (only_evens == NULL) {
        printf("No even nodes\n");
    } else {
        print_list(only_evens);
    }

    return 0;
}

////////////////////////////////////////////////////////////////////////////////
// DO NOT CHANGE THIS FUNCTION
////////////////////////////////////////////////////////////////////////////////
struct node *strings_to_list(int len, char *strings[]) {
    struct node *head = NULL;
    for (int i = len - 1; i >= 0; i--) {
        struct node *n = malloc(sizeof(struct node));
        assert(n != NULL);
        n->data = atoi(strings[i]);
        n->next = head;
        head = n;
    }
    return head;
}

////////////////////////////////////////////////////////////////////////////////
// DO NOT CHANGE THIS FUNCTION
////////////////////////////////////////////////////////////////////////////////
void print_list(struct node *head) {
    struct node *current = head;
    while (current != NULL) {
        printf("%d", current->data);
        if (current->next != NULL) {
            printf(" ");
        }
        current = current->next;
    }
    printf("\n");
}