So, I have a singly linked list. And I want to go through it, and get all the even numbers. And put the even numbers in a new list. And return the new head. The original list should remain untouched.

What I have tried:

(Just my function):

    struct node_t* new_list_head;
    struct node_t*  even_nodes(struct node_t** old){

        new_list_head = nullptr;
        struct node_t* curr_node = *old;
        bool found = false;

        struct node_t* new_list_curr;

        while (curr_node != nullptr){
            if (curr_node->v % 2 == 0)
            {
                struct node_t new_node;
                new_node.v = curr_node->v;
                new_node.next = nullptr;
                if (!found)
                {
                    found = true;
                    new_list_head = &new_node;
                }
                else
                {
                    new_list_curr->next = &new_node;

                };
                new_list_curr = &new_node;
            };
            curr_node = curr_node->next;
        };

        return new_list_head;

    };

Everything (probably TMI):

    #include <iostream>

    struct node_t
    {
        unsigned v; 
        struct node_t* next;
    };

    struct node_t* new_list_head;
    struct node_t*  even_nodes(struct node_t** old){

        new_list_head = nullptr;
        struct node_t* curr_node = *old;
        bool found = false;

        struct node_t* new_list_curr;

        while (curr_node != nullptr){
            if (curr_node->v % 2 == 0)
            {
                struct node_t new_node;
                new_node.v = curr_node->v;
                new_node.next = nullptr;
                if (!found)
                {
                    found = true;
                    new_list_head = &new_node;
                }
                else
                {
                    new_list_curr->next = &new_node;

                };
                new_list_curr = &new_node;
            };
            curr_node = curr_node->next;
        };

        return new_list_head;

    };

    void print(struct node_t* head){
        while (head != nullptr){
            std::cout << head->v << '\n';
            head = head->next;
        }
    }


    int main(){
        struct node_t a;
        struct node_t b;
        struct node_t c;
        struct node_t d;
        a.v = 6;
        a.next = &b;
        b.v = 17;
        b.next = &c;
        c.v = 7;
        c.next = &d;
        d.v = 4;
        d.next = nullptr;

        struct node_t* head = &a;
        //print(head);
        struct node_t* new_list = even_nodes(&head);
        //print(head);
        print(new_list);

    }

So, the new_list prints the last even number and then a random number, then segmentation fault. (10, 4181723112)

​

Edit:I found the solution. I used the new operator.

struct node_t* new_node = new struct node_t;

And changed the rest of the code accordingly. This solved my problem.