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

typedef struct _Node {
    int value;
    struct _Node* next;  // have to use cannonical name (struct _Node) for this part
} Node;

void print_list_of_ints(Node* head) {
    for(Node* curr = head; curr != NULL; curr = curr -> next) {
        printf("[%d] ", curr -> value);
    }
}

void append(int value, Node** a_head, Node** a_tail) {
    // 1.  Allocate memory for new tail.
    Node* new_tail = malloc(sizeof(*new_tail));

    // 2.  Initialize fields of new tail.  .next of tail is always NULL.
    *new_tail = (Node) { .value = value, .next = NULL };

    // 3.  Depending on if list is initially empty or not…
    if(*a_head == NULL) {  // List is initially EMPTY
        // … Set the head to the new node.  We now have a list of size 1, or…
        *a_head = new_tail; // a_head is a Node**. *a_head is a Node*.  new_tail is a Node*.
    }
    else {   // List is initially NOT empty
        // … Connect the old tail to the new tail.  Without this, we'd have separate lists.
        (*a_tail) -> next = new_tail;
    }

    // 4.  Set the tail to the new tail.
    *a_tail = new_tail;
    // IMPORTANT:  This must be last.  Otherwise, you won't be able to connect the old
    //             tail to the new tail.
}

int main(int argc, char* argv[]) {
    Node* head = NULL;
    Node* tail = NULL;
    append(10, &head, &tail);  // [10]
    append(11, &head, &tail);  // [10]→[11]
    append(12, &head, &tail);  // [10]→[11]→[12]

    print_list_of_ints(head);

    return EXIT_SUCCESS;
}
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