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

typedef struct _Node {
    int value;
    struct _Node* next;
} Node;

void print_list(Node* head) {  // print_list(…) now takes address of the head node
    for(Node* curr = head;  curr != NULL;  curr = curr -> next) {
        printf("[%d]", curr -> value);
        
        // If this is not the tail, then print a '─' to connect to the next node.
        if(curr -> next != NULL) {
            printf("─");
        }
    }
    printf("\n");
}

void _append(int value, Node** a_head, Node** a_tail) {
    // Allocate space for one new node.
    Node* new_node = malloc(sizeof(*new_node));

    // Set the .value field of our new node.
    new_node -> value = value;
    new_node -> next = NULL;

    if(*a_head == NULL) {  // List initially had size =1
        *a_head = new_node;
        *a_tail = new_node;
        assert(*a_head == *a_tail);
        // We now have a list of size 1.
    }
    else {  // List initially had size ≥2
        (*a_tail) -> next = new_node;
        *a_tail = new_node;
        assert((*a_head) -> next != NULL);  // Head must not also be the tail.
    }
    assert((*a_tail) -> next == NULL);  // Tail's '.next' field must always be NULL.
    assert(*a_head != NULL && *a_tail != NULL);  // Assert: List is not empty.
}

int main(int argc, char* argv[]) {
    Node* head = NULL;  // linked list of size 0.
    Node* tail = head;
    _append(5, &head, &tail);
    print_list(head);

    _append(6, &head, &tail);
    print_list(head);

    _append(7, &head, &tail);
    print_list(head);


    print_list(head);
    
    return EXIT_SUCCESS;
}
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