#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) {
    for(Node* curr = head;  curr != NULL; curr = curr -> next) {
        printf("[%d]", curr -> value);   
        if(curr -> next != NULL) { // If curr is not the tail...
            printf("→");
        }
    }
    printf("\n");
}

void _append(int value, Node** a_head, Node** a_tail) {
    // Allocate memory on heap for a new node.
    Node* new_node = malloc(sizeof(*new_node));
    
    // Initialize fields of the new node.
    new_node -> value = value;
    new_node -> next  = NULL;

    if(*a_head == NULL) {  // If list is empty (size=0), initialize a list of size one.
        assert(*a_tail == NULL);
        // "Create a new list" meaning before this line, the head and tail (variables)
        *a_head = new_node;   // in the caller were set to NULL.  We will now set them to
        *a_tail = new_node;   // the address of a real node on the heap.
    }                         // Terminology note:  "Initialize" means to assign the
    else {                    // value to a variable for the first time.
        (*a_tail) -> next = new_node;  // Connect tail to new node.  IOW: Set the '.next'
        *a_tail = new_node;            // field of the tail to the address of the new node.
    }
}

int main(int argc, char* argv[]) {
    Node* head = NULL;
    Node* tail = head;

    _append(5, &head, &tail);
    _append(6, &head, &tail);
    _append(7, &head, &tail);
    for(int i = 0; i < 15; i++) {
        _append(i, &head, &tail);
    }

    print_list(head);

    return EXIT_SUCCESS;
}
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