ll.c

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

typedef int T; // Could be anything

T *firstNode = NULL;
T *lastNode = NULL;

void append(T value) {
	// Allocate node:
	T *ptr = (T*) malloc(2 * sizeof(T*) + sizeof(T)); // Prev addr, next addr, value
	*(((T**) ptr) - 2) = lastNode;
	*(((T**) ptr) - 1) = NULL;
	memcpy(ptr, &value, sizeof(T));
	if (firstNode == NULL) {
		firstNode = ptr;
		lastNode = ptr;
	} else {
		*(((T**) lastNode) - 1) = ptr;
		lastNode = ptr;
	}
}

void insert(T *from, int n, T value) {
	if (n <= 0) {
		T *ptr = (T*) malloc(2 * sizeof(T*) + sizeof(T)); // Prev addr, next addr, value
		*(((T**) ptr) - 2) = from;
		*(((T**) ptr) - 1) = *(((T**) from) - 1);
		memcpy(ptr, &value, sizeof(T));
		*(((T**) from) - 1) = ptr;
	} else {
		return insert(*(((T**) from) - 1), n - 1, value);
	}
}

void print(T *node) {
	printf("%d\n", *node);
	T* nxt = *(((T**) node) - 1);
	if (nxt != NULL)
		print(nxt);
}

T get(T *from, int n) {
	if (n <= 0)
		return *from;
	else
		return get(*(((T**) from) - 1), n - 1);
}

void nfree(T *node);

void nfree(T *node) {
	T* nxt = *(((T**) node) - 1);
	if (nxt != NULL)
		nfree(nxt);
	free(node);
}

int main() {
	// Append
	append(1);
	append(2);
	append(3);
	// Insert
	insert(firstNode, 1, 4);
	insert(firstNode, 1, 5);
	printf("Iterate:\n");
	print(firstNode);
	printf("Indexed Get: \n");
	printf("%d\n", get(firstNode, 3));
	nfree(firstNode);
}