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

typedef struct _st_node {
    struct _st_node *next;
    int val;
} st_node;


st_node *node_alloc(int val, st_node *next)
{
    st_node *node = (st_node *)malloc(sizeof (st_node));
    node->next = next;
    node->val = val;
    return node;
}

st_node *node_sum_r(int carry_up, st_node *p, st_node *q)
{
    if (p) carry_up += p->val;
    if (q) carry_up += q->val;
    if (!p && !q && !carry_up) return 0;
    return node_alloc(carry_up % 10,
                        node_sum_r(carry_up / 10,
                                    p ? p->next : 0,
                                    q ? q->next : 0));
}

st_node *node_sum(st_node *p, st_node *q)
{
    if (!p || !q) {
        return 0;
    }
    return node_sum_r(0, p, q);
}

st_node *str_to_node(char *num)
{
    st_node *node = 0;
    for (; *num; num++) {
        st_node *new = node_alloc(*num - '0', 0);
        new->next = node;
        node = new;
    }
    return node;
}

int node_len(st_node *node)
{
    int len = 0;
    for (; node; node = node->next) len += 1;
    return len;
}

void node_show(st_node *node)
{
    int len = node_len(node);
    char *buf = (char *)malloc(len + 1);
    char *p = buf + len;
    *p-- = 0;
    for (; node; node = node->next) {
        *p-- = node->val + '0';
    }
    printf("%s\n", buf);
    free(buf);
    return;
}

int main()
{
    st_node *l1 = str_to_node("99");
    st_node *l2 = str_to_node("9999");
    st_node *ls = node_sum(l1, l2);
    node_show(ls);
    return 0;
}