这题真的好难啊……我研究了3天3夜才打出来的奇丑无比的代码……

#include <cstdio>
using namespace std;

char n[2][10000005];int len, i;

inline void swap(char &x, char &y) {
char t = x; x = y; y = t;
}

inline void scan(bool t) {
char sc; while (((sc = getchar()) < '0' || sc > '9') && sc ^ '-');
bool f; int l = 0; if (!(f = sc == '-')) n[t][l++] = sc - '0';
while ((sc = getchar()) >= '0' && sc <= '9') n[t][l++] = sc - '0';
for (i = 0; i < l >> 1; ++i) swap(n[t][i], n[t][l - i - 1]);
if (f) for (i = 0; i < l; ++i) n[t][i] = -n[t][i];
if (l > len) len = l;
}

int main() {
scan(0); scan(1);
for (i = 0; i < len; ++i) n[0][i] += n[1][i];
while (!n[0][len - 1] && len > 1) --len;
if (n[0][len - 1] < 0) for (putchar('-'), i = 0; i < len; ++i) n[0][i] = -n[0][i];
for (i = 0; i < len; ++i) {
while (n[0][i] < 0) n[0][i] += 10, --n[0][i + 1];
while (n[0][i] > 9) n[0][i] -= 10, ++n[0][i + 1];
}
if (n[0][len]) ++len;
while (!n[0][len - 1] && len > 1) --len;
for (i = len - 1; ~i; --i) putchar(n[0][i] + '0');
putchar('\n');
return 0;
}