大数加减，较大数阶乘(高精度)
10:大整数加法法一：纯STL(string)实现#include <bits/stdc++.h>using namespace std;string add(string a,string b){ a = a.substr(a.find_first_not_of('0'));//去掉前导0并复制该串重新赋值给a b = b.substr(b.find_first_not_of('0')); reverse(a.begin(), a.end());/
