#include <stdio.h>

#include <iostream>

#include <cstring>

#include <string>

#include <algorithm>

using namespace std;

string Convert(string num, int m, int n){

    string ans = "";

    int remainder,current;

    int len = num.length();

    for(int i=0;i<len;){             //字符串除法

        remainder = 0;

        for(int j=0;j<len;j++){

            current = remainder*m+num[j]-'0';

            num[j] = current/n+'0';

            remainder = current%n;

        }

        if (remainder<=9&&remainder>=0)//拼凑余数，所得字符串为反序

         ...