Problem 90: Dual Palindromes

I accidentally thought it was "dual square palindromes", which made me fail until I noticed it.

This one is the last for Chapter 1's Section 1.2!

/*
ID: victor4
PROG: dualpal
LANG: C++
*/
#include <iostream>
#include <fstream>
#include <string>

#include <algorithm>

using namespace std;

inline char to_char(int c){
 if(c >= 10)
  return c - 10 + 'A';
 return c + '0';
}

string tobase(int num, int base){
 string ret;
 int div = base;
 while(div < num)
  div *= base;
 for(div /= base;;){
  ret += to_char(num / div);
  // get remainder
  num = num % div;
  // next
  if(div < 2) break;
  div /= base;
 }
 return ret;
}

string reverse_str(string str){
 reverse(str.begin(), str.end());
 return str;
}

int main() {
 ofstream fout ("dualpal.out");
 ifstream fin ("dualpal.in");
 int N, S;
 fin >> N >> S;
 
 while(N){
  if(++S > 100000)
   break;
  int num = 0;
  for(int j = 2; j <= 10; ++j){
   // fail: I put S * S instead of S
   string check = tobase(S, j);
   if(check == reverse_str(check) && ++num >= 2){
    --N;
    fout << S << endl;
    break;
   }
  }
 }
 
 return 0;
}