Hugo-to_hex-opti1.cxx

#include <iostream>
#include <string> 
#include <cmath>

int find_exp(int dec){
#ifndef __GNUG__
  int n = 0;
  for(int be = 0; dec >= be; ++n){
    be = 1 << (4 * (n + 1));
  }
  return n - 1;
#else
  return (7 - __builtin_clz(dec) / 4);
#endif
}

char conv_to_letter(int num){
  return num + (num > 9 ? 55 : 48);
}

std::string tohex(int integer){
  std::string ret{};
  div_t d{0, integer};
  for(int i = find_exp(integer); i >= 0; --i){
    d = std::div(d.rem, (1 << (4 * i)));
    ret.push_back(conv_to_letter(d.quot));
  }
  return ret;
}

int main(){
	std::cout << "Enter a number you want in hex: " << std::flush;
  int integer;
  std::cin >> integer;
  std::cout << integer << "(10) = " << tohex(integer) << "(16)\n" << std::flush;
  return 0;
}