Conversor INT to HEX C++

#include <iostream>
#include <string>
#include <iomanip>

//using namespace std;
std::string hexa(int h) {
    int i=0;
    std::stringstream s;
    s<< std::hex << h;
    std::string o( s.str() );
     while (o[i]){
        o[i]>='a' ? o[i]-=' ':
        i++;}
return o;

}
int main (){
    std::cout<<hexa(12)<<std::endl;
    std::cout<<hexa(29)<<std::endl;
    return 0;
};