What wrong with this code?

#include <sstream>
#include <string>
using namespace std;

int main()
{
string a = "";
string b = "John";
int c = 2;
string d;
stringstream str;
str << a << " Hello " << b << " bye " << c;
d = str.str();
printf("%d",d);
getchar();
return 0;
}