// Principle: how to get a computed number to a file name 
#include <iostream>
#include <fstream>
#include <math.h>
#include <string>
using namespace std;
int main()
{
  const string str = "res_";
  for (unsigned i=1;i<5;i++){
    ofstream out(str+to_string(cos(i)));
    out.close();
  }
}
/* opened files 
res_0.540302
res_-0.416147
res_-0.989992
res_-0.653644
*/