Creating file names automatically C++

Question

I\'m trying to write a program in C++, which creates some files (.txt) and writes down the result in them. The problem is that an amount of these files is not fixed at the begin

Answer 1

... another way to bulid the filename

#include 

int n = 3;
std::ostringstream os;
os << "file_" << n << ".txt";

std::string s = os.str();