#include <iostream>
#include <string>

using namespace std;

int main() 
{
	std::string vector_name = "positive";
    std::string fullPath = "/home/user/folder/name.of.another_file.txt";
    std::size_t lastIndex = fullPath.find_last_of(".");
    fullPath.insert(lastIndex, "_" + vector_name);
    cout << fullPath;
	return 0;
}