Organize files from exercises in folders by chapter

orgnzr.cc

// script to organize files with the form '1.0' to 'chapter1/1.0'

#include <stdio.h>
#include <iostream>
#include <filesystem>
#include <regex>

namespace fs = std::filesystem;

int main () {
    std::string path = ".";

    for (const auto &entry: fs::directory_iterator(path)) {
      // rename and convert to a string
      std::string old_name = entry.path();

      // erase the first char of the path
      old_name.erase(0,2);

      // set new path
      std::string new_name = "chapter";

      // match files with a digit
      std::regex r("\\d");
      std::smatch m;
      std::regex_search(old_name, m, r);

      // use dat digit to move files
      for (auto c: m) {
        // append c to new name
        new_name += c;

        if (fs::is_directory(old_name))
          continue;
        
        if (!fs::exists(new_name))
            fs::create_directory(new_name);

        new_name += "/";
        new_name += old_name;
        std::cout << "Moving \""
                  << old_name
                  << "\" "
                  << "to \""
                  << new_name 
                  << "\""
                  << std::endl;

        //rename
        if (std::rename(old_name.c_str(), new_name.c_str())) {
          std::perror("Error ranaiming the file");
          return 1;
        }
      }
  }
}

re O(n^3)