Ordered Words Problem C++

#include <string>
#include <iostream>
#include <vector>


bool ordered_word(std::string);

int main(int argc, char* argv[]){
  //testing

  //std::cout << strcasecmp("A","b") << "\n";
  //std::cout << ordered_word("a")<< "\n";

  //stuff the longest words into a vector
  std::vector<std::string> longest;
  int longest_length = 0;

  //iterate over stdin
  for (std::string line; std::getline(std::cin,line);) {
    if (ordered_word(line)) {
      //case 1: new word is longer
      //clear previous results and add
      //new result. Also update our
      //longest length.

      int new_length = line.length();
      if (new_length > longest_length) {
    longest.clear();
    longest.push_back(line);
    longest_length = line.length();

    //case 2: new word is the same length
    //as previous. Add the new result
    //onto the results list.
      } else if (new_length == longest_length) {
    longest.push_back(line);
      }

    }

  }

  //print out the results.

  for (int i = 0; i < longest.size(); i ++) {
    std::cout << longest[i] << " ";
  }

  std::cout << "\n";



}


bool ordered_word(std::string word){
  //check for single-character word
  int len = word.length();
  if (len == 1) return true;

  //check for empty word (just in case)
  if (len == 0) return false;

  std::string first = word.substr(0, 1);
  for (int i = 1; i <= (len - 1); i++){
    std::string second = word.substr(i,1);
    //use c_str to get c equivalen char *
    if (strcasecmp(first.c_str(),second.c_str()) > 0) return false;
    first = second;
  }
  return true;
}