#include <iostream>
#include <sstream>
#include <string>
#include <map>
#include <algorithm>
using namespace std;

int main()
{
    string line;
    getline(cin, line);
    istringstream lineStream(line);
    string word;
    map<string, string> wordsMap;
    vector<string> wordsVec;
    while(lineStream >> word)
        if(word.size() < 5)
            wordsVec.push_back(word);
    transform(wordsVec.begin(), wordsVec.end(), wordsVec.begin(), ::tolower);
    for(int i = 0; i < wordsVec.size(); ++i)
        wordsMap.insert(pair<string, string>(word, 0));
    for(map<string, string>::iterator it = wordsMap.begin(); it != wordsMap.end(); ++it)
    {
        cout << it->first << ", ";
    }
    cout << (--wordsMap.end())->first << endl;
    return 0;
}

Компилатора крещи |4175|error: cannot convert 'std::__cxx11::basic_string<char>' to 'int' in argument passing и ми отваря stl_algo.h сочейки към  for (; __first != __last; ++__first, ++__result)
    *__result = __unary_op(*__first);
      return __result;

Пробвах и със set и ми дава същия error.