Punctuation C++

#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <cctype>
#include <map>
#include <algorithm>

using namespace std;

bool is_punctuation(int ch)
{
    string punct_marks{ ".,!?;:-" };
    return punct_marks.find(ch) != string::npos;
}

int main()
{
    string line;
    getline(cin, line);

    using WordInfo = pair<string, size_t>;
    using WordData = vector<WordInfo>;
    using WordMap = map<int, WordData>;

    WordMap data;
    istringstream iss(line);
    string s;
    while (iss >> s)
    {
        size_t pos;
        if(iss.good())
            pos = static_cast<size_t>(iss.tellg());
        else
            pos = line.length();
        pos -= s.length();

        s.erase(find_if(s.begin(), s.end(), [](int ch) { return is_punctuation(ch); }), s.end());

        data[s.length()].push_back(make_pair(s, pos));
    }

    string result{ line };
    for (auto w : data)
    {
        if (w.second.size() > 1)
        {
            for (size_t fwd = 0, bwd = w.second.size() - 1; fwd < bwd; ++fwd, --bwd)
            {
                string left_str = w.second[fwd].first, right_str = w.second[bwd].first;
                if (left_str != right_str)
                {
                    size_t len = w.first;
                    result.replace(w.second[fwd].second, len, right_str);
                    if (isupper(left_str[0]))
                        left_str[0] = tolower(left_str[0]);
                    result.replace(w.second[bwd].second, len, left_str);
                }
            }
        }
    }

    result[0] = toupper(result[0]);
    cout << result << endl;

    return 0;
}