Входной тест для http://cpp-school.unigine.com без изысков.

kozlyuk_basic.cc

#include <iostream>
#include <fstream>
#include <unordered_map>
#include <algorithm>

using namespace std;

void skip_to_word(istream& stream);
string scan_word(istream& stream);

int
main(int argc, char* argv[]) {
    if (argc != 3) {
        cerr << "Usage: " << argv[0] << " input.txt output.txt\n";
        return EXIT_FAILURE;
    }

    unordered_map<string, size_t> frequences;

    ifstream input(argv[1]);
    while (input) {
        skip_to_word(input);
        if (!input) {
            break;
        }
        const auto& word = scan_word(input);
        frequences[word]++;
    }

    ofstream output(argv[2]);
    while (!frequences.empty()) {
        // VS2013 has no C++14 polymorphic lambdas (for auto parameters).
        using Pair = decltype(frequences)::value_type;
        auto iterator = max_element(begin(frequences), end(frequences),
                [](const Pair& lhs, const Pair& rhs) {
                    if (lhs.second == rhs.second) {
                        return lhs.first >= rhs.first;
                    }
                    return lhs.second < rhs.second;
                });
        output << iterator->second << ' ' << iterator->first << '\n';
        frequences.erase(iterator);
    }

    return EXIT_SUCCESS;
}

string
scan_word(istream& stream) {
    string word;
    while (stream.good()) {
        auto symbol = static_cast<char>(stream.get());
        if (!isalpha(symbol)) {
            stream.unget();
            break;
        } else {
            word += tolower(symbol);
        }
    }
    return word;
}

void
skip_to_word(istream& stream) {
    while (stream.good()) {
        auto symbol = static_cast<char>(stream.get());
        if (isalpha(symbol)) {
            stream.unget();
            break;
        }
    }
}