#include <algorithm>
#include <iostream>
#include <string>

int wordsFourLetters(const std::string& sentence)
{
    int words       = 0;
    auto word_begin = sentence.cbegin();
    auto word_end   = sentence.cbegin();
    while (word_end != sentence.cend())
    {
        word_end = std::find_if(word_begin, sentence.cend(),
                                [](const auto& c) { return c == ' '; });

        if(std::distance(word_begin, word_end) == 4)
            ++words;

        word_begin = word_end + 1;
    }

    return words;
}

int main()
{
    std::cout << wordsFourLetters("Hell World is word hell") << "=3";
}