#include <iostream>
#include <cstdlib>
#include <string>
#include <vector>
#include <cctype>     //for the function islower
#include <iterator>   //for class back_inserter
#include <algorithm>  //for the functions copy_if, count
using namespace std;

//The house with functions and autos.

int main()
{
	vector<char> alphabet;   //will hold the input characters

	cout << "Please input a sentence (please input lowercase) ";
	string sentence;
	getline(cin, sentence); //cin is limiting, replaced with getline.

	if (!cin) {
		cerr << "Sorry, couldn't receive input.\n";
		return EXIT_FAILURE;
	}

	//Copy the lowercase letters from sentence to alphabet.
	copy_if(begin(sentence), end(sentence), back_inserter(alphabet),
		[](char c) {return islower(c);});

	const vector<char>::size_type n {alphabet.size()};

	char freqletter {'\0'}; //the most popular letter
	int mostused {0};       //how many times the most popular letter appeared

	for (auto letter: alphabet) {   //for each letter in alphabet,
		const vector<char>::difference_type timesused
			{count(begin(alphabet), end(alphabet), letter)};

		if (timesused > mostused) {
			mostused = timesused;
			freqletter = letter;
		}
	}	
	
	cout << "Your sentence has the letter, " << freqletter << ", used" << " " << mostused
		<< " time";
	if (mostused != 1) {
		cout << "s";
	}
	cout << ".\n";

	return EXIT_SUCCESS;
}