How to read a complete line from the user using cin?

The code cin >> y; only reads in one word, not the whole line. To get a line, use:

string response;
getline(cin, response);

Then response will contain the contents of the entire line.

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <string>

int main()
{
    char write_to_file;
    std::cout << "Would you like to write to a file?" << std::endl;
    std::cin >> write_to_file;
    std::cin >> std::ws;
    if (write_to_file == 'y' || write_to_file == 'Y')
    {
        std::string str;
        std::cout << "What would you like to write." << std::endl;

        std::getline(std::cin, str);
        std::ofstream file;
        file.open("Characters.txt");
        file << str.size() << " Characters." << std::endl;
        file << std::endl;
        file << str;

        file.close();

        std::cout << "Done. \a" << std::endl;
    }
    else
        std::cout << "K, Bye." << std::endl;
}

string str;
getline(cin, str);
cin >> ws;

You can use getline function to read the whole line instead of reading word by word. And The cin>>ws is there to skip white spaces. And you find some detail about it here : http://en.cppreference.com/w/cpp/io/manip/ws