修改下列程序，使之从文件中读取单词。一种方案是，使用vect

// hangman.cpp -- some string methods
#include <iostream>
#include <string>
#include <cstdlib>
#include <ctime>
#include <cctype>
using std::string;
const int NUM = 26;
const string wordlist[NUM] = {"aplary", "beetle", "cereal",
    "danger", "ensign", "florid", "garage", "health", "insult",
    "jackal", "keeper", "loaner", "manage", "nonce", "onset",
    "plaid", "quilt", "remote", "stolid", "train", "useful",
    "valid", "whence", "xencn", "yearn", "zippy"};

int main()
{
    using std::cout;
    using std::cin;
    using std::tolower;
    using std::endl;
    std::srand(std::time(0));
    char play;
    cout << "Will you play a word game? <y/n> ";
    cin >> play;
    play = tolower(play);
    while (play == 'y')
    {
         string target = wordlist[std::rand() % NUM];
         int length = target.length();
         string attempt(length, '-');
         string badchars;
         int guesses = 6;
         cout << "Guess my secret word. It has " << length
             << " letters, and you guess\n"
             << " one letter at a time. You get " << guesses
    << " wrong guesses.\n";
cout << "Your word: " << attempt << endl;
while (guesses > 0 && attempt != target)
{
    char letter;
    cout << "Guess a letter: ";
    cin >> letter;
    if (badchars.find(letter) != string::npos
        || attempt.find(letter) != string::npos)
    {
        cout  << "You already guessed taht. Try again.\n";
            continue;
    }
    int loc = target.find(letter);
    if (loc == string::npos)
    {
        cout << "Oh, bad guess!\n";
        --guesses;
        badchars += letter; // add to string
    }
    else
    {
        cout << "Good guess!\n";
        attempt[loc]=letter;
        // check if letter appears again
        loc = target.find(letter, loc + 1);
        while (loc != string::npos)
        {
           attempt[loc]=letter;
           loc = target.find(letter,loc + 1);
        }
    }
    cout << "Your word: " << attempt << endl;
    if (attempt != target)
    {
        if (badchars.length() > 0)
            cout << "Bad choices: " << badchars << endl;
        cout << guesses << " bad guesses left\n";
    }
}
if (guesses > 0)
    cout << "That's right!\n";
else
    cout << "Sorry, the word is " << target << ".\n";
        cout << "Will you play another? <y/n> ";
        cin >> play;
        play = tolower(play);
    }

    cout << "Bye\n";

    return 0;
}