Accelerated C++<4-5>

//编写一个函数以从输入流读单词，将读到的单词存储在一个向量中。利用这个函数编写一个程序以计算输入的单词的数目以及每一个单词所出现的次数。

#include <iostream>
#include <string>
#include <vector>


using namespace std;


istream& read_words(istream& in, vector<string>& words) {
  if (in) {
    words.clear();
    string word;
    
    while (in >> word)
      words.push_back(word);
    
    in.clear();
  }
  
  return in;
}


int main() {
  vector<string> words;


  read_words(cin, words);


  cout << "Num of words: " << words.size() << endl;


  sort(words.begin(), words.end());


  string prev_word = "";
  int count = 0;


  for (vector<string>::size_type i = 0; i < words.size(); ++i) {
    if (words[i] != prev_word) {
      if (prev_word != "")
cout << prev_word << " appeared " << count << " times" << endl;


      prev_word = words[i];
      count = 1;
    }
    else
      ++count;
  }


  cout << prev_word << " appeared " << count << " times" << endl;


  return 0;
}