《C++ Primer》P314中使用insert重写单词统计程序的扩展

#include <iostream>
#include <utility>
#include<vector>
#include <string>
#include <map>

using namespace std;

int main()
{
    pair<string,int > sipr;
    string str;
    int ival;
    vector< pair<string,int> > pvec;
    map<string,int> word_count;
    cout<<"Enter a string and an integer ( Ctrl + Z to end) : "
        <<endl;
    while (cin >>str>>ival  )
    {
        sipr = make_pair(str, ival);
        pvec.push_back(sipr);
        word_count.insert(map<string, int>::value_type(str, ival) );
    }
    
    string num;
    cin.clear();
    while ( cin>>num )
    {
        pair<map<string,int>::iterator , bool> ret=
            word_count.insert(make_pair(num, 1));
        if (!ret.second)
        {
            ++ret.first->second;
            cout<<ret.first->first<<" 的值变为："<<ret.first->second<<endl;
        }
    }
    map<string,int>::iterator it = word_count.begin();
    while (it !=word_count.end())
    {
        cout<<"key：" <<it->first<<"value："<< it->second <<endl;
        it++;
    }

    return 0;
    }