第十一章 11.2.3节练习

练习11.12

编写程序，读入string和int的序列，将每个string和int存入一个pair中，pair保存在一个vector中。

解答：

#include <iostream>#include <map>#include <string>#include <vector>#include <iterator>using namespace std;int main(){vector<pair<string, int>> vec;string words[] = { "apple", "pear", "melon", "hello", "world", "google", "baidu" };int nums[] = { 1, 2, 3, 4, 5, 6, 7};auto sfirst = begin(words);auto slast = end(words);auto nfirst = begin(nums);auto nlast = end(nums);auto nit = nfirst;auto sit = sfirst;for (; nit != nlast && sit !=slast ; ++sit, ++nit){pair<string, int> p(*sit, *nit);vec.push_back(p);}for (auto i : vec){cout << i.first << "=>" << i.second << endl;}return 0;}

练习11.13

在上一题的程序中，至少有三种创建pair的方法。编写此程序的三个版本，分别采用不同的方法创建pair。

解释你认为哪种形式最易于编写和理解，为什么?

解答：

#include <iostream>#include <map>#include <string>#include <vector>#include <iterator>using namespace std;#define N 3int main(){vector<pair<string, int>> vec;string words[] = { "apple", "pear", "melon", "hello", "world", "google", "baidu" };int nums[] = { 1, 2, 3, 4, 5, 6, 7};auto sfirst = begin(words);auto slast = end(words);auto nfirst = begin(nums);auto nlast = end(nums);auto nit = nfirst;auto sit = sfirst;#if N == 1for (; nit != nlast && sit !=slast ; ++sit, ++nit){pair<string, int> p(*sit, *nit);vec.push_back(p);}#elif N == 2for (; nit != nlast && sit !=slast ; ++sit, ++nit){pair<string, int> p = { *sit, *nit };vec.push_back(p);}#elif N == 3for (; nit != nlast && sit != slast; ++sit, ++nit){vec.push_back(make_pair(*sit, *nit));}#endiffor (auto i : vec){cout << i.first << "=>" << i.second << endl;}return 0;}

我感觉第三终易与编写，简单明确，不过要求对添加的元素类型比较清楚，否则容易出错。

第一种易与理解，可以明确的知道pair中的类型是否和vec中的元素一致。

练习11.14

扩展你在11.2.1节练习（第378页）中编写的孩子姓到名的map，添加一个pair的vector，保存孩子的名和生日。

解答:

#include <iostream>#include <map>#include <vector>#include <string>using namespace std;int main(){    map<string, vector<pair<string, string>>> families;string family_name, giving_name, birthday;while (cin >> giving_name){cin >> family_name;cin >> birthday;families[family_name].push_back(make_pair(giving_name, birthday));}for (map<string, vector<pair<string, string>>>::iterator it = families.begin();it != families.end(); ++it){cout << "The family name is "<<it->first << " " << endl;for (const auto &i : it->second){cout << "\t" << i.first << "'s birthday is " << i.second << endl;}cout << endl;}return 0;}

代码里面没有输入正确性的检查，也就是鲁棒性比较低，需要按照约定好的格式进行输入才能正确显示。