《C++ Primer》第五版课后习题解答_第五章（4）(20-25)

系统环境： windows 10 1703

编译环境：Visual studio 2017

5.20

#include <iostream>#include <string>using std::cout;using std::endl;using std::cin;using std::string;int main(){string str, temp;cout << "Please enter strings: " << endl;while (cin >> str){if (temp == str){cout << "Repeat!!! " << str << endl;break;}else{temp = str;}}if (cin.eof()) // 这里用了一个 cin.eof 表达式来判断输入的是否为文件尾{cout << "No Repeat!!!" << endl;}return 0;}

  需要注意的是，当 while 循环结束后（无论是读取到末尾或是被 break 语句打断），如果不加判断语句就直接输出“无重复”，则此句一定会被输出。因此必须在循环外添加判断语句，以确定此刻的输入是否为文件尾。上述程序中使用了表达式 cin.eof()。当输入为文件尾时，该表达式返回 1。

5.21

#include <iostream>#include <string>using std::cout;using std::endl;using std::cin;using std::string;int main(){string str, temp;cout << "Please enter strings: " << endl;while (cin >> str){if (temp == str){if (isupper(str[0])) //判断输入的 string 的开头是否为大写{cout << "Repeat!!! " << str << endl;break;}else //如果不是大写，则继续循环{continue;}}else{temp = str;}}if (cin.eof()) // 这里用了一个 cin.eof 表达式来判断输入的是否为文件尾{cout << "No Repeat!!!" << endl;}return 0;}

5.22

for (int sz = get_size(); sz <= 0; sz = get.size()){;}

5.23

#include <iostream>using std::cout;using std::cin;using std::endl;int main(){int i = 0, j = 0, k = 0;cout << "Enter two numbers:" << endl;cin >> i >> j;k = i / j;cout << k << endl;return 0;}

5.24

#include <iostream>using std::cout;using std::cin;using std::endl;using std::runtime_error;int main(){int i = 0, j = 0, k = 0;cout << "Enter two numbers:" << endl;cin >> i >> j;try{if (j == 0){throw runtime_error("Your second number can't be zero!!!");}k = i / j;cout << k << endl;}return 0;}

输出为 error C2317 : 在行“12”上开始的“try”块没有 catch 处理程序。

5.25

#include <iostream>using std::cout;using std::cin;using std::endl;using std::runtime_error;int main(){float i = 0, j = 0, k = 0;cout << "Enter two numbers:" << endl;while (cin >> i >> j){    try{if (j == 0){throw runtime_error("Your second number can't be zero!!!");}k = i / j;cout << k << endl;break;}catch (runtime_error err){cout << err.what() << "\n" << "do you want to start over? enter \"Y\" or \"N\"" << endl;char c;cin >> c;if (!cin || c == 'N'){break;}}}return 0;}