《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;
}