c++ - 如何检查用户输入？

Question

所以我希望能够使除特定单词(如 'K' 或 'C' 之外的所有用户输入无效。我完全不确定该怎么做。因此，如果他们将其拼错为“celcius”或“husdhfjae”，我的程序会说 “Input invalid, please enter K or C.”

请不要太复杂，因为我才刚刚开始。谢谢 :)

//  CS 575,HW #1B, Ravela Smyth

//  This program converts from Fahrenheit to Celsius or Kelvin

#include <iostream>
#include <string>
using namespace std;

int main() {
    string input;
    double Fahrenheit, celsius, kelvin;
    cout << "Hi! What is the weather today in Fahrenheit?? " << endl;
    cin >> Fahrenheit;
    cout << "Would you like to convert this temperature to Celsius or Kelvin? (C/K)" << endl;
    cin >> input;
    if (input == "C")
    {
          celsius = (5 * (Fahrenheit - 32)) / 9;
          cout << "Today's weather in Celsius is " << celsius << " degrees! " << endl;
    }
    else if (input == "c")
    {
          celsius = (5 * (Fahrenheit - 32)) / 9;
          cout << "Today's weather in Celsius is " << celsius << " degrees! " << endl;
    }
    else if (input == "K")
    {
          kelvin = (5 * (Fahrenheit + 459.67)) / 9;
          cout << "Today's weather in Kelvin is " << kelvin << " degrees!" << endl;
    }
    else if (input == "k")
    {
          kelvin = (5 * (Fahrenheit + 459.67)) / 9;
          cout << "Today's weather in Kelvin is " << kelvin << " degrees!" << endl;
    }

return 0;
}

Answer 1

通常使用while 或do...while 循环检查用户输入。 这个想法很简单，您总是会返回到相同的错误消息并再次读取输入，直到它正确为止。

将有效选项放在单个 string 中的优点是允许轻松添加或删除选项，而无需处理长的 if 条件。

我相信像这样简单的事情就能完成这项工作:

std::string valid_options("kKcC");
std::string input;
bool illegal_input;

std::cout << "Would you like to convert this temperature to Celsius or Kelvin? (C/K)" << std::endl;
std::cin >> input;
// check that only one letter was provided and it belongs to the valid options
while (input.size() != 1 || valid_options.find(input) == std::string::npos)
{
    std::cout << "Input invalid, please enter K or C.\n";
    std::cin >> input;
}