检查正确的输入会导致无限循环

Question

这里是sn-p的代码：

#include <iostream>

using namespace std;

int main ()
{
    double degree;

    do {
        cout << "Enter a temperature in degrees Celsius: ";
        cin >> degree;
    } while (cin.fail());


    //reassigns degree to conversion to farenheit
    degree = degree * (9/5) + 32;

    cout << "Your temperature in degrees Farenheit is: " << degree;
    return 0;
}

如果输入无效，程序将进入无限循环，不断重复第一个 cout。

我对 C++ 有点陌生，我不确定这是否只是编译器的行为不正常，还是我自己的问题。

Answer 1

发生这种情况是因为cin.fail() 没有按照您的想法行事。 cin.fail() 测试输入中的错误。就cin.fail() 而言，eof（文件结尾）不是输入错误。

你可能想改写为：

#include <iostream>

using namespace std;

int main ()
{
    double degree;

    while( (cout << "Enter a temperature in degrees Celsius: ")
            && !(std::cin >> degree)) {
        cout << "you entered in the wrong type, please try again" << endl;
        cin.clear();// clear error flags from cin
        cin.ignore(numeric_limits<streamsize>::max(), '\n'); //extracts characters from the stream and discards them until a newline is found 
    }


    //reassigns degree to conversion to farenheit
    degree = degree * (9.0/5) + 32; //need to do floating point division here

    cout << "Your temperature in degrees Farenheit is: " << degree;
    return 0;
}

查看此链接了解更多信息：http://www.cplusplus.com/reference/ios/ios/fail/