c++ - 检查正确的输入会导致无限循环

Question

这是代码片段:

#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。

我是 C++ 的新手，我不确定这是否只是编译器表现不佳，还是我的问题。

Answer 1

发生这种情况是因为 cin.fail() 没有按照您的想法进行。 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。

相反，您可能希望重写为:

#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;
}

有关详细信息，请参阅此链接:http://www.cplusplus.com/reference/ios/ios/fail/