如果给定的条件类型错误，则 C++ 无限 while 循环

Question

[更新]我有以下 C++ 代码(跳过不必要的细节):

#include <iostream>

using namespace std;
int main() {
    double value;
    double sum = 0;
    double max, min;
    string msg = "Enter next value (-1) to end: ";
    int validCounter = 0;

do{
    cout << msg;
    cin >> value;  // Values assumed to be numbers
}
while (value <= 0 and value != -1);

if (value > 0.0){sum+= value, max = value, min = value, validCounter = 1;}  // Initial values of min, max, validCounter = 1
while (value != -1){
    cout << msg;
    cin >> value;

    // Only take positive values into consideration for stats
    if (value > 0) {
        validCounter++;
        sum += value;
        if (value > max) { max = value; }
        if (value < min) { min = value; }
    }
}
cout << to_string(validCounter) + " valid value(s) entered" << endl;
if (validCounter > 0){
    cout << "Minimum: " + to_string(min) << endl;
    cout << "Maximum: " + to_string(max) << endl;
    cout << "Moyenne: " + to_string(sum/validCounter) << endl;
}

return 0;

}

但是，当提示输入一个值(为了简单起见，应该是一个数字，这是一个初学者程序)时，如果输入的值不是双倍，则 while 循环开始无限显示输入提示。为什么是这样？是否是由于比较 String != -1 (或任何其他非 int/double 类型)导致循环重复？我在这里很困惑。

Answer 1

替换

do{
    cout << msg;
    cin >> value;  // Values assumed to be numbers
}
while (value <= 0 and value != -1);

由

do {
  cout << msg;
  if (!(cin >> value)) {
    string dummy;

    cin.clear();   // to be able to read double
    cin >> dummy; // to remove the non float
    value = 0;
  }
  while (value <= 0 and value != -1);

您需要清除错误才能再次读取，然后绕过错误的输入，也许您也可以只读取一个字符，决定发生错误时该怎么办

示例:

#include <iostream>
using namespace std;

int main()
{
  double value;

  do {
    cout << "value please" << endl;
    if (!(cin >> value)) {
      string dummy;

      cin.clear();
      cin >> dummy;
      value = 0;
    }
  } while (value <= 0 and value != -1);

  cout << "valid double :" << value << endl;
  return 0;
}

编译和执行:

% ./a.out
value please
aze
value please
-12
value please
12
valid double :12