尝试：

while (1) {
  if (cin >> x) {
      // valid number
      break;
  } else {
      // not a valid number
      cout << "Invalid Input! Please input a numerical value." << endl;
      cin.clear();
      while (cin.get() != '\n') ; // empty loop
  }
}

这基本上清除错误状态，然后读取并丢弃在上一行输入的所有内容。

This basically clears the error state, then reads and discards everything that was entered on the previous line.