c++ - 如何在if条件下区分零和未定义？

Question

    int todayPrice
cout << "Enter the price of the item this year:\n";
                cin >> todayPrice;
    if ( todayPrice == 0 ) {
            throw DIVIDED_BY_ZERO;
        } else if ( todayPrice < 0 ) {
            throw LESS_THAN_ZERO;
        } else if ( !todayPrice ) {
            throw NOT_A_NUM;
        }

如果用户输入一个零或一个字符串(我猜这将是未定义的)，它将计算为“number == 0”，并且它们都抛出 DIVIDED_BY_ZERO 异常。

如何区分 todayPrice 未定义(当用户输入字符串时)而不是 0？

Answer 1

如果用户输入除整数以外的任何内容，则输入流将进入失败状态，您可以通过流检查:

if (std::cin >> todayPrice)
{
    // Do your other checks
}
else
{
    // User entered something that wasn't a valid integer
    std::cout << "Not a valid integer input\n";
}