Question

我在Stroustrup的PPP第二版中尝试了这个练习之一，该程序应该接受一个值后跟一个表示货币的后缀。这应该转换成美元。以下代码适用于＆＃34; 15y＆＃34;或＆＃34; 5p＆＃34;，但当我进入＆＃34; 6e＆＃34;它给了我＆＃34;未知货币＆＃34;。

constexpr double yen_per_dollar = 124.34;
constexpr double euro_per_dollar = 0.91;
constexpr double pound_per_dollar = 0.64;

/* 
    The program accepts xy as its input where
    x is the amount and y is its currency
    it converts this to dollars.
*/
double amount = 0;
char currency = 0;
cout << "Please enter an amount to be converted to USD\n"
     << "followed by its currency (y for yen, e for euro, p for pound):\n";
cin >> amount >> currency;

if (currency == 'y') // yen
    cout << amount << currency << " == " 
         << amount/yen_per_dollar << " USD.\n";
else if (currency == 'e') // euro
    cout << amount << currency << " == "
         << amount/euro_per_dollar << " USD.\n";
else if (currency == 'p') // pound
    cout << amount << currency << " == "
         << amount/pound_per_dollar << " USD.\n";
else
    cout << "Unknown currency.\n";

如果我输入＆＃34; 6 e＆＃34;相反，它工作正常，但我不明白为什么其他人即使没有空间也能工作。

Answer 1

6e可以解释为双重（6e == 6e0 == 6 * pow(10,0) == 6）格式错误的科学记数法，因此cin >> amount读取它，>> currency读取空字符串。

尝试cin >> std::fixed >> amount（来自<iomanip>）仅强制“正常”＃39}符号。如果这没有帮助（并且它可能不适用于大多数编译器） - 您将必须读取行（std::getline()）并手动解析（拆分为第一个非数字/ dit或从末尾读取等）

另见：How to make C++ cout not use scientific notation

货币选择有效，除非用户选择欧元或＆＃39; e＆＃39;

1 个答案: