C++ 不存在合适的构造函数来转换为

Question

I'm trying to make it so an input of a string gets multiplied by two the subtract 1. I know that my question has been asked here before, but the problem is that I couldn't really comprehend what it was saying was wrong.

string coffeeCode(string input) {           //Coffee code= 2n-1 where n=a number in a string

    vector<double> userInputDoubles;
    istringstream converter(input);
    string token;
    double value{};
    while (getline (converter, token, ',')) {
        value = stod(token);
        value = 2 * value - 1;
        userInputDoubles.push_back(value);

    };


    return value;
};

Answer 1

The function returns a double but its return type is string. There is no default constructor to convert double to string. Return a string:

std::string coffeeCode(std::string input) {           //Coffee code= 2n-1 where n=a number in a string

    std::vector<double> userInputDoubles;
    std::istringstream converter(input);
    std::string token;
    double value{};
    while (std::getline (converter, token, ',')) {
        value = std::stod(token);
        value = 2 * value - 1;
        userInputDoubles.push_back(value);

    };


    return std::to_string(value);
};

or return a double:

double coffeeCode(std::string input) {           //Coffee code= 2n-1 where n=a number in a string

    std::vector<double> userInputDoubles;
    std::istringstream converter(input);
    std::string token;
    double value{};
    while (std::getline (converter, token, ',')) {
        value = std::stod(token);
        value = 2 * value - 1;
        userInputDoubles.push_back(value);

    };


    return value;
};