Question

这是我的第一篇stackoverflow帖子，所以如果写得不好或者类似，请道歉，但我是C ++的超级初学者（可能会在代码中很明显）并且我正在尝试完成100编程挑战，我只能达到＃3 - 温度转换器。

我的朋友在其他语言方面有一些编程经验，今晚会在我的github上浏览它，看看他是否能解决这个问题，但我想我也尝试过stackoverflow。 / p>

我不知道具体是什么导致了错误，所以我将不得不发布整个代码，但基本上我的问题是它编译得很好，但是当输入任何输入时它会触发cin.fail（并且只是在几乎看似它自己的函数之间循环并跳转，但是从不进入CelstoFahr（）或FahrtoCels（）。

如果我的代码很乱，请再次道歉，如果您有任何建议请告诉我，并随时批评我的风格，因为我一直在寻求改进。如有必要，我也可以链接我的github。

以下代码：

#include "stdafx.h"
#include <iostream>
#include <string>
#include <limits>

// Forward declaring the functions
double CinFailCheck(double cin_fail_check);
double CelstoFahr(double celsius_amount, double fahrenheit_amount);
double FahrtoCels(double celsius_amount, double fahrenheit_amount);
int UserSelectionValidate(int user_selection);
void pauseAtEnd();
bool UserRestart();
void menu();

// Initializing the functions, with user input validation, for Cels -> Fahr, Fahr -> Cels and User Selection
double CinFailCheck(double cin_fail_check)
{
    while (std::cin.fail())
    {
        std::cin.clear();
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
        std::cout << "\nBad entry, no text allowed! Enter a Number: ";
        std::cin >> cin_fail_check;
    }

    return cin_fail_check;
}

double CelstoFahr(double celsius_amount, double fahrenheit_amount)
{
    // Declaring cin_fail_check to enable me to have the cin.fail() as a function
    double cin_fail_check = 0;

    // Perform cin.fail() on the users input then grab that input and clone it to celsius_amount
    CinFailCheck(cin_fail_check);

    celsius_amount = cin_fail_check;
    std::cin.clear();
    std::cin.ignore();

    // Make conversion using the formula for C to F
    fahrenheit_amount = (celsius_amount * 1.8) + 32;

    return fahrenheit_amount;
}

double FahrtoCels(double celsius_amount, double fahrenheit_amount)
{
// Declaring cin_fail_check to enable me to have the cin.fail() as a function
double cin_fail_check = 0;

// Perform cin.fail() on the users input then grab that input and clone it to fahrenheit_amount
CinFailCheck(cin_fail_check);

fahrenheit_amount = cin_fail_check;
std::cin.clear();
std::cin.ignore();

// Make conversion using the formula for F to C
celsius_amount = (fahrenheit_amount - 32) * (5 / 9);

return celsius_amount;
}

int UserSelectionValidate(int user_selection)
{
    // Declaring cin_fail_check to enable me to have the cin.fail() as a function
    double cin_fail_check = 0;

    // Perform cin.fail() on the users input then grab that input and clone it to user_selection
    CinFailCheck(cin_fail_check);

    user_selection = cin_fail_check;
    std::cin.clear();
    std::cin.ignore();

    return user_selection;
}

// Function to enable a pause at the end to avoid the use of system("pause")
void pauseAtEnd() 
{
    std::cout << "\n\nPlease press Enter to exit . . .";
    std::cin.sync();
    std::cin.get();
}

// Restart function to avoid having to re-write it all each time
bool UserRestart()
{
    bool CONVERTER_RUNNING = true;
    bool BOOL_RETURNTOMENU = true;
    std::string user_returntomenu;

    // Check if the player wishes to make another conversion or exit the program
    while (BOOL_RETURNTOMENU == true)
    {
        std::cout << "\nDo you wish to make another conversion? Y/N: ";
        std::cin >> user_returntomenu;
        std::cin.ignore();

        if (user_returntomenu == "Y" || user_returntomenu == "y" || user_returntomenu == "N" || user_returntomenu == "n")
        {
            if (user_returntomenu == "Y" || user_returntomenu == "y")
            {
                std::cin.clear();
                std::cin.ignore();
                menu();
            }

            else
            {
                std::cout << "\nGoodbye";
                BOOL_RETURNTOMENU = false;
            }
        }

        else
        {
            std::cout << "\nBad Entry! Numbers not allowed! Please enter Y or N\n";
            std::cin.clear();
            std::cin.ignore();
        }
    }

    CONVERTER_RUNNING = false;

    return CONVERTER_RUNNING;
}

// Writing the menu() function to enable loopback from the restart function
void menu()
{
    int user_selection = 0;
    double celsius_amount = 0;
    double fahrenheit_amount = 0;
    std::cout << "Welcome to the Temperature Converter!\n\n";
    std::cout << "1. Convert Celsius to Fahrenheit\n";
    std::cout << "2. Convert Fahrenheit to Celsius\n";
    std::cout << "3. Exit program\n";

    UserSelectionValidate(user_selection);

    if (user_selection == 1)
    {
        // Run Celsius to Fahrenheit function and retrieve the values to cout here
        CelstoFahr(celsius_amount, fahrenheit_amount);

        // cout the amounts received from the function
        std::cout << "\n" << celsius_amount << " degrees Celsius is equal to " << fahrenheit_amount << " degrees Fahrenheit";
    }

    else if (user_selection == 2)
    {
        // Run Fahrenheit to Celsius function and retrieve the values to cout here
        FahrtoCels(celsius_amount, fahrenheit_amount);

        // cout the amounts received from the function
        std::cout << "\n" << fahrenheit_amount << " degrees Fahrenheit is equal to " << celsius_amount << " degrees Celsius";
    }

    else if (user_selection == 3)
    {
        std::cout << "\nGoodbye";
    }

    else
    {
        std::cin.clear();
         std::cin.ignore();
        std::cout << "\nPlease enter a number between 1 and 3 for your selection!\n\n";
        UserSelectionValidate(user_selection);
    }
}

int main()
{

    // Declare boolean variable to keep converter running
    bool CONVERTER_RUNNING = true;

    while (CONVERTER_RUNNING == true)
    {
        menu();
        UserRestart();
    }

    pauseAtEnd();

    return 0;
}

Answer 1

这是一个问题：

UserSelectionValidate(user_selection);

这不会对user_selection产生影响，因为它是按值传递的，并且不会使用返回值。也许你的意思是

user_selection = UserSelectionValidate();

只需在UserSelectionValidate：

中本地声明user_selection

int UserSelectionValidate()
{
    // Declaring cin_fail_check to enable me to have the cin.fail() as a function
    double cin_fail_check = 0;

    // Perform cin.fail() on the users input then grab that input and clone it to user_selection
    CinFailCheck(cin_fail_check);

    int user_selection = cin_fail_check;
    std::cin.clear();
    std::cin.ignore();

    return user_selection;
}

CinFailCheck()存在类似问题。

Answer 2

您需要编写正确的代码来存储输入user_selection。

std::cout << "Welcome to the Temperature Converter!\n\n";
std::cout << "1. Convert Celsius to Fahrenheit\n";
std::cout << "2. Convert Fahrenheit to Celsius\n";
std::cout << "3. Exit program\n";

UserSelectionValidate(user_selection);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

将以上行替换为：

std::cin >> user_selection;

然后确保要求转换输入值。你可以这样做。

Answer 3

您需要了解按值传递，并通过引用传递。在几乎所有函数中，您都是通过值传递而不是使用返回值。传递值时，通过复制传递给它的一个局部变量（在堆栈上）创建一个局部变量。修改它时，您不会修改传递的原始变量。

例如，在下面的代码中，cin_fail_check永远不会改变，它的初始化值总是为0，因为CinFailCheck不会修改它;你可以看到如何从中获得无限循环。

// Declaring cin_fail_check to enable me to have the cin.fail() as a function
double cin_fail_check = 0;

// Perform cin.fail() on the users input then grab that input and clone it to user_selection
CinFailCheck(cin_fail_check);

int user_selection = cin_fail_check;

更改您的函数定义以获取引用。例如：double CinFailCheck(double& cin_fail_check)或使用返回值。

“何时按值，引用和指针传递参数” http://www.cplusplus.com/articles/z6vU7k9E/

移动黑白函数的C ++初学者问题

3 个答案: