Question

我正在制作一个家庭作业计划，到目前为止，除了星球＆＃34;海王星＆＃34;以外，所有东西都打印得正确。每个其他选择工作正常，并打印出他们应该是的数字，但海王星打印出正确的数字，但作为负面。我被告知要将双重投入很长一段时间，但我相信我已经完成并且没有任何区别。任何帮助或指导将不胜感激。我会附上我的代码，以便你们可以看看它。另一件事是，当海王星被选中时，选择应该是＆＃39; h＆＃39;然后，重量是160，速度是595.此外，以小时为单位的旅行时间打印数字是4537815，天数189076，年份是518.02。小时和天数正确出现，除了最后一个数字需要在我的代码中向上舍入一个，并且年份正确，除非它是负数。

#include <iostream>
#include <iomanip>
#include <cmath>
#include <string>
using namespace std;

int main()
{
    char selection;
    double weight = 0.0;
    double speed = 0.0;
    double surfGrav;
    double distEarthToSun  = 93 * 1000000;
    double distfromSun = 0.0;
    double newSunDist;
    double newWeight;
    double distFromPlanets;
    // double travelTime;
    double travelTimeHours;
    double travelTimeDays;
    double travelTimeYears;
    string planetName;

    cout << "Welcome to INTERPLANETARY TRAVEL PROGRAM!\n";
    cout << "This program enables you to find out your travel time to the planet\n" 
         << "you want to travel to as well as your weight on that planet.\n";
    cout << "Please enjoy the program and find the perfect planet for you!\n";
    cout << '\n';
    cout << '\n';
    cout << "INTERPLANETARY TRAVEL MENU\n";
    cout << "--------------------------\n";
    cout << "a) Mercury\n";
    cout << "b) Venus\n";
    cout << "c) Earth\n";
    cout << "d) Mars\n";
    cout << "e) Jupiter\n";
    cout << "f) Saturn\n";
    cout << "g) Uranus\n";
    cout << "h) Neptune\n";
    cout << "q) quit\n";
    cout << '\n';
    cout << "Select a planet to travel to or q to quit the program: \n";
    cin >> selection;

    if (selection >= 'a' && selection <= 'h')
    {
        cout << "Please enter your weight (in lbs): \n";
        cin >> weight;
        cout << "Please enter the speed (in mile per hour) that you would like to travel at: \n";
        cin >> speed;
    }

    if (selection == 'a')
    {
        planetName = "Mercury";
        surfGrav = 0.27;
        distfromSun = 36;
    }
    else if (selection == 'b')
    {
        planetName = "Venus";
        surfGrav = 0.86;
        distfromSun = 67;
    }
    else if (selection == 'c')
    {
        planetName = "Earth";
        surfGrav = 1.00;
        distfromSun = 93;
    }
    else if (selection == 'd')
    {
        planetName = "Mars";
        surfGrav = 0.37;
        distfromSun = 141;
    }
    else if (selection == 'e')
    {
        planetName = "Jupiter";
        surfGrav = 2.64;
        distfromSun = 483;
    }
    else if (selection == 'f')
    {
        planetName = "Saturn";
        surfGrav = 1.17;
        distfromSun = 886;
    }
    else if (selection == 'g')
    {
        planetName = "Uranus";
        surfGrav = 0.92;
        distfromSun = 1782;
    }
    else if (selection == 'h')
    {
        planetName = "Neptune";
        surfGrav = 1.44;
        distfromSun = 2793;
    }
    else if (selection == 'q')
    {
       cout << "You have chosen to quit the program. Thank you for using the program!\n";
        return 0;
    }
    else
    {
        cout << "You have entered an invalid selection.\n";
        return 0;
    }

    newWeight = weight * surfGrav;
    newSunDist = distfromSun * 1000000;
    unsigned long l1 = newSunDist;

    if (selection <= 'a' || selection >= 'h')
    {
        distFromPlanets = distEarthToSun - l1;
    }
    else
    {
        distFromPlanets = l1 - distEarthToSun;
    }

    travelTimeHours = distFromPlanets/speed;
    travelTimeDays = travelTimeHours/24.0;
    travelTimeYears = travelTimeDays/365.0;

    cout <<'\n';
    cout << "INTERPLANETARY TRAVEL:  Earth to " << planetName << '\n';
    cout << "--------------------------------------------------\n";
    cout << fixed << setprecision(2) << "Your weight on " << planetName << ":      " << newWeight << " lbs\n";
    cout << '\n';
    cout << "Your travel time to " << planetName << ":\n";
    cout << fixed << setprecision(2) << "    " << "In Hours: " << (long int)(travelTimeHours + 0.5) << " hours\n";
    cout << fixed << setprecision(2) << "    " << "In Days : " << (long int)(travelTimeDays + 0.5) << " days\n";
    cout << fixed << setprecision(2) << "    " << "In Years : " << travelTimeYears << " years\n";
    cout << '\n';
    return 0;
}

感谢您提前帮助，如果您需要更多信息，请告诉我们。谢谢。

Answer 1

问题出现在您的变量distFromPlanets，其解析为-2.7e + 9，distEarthToSun = 9.3e+7和newSunDist = 2.8e+9。因此，9.3e+7 - 2.8e+9大致相等-2.8e+9。我不是天文学家，但是如果你改变你的if语句来阅读if(selection <= 'a' || selection > 'h')，海王星的计算将解析为2.8e+9 - 9.3+7 ~ +2.7e+9。同样，我不是天文学家，所以我不确定这是否是你应该计算的。

将double转换为无符号长C ++

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