c++,casting,double,long-integer,unsigned , Cast double to unsigned long C++


Cast double to unsigned long C++

Question:

Tag: c++,casting,double,long-integer,unsigned

Im working on a program for homework and so far everything prints out correctly except for the planet "Neptune". Every other choice works fine and prints out the numbers as they are supposed to be but Neptune prints out the right numbers but as negatives. I have been told to cast the double to a long but I believe I have and it has made no difference. Any help or guidance would be appreciated. I will attach my code so you guys could take a look at it. Another thing is that when Neptune is chosen 'h', the choices are supposed to be 'h' then weight is 160 and speed is 595. Also, the numbers that are supposed to print for travel time in hours are 4537815, days 189076 and years is 518.02. The hours and days come out correctly except that the last number needs to be rounded up one in my code and the years comes out correct except that it is a negative.

#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;
}

Thanks for the help in advance guys and if you need anymore information let me know. Thanks.


Answer:

The problem arises with your variable distFromPlanets which resolves to -2.7e+9, as distEarthToSun = 9.3e+7 and newSunDist = 2.8e+9. Therefore 9.3e+7 - 2.8e+9 does approximately equal -2.8e+9. I'm no astronomer, but if you change your if statement to read if(selection <= 'a' || selection > 'h') the calculation for Neptune will resolve to 2.8e+9 - 9.3+7 ~ +2.7e+9. Again, I'm not an astronomer, so I'm not sure if that is what you're supposed to calculate.


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