C ++将输入字符串与字符串进行比较会给我一个从双精度到整数转换的警告-可能会丢失数据

Question

i have to write a program that asks user for weight and a planet name. Program has to output how much user would weight on that planet. For some reason i get errors: " '=': conversion from 'double' to 'int', possible loss of data.

Before i was trying to use (planet == Mercury) but still no luck.

Here is my code:

    // ConsoleApplication5.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <string>
#include <sstream>
#include "ConsoleApplication5.h"

using namespace std;

int main()
{
    cout << "Assignment 05" << endl;


    int weight = 0;
    string planet = "";
    int weightOnplanet;
    string entry = "You entered a weight of ";

    string Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto;

    cout << "Please Enter Weight <as an integer of pounds>: " << endl;
    cin >> weight;
    cout << "Please Enter Planet name <ie: Earth>: " << endl;
    cin >> planet;
    cout << entry << weight << " and a planet name of " + planet << endl;



    if (planet == Mercury)
    {
        weightOnplanet = weight * 0.4155;
        cout << "On a " + planet + " your weight in pounds would be " << weightOnplanet << endl;
    }
    else if (planet == Venus)
    {
        weightOnplanet = weight * 0.8975;
        cout << "On a " + planet + " your weight in pounds would be " << weightOnplanet << endl;
    }
    else if (planet == Earth)
    {
        weightOnplanet = weight * 1.0;
        cout << "On a " + planet + " your weight in pounds would be " << weightOnplanet << endl;
    }
    else if (planet == Mars)
    {
        weightOnplanet = weight * 0.3507;
        cout << "On a " + planet + " your weight in pounds would be " << weightOnplanet << endl;
    }
    else if (planet == Jupiter)
    {
        weightOnplanet = weight * 2.5374;
        cout << "On a " + planet + " your weight in pounds would be " << weightOnplanet << endl;
    }
    else if (planet == Saturn)
    {
        weightOnplanet = weight * 1.0677;
        cout << "On a " + planet + " your weight in pounds would be " << weightOnplanet << endl;
    }
    else if (planet == Uranus)
    {
        weightOnplanet = weight * 0.8947;
        cout << "On a " + planet + " your weight in pounds would be " << weightOnplanet << endl;
    }
    else if (planet == Neptune)
    {
        weightOnplanet = weight * 1.1794;
        cout << "On a " + planet + " your weight in pounds would be " << weightOnplanet << endl;
    }
    else if (planet == Pluto)
    {
        weightOnplanet = weight * 0.0899;
        cout << "On a " + planet + " your weight in pounds would be " << weightOnplanet << endl;
    }
    else
        cout << "Unknown Planet" << endl;

    system("pause");
    return 0;
}

Answer 1

Each planet variable (Mercury, Venus, etc) should have an actual value such as:

Mercury = "Mercury";

A string doesnt initialize with the name of the variable, you have to actually give it a value.

You don't even have to have a variable for every planet. You could just do this:

if(planet == "Mercury")

Answer 2

The warning you get is for

weightOnplanet = weight * 0.4155;

Since weightOnPlanet is int and weight * 0.4155 is double you will be loosing precision.You probably want weightOnplanet to be double and not int .

Just to mention if (planet == Mercury) would be comparing planet to an empty string which is why you would get undesired result, until you do what @ErrorAtLine0 mentioned.