致死剂量计算器程序中的舍入误差

Question

我接到了一项任务，要求我根据用户输入的重量找出苏打水的致死剂量（以克为单位）。我在舍入错误方面遇到很多问题......这应该很简单，但不确定为什么我会遇到这么多问题。例如，这里有几个导致问题的输入和输出。提前致谢！

1 1000 275 的输入：应为 [124850000, 356714286] 但发现为 [1.2485e+08, 3.56714e+08]

60 390 130 的输入：应为 [383630, 1096086] 但发现为 [383630, 1.09609e+06]

/**
 *  @author 
 *  @date 2-2-22
 *  @file h02.cpp
 */
#include <iostream>
#include <string>
#include <iomanip>
#include <cmath>
using namespace std;


/**
 * Finds lethal dose (in grams) of artificial sweetener for a given dieter weight.
 * Also finds the number of cans of soda that would be lethal for a given weight.
 * @return 0 for success.
 */
int run()
{
    // Add your implementation comments here

    // Write your code here
    
const double dose_per_can {.001}; // percentage of lethal sweetener in one can
const int soda_weight {350}; //in grams
const int pound_to_grams {454}; //in grams
double dieter_weight {};
double mouse_weight {};
double mouse_lethal {};
double dieter_lethal {}; // lethal dose in grams to human/dieter
double lethal_ratio {};
float lethal_per_can {}; //how many grams of art sweetener in a can
double dieter_lethal_cans {};


cout << "Enter mouse weight, lethal dose for mouse (grams), and desired wight of dieter (pounds): " << endl;
cin >> mouse_weight >> mouse_lethal >> dieter_weight;

lethal_ratio = mouse_lethal / mouse_weight; //finding the ratio between the dose given and the weight of the mouse
                                            //lets us use this weight ratio on humans

dieter_lethal = lethal_ratio * (dieter_weight * pound_to_grams); //grams of sweetener that is lethal to dieter with given weight

lethal_per_can = soda_weight * dose_per_can; //find how many grams of sweetener in 1 can.. ends up being constant of .35
dieter_lethal_cans = dieter_lethal / lethal_per_can; // finds how many cans would be lethal to dieter

cout << "Lethal dose in grams, cans is [" << dieter_lethal << ", " <<round(dieter_lethal_cans) << "]" << endl;

    return 0;
    

}

Answer 1

round你使用returns一个浮点值。您需要 lround - 请参阅此处：https://en.cppreference.com/w/cpp/numeric/math/round

cout << "Lethal dose in grams, cans is [" << lround(dieter_lethal) << ", " 
    << lround(dieter_lethal_cans) << "]" << endl;

Lethal dose in grams, cans is [124850000, 356714292]

致死剂量计算器程序中的舍入误差

Rounding errors in lethal dose calculator program

c++

rounding-error