收银功能不适用于特定情况

Cashier function doesn't work for specific cases

本文关键字：情况 适用于 不适用 功能      更新时间：2023-10-16

这是我第一次在这里发帖，所以如果代码太长，我将非常乐意编辑它。

我在做一个收银员，一个用来找零的功能。

奇怪的是:如果我用1.15买1.14，我就能赚回一分钱。但如果我用0.15美元买0.14美元，我一分钱也拿不回来。

同样，如果我用0.20买0.15，我得到5美分。但如果我用25美分买20美分，我得到4美分。我需要你帮我弄明白为什么我只能拿回4美分而不是0美分和1个5美分。我相信这个部门一定是出了什么问题。

#include <iostream>
#include <cmath>
using namespace std;
int main() {
  double buyAmount = 0.0;
  double paidAmount = 0.0;
  double diffAmount = 0.0;
  double smallChange = 0.0;
  int dollars = 0;
  int quarters = 0;
  int dimes = 0;
  int nickels = 0;
  int pennies = 0;
  cout << "Enter purchase amount: ";
  cin >> buyAmount;
  cout << endl;
  cout << "Enter paid amount: ";
  cin >> paidAmount;
  cout << endl;
  diffAmount = paidAmount - buyAmount;
  if (diffAmount < 0 ) {
     cout << "Error: Make sure paid amount exceeds purchase amount. ";
     cout << endl;
  }
  dollars = floor(diffAmount);
  smallChange = (diffAmount - dollars) * 100  
  quarters = (smallChange / 25);
  smallChange = smallChange - (quarters * 25);
  dimes = (smallChange / 10);
  smallChange = smallChange - (dimes * 10);
  nickels = floor(smallChange / 5);
  smallChange = smallChange - (nickels * 5);
  pennies = floor(smallChange / 1); 
  cout << "Total Change: $" << diffAmount;
  cout << endl << endl;
  cout << "dollars " << dollars << endl;
  cout << "quarters " << quarters << endl;
  cout << "dimes " << dimes << endl;
  cout << "nickels " << nickels << endl;
  cout << "pennies " << pennies << endl;
}

浮点运算不精确。有时会出现小错误。例如0.25/0.25可导致1或0.99999999999999。
如果你使用floor，这将无法工作，除非你添加一个额外的'epsilon'来补偿计算错误，例如

quarters = floor(smallChange / 0.25);

可能成为

const double epsilon = 1E-5;
quarters = floor(smallChange / 0.25 + epsilon);


int仍然是管理货币的更好方法:

int diffAmount = ...; // (pennies or cents).
int dollars = diffAmount / 100;
int smallChange = diffAmount % 100;
int quarters = smallChange / 25;
smallChange -= quarters * 25;
int dimes = smallChange / 10;
smallChange -= dimes * 10;
...

您还应该使该数据驱动:创建一个包含不同硬币及其值的数据结构，然后编写代码在该数据结构中循环。这将使兑换其他货币(大多数没有25分硬币)或修复错误变得容易。

你不应该使用浮点数，因为它们不是精确的。

相反，将美元和美分分别读入整数，然后转换为完全以美分计算。
整数除法可以很好地解决这个问题。
如果您只是假设用户将正确输入，您可以像这样阅读:

int purchaseDollars = 0;
int purchaseCents = 0;
char decimalPoint;  // Can be anything except a number in this snippet.
std::cin >> purchaseDollars >> decimalPoint >> purchaseCents;
int buyAmount = purchaseCents + 100 * purchaseDollars; // Convert to cents
// Same for paid amount
int diffAmount = paidAmount - buyAmount;
int dollars = diffAmount / 100;   // Integer division makes this work as you want
diffAmount -= dollars;            // Now diffAmount is just the cents
/// and so on...
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