c - 一分钱一分货，是编程新手吗？在C中

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Is floating point math broken?
（31个答案）
嗨，所以我在努力找出我的代码有什么问题。我真的是新手，所以请容忍我。评论可能有点混乱。

#include <stdio.h>

int main(void)
{
    double cost, gstCost, newCost; // initial cost, cost of gst by itself, new cost after gst
    int loonies, quarters, dimes, nickels, pennies; // used for quantity of coins
    float loonreq, quartreq, dimereq, nickreq, penreq; //  cost required after deduction of the corresponding coin

    printf("Please enter the amount to be paid: $");
    scanf("%lf", &cost); // scanf allows to input an amount as a double ("%lf")

    gstCost = cost * .13 + .005; // .13 for gst and add 0.005 to round up or down
    printf("GST: %.2lf\n", gstCost);

    newCost = cost + gstCost;
    printf("Balance owing: $%.2lf\n", newCost); // original cost + gst cost

    loonies = newCost; // loonies will output as integer when cost has decimals
    printf("Loonies required: %d", loonies);
    if (loonies == 0) // == used to compare equality
        loonies = 1; // if loonies = 0, loonreq will be infinite causing code to crash and stop

    loonreq = (float)((int)(100 * newCost) % (100 * loonies)) / 100; // casting int and * 100 on float values for modulo since it can only calculate for integer value
    printf(", balance owing $%.2f\n", loonreq); // %.2f shows a float with 2 decimal places

    quarters = 100 * loonreq / 25; // 100*loonreq allows the code to find how many quarters by dividing by 25
    printf("Quarters required: %d", quarters);
    if (quarters == 0)
        quarters = 1;

    quartreq = (float)((int)(100 * loonreq) % (int)(100 * (quarters * .25))) / 100;
    printf(", balance owing $%.2f\n", quartreq);

    dimes = 100 * quartreq / 10;
    printf("Dimes required: %d", dimes);
    if (dimes == 0)
        dimes = 1;

    dimereq = (float)((int)(100 * quartreq) % (int)(100 * (dimes * .10))) / 100;
    printf(", balance owing $%.2f\n", dimereq);

    nickels = 100 * dimereq / 5;
    printf("Nickels required: %d", nickels);
    if (nickels == 0)
        nickels = 1;

    nickreq = (float)((int)(100 * dimereq) % (int)(100 * (nickels * .05))) / 100;
    printf(", balance owing $%.2f\n", nickreq);

    pennies = 100 * nickreq / 1;
    printf("Pennies required: %d", pennies);
    if (pennies == 0)
        pennies = 1;

    penreq = (float)((int)(100 * nickreq) % (int)(100 * (pennies * .01))) / 100;
    printf(", balance owing $%.2f\n", penreq);

    return 0;

}

当我在Visual Studio上运行这段代码时，我得到了某些输入的正确输出，比如8.68，但是当我通过PuTTY为我的教授提交这个文件时，它会为我进行测试，并且在扣除一角钱后，我得到了一个不正确的余额（少了一分钱）。当我输入一个76.54这样的值时，扣除疯子后我就少了一分钱。输入一个76.76的值，我得到了正确的输出。我不知道到底发生了什么。我的教授看了看我的代码，说是因为类型的改变？建议我改用这个方法，例如

dimes = (balance / 100) / 0.1;
balance = (int)(balance) % 10;

不过，我不知道如何使用这种方法。
编辑：我需要使用模数运算符和铸型来完成这个任务。当我提交油灰时使用gcc。

最佳答案

舍入逻辑没有给出正确的答案。假设我们有一个输入123。商品及服务税应为15.99。但是你的代码会给出16.00。若要修复此问题，请尝试将gstCost = cost * .13 + .005;替换为gstCost = (round(cost * .13 * 100) / 100);

关于c - 一分钱一分货，是编程新手吗？在C中，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/46438216/