函数ceil()被忽略

Question

我有一个关于ceil()函数的问题。在下面的代码中，我尝试在C中对变量monthlyPayment向上舍入两位小数，而ceil函数似乎在输出中被忽略了。图像中的是与其假设的输出进行比较的结果。img

#include "stdafx.h"
#include "stdio.h"
#include "math.h"
#define MONTHS 12

int main()
{
    double principle;
    double rate;
    double numYears;
    double numMonths;
    double monthlyPayment;
    double monthlyRate;

    printf("Welcome to the morgage calculator.\nEnter your principal amount to get started. ");
    scanf_s("%lf", &principle);
    printf("Enter the yearly morgage interest rate ");
    scanf_s("%lf", &rate);
    printf("Enter the number of years ");
    scanf_s("%lf", &numYears);
    numMonths = numYears * MONTHS;
    monthlyRate = rate / MONTHS / 100;
    monthlyPayment = ((monthlyRate) / (1 - pow((1 + monthlyRate), (-numMonths)))* principle);
    monthlyPayment = monthlyPayment * 100;
    ceil(monthlyPayment);
    monthlyPayment = monthlyPayment / 100;
    double toPrince = 0.0;
    double interest = 0.0;
    printf("Your total monthly payment ammount:$ %.2lf\n", monthlyPayment);
    printf("Month\tPrinciple\tInterest\t $ to Principle\n");
        for (int index = 1; index <= numMonths;) {
            interest = principle * monthlyRate;
            toPrince = monthlyPayment - interest;   
            printf("%2d%16.2lf %16.2lf %16.2lf\n", index, principle, interest, toPrince);
            principle = principle - toPrince;
            index++;
        }
}

Answer 1

只要返回结果，ceil()就不会改变变量。应该是：

double result = ceil(var);

Answer 2

你可以通过观察C函数不能修改它们的参数来发现问题，除非你传递一个指向你想要修改的东西的指针。这就是在对scanf的调用中添加&符号的原因。

ceil(monthlyPayment)中没有与号，而且monthlyPayment也不是指针；因此，不可能进行任何修改。

您可以按如下方式修复monthlyPayment的向上舍入代码：

monthlyPayment = ceil(monthlyPayment * 100) / 100;