c - 执行for循环后获取总和为Nan

Question

我正在使用级数展开来将 sin 的值逼近到有限数。的for循环迭代。我已经使用 j 循环来计算 2i+1 的阶乘值。如果我在某个地方犯了错误，请帮助。

#include <stdio.h>
#include <math.h>

int main(void) {
    printf("Enter the value of angle:" );
    double ag, rad, sum = 0;
    scanf("%lf", &ag);
    rad = 3.14159 * ag / 180.0;
    int i, j, frac = 1;
    for (i = 0; i <= 100; i++) {
        for (j = 1; j <= 2*i+1; j++)                   
            frac *= j;
        if (i % 2 == 0)
            sum += pow(rad, 2*i+1) / frac;
        else
            sum += (-pow(rad, 2*i+1) / frac);
    }
    printf("Required sum=%f", sum);
    return (0);
}

Answer 1

Nan 的原因是在某个时候，由于整数溢出，frac 在循环中变为 0。将 sum 除以 0 得到 Nan。

刚刚测试了你的程序

# include<stdio.h>
# include<math.h>

int main(void)
{
    printf("Enter the value of angle:" );
    double ag,rad,sum=0;
    scanf("%lf",&ag);
    rad=3.14159*ag/180.0;
    printf("%f\n", rad);
    int i,j,frac=1;
    for(i=0;i<=100;i++)
    {
        for(j=1;j<=2*i+1;j++)
            frac*=j;
        if(i%2==0)
        {   
             sum+=pow(rad,2*i+1)/frac; 
             printf("if: %f, %d\n", sum, frac);
        }
        else
        {
             sum+=(-pow(rad,2*i+1)/frac);  
             printf("else: %f, %d\n", sum, frac);
        }
    }
    printf("Required sum=%f\n",sum);
    return(0);
}  

输出:

Enter the value of angle:30
0.523598
if: 0.523598, 1
else: 0.499674, 6
if: 0.499728, 720
else: 0.499728, 3628800
if: 0.499728, -1736015872
else: 0.499728, -2004877312
if: inf, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
else: nan, 0
if: nan, 0
Required sum=nan