c - 为什么我的输出结果是 0？与格式或公式有关吗？

Question

1. 问题是，我正在尝试将弧度转换为度数，并为 theta2 弹出一个以度为单位的数字。然而，对于弧度 theta2(rtheta2) 和 theta2 本身，继续返回 0。我认为该公式是正确的，所以可能是格式错误？

2. 这是我的代码:

   #include <stdlib.h>
   #include <math.h>
   
   #define PI 3.14159
   
   int main(void)
   {
       char input;
       int n1;
       float rn1;
       int n2;
       float rn2;
       int theta1;
       float rtheta1;
       float rtheta2;
       float theta2;
   
       printf("      Program Snell's Law:\n");
       printf("--------------------------------");
       printf("\n\nA> Enter indices of refraction of first angle.");
       printf("\nB> Calculate second angle of incdience.\n");
   
       scanf("%c", &input);
       printf("A> Enter indices of refraction of first angle.\n");
       scanf("%d", &n1);
   
       printf("Enter the index of material 2:\n");
       scanf("%d", &n2);
   
       printf("Enter the angle of incidence in region 1:\n");
       scanf("%d", &theta1);
   
       rn1=(M_PI /180) * n1;
       rn2=(M_PI /180) * n2;
       rtheta1=(M_PI /180) * theta1;
   
       theta2=asin((n1/n2) * sin(rtheta1));
   
       //need to convert back into degrees for radians theta 2~
       theta2=rtheta2*(180/M_PI);
   
       printf("%lf", rn1);
       printf("\n%lf", rn2);
       printf("\n%lf", rtheta1);
   
       printf("\n%lf", theta2);
       printf("\n%lf", rtheta2);
   

Answer 1

使用 float 学而不是整数除法。

整数除法产生整数商，但代码需要 FP 结果。

int n1, n2;
...
//                 v--- integer division.
// theta2= asin((n1/n2) * sin(rtheta1));
theta2 = asin((1.0*n1/n2) * sin(rtheta1));

// or re-order to effect FP divsiosn
theta2 = asin(sin(rtheta1)*n1/n2);

<小时/>

注意在 [-1.0...+1.0] 范围之外使用 asin()，这可能会导致计算结果接近 +/- 1.0

double y = (1.0*n1/n2) * sin(rtheta1);
if (y > 1.0) y = 1.0;
else if (y < -1.0) y = -1.0;
theta2 = asin(y);