为什么我得到0的输出？它与格式或公式有关吗？

Question

1. 这是问题，我试图从弧度转换成度，并弹出一个度数为theta2的数字。然而，对于弧度theta2（rtheta2）和theta2本身，保持返回0。公式是正确的，我想，所以也许是一个格式错误？

2. 这里是我的代码：

   #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

使用浮点运算，而不是整数除法。

整数除法结果为整数商，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); 

---

要当心asin()范围[-1.0...+1.0]之外这可能与附近的+/- 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);