C语言库sin()函数

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

#define PI 3.14159265

int main () {
   double x, ret, val;
   x = 45.0;
   val = PI / 180;
   ret = sin(x*val);
   printf("The sine of %lf is %lf degrees", x, ret);

   return(0);
}