C语言库atan2()函数

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

#define PI 3.14159265

int main () {
   double x, y, ret, val;

   x = -7.0;
   y = 7.0;
   val = 180.0 / PI;

   ret = atan2 (y,x) * val;
   printf("The arc tangent of x = %lf, y = %lf ", x, y);
   printf("is %lf degrees/n", ret);

   return(0);
}