C库函数 atan2()

#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);

}