atan2

atan2, atan2f, atan2l

Defined in header <math.h>
float       atan2f( float y, float x );
(1) (since C99)
double      atan2( double y, double x );
(2)
long double atan2l( long double y, long double x );
(3) (since C99)
Defined in header <tgmath.h>
#define atan2( arg )
(4) <