#include <cmath>
    double atan2( double y, double x );

The atan2() function computes the arc tangent of y/x, using the signs of the arguments to compute the quadrant of the return value. The returned values are in the range [-pi, pi]. Note the order of the arguments passed to this function.

C++ also provides the following overloaded forms:

    #include <cmath>
    float atan2( float y, float x ); // same as atan2f() in C99
    long double atan2( long double y, long double x ); // same as atan2l() in C99

Related Topics: acos, asin, atan, cos, cosh, sin, sinh, tan, tanh