#include <cmath>
    double atan( double arg );

The function atan() returns the arc tangent of arg, which will be in the range [-pi/2, +pi/2].

C++ also provides the following overloaded forms:

    #include <cmath>
    float atan( float arg ); // same as atanf() in C99
    long double atan( long double arg ); // same as atanl() in C99

Related Topics: acos, asin, atan2, cos, cosh, sin, sinh, tan, tanh