c99 [ flag... ] file... –lm [ library... ] #include <math.h> double atan(double x);
float atanf(float x);
long double atanl(long double x);
These functions compute the principal value of the arc tangent of x.
Upon successful completion, these functions return the arc tangent of x in the range [−??/2,??/2] radians.
If x is NaN, NaN is returned.
If x is ±0, x is returned.
If x is ±Inf, ±??/2 is returned.
No errors are defined.
See attributes(5) for descriptions of the following attributes: