C Standard Library

C <math.h> - atan2() Function

The C <math.h> atan2() function returns the angle theta from the conversion of rectangular coordinates (x, y) to polar coordinates (r, theta). The return value will be in the range -𝜋 through 𝜋.


double atan2 (double y, double x);
float atan2f (float y, float x);
long double atan2l (long double y, long double x);


y Specify the ordinate coordinate.
x Specify the abscissa coordinate.

Return Value

Returns theta of the point (r, theta) in polar coordinates that corresponds to the point (x, y) in Cartesian coordinates.


In the example below, atan2() function is used to calculate the theta of a point.

#include <stdio.h>
#include <math.h>
int main (){
  printf("%lf\n", atan2(10, 10));
  printf("%lf\n", atan2(20, 10));
  printf("%lf\n", atan2(-20, 10)); 
  return 0;

The output of the above code will be:


❮ C <math.h> Library