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The C math atan2() function is used to return 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);


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 below example, 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