atan2 Function

Calculates the trigonometric arc tangent function of y/x.

Include

<math.h>

Prototype

double atan2 (double y, double x);

Arguments

y

y value for which to return the arc tangent

x

x value for which to return the arc tangent

Return Value

Returns the arc tangent in radians in the range of -pi to pi (inclusive) with the quadrant determined by the signs of both parameters.

Remarks

A domain error occurs if both x and y are zero or both x and y are +/- infinity.

Example

#include <math.h>
#include <stdio.h>
#include <errno.h>

int main(void)
{
  double x, y, z;

  errno = 0;
  x = 0.0;
  y = 2.0;
  z = atan2(y, x);
  if (errno)
    perror("Error");
  printf("The arctangent of %f/%f is %f\n", y, x, z);

  errno = 0;
  x = -1.0;
  y = 0.0;
  z = atan2(y, x);
  if (errno)
    perror("Error");
  printf("The arctangent of %f/%f is %f\n", y, x, z);

  errno = 0;
  x = 0.0;
  y = 0.0;
  z = atan2(y, x);
  if (errno)
    perror("Error");
  printf("The arctangent of %f/%f is %f\n", y, x, z);
}

Example Output

The arctangent of 2.000000/0.000000 is 1.570796
The arctangent of 0.000000/-1.000000 is 3.141593
Error: domain error
The arctangent of 0.000000/0.000000 is nan