C Reference function atan2()

Usage of atan2():

double atan2(double y, double x);

Parameters:

Both y and x cannot be zero.

Return value:

Arc tangent in radians of y/x based on the signs of both values
to determine the correct quadrant. The returned value is in the range of -p/2 to +p/2 (inclusive).

Source code example of atan2():

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

#define PI 3.14159265

main()
{
	double x,y,output;
	x = 20.0;
	y = 20.0;
	output = atan2 (y,x) * 180 / PI;
	printf ("Arc tangent for x=%lf, y=%lf is %lf degrees\n", x, y, output);
	return 0;
}

Output of the atan2 example program above:

	Arc tangent for x=20.00000, y=20.00000 is 45.00000 degrees