From: Martin Ambuhl <mambuhl AT earthlink DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: math problem
Date: Tue, 23 Feb 1999 18:16:03 -0500
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Erik Johansson wrote:
> 
> if i have a line like this
> y
> |     /
> |    /
> |   /
> |  /
> | /
> |/_____________ x
> 
> How can I calculate the angle of that line in degrees?
> 
> Thanx in advance

This is really not a djgpp question, but what-the-heck.

If the ray runs through the origin to (x,y) then tangent is
defined as 
   tan(theta) = y/x

the angle (in the range of -pi to +pi) is given by
   theta = atan2(y,x);	/* actual code */
If you are not compiling with -ansi, then you have the
constant M_PI from <math.h>.

The angle returned from atan2 will be in radian measure (not 'radians'
since it is unitless).  A circle is 2*M_PI in radian measure,
corresponding to 360 degrees.  You no doubt want your numbers in the
range [0,360), so we must make theta positive:
    if (theta < 0) theta += 2*M_PI;
Now theta is in the range [0,2*M_PI).
To convert this to degrees is trivial
    degrees = 180. * theta / M_PI;



-- 
Martin Ambuhl (mambuhl AT earthlink DOT net)
Note: mambuhl AT tiac DOT net will soon be inactive