Date: Wed, 26 Mar 1997 09:55:55 -0300
Message-Id: <1.5.4.16.19970326095019.2a479348@dce03.ipt.br>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
To: DBerry1 AT dca DOT gov DOT au, djgpp AT delorie DOT com
From: Cesar Scarpini Rabak <csrabak AT ipt DOT br>
Subject: Re: Newbie troubles with Sin and Cos

At , DBerry1 AT dca DOT gov DOT au wrote:
>G'day
>
>I've just started playing around with DJGPP and have come across the 
>following problem.
>
>I'm trying to write a routine that spins a pixel around in a circle.  That 
>works ok so far, except that the X and Y points are never next to each 
>other - I think I have narrowed it down to the results I am getting from 
>using COS and SIN.
>
>for instance here's the output from a simple prog I did to test my idea
>
>Sin of 0 is 0.000000
>Sin of 1 is 0.841471
>Sin of 2 is 0.909297
>Sin of 3 is 0.141120
>Sin of 4 is -0.756802
>

The arguments for the trig functions (btw in almost any prog language) are
in _radians_ and not degrees.

>But using a calculator I get
>
>Sin of 0 is 0
>Sin of 1 is 0.017452
>Sin of 2 is 0.034899
>Sin of 3 is 0.052335
>Sin of 4 is 0.069756
>

Switch you calc to radians and you'll get similar results.

>Here's the simple prog...
>
>#include <math.h>
>#include <stdlib.h>
>#include <stdio.h>
>
>float result = 0.0;
>int theta = 0;
>
>main ()
>{
>while (theta < 360)
>{
>result = sin(theta);
>printf ("Sin of %i is %f\n",theta,result);
>theta++;
>}
>return 0;
>}
>

To use degrees instead of radians you'll need to convert be it via a macro
or a funtion (for a lot of cases) or do calculation up to the calling of the
trig function.


>Am I using the wrong variable types to hold the results ?  Do I need to do 
>something special in DJGPP to get the magic numbers ?
>
>Thanks
>dberry AT dca DOT gov DOT au
>
>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Cesar Scarpini Rabak                      E-mail: csrabak AT ipt DOT br
DME/ASC                                   Phone: 55-11-268-3522 Ext.350
IPT - Instituto de Pesquisas Tecnologicas Fax:   55-11-268-5996
Av. Prof. Almeida Prado, 532.  Sao Paulo - SP 05508-901 BRAZIL
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~