AVR-Chat

unsigned char a;
a=255*20/10;

it gives output 254

for
a=255*200/100;

it gives output 111

why it gives different results.

it there any logical relationship.

      kindly help me to resolve the problem.
                 i will be grateful
                           thanks a lot.......

----- Original Message ----- 

From: "bhadson2001" <bhadson2001@yahoo.com>
To: <AVR-Chat@yahoogroups.com>
Sent: Thursday, February 28, 2008 8:13 AM
Subject: [AVR-Chat] C problem


> 
> unsigned char a;
> a=255*20/10;
> 
> it gives output 254
> 
> for
> a=255*200/100;
> 
> it gives output 111
> 
> why it gives different results.
> 
> it there any logical relationship.
> 

Try 255*(20/10) and 255*(200/10)

Leon
--
Leon Heller
Amateur radio call-sign  G1HSM
Yaesu FT-817ND transceiver
Suzuki SV1000S motorcycle
leon355@btinternet.com
http://www.geocities.com/leon_heller

bhadson2001 wrote:
> unsigned char a;
> a=255*20/10;
> 
> it gives output 254
> 
> for
> a=255*200/100;
> 
> it gives output 111
> 
> why it gives different results.
> 
> it there any logical relationship.
> 
>       kindly help me to resolve the problem.
>                  i will be grateful
>                            thanks a lot.......

255*20/10 -> 510 which overflows "unsigned char" (256).

The remainder is 510 % 256 -> 254.

On Thu, Feb 28, 2008 at 08:13:49AM -0000, bhadson2001 wrote:
> 
> unsigned char a;
> a=255*20/10;
> 
> it gives output 254
> 
> for
> a=255*200/100;
> 
> it gives output 111
> 
> why it gives different results.
> 
> it there any logical relationship.

The intermediate math is signed 16 bit integer. 255*200 = 51,000 which
is -14,546. Divide by 100 = -145 = 111 unsigned.

-- 
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.