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Little math problem, I'm sure the answer is simple...

 
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Sydney



Joined: 13 Feb 2009
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Little math problem, I'm sure the answer is simple...
PostPosted: Fri Feb 13, 2009 4:16 pm     Reply with quote
Hi there, I'm fairly new to this, so can anyone tell me why the 1st code works, but the 2nd one doesn't? I need it to work as in the 2nd code, but it doesn't seem to work for reason I cannot fathom. Any help greatly received! Thank you!

Code:

signed int16 average = 250;
int16 closed = 100, open = 400;
average -= closed;
average *= (float) 100 / (400 - 100);
// average = 50


Code:

signed int16 average = 250;
int16 closed = 100, open = 400;
average -= closed;
average *= (float) 100 / (open - closed);
// average != 50 :(
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Fri Feb 13, 2009 4:31 pm     Reply with quote
Code:
average = (float)average * (100.0 /(open - closed));
FvM



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PostPosted: Fri Feb 13, 2009 4:43 pm     Reply with quote
To my opinion, the second code reveals a case of CCS C ignoring well defined rules of C syntax and required implicite type conversions. Please correct me, if I'm wrong.
PCM programmer



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Posts: 21708

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PostPosted: Fri Feb 13, 2009 4:46 pm     Reply with quote
Ttelmah's comments on this:
http://www.ccsinfo.com/forum/viewtopic.php?t=29749
FvM



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PostPosted: Fri Feb 13, 2009 5:13 pm     Reply with quote
Yes. The observed PCH calculation result of 6188 can't be explained by a wrong operator precedence or missing type conversion, it's rather a totally wrong calculation.

PCD V4.084 , in contrast, is basically providing a correct result. It's 49 instead of 50 due to a apparent rounding error, which is O.K. so far.
Sydney



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PostPosted: Fri Feb 13, 2009 5:33 pm     Reply with quote
Thanks for the fast reply, its working Smile
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