Re: [Mingw-msys] pow(5,2)=24 ?????!!!!!

["Michael Chen" <vancouver.michael@xxxxxxxxx>]

Thanks for all the replies! I followed the suggestions and got
satisfactory results.

Now my question changes focus:

If I compile using GCC, I got wrong answer pow(5,2)=24, but if I use
Lcc-win32, I got correct one. Can anybody explain? Is there a GCC
switch which can alter the behavior? What are your commonly used GCC
switches?

Michael Chen



>   int s = (int) pow(l,d);
>   printf("%d\t%d\t%d\n",l,d,s);
>
>
> And I tried several (l,d), results are:
> 2 2 4
> 3 2 9
> 4 2 16
> 5 2 24  <= this one is wrong
> 6 2 36
> ....
>
> What shall I use then? my variable s, l, and d are integers!




On 9/7/07, Brian Dessent <brian@xxxxxxxxxxx> wrote:
> Michael Chen wrote:
>
> > So I should always add 0.5 to pow() and modf() as shown, when my input
> > parameters and output are all integers?
>
> That, or use an explicit rounding function such as round().  The problem
> is that the C language specifies that simply casting a double or float
> to an integer, as you do with "(int)pow(L,D)", does not do any rounding
> -- it simply discards the fractional parts.  So you should never use a
> cast where you want something rounded to the nearest integer.
>
> Brian
>
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-- 
Michael Chen
PhD Candidate
Northwestern University
2145 Sheridan Road IEMS
Evanston, IL 60208-3119
Phone: 847.467.2043
Fax: 847.491.8005
Web: http://users.iems.northwestern.edu/~mchen/

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