From: suma AT xtra DOT co DOT nz (Alex Clifford Henderson)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: floats and ints
Date: Thu, 09 Jan 1997 22:37:56 GMT
Organization: TWINS Software
Lines: 81
Message-ID: <5b52vh$bm42@wolfman.xtra.co.nz>
References: <5ar6pi$8go AT info DOT service DOT rug DOT nl>
NNTP-Posting-Host: 203.96.101.238
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

span AT PROBLEM_WITH_INEWS_GATEWAY_FILE (M.M. Span) wrote:

>Maybe this is a generic C or C++ question, but I use DJGPP, so why not here?

>int main( int argc, char** argv )
>{

>int i=1;
>int npoints=500;
>float omega = 0.0

>omega = i/npoints;
>cout << omega << endl;

>return 0;
>}

>yields:

>0

>casting (float)i/(float)npoints;

>will yield the correct answer.

>is this a bug or a feature.

The way I learnt C/C++ (from a TurboC++ 3.0 manual in 1992 no less)
was that and integer devided by an integer will return an integer and
that:

omega=i/npoints;

is like having a function to devide integers.

omega=int_div(i,npoints);
which means you are taking the (float) casting of the integer returned
by int_div, which will of course be zero. 

you  must remember 2 things, 

1/ that an expression is evaluated on the right side completely before
any effect of casting and asigning the value to the left side,  the
right side know's nothing of the left side until it has finished being
evaluated.

2/ any of those simple operators +,-,*,/ will promote to the most
acurate or large type present. floating point values overide longs,
and doubles overide floats etc. etc.

i.e  (float) * (int)      returns float
      (long)  * (int)     return long
      (float) * (double)  returns double

where " * " can be substituted for any of the other four simple
operators (note: shift-left and shift-right operators dont count, they
always take the second argument as an int)

so when an integer devides an integer you get.... an integer.

of course I dont explain it half as well as the borland Turbo C++ 3.0
manual could :-)

BTW are you still learning C/C++ or have you learnt a pigeon form of
it (like some Pascal people I know which have 100's of defines which
makes C act like pascal for them, though why they would want to I dont
know...

[sorry for the late posting, I had to pick hay up yesterday]

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