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From: jcbst3@unix.cis.pittsburgh.edu (James C. Benz)
Newsgroups: comp.lang.c
Subject: Re: Help rounding-off numbers (not using printf)
Message-ID: <18226@unix.cis.pittsburgh.edu>
Date: 31 May 89 17:32:36 GMT
References: <2730@oregon.uoregon.edu>
Reply-To: jcbst3@unix.cis.pittsburgh.edu (James C. Benz)
Organization: Univ. of Pittsburgh, Comp & Info Sys
Lines: 42

In article <2730@oregon.uoregon.edu> michelbi@oregon.uoregon.edu (Michel Biedermann) writes:
>Is there a C function (user defined or primitive (?)) that will let me
>truncate or round-off a number UP TO a certain decimal place.  For example
>transforming .567 into .6 or -1.502 into -1.5 (i.e. N = round(.567) would
>set N to .6.  I do not want to simply print a rounded-off number but be
>able to use it as well.
> 
have you tried round(N+.5)-.5?  I seem to remember from a *really* elementary
CS course many moons ago that this is the way to do it.  I haven't tried it
or even thought about it too much, but it seems like it should work.  
Lets see,
	.567 + .5 = 1.067
	round(1.067) = 1.0
	1.0 - .5 = .5

Hmm, that's not right is it?

How about round(N+.5)-.4?
	-1.502 + .5 = -1.002
	round(-1.002) = -1.
	-1 - .4 = -1.4

Grr.  How about
	if (N > 0)
		round(N+.5)-.4
	else
		round(N+.5)-.5

	.567 +.5 = 1.067
	round(1.067) = 1.0
	1.0 - .4 = .6

	-1.502 +.5 = -1.002
	round(-1.002)=-1.
	-1. - .5 = -1.5

Seems right, but will it always work?

-- 
Jim Benz 		     jcbst3@unix.cis.pittsburgh.edu     If a modem 
University of Pittsburgh					 answers,
UCIR			     (412) 648-5930			 hang up!