Path: utzoo!mnetor!uunet!husc6!cmcl2!nrl-cmf!ames!ucsd!sdcsvax!ucsdhub!hp-sdd!hplabs!hpda!hpcupt1!hpisod2!decot
From: decot@hpisod2.HP.COM (Dave Decot)
Newsgroups: comp.lang.c
Subject: Re: The D Programming Language: values and voids (was: == vs =)
Message-ID: <2550071@hpisod2.HP.COM>
Date: 13 Apr 88 05:18:30 GMT
References: <3290@haddock.ISC.COM>
Organization: Hewlett Packard, Cupertino
Lines: 32

> I think this is better written as "if ((status = *statreg))"; some
> people even recommend "if ((status = *statreg), status)".%
> 
> If you write the if as "if (a = b)", many readers of your code
> (possibly including yourself) will first think "aha, this is a typo".
> Many other readers will read it as "if (a == b)".  It is therefore a
> good idea to use a visually distinct form.  The two forms I list above
> both result from the idea that `=' should not be the top level operator
> in a conditional expression.

I agree with the reasoning, but I think an even clearer way of expressing
what you really mean is this:

    if ((status = *statreg) != 0)
       ...

Generally, I will only use an implied comparison to 0 in conditional
contexts when the name of a "Boolean" variable or macro returning
a purely "Boolean" result is the entirety of the condition.

For instance,

    if (strcmp(x, y) != 0)
       ...

but

    if (isprint(*p))
      ...

Dave Decot
hpda!decot