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From: rang@cpsin3.cps.msu.edu (Anton Rang)
Newsgroups: misc.misc,comp.misc
Subject: Re: The "evil" GOTO (Was: 25 Years of BASIC)
Message-ID: <2854@cps3xx.UUCP>
Date: 5 May 89 02:06:16 GMT
References: <1814@ubu.warwick.UUCP> <13113@lanl.gov>
Sender: usenet@cps3xx.UUCP
Reply-To: rang@cpswh.cps.msu.edu (Anton Rang)
Organization: Michigan State University, Computer Science Dept.
Lines: 47
In-reply-to: jlg@lanl.gov's message of 4 May 89 22:38:12 GMT

In article <13113@lanl.gov> jlg@lanl.gov (Jim Giles) writes:

>   Actually, in the above example, "break" is a better way.  This is the
>   classic "loop and a half" problem for which the "break" statement
>   exists.  So the following is a better suggestion:
>
>	 printf ("Enter your sex: ");
>	 for (;;) {
>	    gets (sex);
>	    if (sex == "m" || sex == "f") break;
>	    printf ("<m> or <f> only: ");
>	 }
>
>   Note: since C doesn't have multi-level breaks, GOTO must be used to escape
>   from nested constructs.

This is ugly; it essentially transforms the code

	LABEL: get input
	       if (bad input)
		 print message
		 go back to label

into

	LABEL: get input
	       if (good input)
		 goto LABEL2
	       print message
	       go back to label
	LABEL2:

Now you have two places where control jumps around, instead of just
one.  'break' has its uses, perhaps, but this isn't one of them
(IMHO).  Actually, I feel that 'break' should usually be replaced by
an explicit goto (heresy!).  Why?  Because the place the break goes to
isn't explicit; you have to start matching up loops.  If you have lots
of nesting, this is quite a mess.
  Named loops in Ada are intended to alleviate this problem, and if
used properly seem to do a decent job.

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