Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!otter!kers
From: kers@otter.hpl.hp.com (Chris Dollin)
Newsgroups: comp.misc
Subject: Re: The "evil" GOTO (Was: 25 Years of BASIC)
Message-ID: <1860005@otter.hpl.hp.com>
Date: 5 May 89 07:58:23 GMT
References: <1814@ubu.warwick.UUCP>
Organization: Hewlett-Packard Laboratories, Bristol, UK.
Lines: 62

Mike Taylor said:

(In an probably fruitless attempt to stem a public GOTO war, I am prepared to
have a private email war with Mike and report back later - see end of
article.)

| In article <3, I think> gould@rosemary.cs.reading.ac.uk (Adrian Gould) writes:
| > Lets eradicate the GOTO from all languages.
|
| I hate it when people say things like that; As if you can just wave a
| magic wand over a language by excising GOTO, and everything will be
| alright.  Listen, just 'cause Quiche-eater Wirth connected GOTOs with
| lack of structure geenrally, doesn't mean either that (A) ALL use of
| GOTO is unstructured and obfuscatory, or that (B) ALL obfuscated code
| is due to use of GOTO -- so why is it that so many people seem to
| believe these myths?
|
| How many times have you seen this kind of code?
|
|     printf ("Enter your sex: ");
|     while (sex != "m" && sex != "f") {
|         gets (sex);
|         if  (sex != "m" && sex != "f")
|             printf ("<m> or <f> only: ");
|     }
|

Not very often.

| Why make the test twice?  Huh?  Huh?  Answer me that, all you obsessed
| anti-GOTO campaigners.  The *natural* way to express the above is:
|
|     printf ("Enter your sex: ");
| LABEL:  gets (sex);
|     if (sex != "m" && sex != "f") {
|         printf ("<m> or <f> only: ");
|         GOTO LABEL;
|     }

I don't know about "natural". Is programming "natural"? But, using the word
within the meaning of the Act, I'd say the natural way to write this is:

    printf( "Enter your sex: ");
    repeat
        gets( sex );
        until sex == "m" or sex == "f";
        printf( "<m> or <f> only: " )
    endrepeat;

Of course, if you want to write it like this in C, you'd have to do something
like:

    PROMPT;                                 /* Stuff it, I'm not writing it */
    while( GETS, CONDITION ) REPROMPT;      /* out all over again.          */

Structured programming is not about omitting GOTOs, but using control
structures suitable for the task at hand. The idiom you mention is usually
called the "N-and-a-half-times loop", and should damn well be supported in
*any* imperative programming language.        

Tell you what, Mike; mail me and we'll talk about this without cluttering the
net. Then we can summarise our battle - ahem, enlightened debate - later.