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From: bill@valiant (R.A.L Williams)
Newsgroups: comp.lang.ada
Subject: "Subtract C, add Ada"
Date: 20 Jan 1995 10:20:13 GMT
Organization: GEC-Marconi Research Centre
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Date: 1995-01-20T10:20:13+00:00
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In article <3f5s92$3id@info.epfl.ch> you wrote:
: In article <3f4mbe$rud@cronkite.seas.gwu.edu>, dobrien@seas.gwu.edu (David O'Brien) writes:
: |> R.A.L Williams (bill@valiant) wrote:
: |> : My experience of writing software and running software projects in C
: |> : highlights four common low-level C errors:
: |> :   1. = instead of == and vice versa
: |> 
: |> I have to wonder.  What if C defined the logical equals operator to be
: |> "=" and the assignment operator to be ":=" just like Ada, Algol, Pascal,
: |> Modula-x, etc?  Would this error still exist???

: The problem is in the language definition, not in the choic of symbols.
: C is one of the rare language I use to allow having an assignment after 
: the if statement.  All other languages only allow for a boolean test.

: I never saw a good reason for allowing this.

I think there are three reasons:
 1. It allows your code to be more compact. Many people think this is
    a disadvantage, and so it is if the code will be read by comparative
    novices, but it can improve readability to C experts who are 
    expecting such tricks.

    NB DONT confuse compactness with poor layout! I find that, for example:

       while ((c = getchar()) == ' ')
       {
          /* count spaces */
       }

    is clearer than the 'expanded' alternative (to *me* :-).

 2. All expressions in C have a value. Conditional tests succeed on 
    non-zero and fail on zero. Therefore, to maintain orthogonality, 
    as far as possible, there is no reason to exclude an assignment 
    expression from a condition.
   
 3. Finally, I suspect, this can simplify the optimisation algorithms 
    in the compiler.

Personally, the lack of this sort of compactness in Ada, and things like
pre- and post-increment/decrement are one of my minor gripes about the
language. OK, its no big thing to write:

    P(I) := Q(I);
    I := I + 1;

instead of
 
    *p++ = *q++;

but I actually *do* find the C representation easier/better etc. (perhaps
I'm wierd?)

: -- 
: Laurent Gasser (gasser@dma.epfl.ch)
: Computers do not solve problems, they execute solutions.

: I know very few ideas worth dying for, none is worth killing.

Very true, but quite a few are worth a pint in the pub.

Bill Williams