Re: lcc first experience

On 8 May, 23:15, Keith Thompson <ks...@[EMAIL PROTECTED]
> wrote:
> rich...@[EMAIL PROTECTED]
 (Richard Tobin) writes:
> > In article
<cf0c2e4c-e25f-4ceb-a45d-5e0568175...@[EMAIL PROTECTED]
>,
> > Paul Hsieh  <websn...@[EMAIL PROTECTED]
> wrote:
>
> >>C is an uncommon language in that it does not require a comparison
> >>operator in its if statements
>
> > Really?  Which ones do?
>
> Paul's statement is incorrect as written, but there's a correct and
> somewhat interesting statement hiding behind it.
>
> C is somewhat unusual in the breadth of types that are acceptable as
> conditions in if statements (and while statements, and other contexts
> that require conditions).  In particular, an expression of any scalar
> type (i.e., any arithmetic or pointer type) can be used as a
> condition; the result of the expression is implicitly compared to zero
> (the meaning of "zero" varies for different scalar types), so that
> zero is treated as false, and any non-zero value is treated as true.
>
> For example, in C, this is valid:
>
>     int x = 42;
>     ...
>     if (x) {   /* equivalent to "if (x != 0)" */
>         /* ... */
>     }
>
> By contrast, Pascal requires a condition to be of type boolean (pardon
> any syntax errors; it's been a while).
>
>     var
>         x: integer;
>     ...
>     x := 42;
>     if x <> 0 then   (* would be illegal without the "<> 0" *)
>         (* ... *)
>
> So, in many cases, a comparison operator that would be required in
> some other languages is not required in C.
>
> This feature, as far as I've seen, is peculiar to C, to languages that
> inherited it from C (C++, Perl, etc.), and perhaps to languages that
> got it from C's ancestors (are there any existing B/BCPL derivatives
> other than C?).  Other common languages, particularly Pascal and its
> derivatives, don't do this.

Common Lisp also works this way albeit there the comparison is with
the empty list rather than zero:

(if x (print "True") (print "False"))

will print True if x is not the empty list and False if it is the
empty list.

> (Speaking only for myself, this is not among the features of C that I
> particularly like.)