Re: Command Languages Versus Programming Languages

In article <e47664d3-7f9b-4e67-aa73-b72c6cc0687a@alumni.caltech.edu>,
James Kuyper  <jameskuyper@alumni.caltech.edu> wrote:

On 11/22/24 16:14, Dan Cross wrote:
...

irrelevant.  That's not how C works: C will promote those
`unsigned char` values to `signed int` before it does the
subtraction.  It does this because `unsigned char` has _rank_
lower than _int_ ...

>
True.
>

... and the entire range of values is expressible
in a signed int.

>
Not necessarily. An implementation is allowed to have UCHAR_MAX >
INT_MAX, in which case unsigned char promotes to unsigned int rather
than int. I'm aware of systems where UCHAR_MAX > LONG_MAX was true:
char, short, int, and long were all 32 bits.

Yes, but in this context, that's obviously not the case as he
posted the behavior he saw.  I was merely explaining _why_ he
saw that behavior, vis the standard.

...  These are called, "the usual arithmetic
conversions."

>
Actually, what you're talking about are the integer promotions. The
first step of the usual arithmetic conversions is to apply the integer
promotions to each operand, but then a few other things happen as well.

This is correct, but IMHO too far down into the weeds.  Consider
section 6.3.1.1 para 3, which notes that, "the integer
promotions are applied only: ... 1. as part of the usual
arithmetic conversions".  Since we're talking about operands to
a binary operator, 6.3.1.8 applies.  6.3.1.8 is why converting
one side to unsigned is sufficient to get an unsigned result.

- Dan C.