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From: Dan Purgert <dan@djph.net>
Newsgroups: comp.lang.c
Subject: Re: how cast works?
Date: Wed, 7 Aug 2024 20:00:28 -0000 (UTC)
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On 2024-08-07, Thiago Adams wrote:
> How cast works?
> Does it changes the memory?
> For instance, from "unsigned int" to "signed char".
> Is it just like discarding bytes or something else?
> [...]

I don't know what happens when you're changing datatype lengths, but if
they're the same length, it's just telling the compiler what the
variable should be treated as (e.g. [8-bit] int to char)

>
> I also would like to understand better signed and unsigned.
> There is no such think as "signed" or "unsigned" register, right?

"Signed" just means the first bit indicates negative.

So an "unsigned" 8 bit integer will have the 256 values ranging from

 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 = 0
      (0b00000000)

              TO

 128 + 64 + 32 + 16 + 8 +4 + 2 + 1 = 255
      (0b11111111)


Whereas a "signed" 8 bit integer will have the 256 values ranging from

  (-128) + 0 + 0 + 0 + 0 + 0 + 0 + 0 = -128
      (0b10000000)

              TO 

  0 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 127 
      (0b01111111)

At least in two's compliment (but that's the way it's done in C)


> How about floating point?

Floating point is a huge mess, and has a few variations for encoding;
though I think most C implementations use the one from the IEEE on 1985
(uh, IEEE754, I think?)



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