[chbot] Pop quiz C

[Volker Kuhlmann]

On Wed 26 Apr 2017 10:04:47 NZST +1200, Michael Field wrote:

> What is the value of a? 
> 
>  a =
> 0xFFFFFFFF << 34; 

The language is C, so it's pretty easy, however you failed to specify
all parameters, hence the options are:

1) a is not even declared, so that trashes the challenge as "doesn't even
make the syntactically correct" threshold. Assuming int only gets that
far, as int may be 64 bits. So:

2) a is 64 bits, 0xFFFFFFFF is type int(!!! as you didn't say
otherwise): The result is 0xFFFFFFFC00000000. Or at least I think shifts
in C are always logical, if not, the result should be
0xFFFFFFFFFFFFFFFF.

3) a is 32 bits, 0xFFFFFFFF is type int (thus -1), the result is a=0
unless shifts are signed for signed numbers (int is signed, the type of
a only matters after the shift expression is evaluated).

Contrary to another reply, I don't see why the result in 3) is
undefined. The mathematics are exactly defined. Stupid programming is
entirely different to defined mathematics. -Wall -pedantic should
*always* be present to have a chance of a hint to said stupid
programming. The compiler's job is not to make sure your program works,
it is to translate your program exactly as given, its warnings can't do
more than kick the derriere of the area between keyboard and chair
("left shift exceeds width of type").

The compiler is however allowed to conclude, after due optimising
considerations, that the result is always 0 (or -1), and remove all
expressions deemed constant, and replace them with a constant, that
being an exact result of your program as given.

> Have you checked your answer? 

No. Any results or issues I missed? ;-)

Volker

-- 
Volker Kuhlmann
http://volker.top.geek.nz/	Please do not CC list postings to me.