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How well you know your c++?

General and Gameplay Programming Programming

Started by Pharazon September 19, 2004 05:39 PM

50 comments, last by Enigma 19 years, 6 months ago

1,151

September 20, 2004 02:31 PM

Quote:Original post by Fruny
Quote:Original post by snk_kid
i mean't instead of pointer to member functions or pointer to data members, why no reference to member functions or reference to data members but you can with free/class functions.

Hmmm. Good question. I didn't even know you could not.

i was stuck with that recently.
thread
additional info

I'm a Pascal programmer swiched to C++ not so long ago, yet i have no troubles answering such questions.

BTW :
"
Why does the following code segment display
"x does not equal 0.01, y equals 0.05"?
float x = 0.01;
float y = 0.05;
if (x != 0.01) cout << "x does not equal 0.01, ";
if (y == 0.05) cout << "y equals 0.05";
"

probably there should be 0.5 , not 0.05
0.05 can't be exactly represented by float nor double. When comparing, IIRC on x68 float is converted to double. IIRC by standard, it's double must be converted to float, but i'm not 100% sure.

nmi

978

September 20, 2004 02:32 PM

to Eriond:

4.5 Integral promotions
An rvalue of type bool can be converted to an rvalue of type int, with false becoming zero and true
becoming one.

to Cocalus:

Isn't the 2's complement just a binary not followed by +1 ?

load_bitmap_file

826

September 20, 2004 02:33 PM

Quote:Original post by Eriond
Will 2 >= 1 always evaluate to 1 and not some other number like 51?

Yes. In C++ any non-zero value when intepreted as a boolean expression becomes "true" which basically is "1".

nmi

978

September 20, 2004 02:38 PM

Quote:Original post by Dmytry
BTW :
"
Why does the following code segment display
"x does not equal 0.01, y equals 0.05"?
float x = 0.01;
float y = 0.05;
if (x != 0.01) cout << "x does not equal 0.01, ";
if (y == 0.05) cout << "y equals 0.05";
"

probably there should be 0.5 , not 0.05
0.05 can't be exactly represented by float nor double. When comparing, IIRC on x68 float is converted to double. IIRC by standard, it's double must be converted to float, but i'm not 100% sure.

I tried the 0.05 version, the test fails. For 0.5 it works as Dmytry said.

BTW nice thread, thx for the idea.

daerid

354

September 20, 2004 02:42 PM

Quote:Original post by Eriond
Will 2 >= 1 always evaluate to 1 and not some other number like 51?

Yes

daerid@gmail.com

s_p_oneil

445

September 20, 2004 02:44 PM

Oh, come on. If you're going to ask a question like "How well you know your c++?", you should at least post problems specific to C++. All of those problems can happen in any number of languages.

The first two are tied to the design of the CPU (i.e. 2's complement negative integers and IEEE floating point numbers). The last question is simple boolean algebra, and again is not specific to any language (other than the fact that some languages will evaluate from left-to-right and others from right-to-left).

Eriond

187

September 20, 2004 03:11 PM

The reason I asked was because a friend said some compilers would use another value, which could make 4 >= 3 >= 2 evaluate to true. Thanks for the answer.

nmi

978

September 20, 2004 03:29 PM

The C++ standard says that true has to be converted to 1, nothing else. If the compiler behaves differently it isn't standard conforming.

elementary

154

September 20, 2004 03:30 PM

Quote:
Post your answers. If you don't know, I'll put up answers in a couple days.

How almost insulting...

Cocalus

554

September 20, 2004 03:39 PM

Quote:
to Cocalus:

Isn't the 2's complement just a binary not followed by +1 ?

Mybad, 2's complement is inverting all the bits (I think that's called the one's complement) then adding one. I remember concepts well but not names of things.

-Cocalus

How well you know your c++?

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