C / C++ / MFC

beginner, simple c question.

15-Jan-10 7:45

Cedric Moonen wrote:
Thanks for the nice comment

Well deserved, in my opinion.

Cedric Moonen wrote:
nd by the way, congrats for a well deserved MVP award

Thank you, you'll be in for sure the next year, wife permetting... Roll eyes | :rolleyes:

And maybe I'll kicked off: there are so many clever guys answering in this forum.
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

antionette15-Jan-10 4:39

antionette

15-Jan-10 4:39

int i=-20;

unsigned j=10;

i+j=? And why?

I am a beginner to C. Thanks for reply first.

Richard MacCutchan15-Jan-10 4:45

15-Jan-10 4:45

What has this to do with C? This is simple mathematics, and if you find this hard to understand, I doubt that you will find programming too easy. I would suggest you get a copy of a good C or C++ book and read it thoroughly.

MVP 2010 - are they mad?

image processing toolkits | batch image processing

C^hris L^osinger15-Jan-10 5:11

C^hris L^osinger

15-Jan-10 5:11

Richard MacCutchan wrote:
This is simple mathematics

it really isn't.

try it in a compiler.

Re: beginner, simple c question. [modified]

Richard MacCutchan15-Jan-10 5:38

15-Jan-10 5:38

Chris Losinger wrote:
try it in a compiler.

int i = -20;
unsigned int j = 10;
int k = i + j;

answer is -10. However if I just print the value (i + j) it returns 4294967286 obviously an unsigned integer, so some interesting automatic casting going on. I stand corrected!

[edit]the answer is -10 of course![/edit]

MVP 2010 - are they mad?

modified on Friday, January 15, 2010 12:50 PM

loyal ginger15-Jan-10 4:58

loyal ginger

15-Jan-10 4:58

I guess this should be correct: i + j = -20 + 10 = -10

dxlee15-Jan-10 5:13

dxlee

15-Jan-10 5:13

I noticed the "Joke" icon. I give you a 5.

It is tricky so I think the original post is a pretty good beginner's question. My daughter asks "why" a lot. It's a learning process.

CPallini15-Jan-10 5:05

15-Jan-10 5:05

antionette wrote:
int i=-20;

unsigned j=10;

Fine.

antionette wrote:
i+j=?

The above doesn't compile.

antionette wrote:
And why?

Because it is not a valid C statement.

image processing toolkits | batch image processing

C^hris L^osinger15-Jan-10 5:07

C^hris L^osinger

15-Jan-10 5:07

antionette wrote:
i+j=?

that's actually a tricky question. there are a lot of (really strange and non-intuitive, IMO) rules about how mixed signed/unsigned math is done in C. and a lot of those rules depend on how your compiler interprets the standard, and which standard.

i've found that whenever i'm doing signed/unsigned arithmetic, it's best to cast everything to a signed value, then perform the arithmetic. if the result needs to be unsigned, then i range-check the value to make sure it's non-negative and small enough to fit the result.

in this case, the answer is a huge positive integer.

int i = -20;
unsigned  j = 10;
__int64 k = i + j;

k = 4294967286

modified on Friday, January 15, 2010 11:22 AM

Richard MacCutchan15-Jan-10 6:55

15-Jan-10 6:55

Good info - I think the general rule is: don't use unsigned numbers in calculations.

MVP 2010 - are they mad?

CPallini15-Jan-10 8:36

Index of rows in report view list control with groups enabled is random order

15-Jan-10 8:36

Richard MacCutchan wrote:
Good info - I think the general rule is: don't ~~use unsigned numbers~~ in calculations.

Don't mix unsigned and signed numbers, without proper explicit casts, in calculations.
FFY.
Big Grin | :-D

Keith Worden15-Jan-10 2:49

Re: Index of rows in report view list control with groups enabled is random order

15-Jan-10 2:49

I use custom draw in report view list controls to alternate the background colour of each row to make it easier to read. This works fine. I've just started an application which would benefit from using groups in list controls. Ok, didn't take too much effort to get this working. The only problem now though is that the row background colours don't alternate any more - I get the same colour together for some adjacent rows.

I have found that in group mode the index of each row no longer refers to the physical position on the screen, the index of each row can in fact be anything! [within the total number] So I can no longer use the index to work out which background colour each row should be.

For example, with 5 items in a group of 4 and a group of 1, when I load the data the indexes are 0, 1, 2, 3, 4. When I sort the first column in reverse order the indexes become 1, 2, 3, 4, 0. The more rows I have the more random it gets.

Any ideas how I can work out what is the visible index?

Richard MacCutchan15-Jan-10 4:50

Re: Index of rows in report view list control with groups enabled is random order

15-Jan-10 4:50

You may need to tag your messages with an ID and use the LVM_MAPIDTOINDEX[^] message; there are various other associated messages that should help.

MVP 2010 - are they mad?

Keith Worden15-Jan-10 5:29

Re: Index of rows in report view list control with groups enabled is random order

15-Jan-10 5:29

That doesn't help; LVM_MAPINDEXTOID is just used to tell which item it is. It does not give the physical position on the screen.

Richard MacCutchan15-Jan-10 6:48

Re: Index of rows in report view list control with groups enabled is random order

15-Jan-10 6:48

Keith Worden wrote:
LVM_MAPINDEXTOID is just used to tell which item it is.

Yes, but I suggested LVM_MAPIDTOINDEX, under which the documentation states:
If you need the index of an item after an ID is created you can call LVM_MAPIDTOINDEX with the unique ID and it returns the most current index.

MVP 2010 - are they mad?

Keith Worden15-Jan-10 7:00

Re: Index of rows in report view list control with groups enabled is random order

15-Jan-10 7:00

Yes it gives an index but this is just the internal index, it is not the position on the screen. When group mode is off the index and the physical position are the same thing. When group mode is on there is no relationship (that I can find) between them.

Richard MacCutchan15-Jan-10 7:21

Re: Index of rows in report view list control with groups enabled is random order

15-Jan-10 7:21

OK, I thought there was also a message that gets you the first visible entry and then you could index from that point to go down the window.

MVP 2010 - are they mad?

Keith Worden15-Jan-10 7:31

15-Jan-10 7:31

There is the LVM_GETTOPINDEX message, but this always returns zero when group mode is enabled (it's for the topmost visible item anyway, not the first in the list). There's nothing to iterate over the list in the order it's displayed in group mode.

One Doubt

ashwath197915-Jan-10 2:48

ashwath1979

15-Jan-10 2:48

Hi All,

I want to develop an 3D Image rendering software using DirectX which can perform some 3D Operations.My customer wants the software developed on .Net Framework.

I have experience in coding in MFC in VC6.0.If i develop an MFC based application in Visual Studio 2008,will it be built on .Net Framework?

Thanking in advance,
Ashwath.

Maximilien15-Jan-10 2:55

Maximilien

15-Jan-10 2:55

Can you explain why you felt the need to re-post the same exact question just 2 hours after you posted the original question instead of continuing the discussion ?

I'm genuinely curious.

Thanks for taking the time to answer that.

M,

This signature was proudly tested on animals.

ashwath197915-Jan-10 17:23

ashwath1979

15-Jan-10 17:23

Sorry maxi for reposting ,i will not do it again.Actually as i was not getting answer to my previous post because of lots of questions in it ....i reposted it with only one question.

CPallini15-Jan-10 2:56

15-Jan-10 2:56

No.

LunaticFringe15-Jan-10 2:58

LunaticFringe

15-Jan-10 2:58

Quit spamming the board. You've already asked your question. Do you think people are going to be more inclined to answer now?

Roll eyes | :rolleyes:

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