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I was reading a coding style document put out by a certain company, when I came across an odd claim in their justification for their FOR loop style. I was wondering if someone could shed some light on this for me:
The document states that a pre-increment operator is preferable to a post-increment operator because post-increment introduces potential inefficiencies when iterating over an object. The example they give is C++ code:
std::vector v;
for (std::vector::const_iterator i = v.begin(); i != v.end(); ++i)
{
}
...and an identical sample that uses "i++" instead of "++i" for the increment operation.
I see no difference in the efficiency. Whether using ++i or i++, "i" is going to contain its new value before the termination condition is evaluated. The loop will be iterated an identical number of times.
I was wondering if someone could shed some light on what it is that I'm missing here, or if perhaps the assertion that pre-increment is more efficient. Is there some other language or platform that treats identical FOR loop sytax in a wildly different manner?
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i++;
++i;
In reality most modern compilers will optimise the code so it is of little consequence to the majority of programmers. It only becomes an issue if your program needs to run at sub-atomic speeds.
Just say 'NO' to evaluated arguments for diadic functions! Ash
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Their statement is utter non-sense, as Richard already explained.
And furthermore they should concentrate on the termination test of the for loop; v.end() is getting evaluated over and over, not necessarily what is required (depends on how "alive" v is).
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Yeah, I HATE seeing that in loops. Coders think its efficient because they have less code without thinking that a function call in the conditional part of the loop gets called every itteration.
"It is a remarkable fact that despite the worldwide expenditure of perhaps US$50 billion since 1990, and the efforts of tens of thousands of scientists worldwide, no human climate signal has yet been detected that is distinct from natural variation."
Bob Carter, Research Professor of Geology, James Cook University, Townsville
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I was going to say you should take a look at this code disassembled to see if there is any inefficiency, but Richard has answered that already.
"It is a remarkable fact that despite the worldwide expenditure of perhaps US$50 billion since 1990, and the efforts of tens of thousands of scientists worldwide, no human climate signal has yet been detected that is distinct from natural variation."
Bob Carter, Research Professor of Geology, James Cook University, Townsville
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As Richard and Luc have explained, there is no difference in this case. What they MAY have been referring to is this:
a[i++] = x;
b[++j] = z;
In a primitive CPU, the code might compile to something like this (much liberties taken in pseudo assembler code!)
load r1,i
add r1,=a
load r2,x
store r2,(r1)
load r1,i
inc r1
store r1,i
load r1,j
inc r1
store r1,j
add r1,=b
load r2,z
store r2,(r1)
In the early days of C, there were machines that stupid, but by the time C++ came along, the "issue" was long gone. Essentially, it's about using ++i in an expression compared to using i++. If the value of the side effect isn't used, there's no real difference.
Cheers,
Peter
Software rusts. Simon Stephenson, ca 1994.
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Pre-increment's return value is the iterator itself, while post-increment must return a copy of the iterator before it has been incremented. Since the for loop discards the return value, using the pre-increment version of the ++ operator saves some CPU cycles by not making a copy that will be discarded anyway. A longer explanation is here.[^]
Edit: Oops, I did not see that there were so many replies already. Only the OP was visible at the bottom of the forums window.
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Where's best to start for doing diagrams?
I want to teach myself to plan RIGHT for developing a decent sized project. Is UML still the appropriate standard? What processes should I follow?
I was taught to use Conceptual Schema and Nassi Schneiderman diagrams at school, so I'm looking for something a little more modern. :P
Thanks!
Don't forget to rate my post if it helped! 
"He has no enemies, but is intensely disliked by his friends."
"His mother should have thrown him away, and kept the stork."
"There's nothing wrong with you that reincarnation won't cure."
"He loves nature, in spite of what it did to him."
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dawmail333 wrote: Where's best to start for doing diagrams?
Depends on the job being done, but generally state transition diagrams and event trace diagrams are pretty usefull. (and often the only diagrams done)
"It is a remarkable fact that despite the worldwide expenditure of perhaps US$50 billion since 1990, and the efforts of tens of thousands of scientists worldwide, no human climate signal has yet been detected that is distinct from natural variation."
Bob Carter, Research Professor of Geology, James Cook University, Townsville
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Being a father of children with special needs, I am always asking
myself , with what I know how can I make a difference in my kids
life and others.
What I am looking for here is focus. What platform? What languages
should I learn? So that I can design software that helps individual
that have extra challenges in their life.
We need something cheap, a lot of families that have people with
special needs in them, most extra money goes to medical care, and
other various expenses other have no idea of.
We need something portable and has touch screen. The mouse
and keyboard while a great invention, acts as a barrier sometimes
to people that have disabilities especially mental. Touch is easy.
What platform would met those needs, while having a low cost?
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You can get cheap tablets these days running Android. Here in the UK, Binatone have cheap Android Homesurf tablets on sale for £130. You'd obviously need to develop for Android here, but the good news is that it's free to develop for.
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So that would be using Java and eclipse as my development environment?
Android doesnt have any visual studio tools do they? I have the express
version at home, and use a professional version at work.
I could tackle learning java for that..
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Thank so you so much for the suggestion and help.
Got it all installed, did the hello world thing.
It rocks.
Now to get a better understanding of Java and android
and I am ready to help some kids.
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Great. Wish you good luck.
If u can Dream... U can do it
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Forget about the technology and work with those who are prepared to contribute. If their skill-set is Java, go with Java, if there skill-set is .NET, go with .NET. Work with the people, not the technology.
If you are it! There is a steep learning curve. It's worth while but don't expect to get anywhere in a hurry. Maybe the quickest is VB.NET
Architecture is extensible, code is minimal.
modified on Tuesday, January 4, 2011 9:30 AM
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Thank you for that, appreciate that. I must admit that mostly I am looking
at cost. Lots of special need families dont have the money laying around
to afford the devices from Apple or microsoft. Google offers a cheaper solution
that more people can afford. Yes java is a learning curve for me, going to take
time to get there. Also want to provide these applications for free, the
cost of development for me, I can afford and will allow me to make my
applications free. Its a labor of love.
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So who are these people and what are your goals? Maybe the Codeproject community can help.
Architecture is extensible, code is minimal.
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The people I am mostly interested in reaching are Autistic kids, that are non-verbal.
Being the father of a non-verbal kid, its something that touches my heart. I want
to give my own son a voice , just in case he never develops his own. Most people
assume if you cant speak there are no words in your head. Technology is showing
us this is not true.
AAC devices, while a help with these kids are very expensive. Most units will
run for about 1.5K. Some of the good software out there runs about $225 dollars
plus the expenses of hardware. So an Ipad would run about 1k, still cheaper
than the 1.5k of the JUST AAC units on the market now.
The smart phones, such as the droid and Iphone are great, but for this
we need tablet devices. Because some of these kids also have motor control
issues, where a phone device would be hard to use. A tablet the perfect size
and portability to use in public.
My short term goals is to develop a free AAC device on a droid platform.
My long term goal, is to be able to fund raise to get these type of devices
into the hands of kids that have disabilities. Android is cheap, android tablets
are getting cheaper. I am thinking for the price of just one Ipad, I can produce
3 droid tablets with special software. More kids would be helped.
Yup long road to get there, have to learn java, get myself a droid tablet device.
But for me this seems a Financial reality with the droid, than apple or Microsoft
could provide.
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These tablets will all become around about the same price in time. Java being cross-platform makes it your best bet. Conceptionally I think what you learn from this, will have many applications.
Architecture is extensible, code is minimal.
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Todd
If you have the ideas I'm sure there are a number of professional devs here (I would be one) who would be more than happy to get involved in developing the software for you. The most difficult thing I find is getting the idea, designing the app and coding it comes easy.
I would even go so far as proposing it to CM as an official CP project, there are a lot of us out there who would like to help but do not know how their skills can contribute, this may be one of the ways.
Never underestimate the power of human stupidity
RAH
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I would be very interested in this. Not just for my own son, but for
a lot of people that live with challenges in their life.
I do not have a link to this blog site on me at the time. But something
I read over the weekend really made me realize how important the computer
can be for a challenged individual. A non-verbal Autistic boy wrote this
about his life.. "Before typing my life was poor, now I am free.."
People dont realize that their code can give so much for a person life.
Words are important, without a way to express them, you lead a very lonely life.
I am very interested in AAC -
[^]
Some of the problems with AAC
1. Its expensive and usually only serves one purpose.
2. A lot of them are very big and hard to lug around.
3. These devices the way they are now have no way to tailor
The keyboard to a users needs. Some people respond better with
pictures while others are fine with a alpha numeric keyboard.
4. They also draw unwanted attention sometimes to the person using them.
Android Tablets/Phones, Iphone/Ipad answer some of the call to this.
1. Applications can be free/low cost. Market places make this application more available.
2. Keyboards interface can be modified to be tailored to the users needs.
3. Devices are so common, a person could use these without looking out of place.
4. A computer is a picture device. You can teach with either pictures/sound/text.
5. And of course portable big thing here.
Would love to talk to other developers on how to do this. What kind of applications
we could all make to give an important gift. Words..
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And I can give a lot more detail than this. On some
of the ideas I have. The final product is a AAC device
for communication. But there are many programs that
can be written before that, to help people get to that point.
Like for example:
A program that uses google images. Sends a random
word to the database, an image is returned. The
name is read out loud, then a game is created
showing letters. The person then has choices of
letters they can use. Some are right and some are
wrong. Make it like a game, its fun and it teaches.
Also add the ability to put your own words in to search
on for the game. One of my sons favorite things in the
world is hangers. And I use google images to teach him
with that, because he is interested and fascinate by cloths
hangers. You would not find that in a regular kids game.
Just one example.
Also something people not be aware of. And why I am
leaning more towards the android Tablet. The keyboard
gives a slight vibration when typing. I am not sure
yet but if the keyboard can do that, I am thinking images
on the screen might do that too.. Its feedback that
a person with a development challenge might find calming
to the nervous system.
There is a behavior that some autistic people do. It is called
Stimming. From what I understand about this behavior it is
the vibration from the repeated movement that calms the nervous
system. This is only a theory as I yet have a device to test this
with. But I think the slight vibration of the keyboard would
give an autistic individual an incentive to want to use the device.
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I am going to develop a new class. But I do not have the full list of functionalities to be included in this class right now. But I would like to add new features at different times in the future. i.e I want to add new features to an existing class from time to time in the future as the new requirement arise. How should I start and which design pattern fits my requirement.
I do not have prior experience in using or applying patterns. I am starting out. If this is not the right place please guide me which codeguru forum I should resort to, to have more knowledge on applying design patterns.
Thanks,
ManojE
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xyzsnl wrote: But I do not have the full list of functionalities to be included in this class right now. But I would like to add new features at different times in the future
Classes are small constructs, and ideally they'd only have a single responsibility. Implementing a lot of functionality in a single class, and modifying that, would be rather inefficient and error-prone.
There's a multitude of ways to extend classes, the most obvious being inheritance. In essence, you create a new class and "inherit" all the things from some other class you wrote. There's also the option of creating abstract classes; that would only contain a definition, similar to an interface. You could provide different implementations as required.
xyzsnl wrote: How should I start and which design pattern fits my requirement.
Most design-patterns consist out of more than one single class. I liked the Strategy[^]-pattern as an introduction to design patterns. As you learn more, you'll recognize them in the .NET Framework itself.
Happy Programming 
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