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• Problem with SAT collision detection overlap checking code

  - by handyface

  I'm trying to implement a script that detects whether two rotated rectangles collide for my game, using SAT (Separating Axis Theorem). I used the method explained in the following article for my implementation in Google Dart. 2D Rotated Rectangle Collision I tried to implement this code into my game. Basically from what I understood was that I have two rectangles, these two rectangles can produce four axis (two per rectangle) by subtracting adjacent corner coordinates. Then all the corners from both rectangles need to be projected onto each axis, then multiplying the coordinates of the projection by the axis coordinates (point.x*axis.x+point.y*axis.y) to make a scalar value and checking whether the range of both the rectangle's projections overlap. When all the axis have overlapping projections, there's a collision. First of all, I'm wondering whether my comprehension about this algorithm is correct. If so I'd like to get some pointers in where my implementation (written in Dart, which is very readable for people comfortable with C-syntax) goes wrong. Thanks! EDIT: The question has been solved. For those interested in the working implementation: Click here

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• Working hours for a newbie

  - by martani_net

  This is not a very related software / hardware question, but it's too related to the Tech world. I started a work 3 months before, and I am about to finish this week, and my boss asked me to do a planning of what I've done so far, I think this is totally ok, but he is asking for what I did each day with the hours I spent in these days. This is a sample of what I sent him M T W T F week 29/06 to 03/07 compréhension et analyse du problématique * * architecture de l'application * * * which translates to first task, I spent Monday + Tuesday on, and the last W, T, and Friday. What he is asking for, is what I've done in each day, with the timing I spent on (obviously, I don't think I remember, and because for a programmer, there are no sequence tasks, I mean I change code in a class, then change it in another to fit with the new one and so far) So my question is: is what he asking normal? and if so how can I detail the planning for the 3 months. [update] I used the email account we use to test our software with the extern servers, and I got a good view of what I was doing in every day :), a generic view but it helped too much (PS: The boss doesn't know anything about programming, for him, it's like writing lines and get results back nothing more )

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• Android Service onBind -> onStart

  - by Gernot

  Hello, I have a comprehension question about Android Services. I have a Service that performs background http operations and a Activity that should display the current state of these http operations. So I implementet the Binder interface and so on. I can call the bindService method and onServiceConnected of my ServiceConnnection is getting called. But as far as I know, onBind doesn't calls onStartCommand() and so onStart() of the Service is never called. So how can I call the onStart() method of the service class and start my operations. Or how is the best way to start my operations in the service, when I also want a binding between the Activity and the Service.

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• How to transform phrases and words into MD5 hash?

  - by brilliant

  Can anyone, please, explain to me how to transform a phrase like "I want to buy some milk" into MD5? I read Wikipedia article on MD5, but the explanation given there is beyond my comprehension: "MD5 processes a variable-length message into a fixed-length output of 128 bits. The input message is broken up into chunks of 512-bit blocks (sixteen 32-bit little endian integers)" "sixteen 32-bit little endian integers" is already hard for me. I checked the article on little endians and didn't understand a bit. However, the examples of some phrases and their MD5 hashes are very nice: MD5("The quick brown fox jumps over the lazy dog") = 9e107d9d372bb6826bd81d3542a419d6 MD5("The quick brown fox jumps over the lazy dog.") = e4d909c290d0fb1ca068ffaddf22cbd0 Can anyone, please, explain to me how this MD5 algorithm works on some very simple example? And also, perhaps you know some software or a code that would transform phrases into their MD5. If yes, please, let me know.

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• In what areas might the use of F# be more appropriate than C#?

  - by Peter McGrattan

  Over the last few years F# has evolved into one of Microsoft's fully supported languages employing many ideas incubated in OCaml, ML and Haskell. Over the last several years C# has extended it's general purpose features by introducing more and more functional language features: LINQ (list comprehension), Lamdas, Closures, Anonymous Delegates and more... Given C#'s adoption of these functional features and F#'s taxonomy as an impure functional language (it allows YOU to access framework libraries or change shared state when a function is called if you want to) there is a strong similarity between the two languages although each has it's own polar opposite primary emphasis. I'm interested in any successful models employing these two languages in your production polyglot programs and also the areas within production software (web apps, client apps, server apps) you have written in F# in the past year or so that you would previously have written in C#. EDIT: Edited based on feedback from close votes with the intent of reducing perceived ambiguity.

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• ASP.NET CustomValidator trying to match to System.EventHandler?

  - by annakata

  I have markup so: <asp:TextBox runat="server" ID="Accountname" /> <asp:CustomValidator runat="server" ControlToValidate="Accountname" OnServerValidate="Accountname_CheckUnique" meta:resourcekey="ACCOUNTNAME_UNAVAILABLE" /> Codebehind so: protected void Accountname_CheckUnique(object source, ServerValidateEventArgs arguments) { arguments.IsValid = Foo(); } Which was working just fine, and then without changing anything on the page ASP now insists: No overload for 'Accountname_CheckUnique' matches delegate 'System.EventHandler' Well no, and nor should it according to MSDN. It's late and I'm tired, anybody know how to fix this or point out the glaring flaw in my comprehension?

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• How do you solve this Haskell problem using a fold map and take?

  - by Linda Cohen

  Define a function replicate which given a list of numbers returns a list with each number duplicated its value. Use a fold, map, and take .. replicate [5,1,3,2,8,1,2] output: [5,5,5,5,5,1,3,3,3,2,2,8,8,8,8,8,8,8,8,1,2,2] I've figure this out using List comprehension and recursion: replicate2 [] = [] replicate2 (n:nn) = take n(repeat n) ++ replicate2 nn but how would you use fold and map to do this? so far I have: replicate n = map (foldl1 (take n(repeat n)) n) n which is obviously wrong, but I think I am close.. so any help would be nice, THANKS!

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• What production software have you written in F# in the past year or so that you would previously hav

  - by Peter McGrattan

  Over the last few years F# has evolved into one of Microsoft's fully supported languages employing many ideas incubated in OCaml, ML and Haskell. Over the last several years C# has extended it's general purpose features by introducing more and more functional language features: LINQ (list comprehension), Lamdas, Closures, Anonymous Delegates and more... Given C#'s adoption of these functional features and F#'s taxonomy as an impure functional language (it allows YOU to access framework libraries or change shared state when a function is called if you want to) there is a strong similarity between the two languages although each has it's own polar opposite primary emphasis. I'm interested in any successful models employing these two languages in your production polyglot programs and also the areas within production software (web apps, client apps, server apps) you have written in F# in the past year or so that you would previously have written in C#.

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• Repeating a List in Scala

  - by Ralph

  I am a Scala noob. I have decided to write a spider solitaire solver as a first exercise to learn the language and functional programming in general. I would like to generate a randomly shuffled deck of cards containing 1, 2, or 4 suits. Here is what I came up with: val numberOfSuits = 1 (List["clubs", "diamonds", "hearts", "spades"].take(numberOfSuits) * 4).take(4) which should return List["clubs", "clubs", "clubs", "clubs"] List["clubs", "diamonds", "clubs", "diamonds"] List["clubs", "diamonds", "hearts", "spades"] depending on the value of numberOfSuits, except there is no List "multiply" operation that I can find. Did I miss it? Is there a better way to generate the complete deck before shuffling? BTW, I plan on using an Enumeration for the suits, but it was easier to type my question with strings. I will take the List generated above and using a for comprehension, iterate over the suits and a similar List of card "ranks" to generate a complete deck.

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• In what specific areas has F# proven more applicable than C#?

  - by Peter McGrattan

  Over the last few years F# has evolved into one of Microsoft's fully supported languages employing many ideas incubated in OCaml, ML and Haskell. Over the last several years C# has extended it's general purpose features by introducing more and more functional language features: LINQ (list comprehension), Lamdas, Closures, Anonymous Delegates and more... Given C#'s adoption of these functional features and F#'s taxonomy as an impure functional language (it allows YOU to access framework libraries or change shared state when a function is called if you want to) there is a strong similarity between the two languages although each has it's own polar opposite primary emphasis. I'm interested in any successful models employing these two languages in your production polyglot programs and also the areas within production software (web apps, client apps, server apps) you have written in F# in the past year or so that you would previously have written in C#. EDIT: Altered title with the intent of reducing perceived ambiguity.

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• linq "let" translation

  - by luke

  I understand that when the C# compiler sees a linq query comprehension, it basically does a straight translation to the corresponding Linq Extension methods and lambdas. i.e. from x in list select x.property gets translated to: list.Select(x => x.property) my question is what do let clauses get translated to. for example how would this get translated by the compiler. from x in list let v = SomeComplexExpressionDependingOnx select v (p.s. i know this could be reduced to just select SomeComplexExpressionDependingOnx but i want to know how this is done in general) Thanks!

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• Subtracting two lists in Python

  - by wich

  In Python, How can one subtract two non-unique, unordered lists? Say we have a = [0,1,2,1,0] and b = [0, 1, 1] I'd like to do something like c = a - b and have c be [2, 0] or [0, 2] order doesn't matter to me. This should throw an exception if a does not contain all elements in b. Note this is different from sets! I'm not interested in finding the difference of the sets of elements in a and b, I'm interested in the difference between the actual collections of elements in a and b. I can probably work this out with a for loop, looking up the first element of b in a and then removing the element from b and from a, etc. But this doesn't appeal to me, I'd like to do this with list comprehension in a nice and easy way. Is this possible?

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• idiomatic way to take groups of n items from a list in Python?

  - by Wang

  Given a list A = [1 2 3 4 5 6] Is there any idiomatic (Pythonic) way to iterate over it as though it were B = [(1, 2) (3, 4) (5, 6)] other than indexing? That feels like a holdover from C: for a1,a2 in [ (A[i], A[i+1]) for i in range(0, len(A), 2) ]: I can't help but feel there should be some clever hack using itertools or slicing or something. (Of course, two at a time is just an example; I'd like a solution that works for any n.) Edit: related http://stackoverflow.com/questions/1162592/iterate-over-a-string-2-or-n-characters-at-a-time-in-python but even the cleanest solution (accepted, using zip) doesn't generalize well to higher n without a list comprehension and *-notation.

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• Scala create xhtml elements dynamically

  - by portoalet

  Given a String array val www = List("http://bloomberg.com", "http://marketwatch.com"); I want to dynamically generate <span id="span1">http://bloomberg.com</span> <span id="span2">http://marketwatch.com</span> def genSpan(web: String) = <span id="span1"> + web + </span>; www.map(genSpan); // How can I pass the loop index? How can I use scala map function to generate the ids (span1, span2), as 1 and 2 are the loop indexes ? Or is the only way is to use for comprehension?

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• Python - Create a list with initial capacity

  - by Claudiu

  Code like this often happens: l = [] while foo: #baz l.append(bar) #qux This is really slow if you're about to append thousands of elements to your list, as the list will have to constantly be re-initialized to grow. (I understand that lists aren't just wrappers around some array-type-thing, but something more complicated. I think this still applies, though; let me know if not). In Java, you can create an ArrayList with an initial capacity. If you have some idea how big your list will be, this will be a lot more efficient. I understand that code like this can often be re-factored into a list comprehension. If the for/while loop is very complicated, though, this is unfeasible. Is there any equivalent for us python programmers?

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• Removing items from a nested list Python

  - by johntfoster

  I'm trying to remove items from a nested list in Python. I have a nested list as follows: families = [[0, 1, 2],[0, 1, 2, 3],[0, 1, 2, 3, 4],[1, 2, 3, 4, 5],[2, 3, 4, 5, 6]] I want to remove the entries in each sublist that coorespond to the indexed position of the sublist in the master list. So, for example, I need to remove 0 from the first sublist, 1 from second sublist, etc. I am trying to use a list comrehension do do this. This is what I have tried: familiesNew = [ [ families[i][j] for j in families[i] if i !=j ] for i in range(len(families)) ] This works for range(len(families)) up to 3, however beyond that I get IndexError: list index out of range. I'm not sure why. Can somebody give me an idea of how to do this. Preferably a one-liner (list comprehension). Thanks.

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• In Python, is there a way to call a method on every item of an iterable? [closed]

  - by Thane Brimhall

  Possible Duplicate: Is there a map without result in python? I often come to a situation in my programs when I want to quickly/efficiently call an in-place method on each of the items contained by an iterable. (Quickly meaning the overhead of a for loop is unacceptable). A good example would be a list of sprites when I want to call draw() on each of the Sprite objects. I know I can do something like this: [sprite.draw() for sprite in sprite_list] But I feel like the list comprehension is misused since I'm not using the returned list. The same goes for the map function. Stone me for premature optimization, but I also don't want the overhead of the return value. What I want to know is if there's a method in Python that lets me do what I just explained, perhaps like the hypothetical function I suggest below: do_all(sprite_list, draw)

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• Iterating through a range of dates in Python

  - by ShawnMilo

  This is working fine, but I'm looking for any feedback on how to do it better. Right now I think it's better than nested loops, but it starts to get Perl-one-linerish when you have a generator in a list comprehension. Any suggestions are welcome. day_count = (end_date - start_date).days + 1 for single_date in [d for d in (start_date + timedelta(n) for n in range(day_count)) if d <= end_date]: print strftime("%Y-%m-%d", single_date.timetuple()) Notes: I'm not actually using this to print; that's just for demo purposes. The variables start_date and end_date are datetime.date objects, because I don't need the timestamps (they're going to be used to generate a report). I checked the StackOverflow questions which were similar before posting this, but none were exactly the same. Sample Output (for a start date of 2009-05-30 and an end date of 2009-06-09): 2009-05-30 2009-05-31 2009-06-01 2009-06-02 2009-06-03 2009-06-04 2009-06-05 2009-06-06 2009-06-07 2009-06-08 2009-06-09

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• Erlang - list comprehensions - populating records

  - by tbikeev

  I have a simple record structure consisting of a header (H) and a list of the data lines (D) 1:N. All header lines must start with a digit. All data lines have a leading whitespace. There also might be some empty lines (E) in between that must be ignored. L = [H, D, D, E, H, D, E, H, D, D, D]. I would like to create a list of records: -record(posting,{header,data}). using list comprehension. Whats the best way to do it?

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• Getting Error 91

  - by user1695788

  I have a general comprehension issue with classes and objects. What I'm trying to do is pretty simple but I'm getting errors. In the code example below, sometimes the line "Call tables.MethodInCTables" runs fine and sometimes it produces error 91, object not set. IN all cases, I can "see" the method in the type ahead so I know that the code recognizes the "tables" instance and "sees" MethodInCTables. But then I get the run-time error. Sub MainSub() Dim tables as New CTables Call tables.MethodInCTables End Sub ----Class Module = CTables Sub MethodInCTables() ...do something End Sub

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• Disabling Laptop (PB TJ-75) faulty card reader Linux

  - by Gab

  My problem comes from that my laptop [PB TJ-75] has a faulty Alcor card reader. It’s 100% sure, the device is dead and unusable whatever the OS is. It cannot be disabled in BIOS [latest: Vendor: Phoenix Technologies LTD Version: V1.26 Release Date: 05/04/2010]. If I could take it apart from the main board easily, and if with that, the system would never look again for it, I’ll be very happy! Is it possible, has anyone ever tried this? Or maybe, replacing the BIOS with a more open one, which let you disable the card reader. Does this exists? Here's what I've tried to disable it so far. In Win7, I choose ‘disable’ in device manager and that’s ok. If not, the device keeps on appearing and disappearing and lot of resources are used. In Lubuntu 13.04, I got extra boot time, with the msg:'sdb, assuming drive cache, etc.’ I tried other distros (isos booted by grub). I can boot Puppy, Gparted, and Redobackup apparently without any problem. I cannot boot Debian, live or install + tried Crunchbang and Tails. I got a loop :’usb device, scsi n+1 blabla‘. I tried "nousb", no result, I have blacklisted EHCI, no result, then usb_storage module, better boot time in Lubuntu, with just the message "...data transfer failed", better shutdown time too. But, no way to use usb storage medias. In Debian, it ends with BusyBox prompt. Is it possible to just disable that Alcor card reader? Does it have a specific module? Is there a special kernel boot option that I missed? Does it have something to do with kernel recompiling, and if yes, how to do with isos? Programming a driver which says everything is ok (out of my comprehension for the moment)? Disabling device by vendor id? What is the best way?

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• CLOSE_WAIT sockets burst - perhaps because of iptables settings?

  - by Fabrizio Giudici

  I have an Ubuntu 12.04 server virtual box where basically the installed software and configuration are the default ones, plus the installation of a jetty 6 server which servers a few websites. To keep things simple I didn't install apache httpd and used iptables for exposing jetty (which runs on the 8080 port) to the port 80. These are the results of /sbin/iptables -t nat -L Chain PREROUTING (policy ACCEPT) target prot opt source destination REDIRECT tcp -- anywhere localhost tcp dpt:http redir ports 8080 REDIRECT tcp -- anywhere Ubuntu-1104-natty-64-minimal tcp dpt:http redir ports 8080 Chain INPUT (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination REDIRECT tcp -- anywhere localhost tcp dpt:http redir ports 8080 REDIRECT tcp -- anywhere Ubuntu-1104-natty-64-minimal tcp dpt:http redir ports 8080 Chain POSTROUTING (policy ACCEPT) target prot opt source destination I must confess I have a shallow comprehension of how iptables works, in particular for the different kind of chains. This thing works, but sometimes I have an explosion of sockets that stay permanently in CLOSE_WAIT state. I know about what this state means, but since I didn't write the code that manages servlets (they are handled by jetty) I can't fix the problem by patching my code. Eventually the amount of CLOSE_WAIT sockets builds up and makes the server not responsive, so I have to restart jetty. I've looked around for similar problems wth CLOSE_WAIT, and only found cases related to the programmer's code, or problems with Tomcat, not Jetty. I was wondering whether they could be related to a partially broken iptables configuration (the alternative is a bug in Jetty 6, but I first want to exclude other possible causes). Thanks.

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• Will Windows repair my multi-boot when I format the 1st physical partition with boot sector?

  - by user2353806

  Due to historical reasons I got a laptop with Vista, Windows 7 and Windows Server 2008R2 partitions. (boot from external wasn´t that viable) Nothing (Windows Repair, bootrec /whateveroption) worked when I restored only the Windows 7 and WS2k8 with Acronis TrueImage. Don´t ask me through what idiotic error messages I went during repair tries. (Wrong Windows version,...) So I grudgingly restored all three - with the little additional excursion that I thought changing the active partition to the Windows 7 partition would move the boot sector and let me format the Vista part... Oh no. Seems too logical for MS. (Dunno what I changed, but today it will let me format!) So the real question is: Will formatting the Vista part trash things again beyond comprehension or will Windows Repair bring back the boot rec and remove Vista from the boot options? Or should I just erase all the files to avoid trashing the boot? Where will the boot rec be (after repair) when I format the Vista? On 1st or 2nd partition? And if I get drunk and install Windows 8.1 on the 1st, will anything work? ;-) Thanks

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• Application Performance: The Best of the Web

  - by Michaela Murray

  Wisdom A deep understanding and realization […] resulting in the ability to apply perceptions, judgements and actions. It is also the comprehension of what is true coupled with optimum judgment as to action. - Wikipedia We’re writing a book for ASP.NET developers, and we want you to be a part of it. We know that there’s a huge amount of web developer wisdom that never gets shared, and we want to find those golden nuggets of knowledge and experience, and make sure everyone can learn from them. Right now, we want to find out about your top tips, hard-won lessons, and sage advice for avoiding, finding, and fixing application performance problems. If you work with .NET and SQL, even better – a lot of application performance relies on the interaction with the database, so we want to hear from you! “How Do You Want Me To Be Involved?” Right! Details! We want you, our most excellent readers, to email us with the Best Advice you would give to other developers for getting the best performance out of their applications. It doesn’t matter if your advice is for newbies or veterans, .NET or SQL – so long as it’s about application performance, we want to hear from you. (And if you think that there’s developer wisdom out there that “everyone knows”, a) I’m willing to bet you could find someone who doesn’t know about it, and b) it probably bears repeating anyway!) “I’m Interested. What Can You Do For Me?” Excellent question. For starters, there’s a chance to win a Microsoft Surface (the tablet, not the table-top). Once all the ASP.NET Wisdom has been collected, tallied, and labelled, it will then be weighed and measured by a team of expert judges (whose identities are still a closely-guarded secret).  The top tip in both SQL & .NET categories will each win their author their very own MS Surface. But that’s not all! We can also give you… immortality! More details? Ok. We’ll be collecting all of the tips sent in by our readers (and we can’t wait to learn from you all,) and with the help of our Simple-Talk editors, we will publish and distribute your combined and documented knowledge as a free, community-created, professionally typeset eBook. You will naturally be credited by name / pseudonym / twitter handle / GitHub username / StackOverflow profile / Whatever, as the clearly ingenious author of hot performance tips. The Not-Very-Fine Print Here’s the breakdown: We want to bring together the best application performance knowledge from ASP.NET developers. Closing date for submissions will be 9am GMT, December 4th. Submissions should be made by email – [email protected] Submissions will be judged by a panel of expert judges (who will be revealed soon). The top submission in both the SQL & .NET categories will each win a Microsoft Surface. ALL the tips which make it through the judging process will be polished by Simple-Talk editors, and turned into a professionally typeset eBook, which will be freely available, and promoted alongside the ANTS Performance Profiler tool. Anyone whose entry makes it into the book will be clearly and profusely credited in the method of their choice (or can remain anonymous.) The really REALLY short version Share what you know about ASP.NET application performance for a chance to win a Microsoft Surface, and then get your name credited in a slick eBook with top-notch production values. For more details, see above. We can’t wait to learn from you!

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• Questions to ask to ensure someone understands programming? (and iOS)

  - by Stephen J

  So, I've been tutoring my friend for 2 years. Most people learn programming on their own in 3-6 months, (sans algorithms). It's confusing 'cause he'll run anywhere I tell him to, understands how to read C and C++ honestly better than the average college student, and he'll modify and repeat anything I do... but for the love of god he doesn't move on to new things and he still has test anxiety. I've recently realized he's copied and toyed with existing, but not once gained an understanding of why. I was under the impression he was learning fast because he could write it, but when you say "Make a function that takes an NSString" and he says "How?" and I say "The same way you make ANY function that takes any parameter, NSString is just a type like int" and all I hear is "No, it's an NSString, it's a special thing." and we get into an arguing match 'cause I'm like "It's just a class like any other class, you've used them for months now" and blah... I've subconsciously avoided comprehension questions because of this. Anyway, if you have him copy a program and say "Just initialize it" "Where?" "I don't care, didLoad or initWithCoder or Awake from nib, anywhere it gets initialized" and "No, it has to be exactly where you had it!" "No it doesn't!" I'm sick of this, but he won't give up. So I'm done avoiding these yelling matches and becoming a sadist from now on. I would like some help in finding questions to ask him that force him to understand what he's doing. I'd like some help and any resources I can find. CQuestions looked like a good site, but now I need some iPhone stuff. For example: *What do properties do? How are they changed? How do you change the name of the getter? *Why are Booleans inefficent? What advantage does int have over a boolean and how does the bit-shift operator help? *What does Copy do to a string? *What's the difference between a view controller and a uiview? *Write a program from memory that displays blah on screen, and flashes each view one by one. From beginner up to intermediate, hobbyist with some algebra at most. I'm just looking for resources to work with. I left in backstory so you know to "twist" the questions so he doesn't know he's supposed to init a variable here or there, but has to figure it out, and learn why it goes "here" or that "anywhere is fine as long as it's". Sample programs, anything. I'm relatively open about this because, being a programmer, I seriously doubt he's the only one who has this issue. I'd like to know how others have overcome similar. What made things "click"? for you? Did you have a hard time finding answers on Google, and how did you learn a better way to find what you were looking for? (He's so exact, he'll search for how to write a checkers program with color X and Y inside a uiview, as his search string, instead of breaking it up into components, I need help with that too, and believe it is related). This type of problem has to remind one of us of someone they know. So, Exercises to force them to think? Ways we overcame this thing in the past? I greatly appreciate any help.

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