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  • Infix to Postfix and unary/binary operators

    - by Jaapjan
    I have a piece of code that converts an infix expression to an expression tree in memory. This works just fine. There's just one small trouble. I just connect work out how to involve the unary operators correctly (the right associative ones). With the following infix expression : +1 + +2 - -3 - -4 I would expect an RPN of: 1+2++3-4-- Yet, none of the online infix-post converters I can find handle this example in the way I would expect. Does anyone have a clear explanation of handling right associative operators, specifically the binary ones that can be mistaken for the unary ones?

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  • What is the single most effective thing you did to improve your programming skills?

    - by Oded
    Looking back at my career and life as a programmer, there were plenty of different ways I improved my programming skills - reading code, writing code, reading books, listening to podcasts, watching screencasts and more. My question is: What is the most effective thing you have done that improved your programming skills? What would you recommend to others that want to improve? I do expect varied answers here and no single "one size fits all" answer - I would like to know what worked for different people. Edit: Wow - what great answers! Keep 'em coming people!!!

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  • Well written Perl Open Source to learn from ?

    - by Prix
    Hi, is there any well written perl open source out there (not using any kinda of framework) that i could use as sample for learning and good pratice of the perl... I've searched around and found many things for PHP, but nothing in perl that uses no framework. Thanks in advance.

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  • Blackberry - application settings save/load

    - by Max Gontar
    Hi! I know two ways to save/load application settings: use PersistentStore use filesystem (store, since SDCard is optional) I'd like to know what are you're practicies of working with application settings? Using PersistentStore to save/load application settings The persistent store provides a means for objects to persist across device resets. A persistent object consists of a key-value pair. When a persistent object is committed to the persistent store, that object's value is stored in flash memory via a deep copy. The value can then be retrieved at a later point in time via the key. Example of helper class for storing and retrieving settings: class PSOptions { private PersistentObject mStore; private LongHashtableCollection mSettings; private long KEY_URL = 0; private long KEY_ENCRYPT = 1; private long KEY_REFRESH_PERIOD = 2; public PSOptions() { // "AppSettings" = 0x71f1f00b95850cfeL mStore = PersistentStore.getPersistentObject(0x71f1f00b95850cfeL); } public String getUrl() { Object result = get(KEY_URL); return (null != result) ? (String) result : null; } public void setUrl(String url) { set(KEY_URL, url); } public boolean getEncrypt() { Object result = get(KEY_ENCRYPT); return (null != result) ? ((Boolean) result).booleanValue() : false; } public void setEncrypt(boolean encrypt) { set(KEY_ENCRYPT, new Boolean(encrypt)); } public int getRefreshPeriod() { Object result = get(KEY_REFRESH_PERIOD); return (null != result) ? ((Integer) result).intValue() : -1; } public void setRefreshRate(int refreshRate) { set(KEY_REFRESH_PERIOD, new Integer(refreshRate)); } private void set(long key, Object value) { synchronized (mStore) { mSettings = (LongHashtableCollection) mStore.getContents(); if (null == mSettings) { mSettings = new LongHashtableCollection(); } mSettings.put(key, value); mStore.setContents(mSettings); mStore.commit(); } } private Object get(long key) { synchronized (mStore) { mSettings = (LongHashtableCollection) mStore.getContents(); if (null != mSettings && mSettings.size() != 0) { return mSettings.get(key); } else { return null; } } } } Example of use: class Scr extends MainScreen implements FieldChangeListener { PSOptions mOptions = new PSOptions(); BasicEditField mUrl = new BasicEditField("Url:", "http://stackoverflow.com/"); CheckboxField mEncrypt = new CheckboxField("Enable encrypt", false); GaugeField mRefresh = new GaugeField("Refresh period", 1, 60 * 10, 10, GaugeField.EDITABLE|FOCUSABLE); ButtonField mLoad = new ButtonField("Load settings", ButtonField.CONSUME_CLICK); ButtonField mSave = new ButtonField("Save settings", ButtonField.CONSUME_CLICK); public Scr() { add(mUrl); mUrl.setChangeListener(this); add(mEncrypt); mEncrypt.setChangeListener(this); add(mRefresh); mRefresh.setChangeListener(this); HorizontalFieldManager hfm = new HorizontalFieldManager(USE_ALL_WIDTH); add(hfm); hfm.add(mLoad); mLoad.setChangeListener(this); hfm.add(mSave); mSave.setChangeListener(this); loadSettings(); } public void fieldChanged(Field field, int context) { if (field == mLoad) { loadSettings(); } else if (field == mSave) { saveSettings(); } } private void saveSettings() { mOptions.setUrl(mUrl.getText()); mOptions.setEncrypt(mEncrypt.getChecked()); mOptions.setRefreshRate(mRefresh.getValue()); } private void loadSettings() { mUrl.setText(mOptions.getUrl()); mEncrypt.setChecked(mOptions.getEncrypt()); mRefresh.setValue(mOptions.getRefreshPeriod()); } }

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  • collision with moving objects

    - by blacksheep
    tried to write a collision with the moving "floats" but did not succeed. maybe wrong place of the "collision" code? thanx 4 help! // // FruitsView.m // import "FruitsView.h" import "Constants.h" import "Utilities.h" define kFloat1Speed 0.15 define kFloat2Speed 0.3 define kFloat3Speed 0.2 @interface FruitsView (Private) - (void) stopTimer; @end @implementation FruitsView @synthesize apple, float1, float2, float3, posFloat1, posFloat2, posFloat3; -(void)onTimer { float1.center = CGPointMake(float1.center.x+posFloat1.x,float1.cen ter.y+posFloat1.y); if(float1.center.x 380 || float1.center.x < -60) posFloat1.x = -posFloat1.x; if(float1.center.y 100 || float1.center.y < -40) posFloat1.y = -posFloat1.y; float2.center = CGPointMake(float2.center.x+posFloat2.x,float2.cen ter.y+posFloat2.y); if(float2.center.x 380 || float2.center.x < -50) posFloat2.x = -posFloat2.x; if(float2.center.y 150 || float2.center.y < -30) posFloat2.y = -posFloat2.y; float3.center = CGPointMake(float3.center.x+posFloat3.x,float3.cen ter.y+posFloat3.y); if(float3.center.x 380 || float3.center.x < -70) posFloat3.x = -posFloat3.x; if(float3.center.y 100 || float3.center.y < -20) posFloat3.y = -posFloat3.y; if(CGRectIntersectsRect(apple.frame,float1.frame)) { if(apple.center.y float1.center.y) { posApple.y = -posApple.y; } } if(CGRectIntersectsRect(apple.frame,float2.frame)) { if(apple.center.y float2.center.y) { posFloat2.y = -posFloat2.y; } } if(CGRectIntersectsRect(apple.frame,float3.frame)) { if(apple.center.y float3.center.y) { posFloat3.y = -posFloat3.y; } } } pragma mark Initialisation/destruction (void)awakeFromNib { [NSTimer scheduledTimerWithTimeInterval:0.0001 target:self selector:@selector(onTimer) userInfo:nil repeats:YES]; posFloat1 = CGPointMake(kFloat1Speed, 0); posFloat2 = CGPointMake(kFloat2Speed, 0); posFloat3 = CGPointMake(kFloat3Speed, 0); timer = nil; modeLock = lockNotYetChosen; defaultSize = self.bounds.size.width; modal = self.tag; [[UIAccelerometer sharedAccelerometer] setDelegate:self]; [UIView beginAnimations:nil context:nil]; [UIView setAnimationRepeatCount:1]; eadbea.transform = CGAffineTransformMakeScale(0.5,0.5); [UIView commitAnimations]; [UIView beginAnimations:nil context:nil]; [UIView setAnimationRepeatCount:1]; apple.transform = CGAffineTransformMakeScale(0.5,0.5); [UIView commitAnimations]; } pragma mark Background animation processing (void) startTimer { if (!timer) { timer = [[NSTimer scheduledTimerWithTimeInterval:1.0/60.0 target:self selector:@selector(timerTick:) userInfo:nil repeats:YES] retain]; } } (void) stopTimer { [timer invalidate]; [timer release]; timer = nil; } (void) check:(CGPoint*)position delta:(CGSize*)delta halfSize:(CGSize)halfSize forBouncingAgainst:(CGSize)containerSize { if ((position-x - halfSize.width)<0) { delta-width = fabsf(delta-width)*BOUNCE_DAMPING; position-x = halfSize.width; } if ((position-x + halfSize.width)containerSize.width) { delta-width = fabsf(delta-width)*-BOUNCE_DAMPING; position-x = containerSize.width - halfSize.width; } if ((position-y - halfSize.height)<0) { delta-height = fabsf(delta-height)*BOUNCE_DAMPING; position-y = halfSize.height; } if ((position-y + halfSize.height)containerSize.height) { delta-height = fabsf(delta-height)*-BOUNCE_DAMPING; position-y = containerSize.height - halfSize.height; } } (void) timerTick: (NSTimer*)timer { dragDelta = CGSizeScale(dragDelta, INERTIAL_DAMPING); if ((fabsf(dragDelta.width)DELTA_ZERO_THRESHOLD) || (fabsf(dragDelta.height)DELTA_ZERO_THRESHOLD)) { CGPoint ctr = CGPointApplyDelta(self.center, dragDelta); CGSize halfSize = CGSizeMake(self.bounds.size.width/4, self.bounds.size.height/4); [self check:&ctr delta:&dragDelta halfSize:halfSize forBouncingAgainst:self.superview.bounds.size]; self.center = ctr; } else { [self stopTimer]; } } pragma mark Input Handling (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent )event { NSSet allTouches = [event touchesForView:self]; if ([allTouches count]==1) { if (modeLocklockNotYetChosen) return; UITouch* anyTouch = [touches anyObject]; lastMove = anyTouch.timestamp; CGPoint now = [anyTouch locationInView: self.superview]; CGPoint then = [anyTouch previousLocationInView: self.superview]; dragDelta = CGPointDelta(now, then); self.center = CGPointApplyDelta(self.center, dragDelta); [self stopTimer]; } } (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { NSSet* allTouches = [event touchesForView:self]; if ([touches count]==[allTouches count]) { modeLock = lockNotYetChosen; if ((event.timestamp - lastMove) MOVEMENT_PAUSE_THRESHOLD) return; if ((fabsf(dragDelta.width)INERTIA_THRESHOLD) || (fabsf(dragDelta.height)INERTIA_THRESHOLD)) { [self startTimer]; } } } (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event { modeLock = lockNotYetChosen; [self stopTimer]; } (void)dealloc { [float1 release]; [float2 release]; [float3 release]; [apple release]; [bear_head release]; [self stopTimer]; [super dealloc]; } @end

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  • What skills are needed to be successful at robotics?

    - by Click Upvote
    I'm considering studying to be a robotics engineer. The desire to work in that field is definitely there.. but I'm wondering what my chances of success would be. Generally I'm good with mental tasks of any sort such as programming, maths, physics, etc, and I think i'd be able to do electrical work such as soldering wires, changing batteries, etc. However, I'm not so good with things of a physical nature where I have to use my hands. For example, if you give me some vegetables to slice and dice, all of them will be diced un-evenly and some will look ugly. This might be because I have poor mind-hand coordination or because of a lack of concentration. Thoughts?

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  • Is Programming Right for me?

    - by L1th1um
    I'm interested in programming, but it seems to me that I can't get into it. Every time I've tried to learn a language and stuff by looking through tutorials or books I'd never get past the part where I use the syntax to make something. And by interest, I mean that I read stack overflow a lot, coding horror, and stuff but the actual coding part is hard for me to get into. Did anybody start this way? How did you get past this block?

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  • Clientside going serverside with node.js

    - by Sveisvei
    Hello, I`ve been looking for a serverside language for some time, and python got my attention somewhat. But as I already know and love javascript, I now want learn to code on the server with js and node.js. Now, what books and what subjects do I need to learn to understand the serverside world better? (let me know if Im to vague)

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  • How can I learn to set up a build process?

    - by Satoru.Logic
    Hi, all. What I was taught at school is all about programming languages, software design, but hardly anything about how to automatically build a software, probably with unit testing integrated. Please tell me how do one start learning to set up a build process for his project.

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  • How do you beat procrastination?

    - by Armentia
    I have had horrible procrastination habits since gradeschool, and now that I'm in college, I still am having a hard time beating this bad habit. I find myself easily distracted from doing real "work" and find myself wandering off doing something else that I enjoy more. Tell me how you personally beat procrastination; or share your struggles.

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  • Coding for fun

    - by Klelky
    I would describe myself as a career coder - i.e. a developer at work but never really coded for fun. Early in my career I've hit the management track though. I really like my current job and can't see me going back to coding anytime soon so: Whats the best way to develop my coding skills and learn new languages in my spare time?

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  • Hobbies/Careers that complement programming

    - by Cherian
    Do you cultivate an alternative career/hobby which complements or refreshes your primary role as a developer? If so, what is it and why? Also see these related questions: If you weren't a programmer what would you be doing How do you vent stress as a programmer? What are some exercises you do to make you a better programmer? How do you reward yourself when you've overcome a monster task

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  • What is this particular type of revelation called?

    - by Lars Haugseth
    After struggling with a particular problem or bug in some part of my code for hours, without getting anywhere, I often get a sudden revelation as soon as I try to explain the problem to one of my coworkers, or while formulating it in writing for posting to some forum. Does this kind of experience have a name? Where can I read more about it and how to train it? Do any of you use this consciously in your day-to-day work?

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  • Asymptotic runtime of list-to-tree function

    - by Deestan
    I have a merge function which takes time O(log n) to combine two trees into one, and a listToTree function which converts an initial list of elements to singleton trees and repeatedly calls merge on each successive pair of trees until only one tree remains. Function signatures and relevant implementations are as follows: merge :: Tree a -> Tree a -> Tree a --// O(log n) where n is size of input trees singleton :: a -> Tree a --// O(1) empty :: Tree a --// O(1) listToTree :: [a] -> Tree a --// Supposedly O(n) listToTree = listToTreeR . (map singleton) listToTreeR :: [Tree a] -> Tree a listToTreeR [] = empty listToTreeR (x:[]) = x listToTreeR xs = listToTreeR (mergePairs xs) mergePairs :: [Tree a] -> [Tree a] mergePairs [] = [] mergePairs (x:[]) = [x] mergePairs (x:y:xs) = merge x y : mergePairs xs This is a slightly simplified version of exercise 3.3 in Purely Functional Data Structures by Chris Okasaki. According to the exercise, I shall now show that listToTree takes O(n) time. Which I can't. :-( There are trivially ceil(log n) recursive calls to listToTreeR, meaning ceil(log n) calls to mergePairs. The running time of mergePairs is dependent on the length of the list, and the sizes of the trees. The length of the list is 2^h-1, and the sizes of the trees are log(n/(2^h)), where h=log n is the first recursive step, and h=1 is the last recursive step. Each call to mergePairs thus takes time (2^h-1) * log(n/(2^h)) I'm having trouble taking this analysis any further. Can anyone give me a hint in the right direction?

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  • What should a conference newbie bring to make the most out of their first conference?

    - by skarnis
    I am planning to attend my first developer conference (Microsoft TechDays 2008 in Toronto). I have been looking around for suggestions so that I can prepare and make the most out of my first developer conference. Many articles make suggestions about asking questions, getting involved, being social. These are great! I am also wondering about physical items. I have seen many conference photos with most of the audience having their laptops. Are they just taking notes? Are they working on a problem during the session? Are these photos just during a break and everyone is catching up on blogs/email/outside contact? Thank you StackOverflow-ers (StackOverflow-ites?)

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  • Learning a new language coding 1 program

    - by Steve
    This is not really a programming question Question : Sometimes you have to learn a new language consider this situation for example : you have been programming in C# for some years and then one day you need to code in java. Now being a programmer you already know the programming concepts its just the syntax you need to get used to. Can you think some program to code which covers every(or most) aspect of a programming language? like say you make a desktop search program...it can cover file reading writing, threads maybe interacting with db like sqllite so you get familiar with those topics and the syntax of the new language Just want to know your thoughts about what is the fastest way to go about learning a new language skipping all the basic stuff

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  • Improve my Haskell implementation of Filter

    - by mvid
    I have recently been teaching myself Haskell, and one of my exercises was to re-implement the filter function. However, of all the exercises I have performed, my answer for this one seems to me the most ugly and long. How could I improve it? Are there any Haskell tricks I don't yet know? myfilter :: (a -> Bool) -> [a] -> [a] myfilter f (x:xs) = if f x then x : myfilter f xs else myfilter f xs myfilter _ [] = [] Thank You

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  • what is this 'content_type' mean..

    - by zjm1126
    content_type = ContentType.objects.get_for_model(Map) maps = maps.extra(select=SortedDict([ ('member_count', MEMBER_COUNT_SQL), ('topic_count', TOPIC_COUNT_SQL), ]), select_params=(content_type.id,)) and the ContentType is: class ContentType(models.Model): name = models.CharField(max_length=100) app_label = models.CharField(max_length=100) model = models.CharField(_('python model class name'), max_length=100) objects = ContentTypeManager() class Meta: verbose_name = _('content type') verbose_name_plural = _('content types') db_table = 'django_content_type' ordering = ('name',) unique_together = (('app_label', 'model'),) def __unicode__(self): return self.name def model_class(self): "Returns the Python model class for this type of content." from django.db import models return models.get_model(self.app_label, self.model) def get_object_for_this_type(self, **kwargs): """ Returns an object of this type for the keyword arguments given. Basically, this is a proxy around this object_type's get_object() model method. The ObjectNotExist exception, if thrown, will not be caught, so code that calls this method should catch it. """ return self.model_class()._default_manager.using(self._state.db).get(**kwargs) def natural_key(self): return (self.app_label, self.model) i want to know: what is the 'content_type' used for ??

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  • What are the lesser known but cool data structures ?

    - by f3lix
    There a some data structures around that are really cool but are unknown to most programmers. Which are they? Everybody knows linked lists, binary trees, and hashes, but what about Skip lists, Bloom filters for example. I would like to know more data structures that are not so common, but are worth knowing because they rely on great ideas and enrich a programmer's tool box. PS: I am also interested on techniques like Dancing links which make interesting use of the properties of a common data structure. EDIT: Please try to include links to pages describing the data structures in more detail. Also, try to add a couple of words on why a data structures is cool (as Jonas Kölker already pointed out). Also, try to provide one data-structure per answer. This will allow the better data structures to float to the top based on their votes alone.

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  • Custom login in Django

    - by alpgs
    Django newbie here. I wrote simplified login form which takes email and password. It works great if both email and password are supplied, but if either is missing i get KeyError exception. According to django documentation this should never happen: By default, each Field class assumes the value is required, so if you pass an empty value -- either None or the empty string ("") -- then clean() will raise a ValidationError exception I tried to write my own validators for fields (clean_email and clean_password), but it doesn't work (ie I get KeyError exception). What am I doing wrong? class LoginForm(forms.Form): email = forms.EmailField(label=_(u'Your email')) password = forms.CharField(widget=forms.PasswordInput, label=_(u'Password')) def clean_email(self): data = self.cleaned_data['email'] if not data: raise forms.ValidationError(_("Please enter email")) return data def clean_password(self): data = self.cleaned_data['password'] if not data: raise forms.ValidationError(_("Please enter your password")) return data def clean(self): try: username = User.objects.get(email__iexact=self.cleaned_data['email']).username except User.DoesNotExist: raise forms.ValidationError(_("No such email registered")) password = self.cleaned_data['password'] self.user = auth.authenticate(username=username, password=password) if self.user is None or not self.user.is_active: raise forms.ValidationError(_("Email or password is incorrect")) return self.cleaned_data

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  • Could I be writing this code better?

    - by Ben Dauphinee
    Is there any website out there somewhere where a programmer such as myself might be able to post pieces of code to be looked at by more experienced people? I am thinking of something that programmers could use to have advice given on how to improve their ability. I really like the atmosphere here, but am not sure that posting code for review here is appropriate.

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  • How to learn Haskell

    - by anderstornvig
    For a few days I've tried to wrap my head around the functional programming paradigm in Haskell. I've done this by reading tutorials and watching screencasts, but nothing really seems to stick. Now, in learning various imperative/OO languages (like C, Java, PHP), excercises have been a good way for me to go. But since I don't really know what Haskell is capable of and because there are many new concepts to utilize, I haven't known where to start. So, how did you learn Haskell? What made you really "break the ice"? Also, any good ideas for beginning excercises?

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