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• C vs C++ function questions

  - by james

  I am learning C, and after starting out learning C++ as my first compiled language, I decided to "go back to basics" and learn C. There are two questions that I have concerning the ways each language deals with functions. Firstly, why does C "not care" about the scope that functions are defined in, whereas C++ does? For example, int main() { donothing(); return 0; } void donothing() { } the above will not compile in a C++ compiler, whereas it will compile in a C compiler. Why is this? Isn't C++ mostly just an extension on C, and should be mostly "backward compatible"? Secondly, the book that I found (Link to pdf) does not seem to state a return type for the main function. I check around and found other books and websites and these also commonly do not specify return types for the main function. If I try to compile a program that does not specify a return type for main, it compiles fine (although with some warnings) in a C compiler, but it doesn't compile in a C++ compiler. Again, why is that? Is it better style to always specify the return type as an integer rather than leaving it out? Thanks for any help, and just as a side note, if anyone can suggest a better book that I should buy that would be great!

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• Fastest method to define whether a number is a triangular number

  - by psihodelia

  A triangular number is the sum of the n natural numbers from 1 to n. What is the fastest method to find whether a given positive integer number is a triangular one? I suppose, there must be a hidden pattern in a binary representation of such numbers (like if you need to find whether a number is even/odd you check its least significant bit). Here is a cut of the first 1200th up to 1300th triangular numbers, you can easily see a bit-pattern here (if not, try to zoom out): (720600, '10101111111011011000') (721801, '10110000001110001001') (723003, '10110000100000111011') (724206, '10110000110011101110') (725410, '10110001000110100010') (726615, '10110001011001010111') (727821, '10110001101100001101') (729028, '10110001111111000100') (730236, '10110010010001111100') (731445, '10110010100100110101') (732655, '10110010110111101111') (733866, '10110011001010101010') (735078, '10110011011101100110') (736291, '10110011110000100011') (737505, '10110100000011100001') (738720, '10110100010110100000') (739936, '10110100101001100000') (741153, '10110100111100100001') (742371, '10110101001111100011') (743590, '10110101100010100110') (744810, '10110101110101101010') (746031, '10110110001000101111') (747253, '10110110011011110101') (748476, '10110110101110111100') (749700, '10110111000010000100') (750925, '10110111010101001101') (752151, '10110111101000010111') (753378, '10110111111011100010') (754606, '10111000001110101110') (755835, '10111000100001111011') (757065, '10111000110101001001') (758296, '10111001001000011000') (759528, '10111001011011101000') (760761, '10111001101110111001') (761995, '10111010000010001011') (763230, '10111010010101011110') (764466, '10111010101000110010') (765703, '10111010111100000111') (766941, '10111011001111011101') (768180, '10111011100010110100') (769420, '10111011110110001100') (770661, '10111100001001100101') (771903, '10111100011100111111') (773146, '10111100110000011010') (774390, '10111101000011110110') (775635, '10111101010111010011') (776881, '10111101101010110001') (778128, '10111101111110010000') (779376, '10111110010001110000') (780625, '10111110100101010001') (781875, '10111110111000110011') (783126, '10111111001100010110') (784378, '10111111011111111010') (785631, '10111111110011011111') (786885, '11000000000111000101') (788140, '11000000011010101100') (789396, '11000000101110010100') (790653, '11000001000001111101') (791911, '11000001010101100111') (793170, '11000001101001010010') (794430, '11000001111100111110') (795691, '11000010010000101011') (796953, '11000010100100011001') (798216, '11000010111000001000') (799480, '11000011001011111000') (800745, '11000011011111101001') (802011, '11000011110011011011') (803278, '11000100000111001110') (804546, '11000100011011000010') (805815, '11000100101110110111') (807085, '11000101000010101101') (808356, '11000101010110100100') (809628, '11000101101010011100') (810901, '11000101111110010101') (812175, '11000110010010001111') (813450, '11000110100110001010') (814726, '11000110111010000110') (816003, '11000111001110000011') (817281, '11000111100010000001') (818560, '11000111110110000000') (819840, '11001000001010000000') (821121, '11001000011110000001') (822403, '11001000110010000011') (823686, '11001001000110000110') (824970, '11001001011010001010') (826255, '11001001101110001111') (827541, '11001010000010010101') (828828, '11001010010110011100') (830116, '11001010101010100100') (831405, '11001010111110101101') (832695, '11001011010010110111') (833986, '11001011100111000010') (835278, '11001011111011001110') (836571, '11001100001111011011') (837865, '11001100100011101001') (839160, '11001100110111111000') (840456, '11001101001100001000') (841753, '11001101100000011001') (843051, '11001101110100101011') (844350, '11001110001000111110') For example, can you also see a rotated normal distribution curve, represented by zeros between 807085 and 831405?

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• jquery: i have to use parseInt() even when deal with numbers, why?

  - by Syom

  i have the following script <select id="select1"> <option value="1">1day</option> <option value="2">2day</option> <option value="3">3day</option> </select> <select id="select2"> <option value="1">1day</option> <option value="2">2day</option> <option value="3">3day</option> </select> and jquery $("#select2").change(function() { var max_value = parseInt($("#select2 :selected").val()); var min_value = parseInt($("#select1 :selected").val()); if(max_value < min_value) { $("#select1").val($(this).val()); } }); and now, what i can't understand anyway - if values of option elements are integer numbers, why i have to use parseInt()? in some cases it doesn't work without parseInt(). Thanks

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• syntax for MySQL INSERT with an array of columns

  - by Mike_Laird

  I'm new to PHP and MySQL query construction. I have a processor for a large form. A few fields are required, most fields are user optional. In my case, the HTML ids and the MySQL column names are identical. I've found tutorials about using arrays to convert $_POST into the fields and values for INSERT INTO, but I can't get them working - after many hours. I've stepped back to make a very simple INSERT using arrays and variables, but I'm still stumped. The following line works and INSERTs 5 items into a database with over 100 columns. The first 4 items are strings, the 5th item, monthlyRental is an integer. $query = "INSERT INTO `$table` (country, stateProvince, city3, city3Geocode, monthlyRental) VALUES ( '$country', '$stateProvince', '$city3', '$city3Geocode', '$monthlyRental')"; When I make an array for the fields and use it, as follows: $colsx = array('country,', 'stateProvince,', 'city3,', 'city3Geocode,', 'monthlyRental'); $query = "INSERT INTO `$table` ('$colsx') VALUES ( '$country', '$stateProvince', '$city3', '$city3Geocode', '$monthlyRental')"; I get a MySQL error - check the manual that corresponds to your MySQL server version for the right syntax to use near ''Array') VALUES ( 'US', 'New York', 'Fairport, Monroe County, New York', '(43.09)' at line 1. I get this error whether the array items have commas inside the single quotes or not. I've done a lot of reading and tried many combinations and I can't get it. I want to see the proper syntax on a small scale before I go back to foreach expressions to process $_POST and both the fields and values are arrays. And yes, I know I should use mysql_real_escape_string, but that is an easy later step in the foreach. Lastly, some clues about the syntax for an array of values would be helpful, particularly if it is different from the fields array. I know I need to add a null as the first array item to trigger the MySQL autoincrement id. What else? I'm pretty new, so please be specific.

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• What's up with this reversing bit order function?

  - by MattyW

  I'm rather ashamed to admit that I don't know as much about bits and bit manipulation as I probably should. I tried to fix that this weekend by writing some 'reverse the order of bits' and 'count the ON bits' functions. I took an example from here but when I implemented it as below, I found I had to be looping while < 29. If I loop while < 32 (as in the example) Then when I try to print the integer (using a printBits function i've written) I seem to be missing the first 3 bits. This makes no sense to me, can someone help me out? int reverse(int n) { int r = 0; int i = 0; for(i = 0; i < 29; i++) { r = (r << 1) + (n & 1); n >>=1; } return r; }

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• how to count multiples of numbers in an input file?

  - by user292489

  i was trying to count the number of multiples of 2, 3, and 6 respectielly from the users input file. but for some reason, my counter is not working. can any bosy hep me please. my code: #include <stdio.h> int main (void) { int num[12]; int i; int counttwo; int countthree; int countsix; int total=0; printf("enter 12 integer numbers:\n"); for(i=0;i<12;i++){ scanf("%d", &num[i]); } for(i=0;i<12;i++){ counttwo=0; if(num[i]%2==0){ counttwo++; } countthree=0; if(num[i]%3==0) { countthree++; } countsix=0; if(num[i]%6==0) { countsix++; } printf("There are %d multiples of 2:\n", counttwo); printf("There are %d multiples of 3:\n", countthree); printf("There are %d multiples of 6:\n", countsix); } return 0; }

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• Scientific Data processing (Graph comparison and interpretation)

  - by pinkynobrain

  Hi stackoverflow friends, I'm trying to write a program to automate one of my more boring and repetitive work tasks. I have some programming experience but none with processing or interpreting large volumes of data so I am seeking your advice (both suggestions of techniques to try and also things to read to learn more about doing this stuff). I have a piece of equipment that monitors an experiment by taking repeated samples and displays the readings on its screen as a graph. The input of experiment can be altered and one of these changes should produce a change in a section of the graph which I currently identify by eye and is what I'm looking for in the experiment. I want to automate it so that a computer looks at a set of results and spots the experiment input that causes the change. I can already extract the results from the machine. Currently they results for a run are in the form of an integer array with the index being the sample number and the corresponding value being the measurement. The overall shape of the graph will be similar for each experiment run. The change I'm looking for will be roughly the same and will occur in approximately the same place every time for the correct experiment input. Unfortunately there are a few gotchas that make this problem more difficult. There is some noise in the measuring process which mean there is some random variation in the measured values between different runs. Although the overall shape of the graph remains the same. The time the experiment takes varies slightly each run causing two effects. First, the a whole graph may be shifted slightly on the x axis relative to another run's graph. Second, individual features may appear slightly wider or narrower in different runs. In both these cases the variation isn't particularly large and you can assume that the only non random variation is caused by the correct input being found. Thank you for your time, Pinky

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• How to get java singleton object manager to return any type of object?

  - by Robert

  I'm writing an interactive fiction game in java from scratch. I'm currently storing all of my game object references in a hashmap in a singleton called ObjectManager. ObjectManager has a function called get which takes an integer ID and returns the appropriate reference. The problem is that it returns a BaseObject when I need to return subclasses of BaseObject with more functionality. So, what I've done so far is I've added a getEntity function which returns BaseEntity (which is a subclass of BaseObject). However, when I need the function to return to an object that is a subclass of BaseEntity that has added, required functionality, I will need to make another function. I know there is a better way, but I don't know what it is. I know very little of design patterns, and I'm not sure which one to use here. I tried passing 'class' as a parameter, but that didn't get me anywhere. public BaseObject get(int ID){ return (BaseObject)refMap.get(ID); } public BaseEntity getEntity(int ID){ return (BaseEntity)refMap.get(ID); } Thanks, java ninjas!

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• OutOfMemoryError creating a tree recursively?

  - by Alexander Khaos Greenstein

  root = new TreeNode(N); constructTree(N, root); private void constructTree(int N, TreeNode node) { if (N > 0) { node.setLeft(new TreeNode(N-1)); constructTree(N-1, node.getLeft()); } if (N > 1) { node.setMiddle(new TreeNode(N-2)); constructTree(N-2, node.getMiddle()); } if (N > 2) { node.setRight(new TreeNode(N-3)); constructTree(N-3, node.getRight()); } Assume N is the root number, and the three will create a left middle right node of N-1, N-2, N-3. EX: 5 / | \ 4 3 2 /|\ 3 2 1 etc. My GameNode class has the following variables: private int number; private GameNode left, middle, right; Whenever I construct a tree with an integer greater than 28, I get a OutOfMemoryError. Is my recursive method just incredibly inefficient or is this natural? Thanks!

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• std::bind overload resolution

  - by bpw1621

  The following code works fine #include <functional> using namespace std; using namespace std::placeholders; class A { int operator()( int i, int j ) { return i - j; } }; A a; auto aBind = bind( &A::operator(), ref(a), _2, _1 ); This does not #include <functional> using namespace std; using namespace std::placeholders; class A { int operator()( int i, int j ) { return i - j; } int operator()( int i ) { return -i; } }; A a; auto aBind = bind( &A::operator(), ref(a), _2, _1 ); I have tried playing around with the syntax to try and explicitly resolve which function I want in the code that does not work without luck so far. How do I write the bind line in order to choose the call that takes the two integer arguments?

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• Stored Procedure, 'incorrect syntax error'

  - by jacksonSD

  Attempting to figure out sp's, and I'm getting this error: "Msg 156, Level 15, State 1, Line 5 Incorrect syntax near the keyword 'Procedure'." the error seems to be on the if, but I can drop other existing tables with stored procedures the exact same way so I'm not clear on why this isn't working. can anyone shed some light? Begin Set nocount on Begin Try Create Procedure uspRecycle as if OBJECT_ID('Recycle') is not null Drop Table Recycle create table Recycle (RecycleID integer constraint PK_integer primary key, RecycleType nchar(10) not null, RecycleDescription nvarchar(100) null) insert into Recycle (RecycleID,RecycleType,RecycleDescription) values ('1','Compost','Product is compostable, instructions included in packaging') insert into Recycle (RecycleID,RecycleType,RecycleDescription) values ('2','Return','Product is returnable to company for 100% reuse') insert into Recycle (RecycleID,RecycleType,RecycleDescription) values ('3','Scrap','Product is returnable and will be reclaimed and reprocessed') insert into Recycle (RecycleID,RecycleType,RecycleDescription) values ('4','None','Product is not recycleable') End Try Begin Catch DECLARE @ErrMsg nvarchar(4000); SELECT @ErrMsg = ERROR_MESSAGE(); Throw 50001, @ErrMsg, 1; End Catch -- checking to see if table exists and is loaded: If (Select count(*) from Recycle) >1 begin Print 'Recycle table created and loaded '; Print getdate() End set nocount off End

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• Watching variables in SSIS during debug

  - by Tom H.

  I have a project in SSIS and I've added an Execute SQL Task which sends its result out to a variable. I wanted to confirm the value because I was worried that it would try to write it out as a resultset object rather than an actual integer (in this case I'm returning a COUNT). My first thought was just to run it in debug mode and add the global variable to my Watch window. Unfortunately, when I right-click on the Watch window, the option to "Add Variable" is greyed out. What am I missing here? I've gotten around confirming that my variable is set correctly, so I'm not interested in methods like putting a script in to do a MsgBox with the value or anything like that. For future reference I'd like to be able to watch variables in debug mode. If there are some kind of constraints on that then I'd like to know the what and why of it all if anyone knows. The help is woefully inadequate on this one and every "tutorial" that I can find just says, "Add the variable to the Watch window and debug" as though there should never be a problem doing that. Thanks for any insight!

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• Fastest way to read/store lots of multidimensional data? (Java)

  - by RemiX

  I have three questions about three nested loops: for (int x=0; x<400; x++) { for (int y=0; y<300; y++) { for (int z=0; z<400; z++) { // compute and store value } } } And I need to store all computed values. My standard approach would be to use a 3D-array: values[x][y][z] = 1; // test value but this turns out to be slow: it takes 192 ms to complete this loop, where a single int-assignment int value = 1; // test value takes only 66 ms. 1) Why is an array so relatively slow? 2) And why does it get even slower when I put this in the inner loop: values[z][y][x] = 1; // (notice x and z switched) This takes more than 4 seconds! 3) Most importantly: Can I use a data structure that is as quick as the assignment of a single integer, but can store as much data as the 3D-array?

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• Sending a message to nil?

  - by Ryan Delucchi

  As a Java developer who is reading Apple's Objective-C 2.0 documentation: I wonder as to what sending a message to nil means - let alone how it is actually useful. Taking an excerpt from the documentation: There are several patterns in Cocoa that take advantage of this fact. The value returned from a message to nil may also be valid: If the method returns an object, any pointer type, any integer scalar of size less than or equal to sizeof(void*), a float, a double, a long double, or a long long, then a message sent to nil returns 0. If the method returns a struct, as defined by the Mac OS X ABI Function Call Guide to be returned in registers, then a message sent to nil returns 0.0 for every field in the data structure. Other struct data types will not be filled with zeros. If the method returns anything other than the aforementioned value types the return value of a message sent to nil is undefined. Has Java rendered my brain incapable of grokking the explanation above? Or is there something that I am missing that would make this as clear as glass? Note: Yes, I do get the idea of messages/receivers in Objective-C, I am simply confused about a receiver that happens to be nil.

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• Just a small help about switch's use

  - by Laurent Fournier

  If an answer on this already exist, my apologies i've not found on this question... is this statement correct if i want presice actions on integers from -2 to 0, and for those between 1 and 6 apply the same methods with only my integer who'll change ? Like this: public void setCaseGUI(Point pt, int i, boolean b){ plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setSelected(b); plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setIcon(null); switch(i) { case -2: plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setText("F"); plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setForeground(Color.red); break; case -1: plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setText("B"); plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setForeground(Color.red); break; case 0: plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setText(""); plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setForeground(null); break; case 1: case 2: case 3: case 4: case 5: case 6: case 7: case 8: plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setText(String.valueOf(i)); plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setForeground(null); break; default: System.out.println("Erreur de changement d'état/case !"); } } Please don't be too harsh on me i've started to learn dev only a few month ago

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• How do you deal with breaking changes in a Rails migration?

  - by Adam Lassek

  Let's say I'm starting out with this model: class Location < ActiveRecord::Base attr_accessible :company_name, :location_name end Now I want to refactor one of the values into an associated model. class CreateCompanies < ActiveRecord::Migration def self.up create_table :companies do |t| t.string :name, :null => false t.timestamps end add_column :locations, :company_id, :integer, :null => false end def self.down drop_table :companies remove_column :locations, :company_id end end class Location < ActiveRecord::Base attr_accessible :location_name belongs_to :company end class Company < ActiveRecord::Base has_many :locations end This all works fine during development, since I'm doing everything a step at a time; but if I try deploying this to my staging environment, I run into trouble. The problem is that since my code has already changed to reflect the migration, it causes the environment to crash when it attempts to run the migration. Has anyone else dealt with this problem? Am I resigned to splitting my deployment up into multiple steps?

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• int foo(type& bar); is a bad practice?

  - by Earlz

  Well, here we are. Yet another proposed practice that my C++ book has an opinion on. It says "a returning-value(non-void) function should not take reference types as a parameter." So basically if you were to implement a function like this: int read_file(int& into){ ... } and used the integer return value as some sort of error indicator (ignoring the fact that we have exceptions) then that function would be poorly written and it should actually be like void read_file(int& into, int& error){ } Now to me, the first one is much clearer and nice to use. If you want to ignore the error value, you do so with ease. But this book suggests the later. Note that this book does not say returning value functions are bad. It rather says that you should either only return a value or you should only use references. What are your thoughts on this? Is my book full of crap? (again)

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• How do I create a self referential association (self join) in a single class using ActiveRecord in Rails?

  - by Daniel Chang

  I am trying to create a self join table that represents a list of customers who can refer each other (perhaps to a product or a program). I am trying to limit my model to just one class, "Customer". The schema is: create_table "customers", force: true do |t| t.string "name" t.integer "referring_customer_id" t.datetime "created_at" t.datetime "updated_at" end add_index "customers", ["referring_customer_id"], name: "index_customers_on_referring_customer_id" My model is: class Customer < ActiveRecord::Base has_many :referrals, class_name: "Customer", foreign_key: "referring_customer_id", conditions: {:referring_customer_id => :id} belongs_to :referring_customer, class_name: "Customer", foreign_key: "referring_customer_id" end I have no problem accessing a customer's referring_customer: @customer.referring_customer.name ... returns the name of the customer that referred @customer. However, I keep getting an empty array when accessing referrals: @customer.referrals ... returns []. I ran binding.pry to see what SQL was being run, given a customer who has a "referer" and should have several referrals. This is the SQL being executed. Customer Load (0.3ms) SELECT "customers".* FROM "customers" WHERE "customers"."id" = ? ORDER BY "customers"."id" ASC LIMIT 1 [["id", 2]] Customer Exists (0.2ms) SELECT 1 AS one FROM "customers" WHERE "customers"."referring_customer_id" = ? AND "customers"."referring_customer_id" = 'id' LIMIT 1 [["referring_customer_id", 3]] I'm a bit lost and am unsure where my problem lies. I don't think my query is correct -- @customer.referrals should return an array of all the referrals, which are the customers who have @customer.id as their referring_customer_id.

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• PHP: Need help with simple XML.

  - by Jack

  I am beginner in PHP. I am trying to parse this xml file. <relationship> <target> <following type="boolean">true</following> <followed_by type="boolean">true</followed_by> <screen_name>xxxx</screen_name> <id type="integer">xxxx</id> </target> </relationship> I need to get the value of the field 'following type="boolean" ' and here's my code - $xml = simplexml_load_string($response); foreach($xml->children() as $child) { if ($child->getName() == 'target') { foreach($child->children() as $child_1) if ( $child_1->getName() == 'following') { $is_my_friend = (bool)$child_1; break; } break; } } but I am not getting the correct output. I think the ' type="boolean" ' part of the field is creating problems. I know this might be a very trivial problem. Kindly bear with my ignorance. Please help.

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• JPA entity relations are not populated after .persist()

  - by Tomik

  Hello, this is a sample of my two entities: @Entity public class Post implements Serializable { @OneToMany(mappedBy = "post", fetch = javax.persistence.FetchType.EAGER) @OrderBy("revision DESC") public List<PostRevision> revisions; @Entity(name="post_revision") public class PostRevision implements Serializable { @ManyToOne public Post post; private Integer revision; @PrePersist private void prePersist() { List<PostRevision> list = post.revisions; if(list.size() >= 1) revision = list.get(list.size() - 1).revision + 1; else revision = 1; } So, there's a "post" and it can have several revisions. During persisting of the revision, entity takes a look at the list of the existing revisions and finds the next revision number. Problem is that Post.revisions is NULL but I think it should be automatically populated. I guess there's some kind of problem in my source code but I don't know where. Here's my "persistence" code: Post post = new Post(); PostRevision revision = new PostRevision(); revision.post = post; em.persist(post); em.persist(revision); em.flush(); I think that after persisting "post", it becomes "managed" and all the relations should be populated from now on. Thanks for help! (Note: public attributes are just for demonstration)

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• java Sockets and Threads Problem

  - by vs4vijay

  I am doin a Some Socket Programing Stuff in Java.. Here i have created a button(Create Server)..and when i click it ,it starts server...but i want to change the button name to (Stop Server) after Starting the server... so i did this.. but when i press start server it starts and the button name remains the same... and when a client gets connected to it ,then it change the name to stop server... tell me whats the wrong with this code?? Here is My a SomePart Of Code... public void actionPerformed(ActionEvent ex) { if(ex.getActionCommand() == "CreateServer") { bt1.setText("Stop Server"); bt2.setEnabled(false); b5.setText("Server Started On Port " + tf2.getText()); System.out.println("Server started 1"); create(Integer.parseInt(tf2.getText())); //my func. to create server System.out.println("Server started 2"); } } and my create() fucn. contains some sockets and thread...so tell me what the problem...

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• ArrayIndexOutOfBoundsException double array size

  - by Andy

  I'm going to preface this question with this statement: I know that I can easily handle this problem by reading the amount of lines in a file and making an array that size. I am not allowed to do this. Anyway, here is my question. I need to double my array's size whenever my program encounters an ArrayIndexOutOfBoundsException and then copy all the previous read in information into the larger array. Here is my code public static void main(String[] args) throws IOException { Scanner inScan, fScan = null; int [] A = new int[5]; inScan = new Scanner(System.in); System.out.print("Please enter the file to read from: "); while(true) { try{ String fName = inScan.nextLine(); fScan = new Scanner(new File(fName)); break; } catch (FileNotFoundException ex) { System.out.println("Your file is invalid -- please re-enter"); } } String nextItem; int nextInt = 0; int i = 0; while (fScan.hasNextLine()) { try { nextItem = fScan.nextLine(); nextInt = Integer.parseInt(nextItem); A[i] = nextInt; i++; } catch (NumberFormatException e) { System.out.println("Found an invalid int -- ignored"); } catch (ArrayIndexOutOfBoundsException e) { //double the size of array A until //copy all previous read in information to the larger array } } System.out.println("Here are your " + i + " items:"); for (int j = 0; j < i; j++) { System.out.println(A[j] + " "); } } }

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• Runtime of optimized Primehunter

  - by Setton

  Ok so I need some serious runtime help here! This method should take in an int value, check its primality, and return true if the number is indeed a prime. I understand why the loop only needs to go up to i squared, I understand that the worst case scenario is the case in which either the number is prime (or a multiple of a prime). But I don't understand how to quantify the actual runtime. I have done the loop myself by hand to try to understand the pattern or correlation of the number (n) and how many loops occur, but I literally feel like I keep falling into the same trap every time. I need a new way of thinking about this! I have a hint: "Think about the SIZE of the integer" which makes me want to quantify the literal number of integers in a number in relation to how many iterations it does in the for loop (floor log(n)) +1). BUT IT'S NOT WORKIIIING?! I KNOW it isn't square root n, obviously. I'm asking for Big O notation. public class PrimeHunter { public static boolean isPrime(int n) { boolean answer = (n > 1) ? true : false; //runtime = linear runtime for (int i = 2; i * i <= n; i++) //runtime = ????? { if (n % i == 0) //doesn't occur if it is a prime { answer = false; break; } } return answer; //runtime = linear runtime } }

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• bluetooth BluetoothSocket.connect() thread. how to close this thread

  - by Hia

  I am trying to make an android app that makes connection with bluetooth device. It works fine but when I call BluetoothSocket.connect() and it is not able to connect to devise its blocking. The thread and does not throw any exception. So when I try to close application while connect() is running its not responding. How can I cancel it? Used BluetoothSocket.close() in ... but still its not working for me. protected void simpleComm(Integer port) { // The documents tell us to cancel the discovery process. try { Method m = mmDevice.getClass().getMethod("createRfcommSocket", new Class[] { int.class }); mmSocket = (BluetoothSocket) m.invoke(mmDevice, port); mmSocket.connect(); // <== blocks untill is not connected Log.d(TAG, " connection success==="); }catch(Exception e){ if (!abort) { connectionFailed(); // Close the socket try { mmSocket.close(); // Start the service over to restart listening mode BluetoothService.this.start(); } catch (IOException e2) { Log.e(TAG,"unable to close() socket during connection failure", e2); } } return; } } public void cancel() { try { abort = true; mmSocket.close(); } catch (IOException e) { Log.e(TAG, "close() of connect socket failed", e); } }

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• List of values as keys for a Map

  - by thr

  I have lists of variable length where each item can be one of four unique, that I need to use as keys for another object in a map. Assume that each value can be either 0, 1, 2 or 3 (it's not integer in my real code, but a lot easier to explain this way) so a few examples of key lists could be: [1, 0, 2, 3] [3, 2, 1] [1, 0, 0, 1, 1, 3] [2, 3, 1, 1, 2] [1, 2] So, to re-iterate: each item in the list can be either 0, 1, 2 or 3 and there can be any number of items in a list. My first approach was to try to hash the contents of the array, using the built in GetHashCode() in .NET to combine the hash of each element. But since this would return an int I would have to deal with collisions manually (two equal int values are identical to a Dictionary). So my second approach was to use a quad tree, breaking down each item in the list into a Node that has four pointers (one for each possible value) to the next four possible values (with the root node representing [], an empty list), inserting [1, 0, 2] => Foo, [1, 3] => Bar and [1, 0] => Baz into this tree would look like this: Grey nodes nodes being unused pointers/nodes. Though I worry about the performance of this setup, but there will be no need to deal with hash collisions and the tree won't become to deep (there will mostly be lists with 2-6 items stored, rarely over 6). Is there some other magic way to store items with lists of values as keys that I have missed?

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