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• C/C++ Bit Array or Bit Vector

  - by MovieYoda

  Hi, I am learning C/C++ programming & have encountered the usage of 'Bit arrays' or 'Bit Vectors'. Am not able to understand their purpose? here are my doubts - Are they used as boolean flags? Can one use int arrays instead? (more memory of course, but..) What's this concept of Bit-Masking? If bit-masking is simple bit operations to get an appropriate flag, how do one program for them? is it not difficult to do this operation in head to see what the flag would be, as apposed to decimal numbers? I am looking for applications, so that I can understand better. for Eg - Q. You are given a file containing integers in the range (1 to 1 million). There are some duplicates and hence some numbers are missing. Find the fastest way of finding missing numbers? For the above question, I have read solutions telling me to use bit arrays. How would one store each integer in a bit?

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• An Array returned by a model association is not an Array?

  - by Warren

  We have a model association that looks something like this: class Example < ActiveRecord::Base has_many :others, :order => 'others.rank' end The rank column is an integer type. The details of these particular models are not really important though as we have found the same problem with other has_many associations between other models. We have also added to the Enumerable module: module Enumerable def method_missing(name) super unless name.to_s[0..7] == 'collect_' method = name.to_s[8..-1] collect{|element| element.send(method)} end end This adds a collect_id method that we can use to get an array of record ids from an array of ActiveRecord objects. So if we use a normal ActiveRecord find :all, we get a nice array which we can then use collect_id on but if we use Example.others.collect_id, we get NoMethodError: undefined method `collect_id' for #<Class:0x2aaaac0060a0> Example.others.class returns "Array" so is it lying or confused? Our solution thus far has been to use it this way: Example.others.to_a.collect_id This works but this seems a bit strange. Why would you have to do that? We are on Ruby 1.8.7 and Rails 2.3.4

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• I just learned about C++ functions, can i use if statements onto functions?

  - by Sagistic

  What I am confused on is about the isNumPalindrome() function. It returns a boolean value of either true or false. How am I suppose to use that so I can display if its a palindrome or not. For ex. If (isNumPalindrome = true) cout "Your number is a palindrome" else "your number is not a palindrome." #include "stdafx.h" int _tmain(int argc, _TCHAR* argv[]) { return 0; } #include <iostream> #include <cmath> using namespace std; int askNumber(); bool isNumPalindrome(); int num, pwr; int main() { askNumber(); isNumPalindrome(); return 0; } bool isNumPalindrome() { int pwr = 0; if (num < 10) return true; else { while (num / static_cast<int>(pow(10.0, pwr)) >=10) pwr++; while (num >=10) { int tenTopwr = static_cast<int>(pow(10.0, pwr)); if ((num / tenTopwr) != (num% 10)) return false; else { num = num % tenTopwr; num = num / 10; pwr = pwr-2; } } return true; } } int askNumber() { cout << "Enter an integer in order to determine if it is a palindrome: " ; cin >> num; cout << endl; return num; }

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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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• JSON can't read, key reading fail maybe

  - by Abdullah Al Mubarok

  I wonder why I can't read the JSON Object like this : { "1":{"bulan":"Januari","tahun":"2012","tagihan":"205000","status":"Lunas"}, "2":{"bulan":"Februari","tahun":"2012","tagihan":"180000","status":"Lunas"}, "3":{"bulan":"Maret","tahun":"2012","tagihan":"120000","status":"Lunas"}, "4":{"bulan":"April","tahun":"2012","tagihan":"230000","status":"Lunas"}, "5":{"bulan":"Mei","tahun":"2012","tagihan":"160000","status":"Lunas"}, "6":{"bulan":"Juni","tahun":"2012","tagihan":"150000","status":"Belum Lunas"}, "panjang":6 } with my android code like this : try { int length = jobj.getInt("panjang"); for(int n = 0; n < length; n++){ String m = Integer.toString(n) JSONObject row = jobj.getJSONObject(m); String bulan = row.getString("bulan"); String tahun = row.getString("tahun"); String tagihan = row.getString("tagihan"); String status = row.getString("status"); HashMap<String, String> map = new HashMap<String, String>(); map.put("bulan", bulan); map.put("tahun", tahun); map.put("tagihan", tagihan); map.put("status", status); list.add(map); } } catch (JSONException e) { e.printStackTrace(); } It always return nothing, but it works fine if I change the key m to specific key like if String m = "1"; and I can't use JSONObject row = jobj.getJSONObject(n); because getJSONObject() just accept string, not int. is there something wrong with my code?

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• Could this be considered a well-written class (am I using OOP correctly)?

  - by Ben Dauphinee

  I have been learning OOP principals on my own for a while, and taken a few cracks at writing classes. What I really need to know now is if I am actually using what I have learned correctly, or if I could improve as far as OOP is concerned. I have chopped a massive portion of code out of a class that I have been working on for a while now, and pasted it here. To all you skilled and knowledgeable programmers here I ask: Am I doing it wrong? class acl extends genericAPI{ // -- Copied from genericAPI class protected final function sanityCheck($what, $check, $vars){ switch($check){ case 'set': if(isset($vars[$what])){return(1);}else{return(0);} break; } } // --------------------------------- protected $db = null; protected $dataQuery = null; public function __construct(Zend_Db_Adapter_Abstract $db, $config = array()){ $this->db = $db; if(!empty($config)){$this->config = $config;} } protected function _buildQuery($selectType = null, $vars = array()){ // Removed switches for simplicity sake $this->dataQuery = $this->db->select( )->from( $this->config['table_users'], array('tf' => '(CASE WHEN count(*) > 0 THEN 1 ELSE 0 END)') )->where( $this->config['uidcol'] . ' = ?', $vars['uid'] ); } protected function _sanityRun_acl($sanitycheck, &$vars){ switch($sanitycheck){ case 'uid_set': if(!$this->sanityCheck('uid', 'set', $vars)){ throw new Exception(ERR_ACL_NOUID); } $vars['uid'] = settype($vars['uid'], 'integer'); break; } } private function user($action = null, $vars = array()){ switch($action){ case 'exists': $this->_sanityRun_acl('uid_set', $vars); $this->_buildQuery('user_exists_idcheck', $vars); return($this->db->fetchOne($this->dataQuery->__toString())); break; } } public function user_exists($uid){ return($this->user('exists', array('uid' => $uid))); } } $return = $acl_test->user_exists(1);

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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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• Data Structure / Hash Function to link Sets of Ints to Value

  - by Gaminic

  Given n integer id's, I wish to link all possible sets of up to k id's to a constant value. What I'm looking for is a way to translate sets (e.g. {1, 5}, {1, 3, 5} and {1, 2, 3, 4, 5, 6, 7}) to unique values. Guarantees: n < 100 and k < 10 (again: set sizes will range in [1, k]). The order of id's doesn't matter: {1, 5} == {5, 1}. All combinations are possible, but some may be excluded. All sets and values are constant and made only once. No deletes or inserts, no value updates. Once generated, the only operations taking place will be look-ups. Look-ups will be frequent and one-directional (given set, look up value). There is no need to sort (or otherwise organize) the values. Additionally, it would be nice (but not obligatory) if "neighboring" sets (drop one id, add one id, swap one id, etc) are easy to reach, as well as "all sets that include at least this set". Any ideas?

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• How can I compare the performance of log() and fp division in C++?

  - by Ventzi Zhechev

  Hi, I’m using a log-based class in C++ to store very small floating-point values (as the values otherwise go beyond the scope of double). As I’m performing a large number of multiplications, this has the added benefit of converting the multiplications to sums. However, at a certain point in my algorithm, I need to divide a standard double value by an integer value and than do a *= to a log-based value. I have overloaded the *= operator for my log-based class and the right-hand side value is first converted to a log-based value by running log() and than added to the left-hand side value. Thus the operations actually performed are floating-point division, log() and floating-point summation. My question whether it would be faster to first convert the denominator to a log-based value, which would replace the floating-point division with floating-point subtraction, yielding the following chain of operations: twice log(), floating-point subtraction, floating-point summation. In the end, this boils down to whether floating-point division is faster or slower than log(). I suspect that a common answer would be that this is compiler and architecture dependent, so I’ll say that I use gcc 4.2 from Apple on darwin 10.3.0. Still, I hope to get an answer with a general remark on the speed of these two operators and/or an idea on how to measure the difference myself, as there might be more going on here, e.g. executing the constructors that do the type conversion etc. Cheers!

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• jQuery .height() property not working

  - by Andrew

  I'm attempting to get the height of an element using jQuery, but am receiving some unexpected results. Here's the code: $(function() { var contentheight = $('#subpage-content-small').height; alert(contentheight); }); Where #subpage-content-small has these CSS properties: #subpage-content-small { width: 400px; float: left; margin: 30px 10px 0 0; padding-bottom: 45px; } What I'm getting as an output for my alert is the following: function (f) { var e = this[0]; if (!e) { return f == null ? null : this; } if (c.isFunction(f)) { return this.each(function (j) {var i = c(this);i[d](f.call(this, j, i[d]()));}); } return "scrollTo" in e && e.document ? e.document.compatMode === "CSS1Compat" && e.document.documentElement["client" + b] || e.document.body["client" + b] : e.nodeType === 9 ? Math.max(e.documentElement["client" + b], e.body["scroll" + b], e.documentElement["scroll" + b], e.body["offset" + b], e.documentElement["offset" + b]) : f === w ? c.css(e, d) : this.css(d, typeof f === "string" ? f : f + "px"); } Any idea why I'm getting this as opposed to an integer of the height? Thanks in advance!

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• Include Multiple Labels and change the value of the same in Iphone, Objective C

  - by user576569

  I m trying to insert label in each row of the cell. Displaying integer. and I m trying to increase the quantity if user click on button add or minus I able to insert button in UITableView Cell as well the function to change the value. But when I click on add button it changes value only for the last row and not on the specific row. //MY code to insert label in each cell txtQty = [[UILabel alloc] initWithFrame:CGRectMake(233,7,20,20)]; txtQty.text = [NSString stringWithFormat:@"%@",[nos objectAtIndex:indexPath.row]]; txtQty.tag = count; txtQty.textColor =[UIColor whiteColor]; txtQty.backgroundColor = [UIColor clearColor]; [cell.contentView addSubview:txtQty]; //Button Creation UIButton *button2 = [[UIButton alloc] initWithFrame:CGRectMake(180,5,30,30)]; [button2 addTarget:self action:@selector(subAddSubQty:) forControlEvents:UIControlEventTouchUpInside]; [button2 setTag:count]; [cell.contentView addSubview:button2]; now what happening is suppose there are 3 rows in table and I click on the 1st row add button the value gets change in the last label i.e at 3rd row and not of the 1st row How to solve these?? please help Thank You

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• SQL query for the latest record for each day

  - by Mac

  I've got an Oracle 10g database with a table with a structure and content very similar to the following: CREATE TABLE MyTable ( id INTEGER PRIMARY KEY, otherData VARCHAR2(100), submitted DATE ); INSERT INTO MyTable VALUES (1, 'a', TO_DATE('28/04/2010 05:13', ''DD/MM/YYYY HH24:MI)); INSERT INTO MyTable VALUES (2, 'b', TO_DATE('28/04/2010 03:48', ''DD/MM/YYYY HH24:MI)); INSERT INTO MyTable VALUES (3, 'c', TO_DATE('29/04/2010 05:13', ''DD/MM/YYYY HH24:MI)); INSERT INTO MyTable VALUES (4, 'd', TO_DATE('29/04/2010 17:16', ''DD/MM/YYYY HH24:MI)); INSERT INTO MyTable VALUES (5, 'e', TO_DATE('29/04/2010 08:49', ''DD/MM/YYYY HH24:MI)); What I need to do is query the database for the latest record submitted on each given day. For example, with the above data I would expect the records with ID numbers 1 and 4 to be returned, as these are the latest each for 28 April and 29 April respectively. Unfortunately, I have little expertise as far as SQL is concerned. Could anybody possibly provide some insight as to how to achieve this? Thanks in advance!

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• PHP - Patterns within Arrays

  - by Toby

  I am trying to create a function which maps a recurring pattern of integers using an array. As an example if I have a starting array of (0,1,3) and I know that I want to stop the pattern when I hit 15. The pattern gets incremented by a fixed integer each time (lets say 4) so my final pattern should be.. 0 1 3 4 (0 + 4) 5 (1 + 4) 7 (2 + 4) 8 (4 + 4) 9 (5 + 4) 11(7 + 4) 12(8 + 4) 13(9 + 4) 15(11+ 4) Does anyone have any pointers on how this can be achieved? My current implementation works but is stupidly inefficient which something like this... $array = array(0,1,3); $inc = 4; $end = end($array); $final = 15; while($end < $final) { $tmp = array(); foreach($array AS $row) { $tmp = $row + $inc; } $array = merge($tmp, $array); $end = end($array); }

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• Cannot locate record in delphi ADO query

  - by Danatela

  I can't locate any record in TADOQuery using PK. First, I was trying to use standard Locate method: PPUQuery.Locate('ID', SpPlansQuery['PPONREC'], []); It always returns False, but manual search (passing the whole query matching ID with given PPONREC which is really slow) finds the desired row. I tried using loPartialKey and switched CursorLocation of query to clUseServer, but it didn't help. Next, I tried to filter my PPUQuery: PPUQuery.Filter := 'ID = ' + VarToStr(SpPlansQuery['PPONREC']); PPUQuery.Filtered := True; PPUQuery.First; But after that the PPUQuery.Eof is True and PPUQuery.RecordCount equals 0. Underlying database is Oracle 9 and the ID is of type INTEGER and is PK of table TPORDER_CMK. PPUQuery.SQL is: SELECT tp.*, la.*, lm.*, ld.*, ld1.*, to_cmk.* FROM ppu_plan.tporder_cmk tp JOIN PPU_PLAN.LARTICLES la ON TP.ARTICLE = LA.ID JOIN PPU_PLAN.LMATERIAL lm ON TP.MATERIAL = lm.id JOIN PPU_PLAN.LCADEP ld ON TP.CADEP = LD.ID JOIN PPU_PLAN.LCADEP ld1 ON TP.PRODUCER = LD1.ID JOIN PPU_PLAN.TORDER_CMK to_cmk ON TP.order_id=TO_cmk.ID WHERE TP.PLAN_ID = :pplan_id What should I try next and how to solve this problem?

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• Global State and Singletons Dependency injection

  - by Manu

  this is a problem i face lot of times when i am designing a new app i'll use a sample problem to explain this think i am writing simple game.so i want to hold a list of players. i have few options.. 1.use a static field in some class private static ArrayList<Player> players = new ArrayList<Integer>(); public Player getPlayer(int i){ return players.get(i); } but this a global state 2.or i can use a singleton class PlayerList{ private PlayerList instance; private PlayerList(){...} public PlayerList getInstance() { if(instance==null){ ... } return instance; } } but this is bad because it's a singleton 3.Dependency injection class Game { private PlayerList playerList; public Game(PlayerList list) { this.list = list; } public PlayerList getPlayerList() { return playerList; } } this seems good but it's not, if any object outside Game need to look at PlayerList (which is the usual case) i have to use one of the above methods to make the Game class available globally. so I just add another layer to the problem. didn't actually solve anything. what is the optimum solution ? (currently i use Singleton approach)

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• jQuery ajax request response is empty in Internet Explorer

  - by Aprilia1982

  Hi, I'm doing the following ajax call: //exif loader function LoadExif(cImage) { $.ajax({ type: "POST", url: "http://localhost:62414/Default1.aspx/GetImageExif", data: "{iCurrentImage:" + cImage + "}", contentType: "application/json; charset=utf-8", dataType: "json", error: ajaxFailed, success: function (data, status) { var sStr = ''; for (var count in data.d) { sStr = sStr + data.d[count]; }; alert(sStr); } }); }; In Firefox the request works really fine. When I try to run the code in Internet Explorer, the response is empty. Here is the webmethod witch is called: <WebMethod()> _ <ScriptMethod(ResponseFormat:=ResponseFormat.Json)> _ Public Shared Function GetImageExif(ByVal iCurrentImage As Integer) As String Dim sbTable As New StringBuilder sbTable.AppendLine("<table>") sbTable.AppendLine("<tr>") sbTable.AppendLine("<td>Name</td><td>" & gGallery.Images(iCurrentImage).File.Name & "</td>") sbTable.AppendLine("</tr>") sbTable.AppendLine("</table>") Return sbTable.ToString End Function Any ideas? Jan

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• Saving a Record with Rails Association

  - by tshauck

  Hi, I've been going through the Rails Guides, but have gotten stuck on associations after going through validations and migrations. So, I have the following models Job and Person, where a Person can have many jobs. I know that in reality there'd be a many-to-many, but I'm trying to get my handle on this first. class Job < ActiveRecord::Base belongs_to :people end and class Person < ActiveRecord::Base has_many :jobs end Here's the schema ActiveRecord::Schema.define(:version => 20110108185924) do create_table "jobs", :force => true do |t| t.string "occupation" t.boolean "like" t.datetime "created_at" t.datetime "updated_at" t.integer "person_id" end create_table "people", :force => true do |t| t.string "first_name" t.string "last_name" t.datetime "created_at" t.datetime "updated_at" end end Is there some I can do the following j = Job.first; j.Person? Then that'd give me access to the Person object associated with the j. I couldn't find it on guides.rubyonrails.org, although it has been very helpful getting a grip on migrations and validations thus far. Thanks PS, If there are any tutorials that covers more of this kind of things links would be great.

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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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• LINQ Sorting - First three need to be different manufacturers

  - by Rob

  My OM has a 'product' object. Each product has a 'manufacturer id' (property, integer). When I have a list of products to display, the first three are displayed as the 'featured products'. The list is already sorted in a specific sort order, putting the 'featured' products first in the list. However, I now need to ensure the featured products in the listing are from different Manufacturers. I want to have a method to call to do this re-sorting. Trying to utilize LINQ to to the querying of the input 'products' and the 'results' public List<Product> SetFeatures(List<Product> products, int numberOfFeatures) { List<Product> result; // ensure the 2nd product is different manufacturer than the first .... // ensure the 3rd product is a different manufacturer than the first two... // ... etc ... for the numberOfFeatures return result; } Thanks in advance.

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• Rails - Beginner wants feedback on how they've modeled their app and how to do it better.

  - by adam

  I think the way I've modelled my app is a bit fishy and i need to rejig things, im just not sure how. I've already re-jigged and refactored before. It took a long time ( I'm a beginner ) and I'm hesitant to it again in case i head off in the wrong direction again. Basic Idea, user can submit an answer, another user can mark it correct or incorrect. If incorrect they have to write the correct answer. Users can view their and everybody else's correct and incorrect answers. So I did it this way class Answer has_one: correction end class Correction belongs_to :answer end when a user marks an answer as correct, I set checked_at:DateTime and checked_by_id:integer on the Answer object to keep track of who checked the answer and when. For incorrect answers I create a correction object which holds the correct answer and again checked_by and checked_at details. I don't like this because I have checked_by and checked_at in both models. It just doesn't sit right. Possible solutions are: Create a third model such as VerifiedAnswer and move the checked_by/at attributes to that. It will handle the situtation where an answer is marked correct. Or are these models thin enough (they dont have any other attributes) that I can just have one model ( Answer ) that has all the attributes to store all this information?

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• What is a more "ruby way" to write this code?

  - by steadfastbuck

  This was a homework assignment for my students (I am a teaching assistant) in c and I am trying to learn Ruby, so I thought I would code it up. The goal is to read integers from a redirected file and print some simple information. The first line in the file is the number of elements, and then each integer resides on its own line. This code works (although perhaps inefficiently), but how can I make the code more Ruby-like? #!/usr/bin/ruby -w # first line is number of inputs (Don't need it) num_inputs = STDIN.gets.to_i # read inputs as ints h = Hash.new STDIN.each do |n| n = n.to_i h[n] = 1 unless h[n] and h[n] += 1 end # find smallest mode h.sort.each do |k,v| break puts "Mode is: #{k}", "\n" if v == h.values.max end # mode unique? v = h.values.sort print "Mode is unique: " puts v.pop == v.pop, "\n" # print number of singleton odds, # odd elems repeated odd number times in desc order # even singletons in desc order odd_once = 0 odd = Array.new even = Array.new h.each_pair do |k, v| odd_once += 1 if v == 1 and k.odd? odd << k if v.odd? even << k if v == 1 and k.even? end puts "Number of elements with an odd value that appear only once: #{odd_once}", "\n" puts "Elements repeated an odd number of times:" puts odd.sort.reverse, "\n" puts "Elements with an even value that appear exactly once:" puts even.sort.reverse, "\n" # print fib numbers in the hash class Fixnum def is_fib? l, h = 0, 1 while h <= self return true if h == self l, h = h, l+h end end end puts "Fibonacci numbers:" h.keys.sort.each do |n| puts n if n.is_fib? end

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• C++ : Declaring the array size with a non-constant variable

  - by Jérôme

  I always thought that when declaring an array in C++, the size has to be a constant integer value. For instance : int MyArray[5]; // correct or const int ARRAY_SIZE = 6; int MyArray[ARRAY_SIZE]; // correct but int ArraySize = 5; int MyArray[ArraySize]; // incorrect Here is also what is explained in The C++ Programming Language, by Bjarne Stroustrup : The number of elements of the array, the array bound, must be a constant expression (§C.5). If you need variable bounds, use a vector(§3.7.1, §16.3). For example: void f(int i) { int v1[i]; // error : array size not a constant expression vector<int> v2[i]; // ok } But to my big surprise, the code above does compile fine on my system ! Here is what I tried to compile : void f(int i) { int v2[i]; } int main() { int i = 3; int v1[i]; f(5); } I got no error ! I'm using GCC v4.4.0. Is there something I'm missing ?

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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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• Abstract away a compound identity value for use in business logic?

  - by John K

  While separating business logic and data access logic into two different assemblies, I want to abstract away the concept of identity so that the business logic deals with one consistent identity without having to understand its actual representation in the data source. I've been calling this a compound identity abstraction. Data sources in this project are swappable and various and the business logic shouldn't care which data source is currently in use. The identity is the toughest part because its implementation can change per kind of data source, whereas other fields like name, address, etc are consistently scalar values. What I'm searching for is a good way to abstract the concept of identity, whether it be an existing library, a software pattern or just a solid good idea of some kind is provided. The proposed compound identity value would have to be comparable and usable in the business logic and passed back to the data source to specify records, entities and/or documents to affect, so the data source must be able to parse back out the details of its own compound ids. Data Source Examples: This serves to provide an idea of what I mean by various data sources having different identity implementations. A relational data source might express a piece of content with an integer identifier plus a language specific code. For example. content_id language Other Columns expressing details of content 1 en_us 1 fr_ca The identity of the first record in the above example is: 1 + en_us However when a NoSQL data source is substituted, it might somehow represent each piece of content with a GUID string 936DA01F-9ABD-4d9d-80C7-02AF85C822A8 plus language code of a different standardization, And a third kind of data source might use just a simple scalar value. So on and so forth, you get the idea.

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• how do I use an enum value on a switch statement in C++

  - by BotBotPgm

  I would like to use an enum value for my switch statment in C++. Is it possible to use the enum values enclosed in the "{}" as choices for the "switch()"? I know that switch() needs an integer value in order to direct the flow of programming to the appropriate case number. If this is the case, do I just make a variable for each constant in the 'enum' statment? I also want the user to be able to pick the choice and pass that choice to the switch() statement. for example: cout<< "1 - Easy"; cout<<"2 - Medium"; cout<< "3 -Hard"; enum myChoice {EASY =1 ,MEDIUM = 2, HARD = 3} cin ???? switch(????) case 1/EASY: (can I just type case EAST?) cout << "You picked easy!"; break; case 2/MEDIUM: cout << "You picked medium!"; case 3..... (same thing as case 2 except on hard.) default: return 0; Thanks

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