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• Creating An Utilities Class?

  - by Soo

  Hello SO, I'm very new to OOP and am trying my hardest to keep things strictly class based, while using good coding priciples. I'm a fair ways into my project now and I have a lot of general use methods I want to put into an utilities class. Is there a best way to create an utilities class? public class Utilities { int test; public Utilites() { } public int sum(int number1, int number2) { test = number1+number2; } return test; } After creating this Utilities class, do I just create an Utilities object, and run the methods of my choosing? Do I have this Utilities class idea correct?

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• MySQL Removing Some Foreign keys

  - by Drew

  I have a table whose primary key is used in several other tables and has several foreign keys to other tables. CREATE TABLE location ( locationID INT NOT NULL AUTO_INCREMENT PRIMARY KEY ... ) ENGINE = InnoDB; CREATE TABLE assignment ( assignmentID INT NOT NULL AUTO_INCREMENT PRIMARY KEY, locationID INT NOT NULL, FOREIGN KEY locationIDX (locationID) REFERENCES location (locationID) ... ) ENGINE = InnoDB; CREATE TABLE assignmentStuff ( ... assignmentID INT NOT NULL, FOREIGN KEY assignmentIDX (assignmentID) REFERENCES assignment (assignmentID) ) ENGINE = InnoDB; The problem is that when I'm trying to drop one of the foreign key columns (ie locationIDX) it gives me an "ERROR 1025 (HY000): Error on rename" error. How can I drop the column in the assignment table above without getting this error?

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• How do I marshal a pointer to an array of pointers to structures?

  - by Daniel Stutzbach

  I have a C function with the following signature: int my_function(int n, struct player **players) players is a pointer to an array of pointers to struct player objects. n is the number of pointers in the array. The function does not modify the array nor the contents of the structures, and it does not retain any pointers after returning. I tried the following: [DllImport("mylibary.dll")] static extern int my_function(int n, [In, MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 0)] player_in []players); However, that marshals the data as a pointer to an array of structures, not a pointer to an array of pointers to structures.

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• In C++, what is the "order of precedence" for shadowed variable names?

  - by Emile Cormier

  In C++, what is the "order of precedence" for shadowed variable names? I can't seem to find a concise answer online. For example: #include <iostream> int shadowed = 1; struct Foo { Foo() : shadowed(2) {} void bar(int shadowed = 3) { std::cout << shadowed << std::endl; // What does this output? } int shadowed; }; int main() { Foo().bar(); } I can't think of any other scopes where a variable might conflict. Please let me know if I missed one.

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• HashMap Memory Leak because of Dynamic Array

  - by Jake M

  I am attempting to create my own HashMap to understand how they work. I am using an array of Linked Lists to store the values(strings) in my hashmap. I am creating the array like this: Node** list; Instead of this: Node* list[nSize]; This is so the array can be any size at runtime. But I think I am getting a memory leak because of how I am doing this. I dont know where the error is but when I run the following simple code the .exe crashes. Why is my application crashing and how can I fix it? Note: I am aware that using a vector would be much better than an array but this is just for learning and I want to challenge myself to create the hashmap using a 'Dynamic' Array. PS: is that the correct term(Dynamic Array) for the kind of array I am using? struct Node { // to implement }; class HashMap { public: HashMap(int dynSize) { *list = new Node[dynSize]; size = dynSize; for (int i=0; i<size; i++) list[i] = NULL; cout << "END\n"; } ~HashMap() { for (int i=0; i<size; i++) delete list[i]; } private: Node** list; // I could use a vector here but I am experimenting with a pointer to an array(pointer), also its more elegant int size; }; int main() { // When I run this application it crashes. Where is my memory leak? HashMap h(5); system("PAUSE"); return 0; }

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• typedef declaration syntax

  - by mt_serg

  Some days ago I looked at boost sources and found interesting typedef. There is a code from "boost\detail\none_t.hpp": namespace boost { namespace detail { struct none_helper{}; typedef int none_helper::*none_t ; } // namespace detail } // namespace boost I didn't see syntax like that earlier and can't explain the sense of that. This typedef introduces name "none_t" as pointer to int in boost::detail namespace. What the syntax is? And what difference between "typedef int none_helper::*none_t" and for example "typedef int *none_t" ?

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• Database Structure for CakePHP Models

  - by Michael T. Smith

  We're building a data tracking web app using CakePHP, and I'm having some issues getting the database structure right. We have Companies that haveMany Sites. Sites haveMany DataSamples. Tags haveAndBelongToMany Sites. That is all set up fine. The problem is "ranking" the sites within tags. We need to store it in the database as an archive. I created a Rank model that is setup like this: rank ( id (int), sample_id (int), tag_id (int), site_id (int), rank (int), total_rows) ) So, the question is, how do I create the associations for tag, site and sample to rank? I originally set them as haveMany. But the returned structures don't get me where I'd like to be. It looks like: [Site] => Array ( [Sample] = Array(), [Tag] = Array() ) When I'm really looking for: [Site] => Array ( [Tag] = Array ( [Sample] => Array ( [Rank] => Array ( ...data... ) ) ) ) I think that I may not be structuring the database properly; so if I need to update please let me know. Otherwise, how do I write a find query that gets me where I need to be? Thanks! Thoughts? Need more details? Just ask!

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• What is the difference between Inversion of Control and Dependency injection in C++?

  - by rlbond

  I've been reading recently about DI and IoC in C++. I am a little confused (even after reading related questions here on SO) and was hoping for some clarification. It seems to me that being familiar with the STL and Boost leads to use of dependency injection quite a bit. For example, let's say I made a function that found the mean of a range of numbers: template <typename Iter> double mean(Iter first, Iter last) { double sum = 0; size_t number = 0; while (first != last) { sum += *(first++); ++number; } return sum/number; }; Is this dependency injection? Inversion of control? Neither? Let's look at another example. We have a class: class Dice { public: typedef boost::mt19937 Engine; Dice(int num_dice, Engine& rng) : n_(num_dice), eng_(rng) {} int roll() { int sum = 0; for (int i = 0; i < num_dice; ++i) sum += boost::uniform_int<>(1,6)(eng_); return sum; } private: Engine& eng_; int n_; }; This seems like dependency injection. But is it inversion of control? Also, if I'm missing something, can someone help me out?

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• how to call the method in thread with aruguments and return some value

  - by ratty

  i like to call the method in thread with aruguments and return some value here example class Program { static void Main() { Stopwatch stop = new Stopwatch(); stop.Start(); Thread FirstThread = new Thread(new ThreadStart(Fun1)); Thread SecondThread = new Thread(new ThreadStart(Fun2)); FirstThread.Start(); SecondThread.Start(); } public static void Fun1() { for (int i = 1; i <= 1000; i++) { Console.WriteLine("Fun1 writes:{0}", i); } } public static void Fun2() { for (int i = 1000; i >= 6; i--) { Console.WriteLine("Fun2 writes:{0}", i); } } } i know this above example run successfully but if method fun1 like this public int fun1(int i) { for (int n = i; n >= i+10; n++) { Console.WriteLine("Fun2 writes:{0}", i); } } then how can i call this in thread. Is it possible .Any body Help for me

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• How do I sum values from two dictionaries in C#?

  - by George Stocker

  I have two dictionaries with the same structure: Dictionary<string, int> foo = new Dictionary<string, int>() { {"Table", 5 }, {"Chair", 3 }, {"Couch", 1 } }; Dictionary<string, int> bar = new Dictionary<string, int>() { {"Table", 4 }, {"Chair", 7 }, {"Couch", 8 } }; I'd like to sum the values of the dictionaries together and return a third dictionaries with the keys, and the total values for each key: Table, 9 Chair, 10 Couch, 9 My current solution is to loop through the dictionary and pull them out that way, but I know that solution isn't the most performant or most readable. However, I'm hitting a brick wall trying to come up with a solution in LINQ.

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• Anonymous code blocks in Groovy

  - by piepera

  Is there a way to use anonymous code blocks in Groovy? For example, I'm trying to translate the following Java code into Groovy: { int i = 0; System.out.println(i); } int i = 10; System.out.println(i); The closest translation I can come up with is the following: boolean groovyIsLame = true; if (groovyIsLame) { int i = 0; System.out.println(i); } int i = 10; System.out.println(i); I know anonymous code blocks are often kind of an antipattern. But having variables with names like "inputStream0" and "inputStream1" is an antipattern too, so for this code I'm working on, anonymous code blocks would be helpful.

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• How can I select all records between two dates without using date fields?

  - by Hayden Bech

  Hi, I have a MySQL DB and I need to be able to store dates earlier then 1970 - in my case, as early as 0 AD and earlier too, so I need a custom way to store dates. I have thought to use this format: Year - int(6) | Month -int(2) | day - int (2) | time - time | AD tinyint (1) | mya - int (11) But when it comes to actually using data in this format it becomes difficult. For example, if I want to get all records between two dates it would be like (pseudocode not SQL): get all where year between minYear and maxYear if year == minYear, month = minMonth if year == maxYear, month <= maxMonth if month == minMonth, day = minDay if month == maxMonth, day <= maxDay if day == minDay, time = minTime if day == maxDay, time <= maxTime or something, which seems like a right pain. I could store seconds before/after 0 AD, but that would take up way too much data! 2010 (EDIT: 2011) = 6.4 billion seconds since 0 AD. Does anybody have any ideas for this problem?

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• Does my GetEnumerator cause a deadlock?

  - by Scott Chamberlain

  I am starting to write my first parallel applications. This partitioner will enumerate over a IDataReader pulling chunkSize records at a time from the data-source. TLDR; version private object _Lock = new object(); public IEnumerator GetEnumerator() { var infoSource = myInforSource.GetEnumerator(); //Will this cause a deadlock if two threads lock (_Lock) //use the enumator at the same time? { while (infoSource.MoveNext()) { yield return infoSource.Current; } } } full code protected class DataSourcePartitioner<object[]> : System.Collections.Concurrent.Partitioner<object[]> { private readonly System.Data.IDataReader _Input; private readonly int _ChunkSize; public DataSourcePartitioner(System.Data.IDataReader input, int chunkSize = 10000) : base() { if (chunkSize < 1) throw new ArgumentOutOfRangeException("chunkSize"); _Input = input; _ChunkSize = chunkSize; } public override bool SupportsDynamicPartitions { get { return true; } } public override IList<IEnumerator<object[]>> GetPartitions(int partitionCount) { var dynamicPartitions = GetDynamicPartitions(); var partitions = new IEnumerator<object[]>[partitionCount]; for (int i = 0; i < partitionCount; i++) { partitions[i] = dynamicPartitions.GetEnumerator(); } return partitions; } public override IEnumerable<object[]> GetDynamicPartitions() { return new ListDynamicPartitions(_Input, _ChunkSize); } private class ListDynamicPartitions : IEnumerable<object[]> { private System.Data.IDataReader _Input; int _ChunkSize; private object _ChunkLock = new object(); public ListDynamicPartitions(System.Data.IDataReader input, int chunkSize) { _Input = input; _ChunkSize = chunkSize; } public IEnumerator<object[]> GetEnumerator() { while (true) { List<object[]> chunk = new List<object[]>(_ChunkSize); lock(_Input) { for (int i = 0; i < _ChunkSize; ++i) { if (!_Input.Read()) break; var values = new object[_Input.FieldCount]; _Input.GetValues(values); chunk.Add(values); } if (chunk.Count == 0) yield break; } var chunkEnumerator = chunk.GetEnumerator(); lock(_ChunkLock) //Will this cause a deadlock? { while (chunkEnumerator.MoveNext()) { yield return chunkEnumerator.Current; } } } } IEnumerator IEnumerable.GetEnumerator() { return ((IEnumerable<object[]>)this).GetEnumerator(); } } } I wanted IEnumerable object it passed back to be thread safe (the MSDN example was so I am assuming PLINQ and TPL could need it) will the lock on _ChunkLock near the bottom help provide thread safety or will it cause a deadlock? From the documentation I could not tell if the lock would be released on the yeld return. Also if there is built in functionality to .net that will do what I am trying to do I would much rather use that. And if you find any other problems with the code I would appreciate it.

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• Jumping onto next string when the condition is met

  - by user98235

  This was a problem related to one of the past topcoder exam problems called HowEasy. Let's assume that we're given a sentence, for instance, "We a1re really awe~~~some" I just wanted to take get rid of every word in the sentence that doesn't contain alphabet characters, so in the above sentence, the desired output would be "We really" The below is the code I wrote (incomplete), and I don't know how to move on to the next string when the condition (the string contains a character that's not alphabet) is met. Could you suggest some revisions or methods that would allow me to do that? vect would be the vector of strings containing the desired output string param; cin>>param; stringstream ss(param); vector<string> vect; string c; while(ss >> c){ for(int i=0; i < c.length(); i++){ if(!(97<=int(c[i])&&int(c[i])<=122) && !(65<=int(c[i])&&int(c[i])<=90)){ //I want to jump onto next string once the above condition is met //and ignore string c; } vect.push_back(c); if (ss.peek() == ' '){ ss.ignore(); } } }

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• Dangling pointer

  - by viswanathan

  Does this piece of code lead to dangling pointer. My guess is no. class Sample { public: int *ptr; Sample(int i) { ptr = new int(i); } ~Sample() { delete ptr; } void PrintVal() { cout << "The value is " << *ptr; } }; void SomeFunc(Sample x) { cout << "Say i am in someFunc " << endl; } int main() { Sample s1 = 10; SomeFunc(s1); s1.PrintVal(); }

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• Cannot add or update a child row: a foreign key constraint fails

  - by Tom

  table 1 +----------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+-------------+------+-----+---------+----------------+ | UserID | int(11) | NO | PRI | NULL | auto_increment | | Password | varchar(20) | NO | | | | | Username | varchar(25) | NO | | | | | Email | varchar(60) | NO | | | | +----------+-------------+------+-----+---------+----------------+ table2 +------------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------------+--------------+------+-----+---------+----------------+ | UserID | int(11) | NO | MUL | | | | PostID | int(11) | NO | PRI | NULL | auto_increment | | Title | varchar(50) | NO | | | | | Summary | varchar(500) | NO | | | | +------------------+--------------+------+-----+---------+----------------+ com.mysql.jdbc.exceptions.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (myapp/table2, CONSTRAINT table2_ibfk_1 FOREIGN KEY (UserID) REFERENCES table1 (UserID)) What have I done wrong? I read this: http://www.w3schools.com/Sql/sql_foreignkey.asp and i don't see whats wrong. :S

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• An error saying unidentifed function "push", "pop", and"display" occurs, what should i add to fix i

  - by Alesha Aris

  #include<stdio.h> #include<iostream.h> #include<conio.h> #include<stdlib.h>(TOP) #include<fstream.h> #define MAX 5 int top = -1; int stack_arr[MAX]; main() { int choice; while(1) { printf("1.Push\n"); printf("2.Pop\n"); printf("3.Display\n"); printf("4.Quit\n"); printf("Enter your choice : "); scanf("%d",&choice); switch(choice) { case 1 : push(); break; case 2: pop(); break; case 3: display(); break; case 4: exit(1); default: printf("Wrong choice\n"); }/*End of switch*/ }/*End of while*/ }/*End of main()*/ push() { int pushed_item; if(top == (MAX-1)) printf("Stack Overflow\n"); else { printf("Enter the item to be pushed in stack : "); scanf("%d",&pushed_item); top=top+1; stack_arr[top] = pushed_item; } }/*End of push()*/ pop() { if(top == -1) printf("Stack Underflow\n"); else { printf("Popped element is : %d\n",stack_arr[top]); top=top-1; } }/*End of pop()*/ display() { int i; if(top == -1) printf("Stack is empty\n"); else { printf("Stack elements :\n"); for(i = top; i >=0; i--) printf("%d\n", stack_arr[i] ); } }/*End of display()*/

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• MYSQL Inserting rows that reference main rows.

  - by Andrew M

  I'm transferring my access logs into a database. I've got two tables: urlRequests id : int(10) host : varchar(100) path: varchar(300) unique index (host, path) urlAccesses id : int(10) request : int(10) <-- reference to urlRequests row ip : int(4) query : varchar(300) time : timestamp I need to insert a row into urlAccesses for every page load, but first a row in urlRequests has to exist with the requested host and path so that urlAccesses's row can reference it. I know I can do it this way: A. check if a row exists in urlRequests B. insert a row in urlRequests if it needs it C. insert a row into urlAccesses with the urlRequests's row id referenced That's three queries for every page load if the urlRequests row doesn't exist. I'm very new to MySQL, so I'm guessing that there's a way to go about this that would be faster and use less queries.

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• Find groups with both validated, unvalidated users

  - by Matchu

  (Not my real MySQL schema, but illustrates what needs done.) Users can belong to many groups, and groups have many users. users: id INT validated TINYINT(1) groups: id INT name VARCHAR(20) groups_users: group_id INT user_id INT I need to find groups that contain both validated and unvalidated users (validated being 1 or 0, respectively), in order to perform a specific manual maintenance task. There are thousands of users, all belong to at least one group, but a group usually only has 2-5 users. This is a live production server, so I could probably craft a query myself, but the last one I tried took a matter of minutes before I killed it. (I'm not one of those brilliant SQL wizards.) I suppose I could take the server down for maintenance, but, if possible, a query that gets this job done in a matter of seconds would be fantastic. Thanks!

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• Generate random number histogram using java

  - by Chewart

  Histogram -------------------------------------------------------- 1 ****(4) 2 ******(6) 3 ***********(11) 4 *****************(17) 5 **************************(26) 6 *************************(25) 7 *******(7) 8 ***(3) 9 (0) 10 *(1) -------------------------------------------------------- basically above is what my prgram needs to do.. im missing something somewhere any help would be great :) import java.util.Random; public class Histogram { /*This is a program to generate random number histogram between 1 and 100 and generate a table */ public static void main(String args[]) { int [] randarray = new int [80]; Random random = new Random(); System.out.println("Histogram"); System.out.println("---------"); int i ; for ( i = 0; i<randarray.length;i++) { int temp = random.nextInt(100); //random numbers up to number value 100 randarray[i] = temp; } int [] histo = new int [10]; for ( i = 0; i<10; i++) { /* %03d\t, this generates the random numbers to three decimal places so the numbers are generated with a full number or number with 00's or one 0*/ if (randarray[i] <= 10) { histo[i] = histo[i] + 1; //System.out.println("*"); } else if ( randarray[i] <= 20){ histo[i] = histo[i] + 1; } else if (randarray[i] <= 30){ histo[i] = histo[i] + 1; } else if ( randarray[i] <= 40){ histo[i] = histo[i] + 1; } else if (randarray[i] <= 50){ histo[i] = histo[i] + 1; } else if ( randarray[i] <=60){ histo[i] = histo[i] + 1; } else if ( randarray[i] <=70){ histo[i] = histo[i] + 1; } else if ( randarray[i] <=80){ histo[i] = histo[i] + 1; } else if ( randarray[i] <=90){ histo[i] = histo[i] + 1; } else if ( randarray[i] <=100){ histo[i] = histo[i] + 1; } switch (randarray[i]) { case 1: System.out.print("0-10 | "); break; case 2: System.out.print("11-20 | "); break; case 3: System.out.print("21-30 | "); break; case 4: System.out.print("31-40 | "); break; case 5: System.out.print("41-50 | "); break; case 6: System.out.print("51-60 | "); break; case 7: System.out.print("61-70 | "); break; case 8: System.out.print("71-80 | "); break; case 9: System.out.print("81-90 | "); break; case 10: System.out.print("91-100 | "); } for (int i = 0; i < 80; i++) { randomNumber = random.nextInt(100) index = (randomNumber - 1) / 2; histo[index]++; } } } }

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• Is generating real random numbers this easy in C#?

  - by JL

  I found this code using Google. private int RandomNumber(int min, int max) { Random random = new Random(); return random.Next(min, max); } Is this really all there is to generating REAL random numbers in C#? I intend to generate on a small scale between values 1-10. Thanks

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• Not getting key value from Identity column back after inserting new row with SubSonic ActiveRecord

  - by mikedevenney

  I'm sure I'm missing the obvious answer here, but could use a hand. I'm new to SubSonic and using version 3. I've got myself to the point of being able to query and insert, but I'm stuck with how I would get the value of the identity column back after my insert. I saw another post that mentioned Linq Templates. I'm not using those (at least I don't think I am...?) TIA ... UPDATE ... So I've been debugging through my code watching how the SubSonic code works and I found where the indentity column is being ignored. I use int as the datatype for my ID columns in the database and set them as identity. Since int is a non-nullable data type in c# the logical test in the Add method (public void Add(IDataProvider provider)) that checks if there is a value in the key column by doing a (key==null) could be the issue. The code that gets the new value for the identity field is in the 'true path', since an int can't be null and I use ints as my identity column data types this test will never pass. The ID field for my object has a 0 in it that I didn't put there. I assume it's set during the initialization of the object. Am I off base here? Is the answer to change my data types in the database? Another question (more a curiosity). I noticed that some of the properties in the generated classes are declared with a ? after the datatype. I'm not familiar with this declaration construct... what gives? There are some declared as an int (non key fields) and others that are declared as int? (key fields). Does this have something to do with how they're treated at initialization? Any help is appreciated! --BUMP--

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• undefined reference to static member variable

  - by Max

  Hi. I have this class that has a static member. it is also a base class for several other classes in my program. Here's its header file: #ifndef YARL_OBJECT_HPP #define YARL_OBJECT_HPP namespace yarlObject { class YarlObject { // Member Variables private: static int nextID; // keeps track of the next ID number to be used int ID; // the identifier for a specific object // Member Functions public: YarlObject(): ID(++nextID) {} virtual ~YarlObject() {} int getID() const {return ID;} }; } #endif and here's its implementation file. #include "YarlObject.hpp" namespace yarlObject { int YarlObject::nextID = 0; } I'm using g++, and it returns three undefined reference to 'yarlObject::YarlObject::nextID linker errors. If I change the ++nextID phrase in the constructor to just nextID, then I only get one error, and if I change it to 1, then it links correctly. I imagine it's something simple, but what's going on?

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• which one of these is an example of coercion

  - by user1890210

  I have been pondering a multiple choice question on coercion. One of the 4 examples a,b,c or d is an example of coercion. I narrowed it down to A or B. But I am having a problem choosing between the two. Cane someone please explain why one is coercion and one isn't. A) string s="tomat"; char c='o'; s=s+c; I thought A could be correct because we have two different types, character and string, being added. Meaning that c is promoted to string, hence coercion. B) double x=1.0; double y=2.0; int i=(int)(x+y); I also thought B was the correct answer because the double (x+y) is being turned into a int to be placed in i. But I thought this could be wrong because its being done actively through use of (int) rather than passively such as "int i = x + y" I'll list the other two options, even though I believe that neither one is the correct answer C) char A=0x20; A = A << 1 | 0x01; cout << A << endl; D) double x=1.0; double y=x+1; return 0; I'm not just looking for an answer, but an explanation. I have read tons of things on coercion and A and B both look like the right answer. So why is one correct and the other not.

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• map is not showing correct location in my blackberry applications

  - by Ali

  I am calling blackberry map by converting the real coordinates as you can see public static void showMap(String latitude,String longatude){ try{ int specailLatitude=(int)(Double.parseDouble(latitude))*100000; int specailLongatude=(int)(Double.parseDouble(longatude))*100000; MapView mapView=new MapView(); mapView.setLatitude(specailLatitude); mapView.setLongitude(specailLongatude); mapView.setZoom(07); MapsArguments arg=new MapsArguments(mapView); Invoke.invokeApplication(Invoke.APP_TYPE_MAPS, arg); }catch(Exception e){ CustomUtility.showToast("Map is not available "+e.getMessage()); } }// end of the showMap but problem is this its now showing correct location , it always shows same location in UAE , please help that i am converting correctly ?

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