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• only return random number when it is unique

  - by phil

  My brain is melting today and i cannot think how to do this simple bit of code. numberList is a string of numbers seperated by commas like '2, 34, 10' etc.. when i request a random number i need to check if the string has the number, if it does i want to keep requesting a random number until the random number is definitely not in the string. i cant think what kind of loop i would do to get this to work: Random r = new Random(); public int RandomPos(int max) { int i; do { i = r.Next(max) + 1; } while (!numberList.Contains(i.ToString())); return i; }

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• Pass the current state of a function into another function in C/C++

  - by sand

  Is there a way to pass the current state of a function into another function in C/C++? I mean all the parameters and local variables by current state. For example: void funcA (int a, int b) { char c; int d, e; // Do something with the variables. // ... funcB(); // Do something more. } void funcB() { // funcB() should be able to access variables a,b,c,d & e // and any change in these variables reflect into funcA(). } The code is in bad shape if there is a need for funcB() kind of functions. But can it be achieved? This can help if someone is starting to re-factor a long method with multiple parameters.

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• C++ std::equal -- rationale behind not testing for the 2 ranges having equal size?

  - by ShaChris23

  I just wrote some code to test the behavior of std::equal, and came away surprised: int main() { try { std::list<int> lst1; std::list<int> lst2; if(!std::equal(lst1.begin(), lst1.end(), lst2.begin())) throw std::logic_error("Error: 2 empty lists should always be equal"); lst2.push_back(5); if(std::equal(lst1.begin(), lst1.end(), lst2.begin())) throw std::logic_error("Error: comparing 2 lists where one is not empty should not be equal"); } catch(std::exception& e) { std::cerr << e.what(); } } The output (a surprise to me): Error: comparing 2 lists where one is not empty should not be equal Observation: why is it the std::equal does not first check if the 2 containers have the same size() ? Was there a legitimate reason?

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• Is there a .NET class that represents operator types?

  - by user323774

  I would like to do the following: *OperatorType* o = *OperatorType*.GreaterThan; int i = 50; int increment = -1; int l = 0; for(i; i o l; i = i + increment) { //code } this concept can be kludged in javascript using an eval()... but this idea is to have a loop that can go forward or backward based on values set at runtime. is this possible? Thanks

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• Python to C# Conversion of RGBA values not working

  - by clangers

  I'm currently converting some python code to C#, and I'm having an issue with the RGBA C# libraries # Original Python Code: d = math.sqrt( (x - size/2.0)**2 + (y - size/2.0)**2 ) rgbVal = int(200*d/md + 50) rgba = (0,0,0, 255 - rgbVal) img.putpixel((x,y), rgba) // My C# Code double d = Math.Sqrt(Math.Pow((x - DotSize / 2.0), 2) + Math.Pow((y - DotSize / 2.0), 2)); int rgbVal = (int) (200 * d / md + 50); Color color = Color.FromArgb(255 - rgbVal, 0, 0, 0); // ** ERROR ** img.SetPixel(x,y, color); At both instances of the code d is equal to 106 and md is equal to 53. However the resulting rgbVal value is 450. This would obviously mean that 255 - 450 is -195, which causes an error to be thrown as each individual value must be between 0 and 255. Anyone have any idea how I can fix this. Please note that the data is the same when running both the python and C# versions.

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• Unreachable code detected

  - by habbo95

  Hi all, I'm getting a "Unreachable code detected" message in Visual Studio at the point con.close() in my code below. Can you spot what I've done wrong? Thanks private int chek1(String insert) { OleDbConnection con = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb"); OleDbCommand com = new OleDbCommand("select count(*) from sn where sn='" + insert + "\'", con); con.Open(); int po = (int)com.ExecuteScalar(); if (po > 0) return 1; else return 0; con.Close(); }

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• Abort early in a fold

  - by Heptic

  What's the best way to terminate a fold early? As a simplified example, imagine I want to sum up the numbers in an Iterable, but if I encounter something I'm not expecting (say an odd number) I might want to terminate. This is a first approximation def sumEvenNumbers(nums: Iterable[Int]): Option[Int] = { nums.foldLeft (Some(0): Option[Int]) { case (None, _) => None case (Some(s), n) if n % 2 == 0 => Some(s + n) case (Some(_), _) => None } } However, this solution is pretty ugly (as in, if I did a .foreach and a return -- it'd be much cleaner and clearer) and worst of all, it traverses the entire iterable even if it encounters a non-even number. So what would be the best way to write a fold like this, that terminates early? Should I just go and write this recursively, or is there a more accepted way?

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• Constant embedded for loop condition optimization in C++ with gcc

  - by solinent

  Will a compiler optimize tihs: bool someCondition = someVeryTimeConsumingTask(/* ... */); for (int i=0; i<HUGE_INNER_LOOP; ++i) { if (someCondition) doCondition(i); else bacon(i); } into: bool someCondition = someVeryTimeConsumingTask(/* ... */); if (someCondition) for (int i=0; i<HUGE_INNER_LOOP; ++i) doCondition(i); else for (int i=0; i<HUGE_INNER_LOOP; ++i) bacon(i); someCondition is trivially constant within the for loop. This may seem obvious and that I should do this myself, but if you have more than one condition then you are dealing with permuatations of for loops, so the code would get quite a bit longer. I am deciding on whether to do it (I am already optimizing) or whether it will be a waste of my time.

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• class classname(value); & class classname=value; difference when constructor is explicit

  - by Mahesh

  When constructor is explicit, it isn't used for implicit conversions. In the given snippet, constructor is marked as explicit. Then why in case foo obj1(10.25); it is working and in foo obj2=10.25; it isn't working ? #include <iostream> class foo { int x; public: explicit foo( int x ):x(x) {} }; int main() { foo obj(10.25); // Not an error. Why ? foo obj2 = 10.25; // Error getchar(); return 0; } error: error C2440: 'initializing' : cannot convert from 'double' to 'foo'

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• Abstract class get parameter from implementing subclass?

  - by soren.qvist

  I'm wondering if there is way to do this without breaking encapsulation, I want the abstract class to rely on parameters defined in the implementing subclass. Like so: public abstract class Parent { private int size; private List<String> someList; public Parent() { size = getSize(); someList = new ArrayList<String>(size); } public abstract int getSize(); } public class Child extends Parent { @Override public int getSize() { return 5; } } Is this ugly? Is there a better way? And perhaps more importantly, is this even a good idea?

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• C++ dynamic array sizing problem

  - by Peter

  The basic pseudo code looks like this: void myFunction() { int size = 10; int * MyArray; MyArray = new int[size]; cout << size << endl; cout << sizeof(MyArray) << endl; } The first cout returns 10, as expected, while the second cout returns 4. Anyone have an explanation?

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• writing structs and classes to disk

  - by Phenom

  The following function writes a struct to a file. int btwrite(short rrn, BTPAGE *page_ptr) { long addr; addr = (long) rrn * (long) PAGESIZE + HEADERSIZE; lseek(btfd, addr, 0); return (write(btfd, page_ptr, PAGESIZE)); } The following is the struct. typedef struct { short keycount; /* number of keys in page */ int key[MAXKEYS]; /* the actual keys */ int value[MAXKEYS]; /* the actual values */ short child[MAXKEYS+1]; /* ptrs to rrns of descendants */ } BTPAGE; What would happen if I changed the struct to a class, would it still work the same? If I added class functions, would the size it takes up on disk increase?

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• How to insert into std::map.

  - by Knowing me knowing you

  In code below: map<string,vector<int>> create(ifstream& in, const vector<string>& vec) { /*holds string and line numbers into which each string appears*/ typedef map<string,vector<int>> myMap; typedef vector<string>::const_iterator const_iter; myMap result; string tmp; unsigned int lineCounter = 0; while(std::getline(in,tmp)) { const_iter beg = vec.begin(); const_iter end = vec.end(); while (beg < end) { if ( tmp.find(*beg) != string::npos) { result[*beg].push_back(lineCounter);//THIS IS THE LINE I'M ASKING FOR } ++beg; } ++lineCounter; } return result; } How should I do it (check line commented in code) if I want to use insert method of map instead of using operator[]? Thank you.

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• Java print binary number using bit-wise operator

  - by user69514

  Hi I am creating a method that will take a number and print it along with its binary representation. The problems is that my method prints all 0's for any positive number, and all 1's for any negative number private static void display( int number ){ System.out.print(number + "\t"); int mask = 1 << 31; for(int i=1; i<=32; i++) { if( (mask & number) != 0 ) System.out.print(1); else System.out.print(0); if( (i % 4) == 0 ) System.out.print(" "); } }

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• Unit testing a functions whose purposes is side effects

  - by David

  How would you unit test do_int_to_string_conversion? #include <string> #include <iostream> void do_int_to_string_conversion(int i, std::string& s) { switch(i) { case 1: s="1"; break; case 2: s="2"; break; default: s ="Nix"; } std::cout << s << "\n"; } int main(int argc, char** argv){ std::string little_s; do_int_to_string_conversion(1, little_s); do_int_to_string_conversion(2, little_s); do_int_to_string_conversion(3, little_s); }

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• Heap Error in C++

  - by BobAlmond

  Dear all, I'm a beginner programmer in C++. Recently, I'm working on image processing thing using C++. but I have some problem that I want to ask. Suppose I have some code as follow: for (int i=0;i<100000;i++) { int * a = new int[10000]; //do something delete [] a; } When I executed that code, I receive runtime error, Heap Error... Is there anything wrong with that code, I mean, can I allocate memory and release it in the same loop? Thanks in advance...

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• how to get stl map to construct/destruct inserted object only once.

  - by Alberto Toglia

  I have found a very prejudicial fact about stl maps. For some reason I cant get objects being inserted in the map to get constructed/destructed only once. Example: struct MyObject{ MyObject(){ cout << "constructor" << endl; } ~MyObject(){ cout << "destructor" << endl; } }; int main() { std::map<int, MyObject> myObjectsMap; myObjectsMap[0] = MyObject(); return 0; } returns: constructor destructor destructor constructor destructor If I do: typedef std::pair<int, MyObject> MyObjectPair; myObjectsMap.insert( MyObjectPair(0,MyObject())); returns: constructor destructor destructor destructor I'm inserting Objects responsible for their own memory allocation, so when destructed they'll clean themselves up, being destructed several times is causing me some trouble.

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• C++: Where can I define the body for a private function?

  - by Martijn Courteaux

  Hi, I have a header like this (header guards not shown): class GameSystem { public: GameSystem(Game *pcGame); virtual ~GameSystem(); void Setup(); private: void InitGame(); void RunGame(); void ExitGame(); Game *m_pcGame; /* Properties */ int m_nWidth; int m_nHeight; int m_nFps; bool m_bFullscreen; }; Where can I define the body for InitGame(), RunGame() and ExitGame()? Can I define it in my .cpp file? If so, how? Or am I obliged to make their body in my .h file? I'm using Eclipse and I began typing: void GameSystem:: and then he doesn't suggest the private functions.

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• Reversing a for loop... want to print numbers in reverse

  - by user69514

  How would I change this loop to print prime number in reverse... starting from the biggest one first int main(){ bool prime; for( int i=3; i<=10000; i++){ prime = true; for(int n=2; n<=i-1; n++){ if( i%n == 0){ prime = false; } } if(prime){ cout << i << " "; } } return 0; }

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• Are Triggers Based On Queries Atomic?

  - by David

  I have a table that has a Sequence number. This sequence number will change and referencing the auto number will not work. I fear that the values of the trigger will collide. If two transactions read at the same time. I have ran simulated tests on 3 connections @ ~1 million records each and no collisions. CREATE TABLE `aut` ( `au_id` int(10) NOT NULL AUTO_INCREMENT, `au_control` int(10) DEFAULT NULL, `au_name` varchar(50) DEFAULT NULL, `did` int(10) DEFAULT NULL, PRIMARY KEY (`au_id`), KEY `Did` (`did`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1 TRIGGER `binc_control` BEFORE INSERT ON `aut` FOR EACH ROW BEGIN SET NEW.AU_CONTROL = (SELECT COUNT(*)+1 FROM aut WHERE did = NEW.did); END;

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• Can't subtract in a for loop in C/Objective-C

  - by user1612935

  I'm going through the Big Nerd Ranch book on Objective-C, which takes you through some early C stuff. I've played with C before, and am pretty experienced in PHP. Anyhow, I'm doing the challenges and this one is not working the way I think it should. It's pretty simple - start at 99, loop through and subtract three until you get to zero, and every time you get a number that is divisible by 5 print "Found one." Pretty straightforward. However, subtracting by three in the for loop is not working #include <stdio.h> int main (int argc, const char * argv[]) { int i; for(i = 99; i > 0; i-3){ printf("%d\n", i); if(i % 5 == 0) { printf("Found one!\n"); } } return 0; } It creates and endless loop at 99, and I'm not sure why.

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• Casting complex class into a dataset?

  - by iTayb

  This is the class I'm trying to turn into a dataset: public class BookStore { private List<Book> booksList; } public class Book { private string name; private string imageurl; private string subject; private string author; private int level; private int year; private int rating; private List<string> booksellers; private List<decimal> bookprices; } There are proprieties, of course. How can I turn it into a dataset? Thank you very much.

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• How can I compare two dates, return a number of days.

  - by Dans Eduardo

  Hi, how can I compare two dates return number of days. Ex: Missing X days of the Cup. look my code. NSDateFormatter *df = [[NSDateFormatter alloc]init]; [df setDateFormat:@"d MMMM,yyyy"]; NSDate *date1 = [df dateFromString:@"11-05-2010"]; NSDate *date2 = [df dateFromString:@"11-06-2010"]; NSTimeInterval interval = [date2 timeIntervalSinceDate:date1]; //int days = (int)interval / 30; //int months = (interval - (months/30)) / 30; NSString *timeDiff = [NSString stringWithFormat:@"%dMissing%d days of the Cup",date1,date2, fabs(interval)]; label.text = timeDiff; // output (Missing X days of the Cup)

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• Strange macro declaration in C

  - by Andrey Atapin

  Exploring libusb-1.0.9 source code, I have found such line (./os/poll_windows.c:78): #define CHECK_INIT_POLLING do {if(!is_polling_set) init_polling();} while(0) As for me this is the same like: #define CHECK_INIT_POLLING if(!is_polling_set) init_polling(); Is there any reason to loop that expression? UPDATE: I couldn't still realize what'd be wrong after the answers, and the following example helped: #include <stdio.h> #define TEST if(test) foo(); #define TEST_DO do { if(test) foo(); } while(0) int test = 1; void foo() { printf("%s", "Foo called"); } int main(int argc, char** argv) { if(argc > 1) TEST_DO; /* LINE 12 */ else printf("%s", "skipping..."); return 0; } If you put TEST at line 12, a compiler will give an error "error: ‘else’ without a previous ‘if’". Hope, this will help someone.

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• ASP.NET check if LinqToEntities returned something or not.

  - by Alex

  How to make this method return boolean value, depending on query return. False - nothing, True - data exists. Before i just returned int from uniqueQuote.Count() but does not look like great method. Thank you! private bool CheckEnquiryUser(int enquiryId, Guid userId) { int selectedEnquiryId = enquiryId; Guid currentUserId = userId; Entities ctx3 = new Entities(); var uniqueQuote = from quot in ctx3.Enquiries.Include("aspnet_Users") where quot.EnquiryId == selectedEnquiryId && quot.aspnet_Users.UserId == currentUserId select quot; bool exist = uniqueQuote; return exist;

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