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  • Return the difference between the lowest and highest key

    - by stan
    This is a past exam paper i am attempting and have no way to check if the out put is correct as i am not capable of building one of these things the question is in the title class Tree{ Tree left; Tree right; int key; public static int span(Tree tree) { if ( tree == null ){ return null; } if( tree.left != null) int min = span(tree.left); } if( tree.right != null){ int max = span(tree.right); } return max - min; } } Could anyone suggest what i need to change to get 5/5 marks :D - the only thing we have to do is write the span method, the header was given for us Thanks

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  • Multiple declarations and definations

    - by Yogesh
    X.c >> ------------------------- int i; main () { fun (); } ------------------------- Y.c >> int i; fun () { } why does these two files compile with no error ? (using GCC) but if i use int i = 10; throws multiple definition error

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  • Is it possible to supply template parameters when calling operator()?

    - by Paul
    I'd like to use a template operator() but am not sure if it's possible. Here is a simple test case that won't compile. Is there something wrong with my syntax, or is this simply not possible? struct A { template<typename T> void f() { } template<typename T> void operator()() { } }; int main() { A a; a.f<int>(); // This compiles. a.operator()<int>(); // This compiles. a<int>(); // This won't compile. return 0; }

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  • How do I make this Java code operate properly? [Multi-threaded, race condition]

    - by Fixee
    I got this code from a student, and it does not work properly because of a race condition involving x++ and x--. He added synchronized to the run() method trying to get rid of this bug, but obviously this only excludes threads from entering run() on the same object (which was never a problem in the first place) but doesn't prevent independent objects from updating the same static variable x at the same time. public class DataRace implements Runnable { static volatile int x; public synchronized void run() { for (int i = 0; i < 10000; i++) { x++; x--; } } public static void main(String[] args) throws Exception { Thread [] threads = new Thread[100]; for (int i = 0; i < threads.length; i++) threads[i] = new Thread(new DataRace()); for (int i = 0; i < threads.length; i++) threads[i].start(); for (int i = 0; i < threads.length; i++) threads[i].join(); System.out.println(x); // x not always 0! } } Since we cannot synchronize on x (because it is primitive), the best solution I can think of is to create a new static object like static String lock = ""; and enclose the x++ and x-- within a synchronized block, locking on lock. But this seems really awkward. Is there a better way?

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  • getline with ints C++

    - by Mdjon26
    I have a file 0 3 2 1 2 3 4 5 6 6 8 1 Where the first number for each line is the row, the second number is the column, and the third number is the data contained in that row, column. This will be a given [8][8] array so I have already initialized everything to 0, but how can I store each of these data values? For example, I want [0][3] =2 and [1][2] = 3. I would like to keep track of the line on which I found that row, col, and data value. So, how can I correctly insert these values into my 2-D array? int rowcol[8][8]; for (int i=0; i < 9; i++) for (int j=0; j < 9; j++) { rowcol[i][j] =0; } ifstream myfile; int nums; myfile.open(text.c_str()); while (!myfile.eof()) { myfile >> nums; numbers.push_back(nums); } for (int i=0; i < numbers.size(); i++) { //Not sure what the best approach here would be and I'm not even sure if I should have done a vector... }

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  • OnSize() Problem in VC++

    - by Anu
    Hi, In my VC++ MFC applcaiton,i have different views.And in each view,when i maximize it,i changed the size and position to new thing(Normally it fully get maximixed to screen size).But i dont want tht.So in OnSize() i coded like this. void CChildFrame::OnSize(UINT nType, int cx, int cy) { CMDIChildWnd::OnSize(nType, cx, cy); int XBorder = GetSystemMetrics(SM_CXMAXIMIZED); int YBorder = GetSystemMetrics(SM_CYMAXIMIZED); switch (nType) { case SIZE_MAXIMIZED: SetWindowPos(NULL,0,60,XBorder-45,YBorder-60,SWP_NOZORDER ); break; } } But what happened is?When i maximize the view,its get maximized to above mention size only.But in that blue bar,there si no minimize,maximize,close button. When i double click in the blue bar,its get to resumed to previous postion with all buttons. How can i get that?

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  • byte and short data types in Java can accept the value outside the range by explicit cast. The higher data types however can not. Why?

    - by Lion
    Let's consider the following expressions in Java. byte a = 32; byte b = (byte) 250; int i = a + b; This is valid in Java even though the expression byte b = (byte) 250; is forced to assign the value 250 to b which is outside the range of the type byte. Therefore, b is assigned -6 and consequently i is assigned the value 26 through the statement int i = a + b;. The same thing is possible with short as follows. short s1=(short) 567889999; Although the specified value is outside the range of short, this statement is legal. The same thing is however wrong with higher data types such int, double, folat etc and hence, the following case is invalid and causes a compile-time error. int z=2147483648; This is illegal, since the range of int in Java is from -2,147,483,648 to 2147483647 which the above statement exceeds and issues a compile-time error. Why is such not wrong with byte and short data types in Java?

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  • ANSI C++: Diferences between delete and delete[]

    - by Sunscreen
    I was looking a snipset of code: int* ip; ip = new int[100]; delete ip; The example above states that: "This code will work with many compilers, but it should instead read:" int* ip; ip = new int[100]; delete [] ip; Is this indeed the case? I use the compiler "Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 11.00.7022 for 80x86" and does not complain (first example) while compiling. At runtime the pointer is set to NULL. Other compilers behave diferrently? Can a compiler not compain and issues can appear at runtime? Thanks, Sun

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  • Detect if class has overloaded function fails on Comeau compiler

    - by Frank
    Hi Everyone, I'm trying to use SFINAE to detect if a class has an overloaded member function that takes a certain type. The code I have seems to work correctly in Visual Studio and GCC, but does not compile using the Comeau online compiler. Here is the code I'm using: #include <stdio.h> //Comeau doesnt' have boost, so define our own enable_if_c template<bool value> struct enable_if_c { typedef void type; }; template<> struct enable_if_c< false > {}; //Class that has the overloaded member function class TestClass { public: void Func(float value) { printf( "%f\n", value ); } void Func(int value) { printf( "%i\n", value ); } }; //Struct to detect if TestClass has an overloaded member function for type T template<typename T> struct HasFunc { template<typename U, void (TestClass::*)( U )> struct SFINAE {}; template<typename U> static char Test(SFINAE<U, &TestClass::Func>*); template<typename U> static int Test(...); static const bool Has = sizeof(Test<T>(0)) == sizeof(char); }; //Use enable_if_c to only allow the function call if TestClass has a valid overload for T template<typename T> typename enable_if_c<HasFunc<T>::Has>::type CallFunc(TestClass &test, T value) { test.Func( value ); } int main() { float value1 = 0.0f; int value2 = 0; TestClass testClass; CallFunc( testClass, value1 ); //Should call TestClass::Func( float ) CallFunc( testClass, value2 ); //Should call TestClass::Func( int ) } The error message is: no instance of function template "CallFunc" matches the argument list. It seems that HasFunc::Has is false for int and float when it should be true. Is this a bug in the Comeau compiler? Am I doing something that's not standard? And if so, what do I need to do to fix it?

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  • Converting a string into a double

    - by Koning Baard
    I am trying to convert a string (const char* argv[]) to a double precision floating point number: int main(const int argc, const char *argv[]) { int i; double numbers[argc - 1]; for(i = 1; i < argc; i += 1) { /* -- Convert each argv into a double and put it in `number` */ } /* ... */ return 0; } Can anyone help me? Thanks

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  • What does this C++ construct do?

    - by cambr
    Somewhere in lines of code, I came across this construct... //void* v = void* value from an iterator int i = (int)(long(v)) What possible purpose can this contruct serve? Why not simply use int(v) instead? Why the cast to long first?

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  • Processing a resultset to look up foriegn keys (and poulate a new table!)

    - by Gilly
    Hi, I've been handed a dataset that has some fairly basic table structures with no keys at all. eg {myRubishTable} - Area(varchar),AuthorityName(varchar),StartYear(varchar),StartMonth(varcha),EndYear(varchar),EndMonth(varchar),Amount(Money) there are other tables that use the Area and AuthorityName columns as well as a general use of Month and Years so I I figured a good first step was to pull Area and Authority into their own tables. I now want to process the data in the original table and lookup the key value to put into my new table with foreign keys which looks like this. (lookup Tables) {Area} - id (int, PK), name (varchar(50)) {AuthorityName} - id(int, PK), name(varchar(50) (TargetTable) {myBetterTable} - id (int,PK), area_id(int FK-Area),authority_name_id(int FK-AuthorityName),StartYear (varchar),StartMonth(varchar),EndYear(varchar),EndMonth(varchar),Amount(money) so row one in the old table read MYAREA, MYAUTHORITY,2009,Jan,2010,Feb,10000 and I want to populate the new table with 1,1,1,2009,Jan,2010,Feb,10000 where the first '1' is the primary key and the second two '1's are the ids in the lookup tables. Can anyone point me to the most efficient way of achieving this using just SQL? Thanks in advance Footnote:- I've achieved what I needed with some pretty simple WHERE clauses (I had left a rogue tablename in the FROM which was throwing me :o( ) but would be interested to know if this is the most efficient. ie SELECT [area].[area_id], [authority].[authority_name_id], [myRubishTable].[StartYear], [myRubishTable].[StartMonth], [myRubishTable].[EndYear], [myRubishTable].[EndMonth], [myRubishTable].[Amount] FROM [myRubishTable],[Area],[AuthorityName] WHERE [myRubishTable].[Area]=[Area].[name] AND [myRubishTable].[Authority Name]=[dim_AuthorityName].[name] TIA

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  • C++ How fast is passing around objects?

    - by wndsr
    Assuming we are running a compiled C++ binary: Is passing around an int (e.g. function to function, or writing it into variables) slower than passing around structs/class objects like the following? class myClass { int a; int b; char c; vector d; string e; }

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  • How can i solve "0 " value try to get length value?

    - by Phsika
    if i try to add int value into array with string length Whole data is "0" why? and how can solve it? for (int j = 0; j < dTable.Columns.Count; j++) for (int i = 0; i < dTable.Rows.Count; i++) { mycounter[i] = dTable.Rows[i][j].ToString().Length; } it is not related to mycounter because: string test = ""; foreach(DataColumn dc in dTable.Columns) for (int i = 0; i < dTable.Rows.Count; i++) { // MessageBox.Show(dTable.Rows[i][dc].ToString()); test = dTable.Rows[i][dc].ToString().Length.ToString(); }

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  • Why this doesnt't work in C++?

    - by user3377450
    I'm doing something and I have this: //main.cpp file template<typename t1, typename t2> std::ostream& operator<<(std::ostream& os, const std::pair<t1, t2>& pair) { return os << "< " << pair.first << " , " << pair.second << " >"; } int main() { std::map<int, int> map = { { 1, 2 }, { 2, 3 } }; std::cout << *map.begin() << std::endl;//This works std::copy(map.begin(), map.end(), std::ostream_iterator<std::pair<int,int> >(std::cout, " "));//this doesn't work } I guess this is not working because in the std::copy algorithm the operator isn't defined, but what can I do?

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  • Efficient way to call .Sum() on multiple properties

    - by SherCoder
    I have a function that uses Linq to get data from the database and then I call that function in another function to sum all the individual properties using .Sum on each individual property. I was wondering if there is an efficient way to sum all the properties at once rather than calling .Sum() on each individual property. I think the way I am doing as of right now, is very slow (although untested). public OminitureStats GetAvgOmnitureData(int? fnsId, int dateRange) { IQueryable<OminitureStats> query = GetOmnitureDataAsQueryable(fnsId, dateRange); int pageViews = query.Sum(q => q.PageViews); int monthlyUniqueVisitors = query.Sum(q => q.MonthlyUniqueVisitors); int visits = query.Sum(q => q.Visits); double pagesPerVisit = (double)query.Sum(q => q.PagesPerVisit); double bounceRate = (double)query.Sum(q => q.BounceRate); return new OminitureStats(pageViews, monthlyUniqueVisitors, visits, bounceRate, pagesPerVisit); }

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  • C++ vector reference parameter

    - by Archanimus
    Hello folks, let's say we have a class class MyClass { vector<vector<int > > myMatrice; public : MyClass(vector<vector<int > > &); } MyClass::MyClass(vector<vector<int > > & m) { myMatrice = m; } During the instanciation of MyClass, I pass a big vector < vector < int and I find that the object is actually copied and not only the reference, so it takes the double of the memory ... Please, can anyone help me out with this problem, I'm stuck since too many time ... And thanks a lot!

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  • Do running times match with O(nlogn)?

    - by user472221
    Hi I have written a class(greedy strategy) that at first i used sort method which has O(nlogn) Collections.sort(array, new SortingObjectsWithProbabilityField()); and then i used the insert method of binary search tree which takes O(h) and h here is the tree height. for different n ,the running time will be : n,running time 17,515428 33,783340 65,540572 129,1285080 257,2052216 513,4299709 which I think is not correct because for increasing n , the running time should almost increase. This method will take the running time: Exponent = -1; for(int n = 2;n<1000;n+=Math.pow(2,exponent){ for (int j = 1; j <= 3; j++) { Random rand = new Random(); for (int i = 0; i < n; i++) { Element e = new Element(rand.nextInt(100) + 1, rand.nextInt(100) + 1, 0); for (int k = 0; k < i; k++) { if (e.getDigit() == randList.get(k).getDigit()) { e.setDigit(e.getDigit() + 1); } } randList.add(e); } double sum = 0.0; for (int i = 0; i < randList.size(); i++) { sum += randList.get(i).getProbability(); } for (Element i : randList) { i.setProbability(i.getProbability() / sum); } //Get time. long t2 = System.nanoTime(); GreedyVersion greedy = new GreedyVersion((ArrayList<Element>) randList); long t3 = System.nanoTime(); timeForGreedy = timeForGreedy + t3 - t2; } System.out.println(n + "," + "," + timeForGreedy/3 ); exponent++; } thanks

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  • Operator+ for a subtype of a template classe.

    - by baol
    I have a template class that defines a subtype. I'm trying to define the binary operator+ as a template function, but the compiler cannot resolve the template version of the operator+. #include <iostream> template<typename other_type> struct c { c(other_type v) : cs(v) {} struct subtype { subtype(other_type v) : val(v) {} other_type val; } cs; }; template<typename other_type> typename c<other_type>::subtype operator+(const typename c<other_type>::subtype& left, const typename c<other_type>::subtype& right) { return typename c<other_type>::subtype(left.val + right.val); } // This one works // c<a>::subtype operator+(const c<a>::subtype& left, // const c<a>::subtype& right) // { return c<a>::subtype(left.val + right.val); } int main() { c<int> c1 = 1; c<int> c2 = 2; c<int>::subtype cs3 = c1.cs + c2.cs; std::cerr << cs3.val << std::endl; } I think the reason is because the compiler (g++4.3) cannot guess the template type so it's searching for operator+<int> instead of operator+. What's the reason for that? What elegant solution can you suggest?

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  • Segmentation fault C++ in recursive function

    - by user69514
    Why do I get a segmentation fault in my recursive function. It happens every time i call it when a value greater than 4 as a parameter #include <iostream> #include <limits> using namespace std; int printSeries(int n){ if(n==1){ return 1; } else if( n==2){ return 2; } else if( n==3){ return 3; } else if( n==4){ return printSeries(1) + printSeries(2) + printSeries(3); } else{ return printSeries(n-3) + printSeries((n-2) + printSeries(n-1)); } } int main(){ //double infinity = numeric_limits<double>::max(); for(int i=1; i<=10; i++){ cout << printSeries(i) << endl; } return 0; }

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  • how can this inner enum code be improved ?

    - by mafalda
    I have this construct public class Constants{ enum SystemA implements Marker{ ConstOne(1), ConstTwo(2), ConstThree(3); SystemA(int i) { number =i; } int number; } enum SystemB implements Marker{ ConstFour(4), ConstFive(5), ConstSix(6); SystemB(int i) { number =i; } int number; } } I have Marker so I can pass to method like this method(Constants.SystemA) or method(Constants.SystemB) What is the best way to list all the enum values ? I also want to make sure that it is not duplicating the number in any of the enums

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  • pointers for getting elements of an array in C

    - by Manolo
    I am a newbie in C and I would like to get the elements of an array with a function, I have tried different options, but I still do not get the elements. My function is: void getelements(int *a, int cl) { int *p; for (p=&a[0];p<&a[cl];p++) { printf("%d\n",*p); } } I know that the solution should work like that, but it only prints the first element and then memory positions. I am calling my function with: int v={10,12,20,34,45}; getelements(&v,5); Any help? I need to use arithmetic of pointers. Thanks

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  • What is causing this template-related compile error? (c++)

    - by Setien
    When I try to compile this: #include <map> #include <string> template <class T> class ZUniquePool { typedef std::map< int, T* > ZObjectMap; ZObjectMap m_objects; public: T * Get( int id ) { ZObjectMap::const_iterator it = m_objects.find( id ); if( it == m_objects.end() ) { T * p = new T; m_objects[ id ] = p; return p; } return m_objects[ id ]; } }; int main( int argc, char * args ) { ZUniquePool< std::string > pool; return 0; } I get this: main.cpp: In member function ‘T* ZUniquePool<T>::Get(int)’: main.cpp:12: error: expected `;' before ‘it’ main.cpp:13: error: ‘it’ was not declared in this scope I'm using GCC 4.2.1 on Mac OS X. It works in VS2008. I'm wondering whether it might be a variation of this problem: http://stackoverflow.com/questions/1364837/why-doesnt-this-c-template-code-compile But as my error output is only partially similar, and my code works in VS2008, I am not sure. Can anyone shed some light on what I am doing wrong?

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