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  • Calling base class constructor

    - by The Void
    In the program below, is the line Derived(double y): Base(), y_(y) correct/allowed? That is, does it follow ANSI rules? #include <iostream> class Base { public: Base(): x_(0) { std::cout << "Base default constructor called" << std::endl; } Base(int x): x_(x) { std::cout << "Base constructor called with x = " << x << std::endl; } void display() const { std::cout << x_ << std::endl; } protected: int x_; }; class Derived: public Base { public: Derived(): Base(1), y_(1.2) { std::cout << "Derived default constructor called" << std::endl; } Derived(double y): Base(), y_(y) { std::cout << "Derived constructor called with y = " << y << std::endl; } void display() const { std::cout << Base::x_ << ", " << y_ << std::endl; } private: double y_; }; int main() { Base b1; b1.display(); Derived d1; d1.display(); std::cout << std::endl; Base b2(-9); b2.display(); Derived d2(-8.7); d2.display(); return 0; }

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  • loop is cut one element of the array

    - by Walaa
    The problem is : Write a program that reads a number n and then declares an array of n elements. The program then fills the array with the first n numbers, where each number is two to the power of the previous. Finally, display array’s contents. My code : import java.util.*; public class Q1 { static Scanner scan = new Scanner (System.in); public static void main(String args [] ) { int num; int i = 0; System.out.println("Enter a number :"); num = scan.nextInt(); double [] a=new double[num]; a[0]= num ; for ( ;i<=a.length-1 ; i++) { a[i+1] = Math.pow(2,a[i]); System.out.println((int)(a[i]) ); } } } The error is : ----jGRASP exec: java Q1 Enter a number : 4 4 16 65536 Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4 at Q1.main(Q1.java:16) ----jGRASP wedge2: exit code for process is 1. why it says that? And the number by user printed twice!

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  • creating an object within a function of a program

    - by user1066524
    could someone please tell me what I need to do in order to create an object in a function. I will try to explain by making up some sort of example... Let's say I have a program named TimeScheduler.cpp that implements the class Schedule.h (and I have the implementation in a separate file Schedule.cpp where we define the methods). In the declaration file we have declared two constructors Schedule(); //the default and Schedule(int, int, int);//accepts three arguments to get to the point--let's say in the main program file TimeScheduler.cpp we created our own functions in this program apart from the functions inherited from the class Schedule. so we have our prototypes listed at the top. /*prototypes*/ void makeSomeTime(); etc..... we have main(){ //etc etc... } we then define these program functions void makeSomeTime(){ //process } let's say that inside the function makeSomeTime(), we would like to create an array of Schedule objects like this Schedule ob[]={ summer(5,14, 49), fall(9,25,50) }; what do I have to do to the function makeSomeTime() in order for it to allow me to create this array of objects. The reason I ask is currently i'm having difficulty with my own program in that it WILL allow me to create this array of objects in main()....but NOT in a function like I just gave an example of. The strange thing is it will allow me to create a dynamic array of objects in the function..... like Schedule *ob = new Schedule[n+1]; ob[2]= Schedule(x,y,z); Why would it let me assign to a non-dynamic array in main(), but not let me do that in the function?

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  • Absence of property syntax in Java

    - by Vojislav Stojkovic
    C# has syntax for declaring and using properties. For example, one can declare a simple property, like this: public int Size { get; set; } One can also put a bit of logic into the property, like this: public string SizeHex { get { return String.Format("{0:X}", Size); } set { Size = int.Parse(value, NumberStyles.HexNumber); } } Regardless of whether it has logic or not, a property is used in the same way as a field: int fileSize = myFile.Size; I'm no stranger to either Java or C# -- I've used both quite a lot and I've always missed having property syntax in Java. I've read in this question that "it's highly unlikely that property support will be added in Java 7 or perhaps ever", but frankly I find it too much work to dig around in discussions, forums, blogs, comments and JSRs to find out why. So my question is: can anyone sum up why Java isn't likely to get property syntax? Is it because it's not deemed important enough when compared to other possible improvements? Are there technical (e.g. JVM-related) limitations? Is it a matter of politics? (e.g. "I've been coding in Java for 50 years now and I say we don't need no steenkin' properties!") Is it a case of bikeshedding?

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  • Are there any shortcuts/easier(VB) style way for raising events in C#?

    - by Eric
    Example in VB I have a worker class Public Class worker Public Event EventNumber1(ByVal messages As Dictionary(Of Integer, String)) Public Event EventNumber2(ByVal message As String) Public Sub CallEventNumber1() Dim dict As New Dictionary(Of Integer, String) dict.Add(1, "EventNumber1 First message") dict.Add(2, "EventNumber1 Second message") RaiseEvent EventNumber1(dict) End Sub Public Sub CallEventNumber2() RaiseEvent EventNumber2("I am an EventNumber2 Message") End Sub End Class and wire them up in another class with AddHandler _worker.EventNumber1, AddressOf EventNumber1Handler AddHandler _worker.EventNumber2, AddressOf EventNumber2Handler and in C# the worker class class Worker { public delegate void EventNumber1Handler(Dictionary<int, string> messages); public delegate void EventNumber2Handler(string message); public event EventNumber1Handler EventNumber1; public event EventNumber2Handler EventNumber2; public void CallEventNumber1() { Dictionary<int, string> dict = new Dictionary<int, string>(); dict.Add(1, "EventNumber1 First message"); dict.Add(2, "EventNumber1 Second message"); if (EventNumber1 != null) EventNumber1(dict); } public void CallEventNumber2() { if (EventNumber2 != null) EventNumber2("I am an EventNumber2 Message"); } } and wire that up with worker.EventNumber1 += new Worker.EventNumber1Handler(worker_EventNumber1); worker.EventNumber2 += new Worker.EventNumber2Handler(worker_EventNumber2); So I guess my question is do I always need to add the delegate along with the event in c#? Is there any new syntax for c# 3.0/4.0? Regards _Eric

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  • C# Freq. Table with Random Values

    - by Sef
    Hello, I am trying to write a frequency program that will represent a bar diagram (in console code). The problem is i have no idea how exactly to caculate this frequency or how do i exactly then give the bars different heights according to there frequency (trough calculation). The frequency height is capped at 21. (meaning the bars go from 1 to 21, so the max bar height would be for example 21 stars(* as display sign for the bar itself). A calculation i have so far (although not sure if correct) for frequency: This array takes the random values generated: for (int j = 0; j < T.Length; j++) { T[j] = (MaxHeight* T[j]) / Ber.GreatestElement(T); Console.Write("{0,7}", T[j]); } This results in values between 0 and 21 -- Based on the values my bars should give a certain height compared to all the other frequency values. (for example 8000 could have 21 in height where 39 could have 1). To represent this diagram i used 2 for loops to display height and width (keep in mind i only wish to use Using System; to keep it to the "basics"). for (int height= 1; height<= 21; height++) { for (int width= 0; width<= 10; width++) { if(...??) { Console.Write("{0,7}", bar); // string bar= ("*"); } else { Console.Write("{0,7}", empty); } } Console.WriteLine(); } So so far i have a entire field filled with * and the random values generated along with their frequency value (although i have no idea if the freq value is properly calculated). I assume i need a if (.....) in the second for but i cannot seem to get further then this. Thanks in advance!

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  • Why it's can be compiled in GNU/C++, can't compiled in VC++2010 RTM?

    - by volnet
    #include #include #include #include "copy_of_auto_ptr.h" #ifdef _MSC_VER #pragma message("#include ") #include // http://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html#Diagnostic-Pragmas #endif /* case 1-4 is the requirement of the auto_ptr. which form http://ptgmedia.pearsoncmg.com/images/020163371X/autoptrupdate/auto_ptr_update.html */ /* case 1. (1) Direct-initialization, same type, e.g. */ std::auto_ptr source_int() { // return std::auto_ptr(new int(3)); std::auto_ptr tmp(new int(3)); return tmp; } /* case 2. (2) Copy-initialization, same type, e.g. */ void sink_int(std::auto_ptr p) { std::cout source_derived() { // return std::auto_ptr(new Derived()); std::auto_ptr tmp(new Derived()); return tmp; } /* case 4. (4) Copy-initialization, base-from-derived, e.g. */ void sink_base( std::auto_ptr p) { p-go(); } int main(void) { /* // auto_ptr */ // case 1. // auto_ptr std::auto_ptr p_int(source_int()); std::cout p_derived(source_derived()); p_derived-go(); // case 4. // auto_ptr sink_base(source_derived()); return 0; } In Eclipse(GNU C++.exe -v gcc version 3.4.5 (mingw-vista special r3)) it's two compile error: Description Resource Path Location Type initializing argument 1 of void sink_base(std::auto_ptr<Base>)' from result ofstd::auto_ptr<_Tp::operator std::auto_ptr<_Tp1() [with _Tp1 = Base, _Tp = Derived]' auto_ptr_ref_research.cpp auto_ptr_ref_research/auto_ptr_ref_research 190 C/C++ Problem Description Resource Path Location Type no matching function for call to `std::auto_ptr::auto_ptr(std::auto_ptr)' auto_ptr_ref_research.cpp auto_ptr_ref_research/auto_ptr_ref_research 190 C/C++ Problem But it's right in VS2010 RTM. Questions: Which compiler stand for the ISO C++ standard? The content of case 4 is the problem "auto_ptr & auto_ptr_ref want to resolve?"

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  • C++ string.substr() function problem

    - by VaioIsBorn
    I want to make a program that will read some number in string format and output it like this: if the number is 12345 it should then output 12 23 34 45 . I tried using the substr() function from the c++ string library, but it gives me strange results - it outputs 1 23 345 45 instead of the expected result. Why ? #include <iostream> #include <string> #include <cstdlib> using namespace std; int main(void) { string a;cin >> a; string b;int c; for(int i=0;i<a.size()-1;++i) { b = a.substr(i,i+1); c = atoi(b.c_str()); cout << c << " "; } cout << endl; return 0; }

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  • Assigning a value to an integer in a C linked list

    - by Drunk On Java
    Hello all. I have a question regarding linked lists. I have the following structs and function for example. struct node { int value; struct node *next; }; struct entrynode { struct node *first; struct node *last; int length; }; void addnode(struct entrynode *entry) { struct node *nextnode = (struct node *)malloc(sizeof(struct node)); int temp; if(entry->first == NULL) { printf("Please enter an integer.\n"); scanf("%d", &temp); nextnode->value = temp; nextnode->next = NULL; entry->first = nextnode; entry->last = nextnode; entry->length++; } else { entry->last->next = nextnode; printf("Please enter an integer.\n"); scanf("%d", nextnode->value); nextnode->next = NULL; entry->last = nextnode; entry->length++; } } In the first part of the if statement, I store input into a temp variable and then assign that to a field in the struct. The else branch, I tried to assign it directly which did not work. How would I go about assigning it directly? Thanks for your time.

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  • Same random numbers from instantiated class

    - by user1797202
    I'm learning C# and created a class within my program that holds a random number generator: class RandomNumberGenerator { Random RNG = new Random(); // A bunch of methods that use random numbers are in here } Inside this class are a few methods that use the RNG. Data gets sent here from other parts of the program, gets processed, then gets returned. One of the methods does the following: // Method works something like this int Value1 = RNG.Next(x, y); int Value2 = RNG.Next(x, y); int Value3 = RNG.Next(x, y); The x, y values are to be sent here from another class. So, I have to create an instance of the RandomNumberGenerator within that class so I can call its methods and pass the x and y values to it. class DoStuff { RandomNumberGenerator Randomizer = new RandomNumberGenerator // Here I call a bunch of Randomizer methods that give me values I need } The problem in the above method is that I get the same numbers every time for all three values. I'm not sure if it's because they're so close together and Randomizer's seed value hasn't had time to change or if I'm doing something wrong when I create a new instance of the RandomNumberGenerator class. I've gone through a bunch of answers on here already and typically problems like this are due to people creating many new Random objects when they run methods (thus setting the seed for all of them to the same value), but the only new Random object I create is within the RandomNumberGenerator class. I then instantiate that once within the other class so I can pass it data and use its methods. Why is this happening and how would I fix this?

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  • Is it possible to cache all the data in a SQL Server CE database using LinqToSql?

    - by DanM
    I'm using LinqToSql to query a small, simple SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of what makes LinqToSql so appealing. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance besides resorting to doing all the joins manually? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view. Update Here are the table definitions for the example I used in my question: create table Order ( Id int identity(1, 1) primary key, ProductName ntext null ) create table Customer ( Id int identity(1, 1) primary key, OrderId int null references Order (Id) )

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  • C Static Function Confusion

    - by Lime
    I am trying to make the s_cord_print function visible in the cord_s.c file only. Currently the function is visible/runnable in main.c even when it is declared static. How do I make the s_cord_print function private to cord_s.c? Thanks! s_cord.c typedef struct s_cord{ int x; int y; struct s_cord (*print)(); } s_cord; void* VOID_THIS; #define $(EL) VOID_THIS=&EL;EL static s_cord s_cord_print(){ struct s_cord *THIS; THIS = VOID_THIS; printf("(%d,%d)\n",THIS->x,THIS->y); return *THIS; } const s_cord s_cord_default = {1,2,s_cord_print}; main.c #include <stdio.h> #include <stdlib.h> #include "s_cord.c" int main(){ s_cord mycord = s_cord_default; mycord.x = 2; mycord.y = 3; $(mycord).print().print(); //static didn't seem to hide the function s_cord_print(); return 0; } ~

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  • C++: recursively computer all permutaions of digits 0 - 9

    - by Nate
    I have a homework assignment where part of the requirement is to recursively compute all the permutations of integers 0 - 9. The professor actually gave us the algorithm for this part of the question. I've finished the rest of the assignment, but I can't get the permute function working...I'm implementing it exactly like it was shown on the assignment information. However, when I run it each permutation is repeated multiple times (and I'm not sure if I'm even getting all the correct permutations.) I think he must've made a mistake on the assignment instructions. I've been working on this for a couple of hours and can't seem to figure out where I'm going wrong. Can anybody help point me in the right direction? Here's the current code: void permute(int v[], int curr) { for (int i = curr; i < MAX; i++) { swap(v[i], v[curr]); permute(v, curr + 1); swap(v[curr], v[i]); } } EDIT: Actually, right after posting this I realized it has to do with the swap, right? Because right now i and curr are the same, so I'm swapping identical numbers. Hm, should it be swap(v[i], v[curr+1])?

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  • onActivityResult method not being called Android

    - by Chintan
    I am trying to send data from child activity to parent. But somehow, onActivityResult(..) is not getting called. here is code Parent activity selectedText.setOnTouchListener(new OnTouchListener() { public boolean onTouch(View v, MotionEvent event) { if (event.getActionMasked() == MotionEvent.ACTION_DOWN) { Intent intent = new Intent(Parents.this,Child.class); startActivityForResult(intent, 1); } return true; } }); @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { switch (requestCode) { case 1: if (resultCode == RESULT_OK) { if (data.hasExtra("selText")) { selectedText.setText(data.getExtras().getString( "selText")); } break; } } Child Activity: I can see selected value set in the setResult(). But after finish of child activity, it's not going back to parent activity. textListView.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> arg0, View arg1, int myItemInt, long arg3) { selectedFromList =(String) (textListView.getItemAtPosition(myItemInt)); Intent data = new Intent(); data.putExtra("selText", selectedFromList); setResult(RESULT_OK,data); finish(); } });

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  • Implementing a Version check between an Abstract class and it's implementation

    - by Michael Stum
    I have this abstract class and concrete implementation (they are in different assemblies): public abstract class MyAbstractClass { private static readonly int MyAbstractClassVersion = 1; public abstract int ImplementedVersion { get; } protected MyAbstractClass() { CheckVersion(); } private void CheckVersion() { var message = string.Format( "MyAbstractClass implements Version {0}, concrete is Version {1}", RepositoryVersion, ImplementedVersion); if (!MyAbstractClassVersion.Equals(ImplementedVersion)) throw new InvalidOperationException(message); } } public class ConcreteClass : MyAbstractClass { public ConcreteClass() : base() { // ConcreteClass is guaranteed to have // a constructor that calls the base constructor // I just simplified the example } public override int ImplementedVersion { get { return 2; } } } As you see, I call CheckVersion() from the abstract constructor, to get rid of the "virtual member call in base constructor" message, but I am not sure if that's really the way to do it. Sure, it works, but that doesn't mean it will always work, will it? Also, I wonder if I can get the name of the Concrete Type from the CheckVersion() function? I know that adding new abstract members will force an error anyway (System.TypeLoadException) and I'm not sure if I want this type of strict Versioning, but I'm just curious how it would be done properly given only the abstract class and an implementation (I know I could do it by using interfaces and/or a Factory pattern).

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  • Faster or more memory-efficient solution in Python for this Codejam problem.

    - by jeroen.vangoey
    I tried my hand at this Google Codejam Africa problem (the contest is already finished, I just did it to improve my programming skills). The Problem: You are hosting a party with G guests and notice that there is an odd number of guests! When planning the party you deliberately invited only couples and gave each couple a unique number C on their invitation. You would like to single out whoever came alone by asking all of the guests for their invitation numbers. The Input: The first line of input gives the number of cases, N. N test cases follow. For each test case there will be: One line containing the value G the number of guests. One line containing a space-separated list of G integers. Each integer C indicates the invitation code of a guest. Output For each test case, output one line containing "Case #x: " followed by the number C of the guest who is alone. The Limits: 1 = N = 50 0 < C = 2147483647 Small dataset 3 = G < 100 Large dataset 3 = G < 1000 Sample Input: 3 3 1 2147483647 2147483647 5 3 4 7 4 3 5 2 10 2 10 5 Sample Output: Case #1: 1 Case #2: 7 Case #3: 5 This is the solution that I came up with: with open('A-large-practice.in') as f: lines = f.readlines() with open('A-large-practice.out', 'w') as output: N = int(lines[0]) for testcase, i in enumerate(range(1,2*N,2)): G = int(lines[i]) for guest in range(G): codes = map(int, lines[i+1].split(' ')) alone = (c for c in codes if codes.count(c)==1) output.write("Case #%d: %d\n" % (testcase+1, alone.next())) It runs in 12 seconds on my machine with the large input. Now, my question is, can this solution be improved in Python to run in a shorter time or use less memory? The analysis of the problem gives some pointers on how to do this in Java and C++ but I can't translate those solutions back to Python.

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  • multiple inheritance

    - by hitech
    when we say "a member declated as protected is accessible to any class imediately derived from it" what does this mean. in the follwing example get_number function can be accessible by the result class , as per the statement it sould only be accessile to test class. class student { protected: int roll_number; public: void get_number(int){ cout<< "hello"; } void put_number(void) {cout<< "hello"; } }; class test : public student { protected : float sub1; float sub2; public: void get_marks(float, float) {cout<< "hello"; roll_number = 10; } void put_marks(void) {cout<< "hello"; cout << "roll_number = " << roll_number ; } }; class result :public test { float total; public: void display(){cout<< "hello"; roll_number = 10; } }; int main() { result student; student.get_marks(2.2, 2.2); student.put_marks(); return 0; } i changed the code as per the first statement the protected variable roll_number not be accessible upto the result class ?

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  • Need to sort 3 arrays by one key array

    - by jeff6461
    I am trying to get 3 arrays sorted by one key array in objective c for the iphone, here is a example to help out... Array 1 Array 2 Array 3 Array 4 1 15 21 7 3 12 8 9 6 7 8 0 2 3 4 8 When sorted i want this to look like Array 1 Array 2 Array 3 Array 4 1 15 21 7 2 3 4 8 3 12 8 9 6 7 8 0 So array 2,3,4 are moving with Array 1 when sorted. Currently i am using a bubble sort to do this but it lags so bad that it crashes by app. The code i am using to do this is int flag = 0; int i = 0; int temp = 0; do { flag=1; for(i = 0; i < distancenumber; i++) { if(distance[i] > distance[i+1]) { temp = distance[i]; distance[i]=distance[i + 1]; distance[i + 1]=temp; temp = FlowerarrayNumber[i]; FlowerarrayNumber[i] = FlowerarrayNumber[i+1]; FlowerarrayNumber[i + 1] = temp; temp = BeearrayNumber[i]; BeearrayNumber[i] = BeearrayNumber[i + 1]; BeearrayNumber[i + 1] = temp; flag=0; } } }while (flag==0); where distance number is the amount of elements in all of the arrays, distance is array 1 or my key array. and the other 2 are getting sorted. If anyone can help me get a merge sort(or something faster, it is running on a iPhone so it needs to be quick and light) to do this that would be great i cannot figure out how the recursion works in this method and so having a hard time to get the code to work. Any help would be greatly appreciated

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  • Rotate a linked list

    - by user408041
    I want to rotate a linked list that contains a number. 123 should be rotated to 231. The function created 23 but the last character stays empty, why? typedef struct node node; struct node{ char digit; node* p; }; void rotate(node** head){ node* walk= (*head); node* prev= (*head); char temp= walk->digit; while(walk->p!=NULL){ walk->digit=walk->p->digit; walk= walk->p; } walk->digit=temp; } How I create the list: node* convert_to_list(int num){ node * curr, * head; int i=0,length=0; char *arr=NULL; head = NULL; length =(int) log10(((double) num))+1; arr =(char*) malloc((length)*sizeof(char)); //allocate memory sprintf (arr, "%d" ,num); //(num, buf, 10); for(i=length;i>=0;i--) { curr = (node *)malloc(sizeof(node)); (curr)->digit = arr[i]; (curr)->p = head; head = curr; } curr = head; return curr; }

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  • Encrypting a file in win API

    - by Kristian
    hi I have to write a windows api code that encrypts a file by adding three to each character. so I wrote this now its not doing anything ... where i go wronge #include "stdafx.h" #include <windows.h> int _tmain(int argc, _TCHAR* argv[]) { HANDLE filein,fileout; filein=CreateFile (L"d:\\test.txt",GENERIC_READ,0,NULL,OPEN_ALWAYS,FILE_ATTRIBUTE_NORMAL,NULL); fileout=CreateFile (L"d:\\test.txt",GENERIC_WRITE,0,NULL,CREATE_ALWAYS,FILE_ATTRIBUTE_NORMAL,NULL); DWORD really; //later this will be used to store how many bytes I succeed to read do { BYTE x[1024]; //the buffer the thing Im using to read in ReadFile(filein,x,1024,&really,NULL); for(int i=0 ; i<really ; i++) { x[i]= (x[i]+3) % 256; } DWORD really2; WriteFile(fileout,x,really,&really2,NULL); }while(really==1024); CloseHandle(filein); CloseHandle(fileout); return 0; } and if Im right how can i know its ok

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  • post increment operator java

    - by srandpersonia
    I can't make heads or tails of the following code from "java puzzlers" by joshua bloch. public class Test22{ public static void main(String args[]){ int j=0; for(int i=0;i<100;i++){ j=j++; } System.out.println(j); //prints 0 int a=0,b=0; a=b++; System.out.println(a); System.out.println(b); //prints 1 } } I can't get the part where j prints 0. According to the author, j=j++ is similar to temp=j; j=j+1; j=temp; But a=b++ makes b 1. So it should've evaluated like this, a=b b=b+1 By following the same logic, shouldn't j=j++ be evaluated as, j=j j=j+1 Where does the temp come into picture here? Any explanations would be much appreciated. << I'm breaking my head over this. ;) Thanks in advance.

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  • Reverse String Error?

    - by R41nB0w M47r1z
    I am creating this revese string App but i get a error if i include a space in the string ! #include <iostream> #include <string> using namespace std; int main() { int inputa; cout<<"%%%%%%%%%%%%%%%%%%String Reversing App%%%%%%%%%%%%%%%%%%%%%%%%"<<endl<<endl; cout<<"\nEnter 1 to continue and 0 to exit"<<endl<<endl; cin>>inputa; if(inputa!=0) { do { string a,c=""; cout<<"\nEnter the string you want to Reverse : "; cin>>a; for(int x=a.length()-1; x>=0; x--) { c=c+a.substr(x,1); } cout<<"\nThe Reverse String is : "<<c<<endl; cout<<"\nEnter 1 to continue and 0 to exit"<<endl<<endl; cin>>inputa; } while(inputa!=0); } //not my home work } If I type the following string like "abc def" there i get an error . But otherwise it works perfectly ! Is there some mistake with the codes ! I am new to CPP so it would be helpful if you could help me !

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  • "for" loop from program 7.6 from Kochan's "Programming in Objective-C"

    - by Mr_Vlasov
    "The sigma notation is shorthand for a summation. Its use here means to add the values of 1/2^i, where i varies from 1 to n. That is, add 1/2 + 1/4 + 1/8 .... If you make the value of n large enough, the sum of this series should approach 1. Let’s experiment with different values for n to see how close we get." #import "Fraction.h" int main (int argc, char *argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; Fraction *aFraction = [[Fraction alloc] init]; Fraction *sum = [[Fraction alloc] init], *sum2; int i, n, pow2; [sum setTo: 0 over: 1]; // set 1st fraction to 0 NSLog (@"Enter your value for n:"); scanf ("%i", &n); pow2 = 2; for (i = 1; i <= n; ++i) { [aFraction setTo: 1 over: pow2]; sum2 = [sum add: aFraction]; [sum release]; // release previous sum sum = sum2; pow2 *= 2; } NSLog (@"After %i iterations, the sum is %g", n, [sum convertToNum]); [aFraction release]; [sum release]; [pool drain]; return 0; } Question: Why do we have to create additional variable sum2 that we are using in the "for" loop? Why do we need "release previous sum" here and then again give it a value that we just released? : sum2 = [sum add: aFraction]; [sum release]; // release previous sum sum = sum2; Is it just for the sake of avoiding memory leakage? (method "add" initializes a variable that is stored in sum2)

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  • MySql stored procedure not found in PHP

    - by kaupov
    Hello, I have a trouble with MySql stored procedure that calls itself recursively using PHP (CakePHP). Calling it I receive following error: SQL Error: 1305: FUNCTION dbname.GetAdvertCounts does not exist The procedure itself is following: delimiter // DROP PROCEDURE IF EXISTS GetAdvertCounts// CREATE PROCEDURE GetAdvertCounts(IN category_id INT) BEGIN DECLARE no_more_sub_categories, advert_count INT DEFAULT 0; DECLARE sub_cat_id INT; DECLARE curr_sub_category CURSOR FOR SELECT id FROM categories WHERE parent_id = category_id; DECLARE CONTINUE HANDLER FOR NOT FOUND SET no_more_sub_categories = 1; SELECT COUNT(*) INTO advert_count FROM adverts WHERE category_id = category_id; OPEN curr_sub_category; FETCH curr_sub_category INTO sub_cat_id; REPEAT SELECT advert_count + GetAdvertCounts(sub_cat_id) INTO advert_count; FETCH curr_sub_category INTO sub_cat_id; UNTIL no_more_sub_categories = 1 END REPEAT; CLOSE curr_sub_category; SELECT advert_count; END // delimiter ; If I remove or comment out the recursive call, the procedure is working. Any idea what I'm missing here? The categories are 2 level deep.

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  • SQL: find entries in 1:n relation that don't comply with condition spanning multiple rows

    - by milianw
    I'm trying to optimize SQL queries in Akonadi and came across the following problem that is apparently not easy to solve with SQL, at least for me: Assume the following table structure (should work in SQLite, PostgreSQL, MySQL): CREATE TABLE a ( a_id INT PRIMARY KEY ); INSERT INTO a (a_id) VALUES (1), (2), (3), (4); CREATE TABLE b ( b_id INT PRIMARY KEY, a_id INT, name VARCHAR(255) NOT NULL ); INSERT INTO b (b_id, a_id, name) VALUES (1, 1, 'foo'), (2, 1, 'bar'), (3, 1, 'asdf'), (4, 2, 'foo'), (5, 2, 'bar'), (6, 3, 'foo'); Now my problem is to find entries in a that are missing name entries in table b. E.g. I need to make sure each entry in a has at least the name entries "foo" and "bar" in table b. Hence the query should return something similar to: a_id = 3 is missing name "bar" a_id = 4 is missing name "foo" and "bar" Since both tables are potentially huge in Akonadi, performance is of utmost importance. One solution in MySQL would be: SELECT a.a_id, CONCAT('|', GROUP_CONCAT(name ORDER BY NAME ASC SEPARATOR '|'), '|') as names FROM a LEFT JOIN b USING( a_id ) GROUP BY a.a_id HAVING names IS NULL OR names NOT LIKE '%|bar|foo|%'; I have yet to measure the performance tomorrow, but severly doubt it's any fast for tens of thousand of entries in a and thrice as many in b. Furthermore we want to support SQLite and PostgreSQL where to my knowledge the GROUP_CONCAT function is not available. Thanks, good night.

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