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  • array, I/O file and standard deviation (c++)

    - by JohnWong
    double s_deviation(double data[],int cnt, double mean) { int i; double sum= 0; double sdeviation; double x; //x = mean(billy,a_size); for(i=0; i<cnt; i++) { sum += ((data[i]) - (mean)); } sdeviation = sqrt(sum/((double)cnt)); return sdeviation; } When I cout the result from this function, it gave me NaN. I tested the value of (mean) and data[i] using return data[i] and return mean they are valid. when i replaced mean with an actual number, the operation returned a finite number. but with mean as a variable, it produced NaH. I can't see anything wrong with my code at the moment. Again, I am sure mean, data are getting the right number based on those tests. Thank you

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  • Performance hit from C++ style casts?

    - by Trevor Boyd Smith
    I am new to C++ style casts and I am worried that using C++ style casts will ruin the performance of my application because I have a real-time-critical deadline in my interrupt-service-routine. I heard that some casts will even throw exceptions! I would like to use the C++ style casts because it would make my code more "robust". However, if there is any performance hit then I will probably not use C++ style casts and will instead spend more time testing the code that uses C-style casts. Has anyone done any rigorous testing/profiling to compare the performance of C++ style casts to C style casts? What were your results? What conclusions did you draw?

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  • How to display multiple categories and products underneath each category?

    - by shin
    Generally there is a category menu and each link to a category page where shows all the items under that category. Now I need to show all the categories and products underneath with PHP/MySQL in the same page. So it will be like this. Category 1 description of category 1 item 1 item 2 .. Category 2 description of category 2 item 5 item 6 .. Category 3 description of category 3 item 8 item 9 ... ... I have category and product table in my database. But I am not sure how to proceed. CREATE TABLE IF NOT EXISTS `omc_product` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL, `shortdesc` varchar(255) NOT NULL, `longdesc` text NOT NULL, `thumbnail` varchar(255) NOT NULL, `image` varchar(255) NOT NULL, `product_order` int(11) DEFAULT NULL, `class` varchar(255) DEFAULT NULL, `grouping` varchar(16) DEFAULT NULL, `status` enum('active','inactive') NOT NULL, `category_id` int(11) NOT NULL, `featured` enum('none','front','webshop') NOT NULL, `other_feature` enum('none','most sold','new product') NOT NULL, `price` float(7,2) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ; CREATE TABLE IF NOT EXISTS `omc_category` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL, `shortdesc` varchar(255) NOT NULL, `longdesc` text NOT NULL, `status` enum('active','inactive') NOT NULL, `parentid` int(11) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ; I will appreciate your help. Thanks in advance.

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  • how to start learning JavaScript

    - by antriksh
    Dear All, I am experienced in the technical support like Linux, oracle, sunos etc and but if i say scripting i know little bit of bash. Now i promoted to manage technical engineers including some JavaScript developers, so i want to learn JavaScripting so that i can understand engineers. Hope you understand. Can you please advise me how can i start JavaScripting and point me to some simple docs and examples.

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  • C++ Template problem adding two data types

    - by Sara
    I have a template class with an overloaded + operator. This is working fine when I am adding two ints or two doubles. How do I get it to add and int and a double and return the double? template <class T> class TemplateTest { private: T x; public: TemplateTest<T> operator+(const TemplateTest<T>& t1)const { return TemplateTest<T>(x + t1.x); } } in my main function i have void main() { TemplateTest intTt1 = TemplateTest<int>(2); TemplateTest intTt2 = TemplateTest<int>(4); TemplateTest doubleTt1 = TemplateTest<double>(2.1d); TemplateTest doubleTt2 = TemplateTest<double>(2.5d); std::cout << intTt1 + intTt2 << /n; std::cout << doubleTt1 + doubleTt2 << /n; } I want to be able to also do this std::cout << doubleTt1 + intTt2 << /n;

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  • Why C++ is (one of) the best language to learn at first [closed]

    - by AlexV
    C++ is one of the most used programming language in the world since like 25+ years. My first job as programmer was in C++ and I coded in C++ everyday for nearly 4 years. Now I do mostly PHP, but I will forever cherish this C++ background. C++ has helped me understand many "under the hood" features/behaviors/restrictions of many other (and different) programming languages like PHP and Delphi. I'm a full time programmer for 6+ years now and since I have a quite varied programming background I often get questions by "newbies" as where to start to become a "good" programmer. I think C++ is one of the best language to start with because it gives you a real usefull experience that will last and will teach you how things work under the hood. It's not the easier one to learn for a newbie, but in my opinion it's the one who will reward the most in long term. I would like to know your opinion on this matter to add to my arguments when I guide "newbies". After this introduction, here's my question : Why C++ is for you (one of) the best language to learn at first. Since it's subjective, I've marked this question as community wiki.

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  • C Array of string

    - by Meko
    HI. This is maybe simple question but I want to create two dimensional array and add it string like in java string str = "text" ; string [][] array = new [][] string ; array[i][j] = str ; But in C there is no string .I tried like this but here strcpy() gives error.It returns to assembly code. I am trying to read line by line from text and split line by space and add them to structure.But first I think that I must add each line and row in array and then making iteration and adding to structures fields. static const char filename[] = "student.txt"; FILE *file = fopen ( filename, "r" ); char line [ 128 ]; /* or other suitable maximum line size */ char delims [ ]=" "; char *result =NULL; char list[15]; char arra[128][128]; int i=0; int j=0; struct { char gruppa[10]; char familiya[20]; int uchaste; struct { int firsth; int second; int third; int fourht; int fifth; } exam; }student; for(i=0; i<128; i++) for(j=0; j<128; j++) arra[i][j] = '\0'; for(i=0; i<15; i++) list[i] = '\0'; if ( file != NULL ) { while ( fgets ( line, sizeof line, file ) != NULL ) { result = strtok(line,delims); while (result !=NULL) { strcpy(list,("%s",result)); strcpy(arra[i][j],list); // Here it gives errror j++; result = strtok(NULL,delims); } j=0; i++; } fclose ( file ); } else { perror ( filename ); } getchar(); return 0; }

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  • Beginning python for the web

    - by Josh K
    I'm looking for a nice tutorial or framework for developing Python written web applications. I've done lots in PHP, but very little in Python or Ruby and figured I'd start with the first one alphabetically.

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  • NoneType has no attribute Append

    - by Rosarch
    I'm new to Python. I can't understand why a variable is None at a certain point in my code: class UsersInRoom(webapp.RequestHandler): def get(self): room_id = self.request.get("room_id") username = self.request.get("username") UserInRoom_entities = UserInRoom.gql("WHERE room = :1", room_id).get() if UserInRoom_entities: for user_in_room in UserInRoom_entities: if user_in_room.username == username: user_in_room.put() # last_poll auto updates to now whenenever user_in_room is saved else: user_in_room = UserInRoom() user_in_room.username = username user_in_room.put() UserInRoom_entities = [] UserInRoom_entities.append(user_in_room) // error here # name is `user_at_room` intead of `user_in_room` to avoid confusion usernames = [user_at_room.username for user_at_room in UserInRoom_entities] self.response.out.write(json.dumps(usernames)) The error is: Traceback (most recent call last): File "C:\Program Files\Google\google_appengine\google\appengine\ext\webapp\__init__.py", line 507, in __call__ handler.get(*groups) File "path\to\chat.py", line 160, in get AttributeError: 'NoneType' object has no attribute 'append' How is this possible? I'm setting UserInRoom_entities = [] immediately before that call. Or is something else the None in question?

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  • How do I define a monadic function to work on a list in J?

    - by Gregory Higley
    Let's say I have the following J expression: # 3 ((|=0:)#]) 1+i.1000 This counts the number of numbers between 1 and 1000 that are evenly divisible by 3. (Now, before anyone points out that there's an easier way to do this, this question is about the syntax of J, and not mathematics.) Let's say I define a monadic function for this, as follows: f =: monad define # y ((|=0:)#]) 1+i.1000 ) This works great with a single argument, e.g., f 4 250 If I pass a list in, I get a length error: f 1 2 3 |length error: f Now, I completely understand why I get the length error. When you substitute the list 1 2 3 for the y argument of the monad, you get: # 1 2 3 ((|=0:)#]) 1+i.1000 If you know anything about J, it's pretty clear why the length error is occurring. So, I don't need an explanation of that. I want to define the function such that when I pass a list, it returns a list, e.g., f 1 2 3 1000 500 333 How can I either (a) redefine this function to take a list and return a list or (b) get the function to work on a list as-is without being redefined, perhaps using some adverb or other technique?

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  • Using Python, How to copy files in 'temporary internet files' folder in Windows

    - by pythBegin
    I am using this code to find files recursively in a folder , with size greater than 50000 bytes. def listall(parent): lis=[] for root, dirs, files in os.walk(parent): for name in files: if os.path.getsize(os.path.join(root,name))>500000: lis.append(os.path.join(root,name)) return lis This is working fine. But when I used this on 'temporary internet files' folder in windows, am getting this error. Traceback (most recent call last): File "<pyshell#4>", line 1, in <module> listall(a) File "<pyshell#2>", line 5, in listall if os.path.getsize(os.path.join(root,name))>500000: File "C:\Python26\lib\genericpath.py", line 49, in getsize return os.stat(filename).st_size WindowsError: [Error 123] The filename, directory name, or volume label syntax is incorrect: 'C:\\Documents and Settings\\khedarnatha\\Local Settings\\Temporary Internet Files\\Content.IE5\\EDS8C2V7\\??????+1[1].jpg' I think this is because windows gives names with special characters in this specific folder... Please help to sort out this issue.

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  • Is there an algorithm for finding an item that matches certain properties, like a 20 questions game?

    - by lala
    A question about 20 questions games was asked here: However, if I'm understanding it correctly, the answers seem to assume that each question will go down a hierarchal branching tree. A binary tree should work if the game went like this: Is it an animal? Yes. Is it a mammal? Yes. Is it a feline? Yes. Because feline is an example of a mammal and mammal is an example of an animal. But what if the questions go like this? Is it a mammal? Yes. Is it a predator? Yes. Does it have a long nose? No. You can't branch down a tree with those kinds of questions, because there are plenty of predators that aren't mammals. So you can't have your program just narrow it down to mammal and have predators be a subset of mammals. So is there a way to use a binary search tree that I'm not understanding or is there a different algorithm for this problem?

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  • Dynamically calling functions - Python

    - by RadiantHex
    Hi folks, I have a list of functions... e.g. def filter_bunnies(pets): ... def filter_turtles(pets): ... def filter_narwhals(pets): ... Is there a way to call these functions by using a string representing their name? e.g. 'filter_bunnies', 'filter_turtles', 'filter_narwhals'

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  • Concatenation of many lists in Python

    - by Space_C0wb0y
    Suppose i have a function like this: def getNeighbors(vertex) which returns a list of vertices that are neighbors of the given vertex. Now i want to create a list with all the neighbors of the neighbors. I do that like this: listOfNeighborsNeighbors = [] for neighborVertex in getNeighbors(vertex): listOfNeighborsNeighbors.append(getNeighbors(neighborsVertex)) Is there a more pythonic way to do that?

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  • Why does initWithFrame have the wrong frame value?

    - by greypoint
    I have a subclass of UIButton called INMenuCard and I am overriding the initWithFrame to include an activity indicator. The menuCard places correctly but any internal reference to "frame" give me "inf,inf,0,0" which means my activityIndicator subview is not placed correctly. What might I be missing? @implementation INMenuCard - (id)initWithFrame:(CGRect)frame { if (self = [super initWithFrame:frame]) { CGRect innerFrame = CGRectInset(frame, 50.0f, 100.0f); activityIndicator = [[UIActivityIndicatorView alloc] initWithFrame:innerFrame]; activityIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyleWhite; [self addSubview:activityIndicator]; } return self; } I am instantiating INMenuCard with (debugging shows the CGRect values are correct): CGRect cardFrame = CGRectMake(cardX, cardStartY, cardWidth, cardHeight); INMenuCard *menuCard = [[INMenuCard buttonWithType:UIButtonTypeCustom] initWithFrame:cardFrame]; [theView addSubView:menuCard];

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  • Array of function pointers in Java

    - by Waltzy
    I have read this question and I'm still not sure whether it is possible to keep pointers to methods in an array in Java, if anyone knows if this is possible or not it would be a real help. I'm trying to find an elegant solution of keeping a list of Strings and associated functions without writing a mess of hundreds of 'if's. Cheers edit- 'functions' changed to 'methods', seems to bug people.

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  • Permutations in python 2.5.2

    - by flpgdt
    Hi, I have a list of numbers for input, e.g. 671.00 1,636.00 436.00 9,224.00 and I want to generate all possible sums with a way to id it for output, e.g.: 671.00 + 1,636.00 = 2,307.00 671.00 + 436.00 = 1,107.00 671.00 + 9,224.00 = 9,224.00 671.00 + 1,636.00 + 436.00 = 2,743.00 ... and I would like to do it in Python My current constrains are: a) I'm just learning python now (that's part of the idea) b) I will have to use Python 2.5.2 (no intertools) I think I have found a piece of code that may help: def all_perms(str): if len(str) <=1: yield str else: for perm in all_perms(str[1:]): for i in range(len(perm)+1): #nb str[0:1] works in both string and list contexts yield perm[:i] + str[0:1] + perm[i:] ( from these guys ) But I'm not sure how to use it in my propose. Could someone trow some tips and pieces of code of help? cheers, f.

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  • C++: calling member functions within constructor?

    - by powerboy
    The following code raises a runtime error: #include <iostream> #include <iterator> #include <ext/slist> class IntList : public __gnu_cxx::slist<int> { public: typedef IntList::iterator iterator; IntList() { tail_ = begin(); } // seems that there is a problem here void append(const int node) { tail_ = insert_after(tail_, node); } private: iterator tail_; }; int main() { IntList list; list.append(1); list.append(2); list.append(3); for (IntList::iterator i = list.begin(); i != list.end(); ++i) { std::cout << *i << " "; } return 0; } Seems that the problem is in the constructor IntList(). Is it because it calls the member function begin()?

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  • jQuery: What does (function($) {})(jQuery); mean?

    - by Legend
    I am just starting out with writing jQuery plugins. I wrote three small plugins but I have been simply copying the line into all my plugins without actually knowing what it means. Can someone tell me a little more about these? What does this do? (I know it extends jQuery somehow but is there anything else interesting to know about this) (function($) { })(jQuery); What is the difference between the following two ways of writing a plugin: Type 1: (function($) { $.fn.jPluginName = { }, $.fn.jPluginName.defaults = { } })(jQuery); Type 2: (function($) { $.jPluginName = { } })(jQuery); I could be way off here and maybe both mean the same thing. In some cases, this doesn't seem to be working in a plugin that I was writing using Type 1. Any idea why? But in either case, I would appreciate any explanation.

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