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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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  • Adding li element only if it not already there?

    - by Legend
    I am constructing an <li> element like this: var element = $("<li></li>") .html(mHTML) .attr('id', "elemid"); I am trying to add this element to a <ul> element only if it doesn't already exist. Any ideas on how to do this? Am I supposed to use contains() to see if the ul element contain the html and then decide? For instance, <ul id="elemul"> <li id="elemli1">Element 1</li> <li id="elemli2">Element 2</li> <li id="elemli3">Element 3</li> </ul> If I try adding Element 1, it should not add it. What should I do if its a longer string (not really long but about 150 characters). Note: I cannot rely on IDs to determine the uniqueness. i.e. I might end up forming something like: <li id="elemli3">Element 1</li> Do I go about using hashmaps?

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  • What are the books about Open-Source that everyone interested in should read?

    - by Edu Zamora
    Currently I am working and running my first Open-Source project and though I am quite happy how things are working so far, I have the feeling that a lot of things could be done better. So, what books about Open-Source would you recommend me in order to help filling this gap and making things better every day? What are the books that influenced you the most? I am especially interested in: - How to organize and run an Open-Source project - Best practices - Manage and involve users and developers - How to announce and do the releases - Legal issues

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  • What are "named tuples" in Python?

    - by Denilson Sá
    Reading the changes in Python 3.1, I found something... unexpected: The sys.version_info tuple is now a named tuple: I never heard about named tuples before, and I thought elements could either be indexed by numbers (like in tuples and lists) or by keys (like in dicts). I never expected they could be indexed both ways. Thus, my questions are: What are named tuples? How to use them? Why/when should I use named tuples instead of normal tuples? Why/when should I use normal tuples instead of named tuples? Is there any kind of "named list" (a mutable version of the named tuple)?

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  • do the Python libraries have a natural dependence on the global namespace?

    - by msw
    I first ran into this when trying to determine the relative performance of two generators: t = timeit.repeat('g.get()', setup='g = my_generator()') So I dug into the timeit module and found that the setup and statement are evaluated with their own private, initially empty namespaces so naturally the binding of g never becomes accessible to the g.get() statement. The obvious solution is to wrap them into a class, thus adding to the global namespace. I bumped into this again when attempting, in another project, to use the multiprocessing module to divide a task among workers. I even bundled everything nicely into a class but unfortunately the call pool.apply_async(runmc, arg) fails with a PicklingError because buried inside the work object that runmc instantiates is (effectively) an assignment: self.predicate = lambda x, y: x > y so the whole object can't be (understandably) pickled and whereas: def foo(x, y): return x > y pickle.dumps(foo) is fine, the sequence bar = lambda x, y: x > y yields True from callable(bar) and from type(bar), but it Can't pickle <function <lambda> at 0xb759b764>: it's not found as __main__.<lambda>. I've given only code fragments because I can easily fix these cases by merely pulling them out into module or object level defs. The bug here appears to be in my understanding of the semantics of namespace use in general. If the nature of the language requires that I create more def statements I'll happily do so; I fear that I'm missing an essential concept though. Why is there such a strong reliance on the global namespace? Or, what am I failing to understand? Namespaces are one honking great idea -- let's do more of those!

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  • How to wrap a C function whose parameters are pointer to structs, so that it can be called from Lua?

    - by pierr
    I have the follwing C function. How should I wrap it so it can be called from a Lua script? typedef struct tagT{ int a ; int b ; } type_t; int lib_a_f_4(type_t *t) { return t->a * t->b ; } I know how to wrapr it if the function parameter type were int or char *. Should I use table type for a C structure? EDIT: I am using SWIG for the wraping , according to this doc, It seems that I should automatically have this funtion new_type_t(2,3) , but it is not the case. If you wrap a C structure, it is also mapped to a Lua userdata. By adding a metatable to the userdata, this provides a very natural interface. For example, struct Point{ int x,y; }; is used as follows: p=example.new_Point() p.x=3 p.y=5 print(p.x,p.y) 3 5 Similar access is provided for unions and the data members of C++ classes. C structures are created using a function new_Point(), but for C++ classes are created using just the name Point().

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  • jQuery: Adding li element only if it not already there?

    - by Legend
    I am constructing an <li> element like this: var element = $("<li></li>") .html(mHTML) .attr('id', "elemid"); I am trying to add this element to a <ul> element only if it doesn't already exist. Any ideas on how to do this? Am I supposed to use contains() to see if the ul element contain the html and then decide? For instance, <ul id="elemul"> <li id="elemli1">Element 1</li> <li id="elemli2">Element 2</li> <li id="elemli3">Element 3</li> </ul> If I try adding Element 1, it should not add it. What should I do if its a longer string (not really long but about 150 characters). Do I go about using hashmaps?

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  • Assigning a value to a variable gets stored in the wrong spot?

    - by scribbloid
    Hello, I'm relatively new to C, and this is baffling me right now. It's part of a much larger program, but I've written this little program to depict the problem I'm having. #include <stdio.h> int main() { signed int tcodes[3][1]; tcodes[0][0] = 0; tcodes[0][1] = 1000; tcodes[1][0] = 1000; tcodes[1][1] = 0; tcodes[2][0] = 0; tcodes[2][1] = 1000; tcodes[3][0] = 1000; tcodes[3][1] = 0; int x, y, c; for(c = 0; c <= 3; c++) { printf("%d %d %d\r\n", c, tcodes[c][0], tcodes[c][1]); x = 20; y = 30; } } I'd expect this program to output: 0 0 1000 1 1000 0 2 0 1000 3 1000 0 But instead, I get: 0 0 1000 1 1000 0 2 0 20 3 20 30 It does this for any number assigned to x and y. For some reason x and y are overriding parts of the array in memory. Can someone explain what's going on? Thanks!

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  • How can I know whether my C++ string variable is a number or not

    - by user342580
    I have a string of class string string str; how can I check if it is a number or not, str can only have 3 possible types described below like abcd or a number like 123.4 or a number with a parenthesis attach to the end it for example 456) note the parenthesis at the end of "str" is the only possible combination of number and none number where the bottom two are considered valid numbers, I know I could use lexical_cast if only the first 2 cases occur, but how about considering all 3 possible cases to occur? I don't need to do anything fancy with str, I just need to know whether it is a valid number as I described

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  • number of elements in a static array of a predefined size

    - by cppb
    I have an array like this: int a[100]; I am filling only the first 4 elements in this array: a[0] = 1; a[1] = 2; a[2] = 3; a[3] = 4; When I do sizeof(a)/sizeof(a[0]) it returns 100. Is there a way I can get number of elements to which I have assinged a value and thus filtering out the remaining 96 unassigned elements? thanks

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  • Java newbie problem: classes of the same package accessing one another?

    - by HH
    Test.java and SetWord.java belong to the package tools. Test.java needs to access SetWord but an odd error 'cannot find' SetWord appear. The package limits the visibility, it works without 'package tools;' lines. How can I acess the SetWords with Test in the same pkg? In general, how can classes access one another in the same pkg? Test.java package tools; import java.io.*; import java.util.*; public class Test{ public static void main(String[] args) { //IT CANNOT FIND SetWords despite the same folder, why? SetWord sw=new SetWord(); System.out.println(st.set("HELLO)"); } } SetWord.java package tools; import java.io.*; import java.util.*; public class SetWord{ public SetWord(){} public String set(String s) { return s.trim().toLowerCase(); } }

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  • simple putStrLn in Haskell/Yampa with arrows syntax

    - by sisif
    i'm using Haskell with the Yampa FRP library which uses the arrows language extension. how can i do a simple putStrLn in a SF? mySF = proc x -> do y <- identity -< x*x putStrLn "Hello World!" ++ show y returnA -< y the arrow syntax complains about the expression not bein an arrow (of course), but even with arrows i get no output output <- identity -< putStrLn "Hello World!"

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  • Problems with Ruby "||" "or"?

    - by Kevin
    Beginning Ruby Question: I'm trying to see if a string variable's contents is either "personal" "email" or "password". I'm trying: if params[:action] == "password" || "email" || "personal" foo else don't foo end But that doesn't work and returns strange results, and using IRB to play around with "or" statements I have no idea why the following happens: irb(main):040:0> a = "email" => "email" irb(main):041:0> a == "password" || "email" => "email" irb(main):042:0> a == "email" || "password" => true I just want something that if any of the 3 variables are true no matter what order they are in it returns true, if not it returns false. Anyone want to help this n00b out?

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  • Understanding CGI and SQL security from the ground up

    - by Steve
    This question is for learning purposes. Suppose I am writing a simple SQL admin console using CGI and Python. At http://something.com/admin, this admin console should allow me to modify a SQL database (i.e., create and modify tables, and create and modify records) using an ordinary form. In the least secure case, anybody can access http://something.com/admin and modify the database. You can password protect http://something.com/admin. But once you start using the admin console, information is still transmitted in plain text. So then you use HTTPS to secure the transmitted data. Questions: To describe to a learner, how would you incrementally add security to the least secure environment in order to make it most secure? How would you modify/augment my three (possibly erroneous) steps above? What basic tools in Python make your steps possible? Optional: Now that I understand the process, how do sophisticated libraries and frameworks inherently achieve this level of security?

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  • mapping list of different types implementing same function?

    - by sisif
    I want to apply a function to every element in a list (map) but the elements may have different types but all implement the same function (here "putOut") like an interface. However I cannot create a list of this "interface" type (here "Outputable"). How do I map a list of different types implementing the same function? main :: IO () main = do map putOut lst putStrLn "end" where lst :: [Outputable] -- ERROR: Class "Outputable" used as a type lst = [(Out1 1),(Out2 1 2)] class Outputable a where putOut :: a -> IO () -- user defined: data Out1 = Out1 Int deriving (Show) data Out2 = Out2 Int deriving (Show) instance Outputable Out1 where putOut out1 = putStrLn $ show out1 instance Outputable Out2 where putOut out2 = putStrLn $ show out2 I cannot define it this way: data Out = Out1 Int | Out2 Int Int putOut Out1 = ... putOut Out2 = ... because this is a library and users should be able to extend Out with their own types

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  • c++ meaning of the use of const in the signature

    - by jbu
    Please help me understand the following signature: err_type funcName(const Type& buffer) const; so for the first const, does that mean the contents of Type cannot change or that the reference cannot change? secondly, what does the second const mean? I don't really even have a hint. Thanks in advance, jbu

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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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