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  • Expression Tree : C#

    - by nettguy
    My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally when our LINQ to SQL query compiler translates it to parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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  • Use case modelling for calculator

    - by kyrogue
    hi, i need help modelling a use case diagram from a topic, it will be in java GUI Design a Calculator that 1.Allow user to key in a legitimate arithmetic statement that involves number, operator +, - and bracket '(' and ')' ; 2.When user press “Calculate” button, display result; 3.Some legitimate statement would be ((3+2)-4+2) (equals 3) and (-2+3)-(3-1) (equals -1); 4.You should NOT use a pre-existing function that just take in the statement as a parameter and returns the result but you should write the logic of parsing every character in your code. 5.Store the last statement and answer so it is displayed when user press the “Last calculation” button. i have designed two use case diagrams using UML on netbeans 6.5.1, one of the use case i am not sure whether is it containing too much use cases etc, while the other is what i think could be too vague for the topic.i hope to get some feedback on whether the use case diagram are appropriate, thanks.

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  • Is there any sense in performing binary AND with a number where all bits are set to 1

    - by n535
    Greetings everybody. I have seen examples of such operations for so many times that I begin to think that I am getting something wrong with binary arithmetic. Is there any sense to perform the following: byte value = someAnotherByteValue & 0xFF; I don't really understand this, because it does not change anything anyway. Thanks for help. P.S. I was trying to search for information both elsewhere and here, but unsuccessfully. EDIT: Well, off course i assume that someAnotherByteValue is 8 bits long, the problem is that i don't get why so many people ( i mean professionals ) use such things in their code. For example in Jon Skeet's MiscUtil there is: uint s1 = (uint)(initial & 0xffff); where initial is int.

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  • Are all the system's floating points operations the same?

    - by Jj
    We're making this web app in PHP and when working in the reports we have Excel files to compare our results to make sure our coding is doing the right operations. Now we're running into some differences due floating point arithmetics. We're doing the same divisions and multiplications and running into slightly different numbers, that add up to a notable difference. My question is if Excel is delegating it's floating point arithmetic to the CPU and PHP is also relying in the CPU for it's operations. Or does each application implements its own set of math algorithms?

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  • Currency Math in JavaScript

    - by Jared
    Can someone please help me out with a JavaScript/jQuery solution for this arithmetic problem: I need to subtract one number from the other. The problem is that the numbers have a dollar sign (because its money), therefore jQuery is treating them as strings instead of numbers. I have created two variables - toalAssets and totalLiabilites. I would like to subtract the latter from the former and place the result into another variable called netWorth. Perhaps i need to use parseFloat()? But I'm not sure how - This is all a little over my head!

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  • Manipulating and comparing floating points in java

    - by Praneeth
    In Java the floating point arithmetic is not represented precisely. For example following snippet of code float a = 1.2; float b= 3.0; float c = a * b; if(c == 3.6){ System.out.println("c is 3.6"); } else { System.out.println("c is not 3.6"); } actually prints "c is not 3.6". I'm not interested in precision beyond 3 decimals (#.###). How can I deal with this problem to multiply floats and compare them reliably? Thanks much

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  • Why won't this SQL CAST work?

    - by Kev
    I have a nvarchar(50) column in a SQL Server 2000 table defined as follows: TaskID nvarchar(50) NULL I need to fill this column with some random SQL Unique Identifiers (I am unable to change the column type to uniqueidentifier). I tried this: UPDATE TaskData SET TaskID = CAST(NEWID() AS nvarchar) but I got the following error: Msg 8115, Level 16, State 2, Line 1 Arithmetic overflow error converting expression to data type nvarchar. I also tried: UPDATE TaskData SET TaskID = CAST(NEWID() AS nvarchar(50)) but then got this error: Msg 8152, Level 16, State 6, Line 1 String or binary data would be truncated. I don't understand why this doesn't work but this does: DECLARE @TaskID nvarchar(50) SET @TaskID = CAST(NEW() AS nvarchar(50)) I also tried CONVERT(nvarchar, NEWID()) and CONVERT(nvarchar(50), NEWID()) but got the same errors.

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  • Performance intensive string splitting and manipulation in java

    - by juhanic
    What is the most efficient way to split a string by a very simple separator? Some background: I am porting a function I wrote in C with a bunch of pointer arithmetic to java and it is incredibly slow(After some optimisation still 5* slower). Having profiled it, it turns out a lot of that overhead is in String.split The function in question takes a host name or ip address and makes it generic: 123.123.123.123-*.123.123.123 a.b.c.example.com-*.example.com This can be run over several million items on a regular basis, so performance is an issue.

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  • not output exception stack trace in EUnit

    - by hpyhacking
    I'm write a test with EUnit, but not anything exception detail output in console. exp_test() -> ?assertEqual(0, 1/0). Run this module:exp_test() in the Erlang Shell output following ** exception error: bad argument in an arithmetic expression in function exp_test:'-exp_test/0-fun-0-'/1 (src/test/eunit/xxx_test.erl, line 8) But in EUnit output following > eunit:test(xxx). > xxx_test: exp_test...*failed* ::badarith EUnit not output anything exception trace info Im trying the verbose config in eunit, but no effect. I want to output some exception detail in eunit test result. Thanks~

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  • C++ infix to postfix conversion for logical conditions

    - by Gopalakrishnan Subramani
    I want to evaluate one expression in C++. To evaluate it, I want the expression to be converted to prefix format. Here is an example wstring expression = "Feature1 And Feature2"; Here are possible ways. expression = "Feature1 And (Feature2 Or Feature3)"; expression = "Not Feature1 Or Feature3"; Here And, Or, Not are reserved words and parentheses ("(", )) are used for scope Not has higher precedence And is set next precedence to Not Or is set to next precedence to And WHITE SPACE used for delimiter. Expression has no other elements like TAB, NEWLINE I don't need arithmetic expressions. I can do the evaluation but can somebody help me to convert the strings to prefix notation?

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  • C++ Passing `this` into method by reference

    - by David
    I have a class constructor that expects a reference to another class object to be passed in as an argument. I understand that references are preferable to pointers when no pointer arithmetic will be performed or when a null value will not exist. This is the header declaration of the constructor: class MixerLine { private: MIXERLINE _mixerLine; public: MixerLine(const MixerDevice& const parentMixer, DWORD destinationIndex); ~MixerLine(); } This is the code that calls the constructor (MixerDevice.cpp): void MixerDevice::enumerateLines() { DWORD numLines = getDestinationCount(); for(DWORD i=0;i<numLines;i++) { MixerLine mixerLine( this, i ); // other code here removed } } Compilation of MixerDevice.cpp fails with this error: Error 3 error C2664: 'MixerLine::MixerLine(const MixerDevice &,DWORD)' : cannot convert parameter 1 from 'MixerDevice *const ' to 'const MixerDevice &' But I thought pointer values could be assigned to pointers, e.g. Foo* foo = new Foo(); Foo& bar = foo;

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  • Integers in JavaScript

    - by muntoo
    I'm a beginner to Javascript so forgive me if I sound dumb because I learned some Javascript from W3Fools (which are really difficult tutorials - they don't explain anything I want to know, but everything I probably can guess from my experience with C++). I may be switching over to MDN, but if you can recommend any other tutorials, that be great. Anyways, so here's my question: I just read a few lines of this, and apparently: Numbers in JavaScript are "double-precision 64-bit format IEEE 754 values", according to the spec. This has some interesting consequences. There's no such thing as an integer in JavaScript, so you have to be a little careful with your arithmetic if you're used to math in C or Java. I've already seen that there are few of the data types (for variables) I'm used to from C++. But I didn't expect all numbers to automatically be floats. Isn't there any way to use integers, not float? Will a future version of JavaScript support ints?

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  • rewrite a function using only pointer increment/decrement

    - by Richard Nguyen
    can anyone help me rewrite the function i wrote below using only points and pointer increment/decrement? I dont have much experience with pointer so I dont know what to do. void reverse(char * s) { int i, l = strlen(s); char c; for(i = 0; i < (l >> 1); i++) { c = s[i]; s[i] = s[l - i - 1]; s[l - i - 1] = c; } } do not use pointer arithmetic or array notation. any help or hint on how to rewrite the function above is appriciated. Thanks!

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  • Interpreter in C++: Function table storage problem

    - by sub
    In my interpreter I have built-in functions available in the language like print exit input, etc. These functions can obviously be accessed from inside the language. The interpreter then looks for the corresponding function with the right name in a vector and calls it via a pointer stored with its name. So I gather all these functions in files like io.cpp, string.cpp, arithmetic.cpp. But I have to add every function to the function list in the interpreter in order for it to be found. So in these function files I have things like: void print( arg ) { cout << arg.ToString; } I'd add this print function to the interpreter function list with: interpreter.AddFunc( "print", print ); But where should I call the interpreter.AddFunc? I can't just put it there below the print function as it has to be in a function according to the C++ syntax. Where and how should all the functions be added to the list?

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  • How do I write in-code comments and documentation in a proper way? Is there any standard for this?

    - by hkBattousai
    I want to add documentation in my code by means of comment lines. Is there any standard format for this? For example, consider the code below: class Arithmetic { // This method adds two numbers, and returns the result. // dbNum1 is the first number to add, and dbNum2 is second. // The returning value is dbNum1+dbNum2. static double AddTwoNumbers(double dbNum1, double dbNum2); } For this example code, is there any better way of writing the comment lines?

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  • Initializing and accessing a pointer from an array of pointers

    - by idealistikz
    Suppose I have the following: void **Init(int numElems) { //What is the best way to intialize 'ptrElems' to store an array of void *'s? void **ptrElems = malloc(numElems * sizeof(void *)); return ptrElems; } //What is the best way to return a pointer pointing at the index passed as a parameter? void **GetPtr(void **ptrElems, int index) { void **elem = elems + (index * sizeof(void *)); return elem; } First, what is the best way to intialize 'ptrElems' to store an array of pointers? I use malloc because assigning it to an array will not persist after the end of the function. Second, what is the best way to point to the pointer at the specified index? I tried typecasting the first line of the 'GetPtr' function to ensure proper pointer arithmetic, but I receive the warning, 'initialization from incompatible pointer type'. Is it necessary to typecast?

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  • A programming language for teaching data structures and algorithms with? [closed]

    - by Andreas Grech
    Possible Duplicate: Choice of programming language for learning data structures and algorithms Teachers have different opinions on what programming language they would choose to teach data structures and algorithms with. Some would prefer a lower level language such as C because it allows the student to learn more about what goes on beyond the abstractions in terms of memory allocation and deallocation and pointers and pointer arithmetic. On the other hand, others would say that they would prefer a higher level language like Java because it allows the student to learn more about the concepts of the structures and the algorithm design rather than 'waste time' and fiddle around with memory segmentation faults and all the blunders that come with languages where memory management is manual. What is your take on this issue? And also, please post any references you may know of that also discuss this argument.

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  • Strange pattern matching with functions instancing Show

    - by Sean D
    So I'm writing a program which returns a procedure for some given arithmetic problem, so I wanted to instance a couple of functions to Show so that I can print the same expression I evaluate when I test. The trouble is that the given code matches (-) to the first line when it should fall to the second. {-# OPTIONS_GHC -XFlexibleInstances #-} instance Show (t -> t-> t) where show (+) = "plus" show (-) = "minus" main = print [(+),(-)] returns [plus,plus] Am I just committing a motal sin printing functions in the first place or is there some way I can get it to match properly? edit:I realise I am getting the following warning: Warning: Pattern match(es) are overlapped In the definition of `show': show - = ... I still don't know why it overlaps, or how to stop it.

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  • grouping objects to achieve a similar mean property for all groups

    - by cytochrome
    I have a collection of objects, each of which has a numerical 'weight'. I would like to create groups of these objects such that each group has approximately the same arithmetic mean of object weights. The groups won't necessarily have the same number of members, but the size of groups will be within one of each other. In terms of numbers, there will be between 50 and 100 objects and the maximum group size will be about 5. Is this a well-known type of problem? It seems a bit like a knapsack or partition problem. Are efficient algorithms known to solve it? As a first step, I created a python script that achieves very crude equivalence of mean weights by sorting the objects by weight, subgrouping these objects, and then distributing a member of each subgroup to one of the final groups. I am comfortable programming in python, so if existing packages or modules exist to achieve part of this functionality, I'd appreciate hearing about them. Thank you for your help and suggestions.

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  • Is it possible to compute the minimum of three numbers by using two comparisons at the same time?

    - by Milo Hou
    I've been trying to think up of some way that I could do two comparisons at the same time to find the greatest/least of three numbers. Arithmetic operations on them are considered "free" in this case. That is to say, the classical way of finding the greater of two, and then comparing it to the third number isn't valid in this case because one comparison depends on the result of the other. Is it possible to use two comparisons where this isn't the case? I was thinking maybe comparing the differences of the numbers somehow or their products or something, but came up with nothing. Just to reemphasize, two comparisons are still done, just that neither comparison relies on the result of the other comparison. EDIT: what about: boolA = A^2 + B^2 < C^2 boolB = A > B if boolA then max=C else if boolB then max=A else max=B

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  • Which tool can list writing access to a specific variable in C?

    - by Lichtblitz
    Unfortunately I'm not even sure how this sort of static analysis is called. It's not really control flow analysis because I'm not looking for function calls and I don't really need data flow analysis because I don't care about the actual values. I just need a tool that lists the locations (file, function) where writing access to a specific variable takes place. I don't even care if that list contained lines that are unreachable. I could imagine that writing a simple parser could suffice for this task but I'm certain that there must be a tool out there that does this simple analysis. As a poor student I would appreciate free or better yet open source tools and if someone could tell me how this type of static analysis is actually called, I would be equally grateful! EDIT: I forgot to mention there's no pointer arithmetic in the code base.

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  • STL deque accessing by index is O(1)?

    - by jasonline
    I've read that accessing elements by position index can be done in constant time in a STL deque. As far as I know, elements in a deque may be stored in several non-contiguous locations, eliminating safe access through pointer arithmetic. For example: abc-defghi-jkl-mnop The elements of the deque above consists of a single character. The set of characters in one group indicate it is allocated in contiguous memory (e.g. abc is in a single block of memory, defhi is located in another block of memory, etc.). Can anyone explain how accessing by position index can be done in constant time, especially if the element to be accessed is in the second block? Or does a deque have a pointer to the group of blocks? Update: Or is there any other common implementation for a deque?

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  • What's the silliest programming mistake you've ever done? [closed]

    - by bgo
    Despite not being a professional programmer, i use python or c to accomplish simple tasks. Once I needed a nasty equation to use with various data for physics lab. I thought that it would take a few hours if i used some mechanic calculator. Then i've written a python script to make things easier but something was wrong. After finding my mistakes one of which was forgetting to put ":", i realized that it had already took 2-3 hours, not to mention inventing satanic arithmetic techniques since i thought the errors was caused by my math :) Sometimes when you don't see it, you don't see it! Now i can find the syntax errors without thinking for a moment :) Any similar annoying mistakes that you've experienced?

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  • python convert 12 bit image encoded in a string to 8 bit png

    - by ks
    I have a string that is read from a usb apogee camera that is a 12-bit grayscale image with the 12-bits each occupying the lowest 12 bits of 16-bits words. I want to create a 8-bit png from this string by ignoring the lowest 4 bits. I can convert it to a 16-bit image where the highest 4 bits are always zero using PIL with import Image imageStr is the image string imageSize is the image size img=Image.fromstring("I", imageSize, imageStr, "raw", "I;16", 0,1) img.save("MyImage.png", "PNG") Anyway I can do something similar to create a 8-bit image without completely unpacking the string doing arithmetic and making a new string?

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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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