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  • Overriding rubies spaceship operator <=>

    - by ericsteen1
    I am trying to override rubies <= (spaceship) operator to sort apples and oranges so that apples come first sorted by weight, and oranges second, sorted by sweetness. Like so: module Fruity attr_accessor :weight, :sweetness def <=>(other) # use Array#<=> to compare the attributes [self.weight, self.sweetness] <=> [other.weight, other.sweetness] end include Comparable end class Apple include Fruity def initialize(w) self.weight = w end end class Orange include Fruity def initialize(s) self.sweetness = s end end fruits = [Apple.new(2),Orange.new(4),Apple.new(6),Orange.new(9),Apple.new(1),Orange.new(22)] p fruits #should work? p fruits.sort But this does not work, can someone tell what I am doing wrong here, or a better way to do this?

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  • USing Min/Max with conditional operator

    - by user638501
    Hello All, I am trying to run a query to find max and min values, and then use a conditional operator. however when I try to run the following query, it gives me error - "misuse of aggregate: min()". My query is: SELECT a.prim_id, min(b.new_len*36) as min_new_len, max(b.new_len*36) as max_new_len FROM tb_first a, tb_second b WHERE a.sec_id = b.sec_id AND min_new_len > 1900 AND max_new_len < 75000 GROUP BY a.prim_id ORDER BY avg(b.new_len*36); Any suggestions ?

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  • Boolean Not operator in VBScript

    - by Lumi
    Consider the following two conditionals (involving bitwise comparisons) in VBScript: If 1 And 3 Then WScript.Echo "yes" Else WScript.Echo "no" If Not(1 And 3) Then WScript.Echo "yes" Else WScript.Echo "no" Prints first yes, then no, right? cscript not.vbs Wrong! It prints yes twice! Wait a second, the Not operator is supposed to perform logical negation on an expression. The logical negation of true is false, as far as I know. Must I conclude that it doesn't live up to that promise? How and why and what is going on here? What is the rationale, if any?

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  • C++ array initialization without assignment

    - by david
    This question is related to the post here. Is it possible to initialize an array without assigning it? For example, class foo's constructor wants an array of size 3, so I want to call foo( { 0, 0, 0 } ). I've tried this, and it does not work. I'd like to be able to initialize objects of type foo in other objects' constructor initialization lists. Is this possible?

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  • Linked lists in Java - help with assignment

    - by user368241
    Representation of a string in linked lists In every intersection in the list there will be 3 fields : The letter itself. The number of times it appears consecutively. A pointer to the next intersection in the list. The following class CharNode represents a intersection in the list : public class CharNode { private char _data; private int _value; private charNode _next; public CharNode (char c, int val, charNode n) { _data = c; _value = val; _next = n; } public charNode getNext() { return _next; } public void setNext (charNode node) { _next = node; } public int getValue() { return _value; } public void setValue (int v) { value = v; } public char getData() { return _data; } public void setData (char c) { _data = c; } } The class StringList represents the whole list : public class StringList { private charNode _head; public StringList() { _head = null; } public StringList (CharNode node) { _head = node; } } Add methods to the class StringList according to the details : (I will add methods gradually according to my specific questions) (Pay attention, these are methods from the class String and we want to fulfill them by the representation of a string by a list as explained above) public int indexOf (int ch) - returns the index in the string it is operated on of the first appeareance of the char "ch". If the char "ch" doesn't appear in the string, returns -1. If the value of fromIndex isn't in the range, returns -1. Pay attention to all the possible error cases. Write what is the time complexity and space complexity of every method that you wrote. Make sure the methods you wrote are effective. It is NOT allowed to use ready classes of Java. It is NOT allowed to move to string and use string operations. Here is my try to write the method indexOf (int ch). Kindly assist me with fixing the bugs so I can move on. public int indexOf (int ch) { int count = 0; charNode pose = _head; if (pose == null ) { return -1; } for (pose = _head; pose!=null && pose.getNext()!='ch'; pose = pose.getNext()) { count++; } if (pose!=null) return count; else return -1; }

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  • Why does std::map operator[] create an object if the key doesn't exist?

    - by n1ck
    Hi, I'm pretty sure I already saw this question somewhere (comp.lang.c++? Google doesn't seem to find it there either) but a quick search here doesn't seem to find it so here it is: Why does the std::map operator[] create an object if the key doesn't exist? I don't know but for me this seems counter-intuitive if you compare to most other operator[] (like std::vector) where if you use it you must be sure that the index exists. I'm wondering what's the rationale for implementing this behavior in std::map. Like I said wouldn't it be more intuitive to act more like an index in a vector and crash (well undefined behavior I guess) when accessed with an invalid key? Refining my question after seeing the answers: Ok so far I got a lot of answers saying basically it's cheap so why not or things similar. I totally agree with that but why not use a dedicated function for that (I think one of the comment said that in java there is no operator[] and the function is called put)? My point is why doesn't map operator[] work like a vector? If I use operator[] on an out of range index on a vector I wouldn't like it to insert an element even if it was cheap because that probably mean an error in my code. My point is why isn't it the same thing with map. I mean, for me, using operator[] on a map would mean: i know this key already exist (for whatever reason, i just inserted it, I have redundancy somewhere, whatever). I think it would be more intuitive that way. That said what are the advantage of doing the current behavior with operator[] (and only for that, I agree that a function with the current behavior should be there, just not operator[])? Maybe it give clearer code that way? I don't know. Another answer was that it already existed that way so why not keep it but then, probably when they (the ones before stl) choose to implement it that way they found it provided an advantage or something? So my question is basically: why choose to implement it that way, meaning a somewhat lack of consistency with other operator[]. What benefit do it give? Thanks

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  • Analyzing Python Code: Modulus Operator

    - by Bhubhu Hbuhdbus
    I was looking at some code in Python (I know nothing about Python) and I came across this portion: def do_req(body): global host, req data = "" s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((host, 80)) s.sendall(req % (len(body), body)) tmpdata = s.recv(8192) while len(tmpdata) > 0: data += tmpdata tmpdata = s.recv(8192) s.close() return data This is then called later on with body of huge size, as in over 500,000 bytes. This is sent to an Apache server that has the max request size on the default 8190 bytes. My question is what is happening at the "s.sendall()" part? Obviously the entire body cannot be sent at once and I'm guessing it is reduced by way of the modulus operator. I don't know how it works in Python, though. Can anyone explain? Thanks.

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  • ms-access: missing operator in query expression

    - by every_answer_gets_a_point
    i have this sql statement in access: SELECT * FROM (SELECT [Occurrence Number], [1 0 Preanalytical (Before Testing)], NULL, NULL,NULL FROM [Lab Occurrence Form] WHERE NOT ([1 0 Preanalytical (Before Testing)] IS NULL) UNION SELECT [Occurrence Number], NULL, [2 0 Analytical (Testing Phase)], NULL,NULL FROM [Lab Occurrence Form] WHERE NOT ([2 0 Analytical (Testing Phase)] IS NULL) UNION SELECT [Occurrence Number], NULL, NULL, [3 0 Postanalytical ( After Testing)],NULL FROM [Lab Occurrence Form] WHERE NOT ([3 0 Postanalytical ( After Testing)] IS NULL) UNION SELECT [Occurrence Number], NULL, NULL,NULL [4 0 Other] FROM [Lab Occurrence Form] WHERE NOT ([4 0 Other] IS NULL) ) AS mySubQuery ORDER BY mySubQuery.[Occurrence Number]; everything was fine until i added the last line: SELECT [Occurrence Number], NULL, NULL,NULL [4 0 Other] FROM [Lab Occurrence Form] WHERE NOT ([4 0 Other] IS NULL) i get this error: syntax error (missing operator) in query expression 'NULL [4 0 Other]' anyone have any clues why i am getting this error?

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  • Objective-C NSString Assignment Problem

    - by golfromeo
    In my Cocoa application, in the header file, I declare a NSString ivar: NSString *gSdkPath; Then, in awakeFromNib, I assign it to a value: gSdkPath = @"hello"; Later, it's value is changed in the code: gSdkPath = [NSString stringWithString:[folderNames objectAtIndex:0]]; (the object returned from objectAtIndex is an NSString) However, after this point, in another method when I try to NSLog() (or do anything with) the gSdkPath variable, the app crashes. I'm sure this has something to do with memory management, but I'm beginning with Cocoa and not sure exactly how this all works. Thanks for any help in advance.

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  • Classical task-scheduling assignment

    - by Bruno
    I am working on a flight scheduling app (disclaimer: it's for a college project, so no code answers, please). Please read this question w/ a quantum of attention before answering as it has a lot of peculiarities :( First, some terminology issues: You have planes and flights, and you have to pair them up. For simplicity's sake, we'll assume that a plane is free as soon as the flight using it prior lands. Flights are seen as tasks: They have a duration They have dependencies They have an expected date/time for beginning Planes can be seen as resources to be used by tasks (or flights, in our terminology). Flights have a specific type of plane needed. e.g. flight 200 needs a plane of type B. Planes obviously are of one and only one specific type, e.g., Plane Airforce One is of type C. A "project" is the set of all the flights by an airline in a given time period. The functionality required is: Finding the shortest possible duration for a said project The earliest and latest possible start for a task (flight) The critical tasks, with basis on provided data, complete with identifiers of preceding tasks. Automatically pair up flights and planes, so as to get all flights paired up with a plane. (Note: the duration of flights is fixed) Get a Gantt diagram with the projects scheduling, in which all flights begin as early as possible, showing all previously referred data graphically (dependencies, time info, etc.) So the questions is: How in the world do I achieve this? Particularly: We are required to use a graph. What do the graph's edges and nodes respectively symbolise? Are we required to discard tasks to achieve the critical tasks set? If you could also recommend some algorithms for us to look up, that'd be great.

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  • Objective-c pointer assignment and reassignment dilema

    - by moshe
    Hi, If I do this: 1 NSMutableArray *near = [[NSMutableArray alloc] init]; 2 NSMutableArray *all = [[NSMutableArray alloc] init]; 3 NSMutableArray *current = near; 4 current = all; What happens to near? At line 3, am I setting current to point to the same address as near so that I now have two variables pointing to the same place in memory, or am I setting current to point to the location of near in memory such that I now have this structure: current - near - NSMutableArray The obvious difference would be the value of near at line 4. If the former is happening, near is untouched and still points to its initial place in memory. If the latter is happening,

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  • Overriding Ruby's spaceship operator <=>

    - by ericsteen1
    I am trying to override Ruby's <= (spaceship) operator to sort apples and oranges so that apples come first sorted by weight, and oranges second, sorted by sweetness. Like so: module Fruity attr_accessor :weight, :sweetness def <=>(other) # use Array#<=> to compare the attributes [self.weight, self.sweetness] <=> [other.weight, other.sweetness] end include Comparable end class Apple include Fruity def initialize(w) self.weight = w end end class Orange include Fruity def initialize(s) self.sweetness = s end end fruits = [Apple.new(2),Orange.new(4),Apple.new(6),Orange.new(9),Apple.new(1),Orange.new(22)] p fruits #should work? p fruits.sort But this does not work, can someone tell what I am doing wrong here, or a better way to do this?

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  • numpy array assignment problem

    - by Sujan
    Hi All: I have a strange problem in Python 2.6.5 with Numpy. I assign a numpy array, then equate a new variable to it. When I perform any operation to the new array, the original's values also change. Why is that? Please see the example below. Kindly enlighten me, as I'm fairly new to Python, and programming in general. -Sujan >>> import numpy as np >>> a = np.array([[1,2],[3,4]]) >>> b = a >>> b array([[1, 2], [3, 4]]) >>> c = a >>> c array([[1, 2], [3, 4]]) >>> c[:,1] = c[:,1] + 5 >>> c array([[1, 7], [3, 9]]) >>> b array([[1, 7], [3, 9]]) >>> a array([[1, 7], [3, 9]])

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  • Ruby weird assignment behaviour

    - by jaycode
    Is this a ruby bug? target_url_to_edit = target_url if target_url_to_edit.include?("http://") target_url_to_edit["http://"] = "" end logger.debug "target url is now #{target_url}" This returns target_url without http://

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  • C++ vector<T>::iterator operator +

    - by Tom
    Hi, Im holding an iterator that points to an element of a vector, and I would like to compare it to the next element of the vector. Here is what I have Class Point{ public: float x,y; } //Somewhere in my code I do this vector<Point> points = line.getPoints(); foo (points.begin(),points.end()); where foo is: void foo (Vector<Point>::iterator begin,Vector<Point>::iterator end) { std::Vector<Point>::iterator current = begin; for(;current!=end-1;++current) { std::Vector<Point>::iterator next = current + 1; //Compare between current and next. } } I thought that this would work, but current + 1 is not giving me the next element of the vector. I though operator+ was the way to go, but doesnt seem so. Is there a workaround on this? THanks

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  • Only assignment, call, increment, decrement, and new object expressions can be used as a statement : Messagebox

    - by Nuru Salihu
    This what i am trying to achieved if(this.BeginInvoke((Action)(() => MessageBox.Show("Test", MessageBoxButtons.YesNo) == DialogResult.No))) The above gives error. I try seperating the delegate to an outside method like delegate void test(string text); private void SetTest(string text) { if(MessageBox.Show(text,"", MessageBoxButtons.YesNo) == DialogResult.No) } But it breach the very reason why i need the delegate. I found out the first works for me but i don't know how to put it in an if/else statement. Pls any help in a better way i can achieve some thing like below would be appreciated. if(this.BeginInvoke((Action)(() => MessageBox.Show("Test", MessageBoxButtons.YesNo) == DialogResult.No)))

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  • "assignment makes integer from pointer without a cast " warning in c

    - by mekasperasky
    #include<stdio.h> /* this is a lexer which recognizes constants , variables ,symbols, identifiers , functions , comments and also header files . It stores the lexemes in 3 different files . One file contains all the headers and the comments . Another file will contain all the variables , another will contain all the symbols. */ int main() { int i=0,j; char a,b[20],c[30]; FILE *fp1,*fp2; c[0]='"if"; c[1]="then"; c[2]="else"; c[3]="switch"; c[4]="printf"; c[5]="scanf"; c[6]="NULL"; c[7]="int"; c[8]="char"; c[9]="float"; c[10]="long"; c[11]="double"; c[12]="char"; c[13]="const"; c[14]="continue"; c[15]="break"; c[16]="for"; c[17]="size of"; c[18]="register"; c[19]="short"; c[20]="auto"; c[21]="while"; c[22]="do"; c[23]="case"; fp1=fopen("source.txt","r"); //the source file is opened in read only mode which will passed through the lexer fp2=fopen("lext.txt","w"); //now lets remove all the white spaces and store the rest of the words in a file if(fp1==NULL) { perror("failed to open source.txt"); //return EXIT_FAILURE; } i=0; while(!feof(fp1)) { a=fgetc(fp1); if(a!=' ') { b[i]=a; } else { for (j=0;j<23;j++) { if(c[j]==b) { fprintf(fp2, "%.20s\n", c[j]); continue ; } b[i]='\0'; fprintf(fp2, "%.20s\n", b); i=0; continue; } //else if //{ i=i+1; /*Switch(a) { case EOF :return eof; case '+':sym=sym+1; case '-':sym=sym+1; case '*':sym=sym+1; case '/':sym=sym+1; case '%':sym=sym+1; case ' */ } fclose(fp1); fclose(fp2); return 0; } This is my c code for lexical analysis .. its giving warnings and also not writing anything into the lext file ..

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  • Python ctypes in_dll string assignment

    - by ackdesha
    I could use some help assigning to a global C variable in DLL using ctypes. The following is an example of what I'm trying: test.c contains the following #include <stdio.h> char name[60]; void test(void) { printf("Name is %s\n", name); } On windows (cygwin) I build a DLL (Test.dll) as follows: gcc -g -c -Wall test.c gcc -Wall -mrtd -mno-cygwin -shared -W1,--add-stdcall-alias -o Test.dll test.o When trying to modify the name variable and then calling the C test function using the ctypes interface I get the following... >>> from ctypes import * >>> dll = windll.Test >>> dll <WinDLL 'Test', handle ... at ...> >>> f = c_char_p.in_dll(dll, 'name') >>> f c_char_p(None) >>> f.value = 'foo' >>> f c_char_p('foo') >>> dll.test() Name is Name is 48+? 13 Why does the test function print garbage in this case?

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  • C# == operator in Immediate window behaves differently than at run-time

    - by Damiano
    Try the following in the Immediate window: object a1 = "a"; object a2 = "a"; a1==a2 // outputs false and you'll see that a1 == a2 outputs false. However, at runtime in either a window app or console, you'll get true: object t1 = "a"; object t2 = "a"; MessageBox.Show((t1 == t2).ToString()); // outputs true The runtime behavior is consistent with the definition for the == operator and strings. Does anybody know if this a bug in the Immediate window?

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  • Logical xor operator in c++?

    - by RAC
    Is there such a thing? First time I encountered a practical need for it, but I don't see one listed in stroustrup. I intend to write: // Detect when exactly one of A,B is equal to five. return (A==5) ^^ (B==5); But there is no ^^ operator. Can I use bitwise ^ here and get the right answer (regardless of machine representation of true and false)? I never mix & and &&, or | and ||, so I hesitate to do that with ^ and ^^. I'd be more comfortable writing my own "bool XOR(bool,bool)" function instead.

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  • Suppress error with @ operator in PHP

    - by Mez
    In your opinion, is it ever valid to use the @ operator to suppress an error/warning in PHP whereas you may be handling the error? If so, in what circumstances would you use this? Code examples are welcome. Edit: Note to repliers. I'm not looking to turn error reporting off, but, for example, common practice is to use @fopen($file); and then check afterwards... but you can get rid of the @ by doing if (file_exists($file)) { fopen($file); } else { die('File not found'); } or similar. I guess the question is - is there anywhere that @ HAS to be used to supress an error, that CANNOT be handled in any other manner?

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  • database assignment

    - by eric
    Hi, Given the following table: CREATE TABLE T1 (A INTEGER NOT NULL); CREATE TABLE T3 (A SMALLINT NOT NULL); INSERT T1 VALUES (32768.5); SELECT * FROM T1; INSERT T3 SELECT * FROM T1; SELECT * FROM T3; What is the output of above query? If any error occured please declare the line of it?Explain your answer!

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  • C++: Why does gcc prefer non-const over const when accessing operator[]?

    - by JonasW
    This question might be more appropriately asked regarding C++ in general, but as I am using gcc on linux that's the context. Consider the following program: #include <iostream> #include <map> #include <string> using namespace std; template <typename TKey, typename TValue> class Dictionary{ public: map<TKey, TValue> internal; TValue & operator[](TKey const & key) { cout << "operator[] with key " << key << " called " << endl; return internal[key]; } TValue const & operator[](TKey const & key) const { cout << "operator[] const with key " << key << " called " << endl; return internal.at(key); } }; int main(int argc, char* argv[]) { Dictionary<string, string> dict; dict["1"] = "one"; cout << "first one: " << dict["1"] << endl; return 0; } When executing the program, the output is: operator[] with key 1 called operator[] with key 1 called first one: one What I would like is to have the compiler choose the operator[]const method instead in the second call. The reason is that without having used dict["1"] before, the call to operator[] causes the internal map to create the data that does not exist, even if the only thing I wanted was to do some debugging output, which of course is a fatal application error. The behaviour I am looking for would be something like the C# index operator which has a get and a set operation and where you could throw an exception if the getter tries to access something that doesn't exist: class MyDictionary<TKey, TVal> { private Dictionary<TKey, TVal> dict = new Dictionary<TKey, TVal>(); public TVal this[TKey idx] { get { if(!dict.ContainsKey(idx)) throw KeyNotFoundException("..."); return dict[idx]; } set { dict[idx] = value; } } } Thus, I wonder why the gcc prefers the non-const call over the const call when non-const access is not required.

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  • How to replace a codebehind method with an aspx method using ternary operator

    - by user466663
    I have an asp:hyperlink control as part of a gridview template. The code in the aspx page is given below: asp:HyperLink runat="server" ID="lnkEdit" ToolTip="Edit article" NavigateUrl='<%# GetUrl(Eval("ID").ToString(), Eval("CategoryID").ToString()) %' ImageUrl="~/Images/Edit.gif" The NavigateUrl value is obtained from the codebehind method GetUrl(string, string). The code works fine and is as follows: protected string GetUrl(string id, string categoryID) { var CategoryID = string.Empty; if (!String.IsNullOrEmpty(Request.QueryString["CatID"])) { CategoryID = Request.QueryString["CatID"].ToString(); } else if (!String.IsNullOrEmpty(categoryID)) { CategoryID = categoryID; } return "~/TBSArticles/WriteOrEditArticle.aspx?ID=" + id + "&CatID=" + CategoryID; } I want to replace the code behind method by using a ternary operator within the aspx page. I tried something like below, but didn't work: asp:HyperLink runat="server" ID="lnkEdit" ToolTip="Edit article" NavigateUrl='<%# "~/TBSArticles/WriteOrEditArticle.aspx?ID=" + Eval("ID") + "&CatID=" + Eval(this.Request.QueryString["CatID"].ToString()) != ""? this.Request.QueryString["CatID"] : Eval("CategoryID")) %' ImageUrl="~/Images/Edit.gif" Any help will be greatly appreciated. Thanks

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  • Prevent Erroneous Property Assignment

    - by Gordon
    Porting android applications to iphone applications always gives me the following pattern that I accidentally create: - (void) myFunc:(id)prop { self.property = property; } Which instead should be: - (void) myFunc:(id)prop { self.property = prop; } This always causes my program to quietly break because property gets reset to its existing value rather than being set to the new value, 'prop'. I cannot name the parameter 'prop' to 'property' since the compile complains that the parameter masks the instance variables visibility. Is there a good way to avoid this situation? There are no compiler warnings. Is there a way to make xcode prevent this? I cannot see very many situations where you would set a property to the value of its underlying instance variable (maybe to trigger a KVO binding?), but I don't see myself doing that in majority of cases. I understand the above code is synthetic and should be done with @synthesize, but I am just using it as a simplified example to illustrate my point.

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