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• Creating a 2d matrix from an array (java)

  - by anna

  I'm supposed to write a method that creates a 2d matrix from an array, for instance: ({1, 2, 3, 4}, 3) should return the matrix {{1, 2, 3}, {4}} public class Matrix { public static int[][]toM(int[] array, int a) { int[][]matrix = new int [(array.length + a- 1)/ a][a]; for (int i = 0; i < array.length; i++){ int value = array[i]; value = value++; for (int row = 0; row < (array.length + a- 1)/a; row++) { for (int col = 0; col < a; col++) { matrix[row][col]= value++; } } } return matrix; } } I'm getting [[4, 5, 6], [7, 8, 9]]?

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• How to delete a Dictionary row that is a Double by using an Int?

  - by Richard Reddy

  Hi, I have a Dictionary object that is formed using a double as its key values. It looks like this: Dictionary<double, ClassName> VariableName = new Dictionary<double, ClassName>(); For my project I have to have the key as the double as I require values like 1.1,1.2,2.1,2.2,etc in my system. Everything in my system works great except when I want to delete all the keys in a group eg all the 1 values would be 1.1,1.2, etc. I can delete rows if I know the full value of the key eg 1.1 but in my system I will only know the whole number. I tried to do the following but get an error: DictionaryVariable.Remove(j => Convert.ToInt16(j.Key) == rowToEdit).OrderByDescending(j => j.Key); Is there anyway to remove all rows per int value by converting the key? Thanks, Rich

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• What will happen if I change the type of a column from int to year?

  - by MachinationX

  I have a table in MySQL 4.0 which currently has a year field as a smallint(6) type. What will happen if I convert it directly to a Year type with a query like the following: ALTER TABLE t MODIFY y YEAR(4) NOT NULL DEFAULT CURRENT_TIMESTAMP; When the current members of column y have values like 2010? I assume that because the year type is technically values from 1-255, values above that will be truncated or broken. So if MySQL isn't smart enough to realize that 2010(int) = 110(year), what would be the simplest query or queries to convert the values? Thanks for your help!

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• Why "constructor-way" of declaring variable in "for-loop" allowed but in "if-statement" not allowed?

  - by PiotrNycz

  Consider this simple example: /*1*/ int main() { /*2*/ for (int i(7); i;){break;} /*3*/ if (int i(7)) {} /*4*/ } Why line-2 compiles just fine, whilst line-3 gives the error? This is little strange to me why if-statement is in this aspect treated worse than for-loop? If this is compiler specific - I tested with gcc-4.5.1: prog.cpp: In function 'int main()': prog.cpp:3:7: error: expected primary-expression before 'int' prog.cpp:3:7: error: expected ')' before 'int' I was inspired by this question [UPDATE] I know this compiles just fine: /*1*/ int main() { /*2*/ for (int i = 7; i;){break;} /*3*/ if (int i = 7) {} /*4*/ }

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• how do I check if a c++ string is an int?

  - by user342231

  when I use getline, I would input a bunch of strings or numbers, but I only want the while loop to output the "word" if it is not a number. so is there any way to check if "word" is a number or not, I know I could use atoi() for c-strings but how about for strings of the string class int main () { stringstream ss (stringstream::in | stringstream::out); string word; string str; getline(cin,str); ss<<str; while(ss>>word) { //if( ) cout<<word<<endl; } }

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• how to make this piece of code work in C++?

  - by cambr

  #include<stdio.h> void print(int *arr[], int s1, int s2) { int i, j; printf("\n"); for(i = 0; i<s1; i++) { for(j = 0; j<s2; j++) { printf("%d, ", *((arr+i)+j)); } } printf("\n"); } int main() { int a[4][4] = {{0}}; print(a,4,4); } This works in C, but not in C++. error: cannot convert `int (*)[4]' to `int**' for argument `1' to `void print(int**, int, int)' Why does it not work in C++? What change is needed to be made?

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• C++ pointer to functions, Beginner Question...

  - by BobAlmond

  Hi all, I want to ask about pointer in C++ I have some simple code: int add(int a, int b){ return a+b; } int runner(int x,int y, int (*functocall)(int, int)){ return (*functocall)(x,y); } now, suppose I call those functions using this way : cout<<runner(2,5,&add); or maybe cout<<runner(2,5,add); is there any difference? because when I tried, the result is the same and with no error. Thanks a lot

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• Scala puts precedence on implicit conversion over "natural" operations... Why? Is this a bug? Or am

  - by Alex R

  This simple test, of course, works as expected: scala var b = 2 b: Int = 2 scala b += 1 scala b res3: Int = 3 Now I bring this into scope: class A(var x: Int) { def +=(y:Int) { this.x += y } } implicit def int2A(i:Int) : A = new A(i) I'm defining a new class and a += operation on it. I never expected this would affect the way my regular Ints behave. But it does: scala var b:Int = 0 b: Int = 0 scala b += 1 scala b res29: Int = 0 scala b += 2 scala b res31: Int = 0 Scala seems to prefer the implicit conversion over the natural += that is already defined to Ints. That leads to several questions... Why? Is this a bug? Is it by design? Is there a work-around (other than not using "+=")? Thanks

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• Functions without arguments, with unit as argument in scala

  - by scout

  def foo(x:Int, f:Unit=>Int) = println(f()) foo(2, {Unit => 3+4} //case1 def loop:Int = 7 foo(2, loop) //does not compile changing loop to //case 2 def loop():Int = 7 foo(2, loop) // does not compile changing loop to //case 3 def loop(x:Unit): Int = 7 //changing according to Don's Comments foo(2,loop) // compiles and works fine should'nt case 1 and case 2 also work? why are they not working? defining foo as def foo(x:Int, y:()=>Int) then case 2 works but not case 1. Arent they all supposed to work, defining the functions either way. //also i think ()=Int in foo is a bad style, y:=Int does not work, comments??

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• Shuffle array variables in a pre-specified order, without using extra memory of "size of input array"

  - by Eternal Learner

  Input : A[4] = {0,4,-1,1000} - Actual Array P[4] = {1,0,3,2} - Order to be reshuffled Output: A[4] = {4,0,1000,-1} Condition : Don't use an additional array as memory. Can use an extra variable or two. Problem : I have the below program in C++, but this fails for certain inputs of array P. #include<iostream> using namespace std; void swap(int *a_r,int *r) { int temp = *r; *r = *a_r; *a_r = temp; } int main() { int A[4] = {0,4,-1,1000}; int P[4] = {3,0,1,2}; int value = A[0] , dest = P[0]; for(int i=0; i<4;i++) { swap(&A[dest],&value); dest = P[dest]; } for(int i=0;i<4;i++) cout<<A[i]<<" "; }

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• Stucture with array of pointers in C

  - by MVTCplusplus

  What's wrong with this? Can I have an array of pointers to SDL_Surfaces in a struct in C? typedef struct { int next_wheel; int pos_X; int pos_Y; int front_wheel_pos_X; int front_wheel_pos_Y; int velocity; int rear_wheel_pos_X; int rear_wheel_pos_Y; SDL_Surface* body; SDL_Surface* rear_wheel[9]; SDL_Surface* front_wheel[9]; } mars_rover; ... mars_rover* init_rover() { mars_rover* rover = (mars_rover*)malloc(sizeof(mars_rover) + sizeof(SDL_Surface) * 19); ... return rover; } int main() { mars_rover* rover = init_rover(); ... }

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• what is the accepted naming convention for int, string, array, list, object, etc...

  - by RJ

  The company I work for now uses a set naming convention for their C# variables such as iSomeName for int, sSomeName for string, aSomeName for arrays, bSomeName for boolean, dSomeName for datetime and so on. My previous employer did not use the i, s, a, b and d prefixes and just named the variables a good understandable name. My impression is that these prefixes lost favor a while ago and from what I read it is not the current trend. It seems fine to me either way as long as the variable is descriptive enough to understand what it is doing but I was wondering what the now-a-day accepted practice is for naming variables?

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• How to change the text int JLabel under the while or for loop?

  - by guilgamos

  I want to create a simple clock by using java. The code is very simply that i will give an example shown below for(int i=0;i<=60;i++) jLabel11.setText( Integer.toString(i) ); The problem is while I'm running my program the result didn't show the update in sequence. I mean it show only 60 digit immediately. It didn't show the change from 1 to 2 to 3 ... something like this. How can i fix this problem. Thank you in advance.

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• Why do dicts of defaultdict(int)'s use so much memory? (and other simple python performance question

  - by dukhat

  import numpy as num from collections import defaultdict topKeys = range(16384) keys = range(8192) table = dict((k,defaultdict(int)) for k in topKeys) dat = num.zeros((16384,8192), dtype="int32") print "looping begins" #how much memory should this use? I think it shouldn't use more that a few #times the memory required to hold (16384*8192) int32's (512 mb), but #it uses 11 GB! for k in topKeys: for j in keys: dat[k,j] = table[k][j] print "done" What is going on here? Furthermore, this similar script takes eons to run compared to the first one, and also uses an absurd quantity of memory. topKeys = range(16384) keys = range(8192) table = [(j,0) for k in topKeys for j in keys] I guess python ints might be 64 bit ints, which would account for some of this, but do these relatively natural and simple constructions really produce such a massive overhead? I guess these scripts show that they do, so my question is: what exactly is causing the high memory usage in the first script and the long runtime and high memory usage of the second script and is there any way to avoid these costs?

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• Quick C Style Question

  - by LearningC

  Which is considered better style? int set_int(int *source){ *source = 5; return 0; } int main(){ int x*; set_int(x); } OR int *set_int(){ int *temp = NULL; temp = malloc(sizeof (int)); *temp = 5; return temp; } int main(){ int *x = set_int(); } Coming for a higher level programming background I gotta say I like the second version more. Any, tips would be very helpful. Still learning C.

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• Java Basics: create class object

  - by user1767853

  In C++: class Rectangle { int x, y; public: void set_values (int,int); int area () {return (x*y);} }; int main () { Rectangle rect; rect.set_values (3,4); } In Java: class Rectangle { int x, y; void set_values (int x,int y); int area () {return (x*y);} } public static void main(String[] args) { Rectangle rect=new Rectangle(3,4); } In C++ compiler will create rect object & reserve memory 4 bytes. I want to know How Java is creating object?

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• Tile map collision is not working properly

  - by Sigh-AniDe

  I am having problems setting collision between my sprite and the tiles. I have only done the code for colision for moving upwards but some places on the map it moves up and some places it doesn't. Here is what I have so far: Vector2 position; private static float scalingFactor = 32; static int tileWidth = 32; static int tileHeight = 32; int[ , ] map = { {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, }; // This is in turtle.update if ( keyboardState.IsKeyDown( Keys.Up ) ) { if ( position.Y > screenHeight / 4 ) { //// current position of the turtle on the tiles int mapX = ( int )( position.X / scalingFactor ); int mapY = ( int )( position.Y / scalingFactor ) - 1; if ( isMovable( mapX , mapY , map ) ) { position.Y = position.Y - scalingFactor; } } else { MoveUp(); } } private void MoveUp() { motion.Y = -1; } public bool isMovable( int mapX , int mapY , int[ , ] map ) { if ( mapX < 0 || mapX > 19 || mapY < 0 || mapY > 20 ) { return false; } int tile = map[ mapX , mapY ]; if ( tile == 0 ) { return false; } return true; } protected override void Update( GameTime gameTime ) { turtle.Update( screenHeight , scalingFactor , map ); base.Update( gameTime ); }

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• How can I have multiple layers in my map array?

  - by Manl400

  How do I load Levels in my game, as in Layer 1 would be Objects, Layer 2 would be Characters and so on. I only need 3 layers, and they will all be put on top of each other. i.e having a flower with a transparent background to be put on grass or dirt on the layer below.I would like to Read From the same file too. How would i go about doing this? Any help would be appreciated. I load the map from a level file which are just numbers corresponding to a tile in the tilesheet. Here is the level file [Layer1] 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 [Layer2] 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 [Layer3] 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 And here is the code that interprets it void LoadMap(const char *filename, std::vector< std::vector <int> > &map) { std::ifstream openfile(filename); if(openfile.is_open()) { std::string line, value; int space; while(!openfile.eof()) { std::getline(openfile, line); if(line.find("[TileSet]") != std::string::npos) { state = TileSet; continue; } else if (line.find("[Layer1]") != std::string::npos) { state = Map; continue; } switch(state) { case TileSet: if(line.length() > 0) tileSet = al_load_bitmap(line.c_str()); break; case Map: std::stringstream str(line); std::vector<int> tempVector; while(!str.eof()) { std::getline(str, value, ' '); if(value.length() > 0) tempVector.push_back(atoi(value.c_str())); } map.push_back(tempVector); break; } } } else { } } and this is how it draws the map. Also the tile sheet is 1280 by 1280 and the tilesizeX and tilesizeY is 64 void DrawMap(std::vector <std::vector <int> > map) { int mapRowCount = map.size(); for(int i, j = 0; i < mapRowCount; i ++) { int mapColCount = map[i].size(); for (int j = 0; j < mapColCount; ++j) { int tilesetIndex = map[i][j]; int tilesetRow = floor(tilesetIndex / TILESET_COLCOUNT); int tilesetCol = tilesetIndex % TILESET_COLCOUNT; al_draw_bitmap_region(tileSet, tilesetCol * TileSizeX, tilesetRow * TileSizeY, TileSizeX, TileSizeY, j * TileSizeX, i * TileSizeX, NULL); } } } EDIT: http://i.imgur.com/Ygu0zRE.jpg

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• Collision 2D Quads

  - by Vico Pelaez

  I want to detect collision between two 2D squares, one square is static and the other one moves according to keyboard arrows. I have implemented some code, however nothing happens when they overlap each other and what I tried to achieve in the code was to detect an overlapping between them. I think I am either not understanding the concept really well or that because one of the squares is moving this is not working. Please I would really appreciate your help. Thank you! float x1=0.05 ,Y1=0.05; float x2=0.05 ,Y2=0.05; float posX1 =0.5, posY1 = 0.5; float movX2 = 0.0 , movY2 = 0.0; struct box{ int width=0.1; int heigth=0.1; }; void init(){ glClearColor(0.0, 0.0, 0.0, 0.0); glColor3f(1.0, 1.0, 1.0); } void quad1(){ glTranslatef(posX1, posY1, 0.0); glBegin(GL_POLYGON); glColor3f(0.5, 1.0, 0.5); glVertex2f(-x1, -Y1); glVertex2f(-x1, Y1); glVertex2f(x1,Y1); glVertex2f(x1,-Y1); glEnd(); } void quad2(){ glMatrixMode(GL_PROJECTION); glLoadIdentity(); glPushMatrix(); glTranslatef(movX2, movY2, 0.0); glBegin(GL_POLYGON); glColor3f(1.5, 1.0, 0.5); glVertex2f(-x2, -Y2); glVertex2f(-x2, Y2); glVertex2f(x2,Y2); glVertex2f(x2,-Y2); glEnd(); glPopMatrix(); } void reset(){ //Reset position of square??? movX2 = 0.0; movY2 = 0.0; collisionB = false; } bool collision(box A, box B){ int leftA, leftB; int rightA, rightB; int topA, topB; int bottomA, bottomB; //Calculate the sides of box A leftA = x1; rightA = x1 + A.width; topA = Y1; bottomA = Y1 + A.heigth; //Calculate the sides of box B leftB = x2; rightB = x2 + B.width; topB = Y1; bottomB = Y1+ B.heigth ; if( bottomA <= topB ) return false; if( topA >= bottomB ) return false; if( rightA <= leftB ) return false; if( leftA >= rightB ) return false; return true; } float move_unit = 0.1; void keyboardown(int key, int x, int y) { switch (key){ case GLUT_KEY_UP: movY2 += move_unit; break; case GLUT_KEY_RIGHT: movX2 += move_unit; break; case GLUT_KEY_LEFT: movX2 -= move_unit; break; case GLUT_KEY_DOWN: movY2 -= move_unit; break; default: break; } glutPostRedisplay(); } void display(){ glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glMatrixMode(GL_PROJECTION); glLoadIdentity(); cuad1(); if (!collision) { cuad2(); } else{ reset(); } glFlush(); } int main(int argc, char** argv){ glutInit(&argc, argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutInitWindowSize(500,500); glutInitWindowPosition(0, 0); glutCreateWindow("Collision Practice"); glutSpecialFunc(keyboardown); glutDisplayFunc(display); init(); glutMainLoop(); }

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• Refactoring FizzBuzz

  - by MarkPearl

  A few years ago I blogger about FizzBuzz, at the time the post was prompted by Scott Hanselman who had podcasted about how surprized he was that some programmers could not even solve the FizzBuzz problem within a reasonable period of time during a job interview. At the time I thought I would give the problem a go in F# and sure enough the solution was fairly simple – I then also did a basic solution in C# but never posted it. Since then I have learned that being able to solve a problem and how you solve the problem are two totally different things. Today I decided to give the problem a retry and see if I had learnt anything new in the last year or so. Here is how my solution looked after refactoring… Solution 1 – Cheap and Nasty public class FizzBuzzCalculator { public string NumberFormat(int number) { var numDivisibleBy3 = (number % 3) == 0; var numDivisibleBy5 = (number % 5) == 0; if (numDivisibleBy3 && numDivisibleBy5) return String.Format("{0} FizzBuz", number); else if (numDivisibleBy3) return String.Format("{0} Fizz", number); else if (numDivisibleBy5) return String.Format("{0} Buz", number); return number.ToString(); } } class Program { static void Main(string[] args) { var fizzBuzz = new FizzBuzzCalculator(); for (int i = 0; i < 100; i++) { Console.WriteLine(fizzBuzz.NumberFormat(i)); } } } My first attempt I just looked at solving the problem – it works, and could be an acceptable solution but tonight I thought I would see how far  I could refactor it… The section I decided to focus on was the mass of if..else code in the NumberFormat method. Solution 2 – Replacing If…Else with a Dictionary public class FizzBuzzCalculator { private readonly Dictionary<Tuple<bool, bool>, string> _mappings; public FizzBuzzCalculator(Dictionary<Tuple<bool, bool>, string> mappings) { _mappings = mappings; } public string NumberFormat(int number) { var numDivisibleBy3 = (number % 3) == 0; var numDivisibleBy5 = (number % 5) == 0; var mappedKey = new Tuple<bool, bool>(numDivisibleBy3, numDivisibleBy5); return String.Format("{0} {1}", number, _mappings[mappedKey]); } } class Program { static void Main(string[] args) { var mappings = new Dictionary<Tuple<bool, bool>, string> { { new Tuple<bool, bool>(true, true), "- FizzBuzz"}, { new Tuple<bool, bool>(true, false), "- Fizz"}, { new Tuple<bool, bool>(false, true), "- Buzz"}, { new Tuple<bool, bool>(false, false), ""} }; var fizzBuzz = new FizzBuzzCalculator(mappings); for (int i = 0; i < 100; i++) { Console.WriteLine(fizzBuzz.NumberFormat(i)); } Console.ReadLine(); } } In my second attempt I looked at removing the if else in the NumberFormat method. A dictionary proved to be useful for this – I added a constructor to the class and injected the dictionary mapping. One could argue that this is totally overkill, but if I was going to use this code in a large system an approach like this makes it easy to put this data in a configuration file, which would up its OC (Open for extensibility, closed for modification principle). I could of course take the OC principle even further – the check for divisibility by 3 and 5 is tightly coupled to this class. If I wanted to make it 4 instead of 3, I would need to adjust this class. This introduces my third refactoring. Solution 3 – Introducing Delegates and Injecting them into the class public delegate bool FizzBuzzComparison(int number); public class FizzBuzzCalculator { private readonly Dictionary<Tuple<bool, bool>, string> _mappings; private readonly FizzBuzzComparison _comparison1; private readonly FizzBuzzComparison _comparison2; public FizzBuzzCalculator(Dictionary<Tuple<bool, bool>, string> mappings, FizzBuzzComparison comparison1, FizzBuzzComparison comparison2) { _mappings = mappings; _comparison1 = comparison1; _comparison2 = comparison2; } public string NumberFormat(int number) { var mappedKey = new Tuple<bool, bool>(_comparison1(number), _comparison2(number)); return String.Format("{0} {1}", number, _mappings[mappedKey]); } } class Program { private static bool DivisibleByNum(int number, int divisor) { return number % divisor == 0; } public static bool Divisibleby3(int number) { return number % 3 == 0; } public static bool Divisibleby5(int number) { return number % 5 == 0; } static void Main(string[] args) { var mappings = new Dictionary<Tuple<bool, bool>, string> { { new Tuple<bool, bool>(true, true), "- FizzBuzz"}, { new Tuple<bool, bool>(true, false), "- Fizz"}, { new Tuple<bool, bool>(false, true), "- Buzz"}, { new Tuple<bool, bool>(false, false), ""} }; var fizzBuzz = new FizzBuzzCalculator(mappings, Divisibleby3, Divisibleby5); for (int i = 0; i < 100; i++) { Console.WriteLine(fizzBuzz.NumberFormat(i)); } Console.ReadLine(); } } I have taken this one step further and introduced delegates that are injected into the FizzBuzz Calculator class, from an OC principle perspective it has probably made it more compliant than the previous Solution 2, but there seems to be a lot of noise. Anonymous Delegates increase the readability level, which is what I have done in Solution 4. Solution 4 – Anon Delegates public delegate bool FizzBuzzComparison(int number); public class FizzBuzzCalculator { private readonly Dictionary<Tuple<bool, bool>, string> _mappings; private readonly FizzBuzzComparison _comparison1; private readonly FizzBuzzComparison _comparison2; public FizzBuzzCalculator(Dictionary<Tuple<bool, bool>, string> mappings, FizzBuzzComparison comparison1, FizzBuzzComparison comparison2) { _mappings = mappings; _comparison1 = comparison1; _comparison2 = comparison2; } public string NumberFormat(int number) { var mappedKey = new Tuple<bool, bool>(_comparison1(number), _comparison2(number)); return String.Format("{0} {1}", number, _mappings[mappedKey]); } } class Program { static void Main(string[] args) { var mappings = new Dictionary<Tuple<bool, bool>, string> { { new Tuple<bool, bool>(true, true), "- FizzBuzz"}, { new Tuple<bool, bool>(true, false), "- Fizz"}, { new Tuple<bool, bool>(false, true), "- Buzz"}, { new Tuple<bool, bool>(false, false), ""} }; var fizzBuzz = new FizzBuzzCalculator(mappings, (n) => n % 3 == 0, (n) => n % 5 == 0); for (int i = 0; i < 100; i++) { Console.WriteLine(fizzBuzz.NumberFormat(i)); } Console.ReadLine(); } }   Using the anonymous delegates I think the noise level has now been reduced. This is where I am going to end this post, I have gone through 4 iterations of the code from the initial solution using If..Else to delegates and dictionaries. I think each approach would have it’s pro’s and con’s and depending on the intention of where the code would be used would be a large determining factor. If you can think of an alternative way to do FizzBuzz, add a comment!

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• Recursion in the form of a Recursive Func&lt;T, T&gt;

  - by ToStringTheory

  I gotta admit, I am kind of surprised that I didn’t realize I could do this sooner.  I recently had a problem which required a recursive function call to come up with the answer.  After some time messing around with a recursive method, and creating an API that I was not happy with, I was able to create an API that I enjoy, and seems intuitive. Introduction To bring it to a simple example, consider the summation to n: A mathematically identical formula is: In a .NET function, this can be represented by a function: Func<int, int> summation = x => x*(x+1)/2 Calling summation with an input integer will yield the summation to that number: var sum10 = summation(4); //sum10 would be equal to 10 But what if I wanted to get a second level summation…  First some to n, and then use that argument as the input to the same function, to find the second level summation: So as an easy example, calculate the summation to 3, which yields 6.  Then calculate the summation to 6 which yields 21. Represented as a mathematical formula - So what if I wanted to represent this as .NET functions.  I can always do: //using the summation formula from above var sum3 = summation(3); //sets sum3 to 6 var sum3_2 = summation(sum3); //sets sum3 to 21 I could always create a while loop to perform the calculations too: Func<int, int> summation = x => x*(x+1)/2; //for the interests of a smaller example, using shorthand int sumResultTo = 3; int level = 2; while(level-- > 0) { sumResultTo = summation(sumResultTo); } //sumResultTo is equal to 21 now. Or express it as a for-loop, method calls, etc…  I really didn’t like any of the options that I tried.  Then it dawned on me – since I was using a Func<T, T> anyways, why not use the Func’s output from one call as the input as another directly. Some Code So, I decided that I wanted a recursion class.  Something that I would be generic and reusable in case I ever wanted to do something like this again. It is limited to only the Func<T1, T2> level of Func, and T1 must be the same as T2. The first thing in this class is a private field for the function: private readonly Func<T, T> _functionToRecurse; So, I since I want the function to be unchangeable, I have defined it as readonly.  Therefore my constructor looks like: public Recursion(Func<T, T> functionToRecurse) { if (functionToRecurse == null) { throw new ArgumentNullException("functionToRecurse", "The function to recurse can not be null"); } _functionToRecurse = functionToRecurse; } Simple enough.  If you have any questions, feel free to post them in the comments, and I will be sure to answer them. Next, I want enough. If be able to get the result of a function dependent on how many levels of recursion: private Func<T, T> GetXLevel(int level) { if (level < 1) { throw new ArgumentOutOfRangeException("level", level, "The level of recursion must be greater than 0"); } if (level == 1) return _functionToRecurse; return _GetXLevel(level - 1, _functionToRecurse); } So, if you pass in 1 for the level, you get just the Func<T,T> back.  If you say that you want to go deeper down the rabbit hole, it calls a method which accepts the level it is at, and the function which it needs to use to recurse further: private Func<T, T> _GetXLevel(int level, Func<T, T> prevFunc) { if (level == 1) return y => prevFunc(_functionToRecurse(y)); return _GetXLevel(level - 1, y => prevFunc(_functionToRecurse(y))); } That is really all that is needed for this class. If I exposed the GetXLevel function publicly, I could use that to get the function for a level, and pass in the argument..  But I wanted something better.  So, I used the ‘this’ array operator for the class: public Func<T,T> this[int level] { get { if (level < 1) { throw new ArgumentOutOfRangeException("level", level, "The level of recursion must be greater than 0"); } return this.GetXLevel(level); } } So, using the same example above of finding the second recursion of the summation of 3: var summator = new Recursion<int>(x => (x * (x + 1)) / 2); var sum_3_level2 = summator[2](3); //yields 21 You can even find just store the delegate to the second level summation, and use it multiple times: var summator = new Recursion<int>(x => (x * (x + 1)) / 2); var sum_level2 = summator[2]; var sum_3_level2 = sum_level2(3); //yields 21 var sum_4_level2 = sum_level2(4); //yields 55 var sum_5_level2 = sum_level2(5); //yields 120 Full Code Don’t think I was just going to hold off on the full file together and make you do the hard work…  Copy this into a new class file: public class Recursion<T> { private readonly Func<T, T> _functionToRecurse; public Recursion(Func<T, T> functionToRecurse) { if (functionToRecurse == null) { throw new ArgumentNullException("functionToRecurse", "The function to recurse can not be null"); } _functionToRecurse = functionToRecurse; } public Func<T,T> this[int level] { get { if (level < 1) { throw new ArgumentOutOfRangeException("level", level, "The level of recursion must be greater than 0"); } return this.GetXLevel(level); } } private Func<T, T> GetXLevel(int level) { if (level < 1) { throw new ArgumentOutOfRangeException("level", level, "The level of recursion must be greater than 0"); } if (level == 1) return _functionToRecurse; return _GetXLevel(level - 1, _functionToRecurse); } private Func<T, T> _GetXLevel(int level, Func<T, T> prevFunc) { if (level == 1) return y => prevFunc(_functionToRecurse(y)); return _GetXLevel(level - 1, y => prevFunc(_functionToRecurse(y))); } } Conclusion The great thing about this class, is that it can be used with any function with same input/output parameters.  I strived to find an implementation that I found clean and useful, and I finally settled on this.  If you have feedback – good or bad, I would love to hear it!

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• What's the best/most efficent way to create a semi-intelligent AI for a tic tac toe game?

  - by Link

  basically I am attempting to make a a efficient/smallish C game of Tic-Tac-Toe. I have implemented everything other then the AI for the computer so far. my squares are basically structs in an array with an assigned value based on the square. For example s[1].value = 1; therefore it's a x, and then a value of 3 would be a o. My question is whats the best way to create a semi-decent game playing AI for my tic-tac-toe game? I don't really want to use minimax, since It's not what I need. So how do I avoid a a lot of if statments and make it more efficient. Here is the rest of my code: #include <stdio.h> #include <stdlib.h> #include <string.h> #include <time.h> struct state{ // defined int state; // 0 is tie, 1 is user loss, 2 is user win, 3 is ongoing game int moves; }; struct square{ // one square of the board int value; // 1 is x, 3 is o char sign; // no space used }; struct square s[9]; //set up the struct struct state gamestate = {0,0}; //nothing void setUpGame(){ // setup the game int i = 0; for(i = 0; i < 9; i++){ s[i].value = 0; s[i].sign = ' '; } gamestate.moves=0; printf("\nHi user! You're \"x\"! I'm \"o\"! Good Luck :)\n"); } void displayBoard(){// displays the game board printf("\n %c | %c | %c\n", s[6].sign, s[7].sign, s[8].sign); printf("-----------\n"); printf(" %c | %c | %c\n", s[3].sign, s[4].sign, s[5].sign); printf("-----------\n"); printf(" %c | %c | %c\n\n", s[0].sign, s[1].sign, s[2].sign); } void getHumanMove(){ // get move from human int i; while(1){ printf(">>:"); char line[255]; // input the move to play fgets(line, sizeof(line), stdin); while(sscanf(line, "%d", &i) != 1) { //1 match of defined specifier on input line printf("Sorry, that's not a valid move!\n"); fgets(line, sizeof(line), stdin); } if(s[i-1].value != 0){printf("Sorry, That moves already been taken!\n\n");continue;} break; } s[i-1].value = 1; s[i-1].sign = 'x'; gamestate.moves++; } int sum(int x, int y, int z){return(x*y*z);} void getCompMove(){ // get the move from the computer } void checkWinner(){ // check the winner int i; for(i = 6; i < 9; i++){ // check cols if((sum(s[i].value,s[i-3].value,s[i-6].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;} if((sum(s[i].value,s[i-3].value,s[i-6].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;} } for(i = 0; i < 7; i+=3){ // check rows if((sum(s[i].value,s[i+1].value,s[i+2].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;} if((sum(s[i].value,s[i+1].value,s[i+2].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;} } if((sum(s[0].value,s[4].value,s[8].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;} if((sum(s[0].value,s[4].value,s[8].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;} if((sum(s[2].value,s[4].value,s[6].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;} if((sum(s[2].value,s[4].value,s[6].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;} } void playGame(){ // start playing the game gamestate.state = 3; //set-up the gamestate srand(time(NULL)); int temp = (rand()%2) + 1; if(temp == 2){ // if two comp goes first temp = (rand()%2) + 1; if(temp == 2){ s[4].value = 2; s[4].sign = 'o'; gamestate.moves++; }else{ s[2].value = 2; s[2].sign = 'o'; gamestate.moves++; } } displayBoard(); while(gamestate.state == 3){ if(gamestate.moves<10); getHumanMove(); if(gamestate.moves<10); getCompMove(); checkWinner(); if(gamestate.state == 3 && gamestate.moves==9){ printf("The game is a tie :p\n"); break; } displayBoard(); } } int main(int argc, const char *argv[]){ printf("Welcome to Tic Tac Toe\nby The Elite Noob\nEnter 1-9 To play a move, standard numpad\n1 is bottom-left, 9 is top-right\n"); while(1){ // while game is being played printf("\nPress 1 to play a new game, or any other number to exit;\n>>:"); char line[255]; // input whether or not to play the game fgets(line, sizeof(line), stdin); int choice; // user's choice about playing or not while(sscanf(line, "%d", &choice) != 1) { //1 match of defined specifier on input line printf("Sorry, that's not a valid option!\n"); fgets(line, sizeof(line), stdin); } if(choice == 1){ setUpGame(); // set's up the game playGame(); // Play a Game }else {break;} // exit the application } printf("\nThank's For playing!\nHave a good Day!\n"); return 0; }

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• Solving the EXC_BAD_ACCESS in WhatATool Part 2

  - by Allen

  #import <Cocoa/Cocoa.h> @interface PolygonShape : NSObject { int numberOfSides, maximumNumberOfSides, minimumNumberOfSides; } @property (readwrite) int numberOfSides, maximumNumberOfSides, minimumNumberOfSides; @property (readonly) float angleInDegrees, angleInRadians; @property (readonly) NSString * name; @property (readonly) NSString * description; -(id) init; -(void) setNumberOfSides:(int)sides; -(void) setMinimumNumberOfSides:(int)min; -(void) setMaximumNumberOfSides:(int)max; -(float) angleInDegrees; -(float) angleInRadians; -(NSString *) name; -(id) initWithNumberOfSides:(int) sides minimumNumberOfSides:(int) min maximumNumberOfSides:(int) max; -(NSString *) description; -(void) dealloc; @end #import "PolygonShape.h" @implementation PolygonShape -(id) init { return [self initWithNumberOfSides:4 minimumNumberOfSides:3 maximumNumberOfSides:5]; } @synthesize numberOfSides, minimumNumberOfSides, maximumNumberOfSides, angleInRadians; -(void) setNumberOfSides:(int)sides { numberOfSides = sides; NSLog(@"The number of sides is off limit so the number of sides is %@.",sides); } -(void)setMaximumNumberOfSides:(int)max { if (maximumNumberOfSides <= 12) { maximumNumberOfSides = max; } } -(void)setMinimumNumberOfSides: (int)min { if (minimumNumberOfSides > 2) { minimumNumberOfSides = min; } } - (id)initWithNumberOfSides:(int)sides minimumNumberOfSides:(int)min maximumNumberOfSides:(int)max { if(self=[super init]) { [self setNumberOfSides:(int)sides]; [self setMaximumNumberOfSides:(int)max]; [self setMinimumNumberOfSides: (int)min]; } return self; } -(float) angleInDegrees { float anglesInDegrees = (180 * (numberOfSides - 2) / numberOfSides); return anglesInDegrees; } -(float)angleInRadiants { float anglesInRadiants = ((180 * (numberOfSides - 2) / numberOfSides) * (180 / M_PI)); return anglesInRadiants; } -(NSString *)name { NSString * output; switch (numberOfSides) { case 3: output = @"Triangle"; break; case 4: output = @"Square"; break; case 5: output = @"Pentagon"; break; case 6: output = @"Hexagon"; break; case 7: output = @"Heptagon"; break; case 8: output = @"Octagon"; break; case 9: output = @"Nonagon"; break; case 10: output = @"Decagon"; break; case 11: output = @"Hendecagon"; break; case 12: output = @"Dodecabgon"; break; default: output = @"Invalid number of sides: %i is greater than maximum of five allowed."; } return output; } -(NSString *)description { NSString * output; NSLog(@"Hello I am a %i-sided polygon (aka a %@) with angles of %f degrees (%f radians).", numberOfSides, output, [self angleInDegrees], [self angleInRadiants]); return [self description]; } -(void)dealloc { [super dealloc]; } @end #import <Foundation/Foundation.h> #import "PolygonShape.h" void PrintPathInfo() { NSLog(@"Section 1"); NSLog(@"--------------------"); NSString *path = [@"~" stringByExpandingTildeInPath]; NSLog(@"My home folder is at '%@'.", path); NSArray *pathComponent = [path pathComponents]; for (path in pathComponent) { NSLog(@"%@",path); } NSLog(@"--------------------"); NSLog(@"\n"); } void PrintProcessInfo() { NSLog(@"Section 2"); NSLog(@"--------------------"); NSString * processName = [[NSProcessInfo processInfo] processName]; int processIdentifier = [[NSProcessInfo processInfo] processIdentifier]; NSLog(@"Process Name: '%@', Process ID: '%i'", processName, processIdentifier); NSLog(@"--------------------"); NSLog(@"\n"); } void PrintBookmarkInfo() { NSLog(@"Section 3"); NSLog(@"--------------------"); NSArray * keys = [NSArray arrayWithObjects: @"Stanford University", @"Apple", @"CS193P", @"Stanford on iTunes U", @"Stanford Mall", nil]; NSArray * objects = [NSArray arrayWithObjects: [NSURL URLWithString: @"http://www.stanford.edu"], @"http://www.apple.com", @"http://cs193p.stanford.edu", @"http://itunes.stanford.edu", @"http://stanfordshop.com",nil]; NSMutableDictionary * dictionary = [NSMutableDictionary dictionaryWithObjects:objects forKeys:keys]; NSEnumerator * enumerator = [keys objectEnumerator]; for (id keys in dictionary) { NSLog(@"key: '%@', value: '%@'", keys, [dictionary objectForKey:keys]); } NSLog(@" "); NSLog(@"These are the ones that has the prefix 'Stanford'."); NSLog(@" "); id object; while (object = [enumerator nextObject]) { if ([object hasPrefix: @"Stanford"]) { NSLog(@"key: '%@', value: '%@'", object, [dictionary objectForKey:object]); } } NSLog(@"--------------------"); NSLog(@"\n"); } void PrintIntrospectionInfo() { NSLog(@"Section 4"); NSLog(@"--------------------"); SEL lowercase = @selector (lowercaseString); NSMutableArray * array = [NSMutableArray array]; [array addObject: [NSString stringWithString: @"Here is a string"]]; [array addObject: [NSDictionary dictionary]]; [array addObject: [NSURL URLWithString: @"http://www.stanford.edu"]]; [array addObject: [[NSProcessInfo processInfo]processName]]; for (id keys in array) { NSLog(@"\n"); NSLog(@"Class Name: %@", [keys className]); NSLog(@"Is Member of NSString: %@", [keys isMemberOfClass:[NSString class]]?@"Yes":@"No"); NSLog(@"Is Kind of NSString: %@", [keys isKindOfClass:[NSString class]]?@"Yes":@"No"); if ([keys respondsToSelector: lowercase]==YES) { NSLog(@"Responds to lowercaseString: %@",[keys respondsToSelector: lowercase]?@"Yes":@"No"); NSLog(@"lowercaseString is: %@", [keys performSelector: lowercase]); } else { NSLog(@"Responds to lowercaseString: %@",[keys respondsToSelector: lowercase]?@"Yes":@"No" ); } } NSLog(@"--------------------"); } void PrintPolygonInfo() { NSMutableArray * array = [NSMutableArray array]; PolygonShape * polygon1 = [[PolygonShape alloc]initWithNumberOfSides:4 minimumNumberOfSides:3 maximumNumberOfSides:7]; [array addObject:polygon1]; [array description]; PolygonShape * polygon2 = [[PolygonShape alloc]initWithNumberOfSides:6 minimumNumberOfSides:5 maximumNumberOfSides:9]; [array addObject:polygon2]; [array description]; PolygonShape * polygon3 = [[PolygonShape alloc]initWithNumberOfSides:12 minimumNumberOfSides:9 maximumNumberOfSides:12]; [array addObject:polygon3]; [array description]; [array release]; [polygon1 release]; [polygon2 release]; [polygon3 release]; } int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; PrintPathInfo(); PrintProcessInfo(); PrintBookmarkInfo(); PrintIntrospectionInfo(); PrintPolygonInfo(); [pool release]; return 0; } //The result was "EXC_BAD_ACCESS", but I couldn't figure out how to resolve this problem.

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• Mysql - help me optimize this query

  - by sandeepan-nath

  About the system: -The system has a total of 8 tables - Users - Tutor_Details (Tutors are a type of User,Tutor_Details table is linked to Users) - learning_packs, (stores packs created by tutors) - learning_packs_tag_relations, (holds tag relations meant for search) - tutors_tag_relations and tags and orders (containing purchase details of tutor's packs), order_details linked to orders and tutor_details. For a more clear idea about the tables involved please check the The tables section in the end. -A tags based search approach is being followed.Tag relations are created when new tutors register and when tutors create packs (this makes tutors and packs searcheable). For details please check the section How tags work in this system? below. Following is a simpler representation (not the actual) of the more complex query which I am trying to optimize:- I have used statements like explanation of parts in the query select SUM(DISTINCT( t.tag LIKE "%Dictatorship%" )) as key_1_total_matches, SUM(DISTINCT( t.tag LIKE "%democracy%" )) as key_2_total_matches, td., u., count(distinct(od.id_od)), if (lp.id_lp > 0) then some conditional logic on lp fields else 0 as tutor_popularity from Tutor_Details AS td JOIN Users as u on u.id_user = td.id_user LEFT JOIN Learning_Packs_Tag_Relations AS lptagrels ON td.id_tutor = lptagrels.id_tutor LEFT JOIN Learning_Packs AS lp ON lptagrels.id_lp = lp.id_lp LEFT JOIN `some other tables on lp.id_lp - let's call learning pack tables set (including Learning_Packs table)` LEFT JOIN Order_Details as od on td.id_tutor = od.id_author LEFT JOIN Orders as o on od.id_order = o.id_order LEFT JOIN Tutors_Tag_Relations as ttagrels ON td.id_tutor = ttagrels.id_tutor JOIN Tags as t on (t.id_tag = ttagrels.id_tag) OR (t.id_tag = lptagrels.id_tag) where some condition on Users table's fields AND CASE WHEN ((t.id_tag = lptagrels.id_tag) AND (lp.id_lp 0)) THEN `some conditions on learning pack tables set` ELSE 1 END AND CASE WHEN ((t.id_tag = wtagrels.id_tag) AND (wc.id_wc 0)) THEN `some conditions on webclasses tables set` ELSE 1 END AND CASE WHEN (od.id_od0) THEN od.id_author = td.id_tutor and some conditions on Orders table's fields ELSE 1 END AND ( t.tag LIKE "%Dictatorship%" OR t.tag LIKE "%democracy%") group by td.id_tutor HAVING key_1_total_matches = 1 AND key_2_total_matches = 1 order by tutor_popularity desc, u.surname asc, u.name asc limit 0,20 ===================================================================== What does the above query do? Does AND logic search on the search keywords (2 in this example - "Democracy" and "Dictatorship"). Returns only those tutors for which both the keywords are present in the union of the two sets - tutors details and details of all the packs created by a tutor. To make things clear - Suppose a Tutor name "Sandeepan Nath" has created a pack "My first pack", then:- Searching "Sandeepan Nath" returns Sandeepan Nath. Searching "Sandeepan first" returns Sandeepan Nath. Searching "Sandeepan second" does not return Sandeepan Nath. ====================================================================================== The problem The results returned by the above query are correct (AND logic working as per expectation), but the time taken by the query on heavily loaded databases is like 25 seconds as against normal query timings of the order of 0.005 - 0.0002 seconds, which makes it totally unusable. It is possible that some of the delay is being caused because all the possible fields have not yet been indexed, but I would appreciate a better query as a solution, optimized as much as possible, displaying the same results ========================================================================================== How tags work in this system? When a tutor registers, tags are entered and tag relations are created with respect to tutor's details like name, surname etc. When a Tutors create packs, again tags are entered and tag relations are created with respect to pack's details like pack name, description etc. tag relations for tutors stored in tutors_tag_relations and those for packs stored in learning_packs_tag_relations. All individual tags are stored in tags table. ==================================================================== The tables Most of the following tables contain many other fields which I have omitted here. CREATE TABLE IF NOT EXISTS users ( id_user int(10) unsigned NOT NULL AUTO_INCREMENT, name varchar(100) NOT NULL DEFAULT '', surname varchar(155) NOT NULL DEFAULT '', PRIMARY KEY (id_user) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=636 ; CREATE TABLE IF NOT EXISTS tutor_details ( id_tutor int(10) NOT NULL AUTO_INCREMENT, id_user int(10) NOT NULL DEFAULT '0', PRIMARY KEY (id_tutor), KEY Users_FKIndex1 (id_user) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=51 ; CREATE TABLE IF NOT EXISTS orders ( id_order int(10) unsigned NOT NULL AUTO_INCREMENT, PRIMARY KEY (id_order), KEY Orders_FKIndex1 (id_user), ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=275 ; ALTER TABLE orders ADD CONSTRAINT Orders_ibfk_1 FOREIGN KEY (id_user) REFERENCES users (id_user) ON DELETE NO ACTION ON UPDATE NO ACTION; CREATE TABLE IF NOT EXISTS order_details ( id_od int(10) unsigned NOT NULL AUTO_INCREMENT, id_order int(10) unsigned NOT NULL DEFAULT '0', id_author int(10) NOT NULL DEFAULT '0', PRIMARY KEY (id_od), KEY Order_Details_FKIndex1 (id_order) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=284 ; ALTER TABLE order_details ADD CONSTRAINT Order_Details_ibfk_1 FOREIGN KEY (id_order) REFERENCES orders (id_order) ON DELETE NO ACTION ON UPDATE NO ACTION; CREATE TABLE IF NOT EXISTS learning_packs ( id_lp int(10) unsigned NOT NULL AUTO_INCREMENT, id_author int(10) unsigned NOT NULL DEFAULT '0', PRIMARY KEY (id_lp), KEY Learning_Packs_FKIndex2 (id_author), KEY id_lp (id_lp) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=23 ; CREATE TABLE IF NOT EXISTS tags ( id_tag int(10) unsigned NOT NULL AUTO_INCREMENT, tag varchar(255) DEFAULT NULL, PRIMARY KEY (id_tag), UNIQUE KEY tag (tag), KEY id_tag (id_tag), KEY tag_2 (tag), KEY tag_3 (tag) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=3419 ; CREATE TABLE IF NOT EXISTS tutors_tag_relations ( id_tag int(10) unsigned NOT NULL DEFAULT '0', id_tutor int(10) DEFAULT NULL, KEY Tutors_Tag_Relations (id_tag), KEY id_tutor (id_tutor), KEY id_tag (id_tag) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; ALTER TABLE tutors_tag_relations ADD CONSTRAINT Tutors_Tag_Relations_ibfk_1 FOREIGN KEY (id_tag) REFERENCES tags (id_tag) ON DELETE NO ACTION ON UPDATE NO ACTION; CREATE TABLE IF NOT EXISTS learning_packs_tag_relations ( id_tag int(10) unsigned NOT NULL DEFAULT '0', id_tutor int(10) DEFAULT NULL, id_lp int(10) unsigned DEFAULT NULL, KEY Learning_Packs_Tag_Relations_FKIndex1 (id_tag), KEY id_lp (id_lp), KEY id_tag (id_tag) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; ALTER TABLE learning_packs_tag_relations ADD CONSTRAINT Learning_Packs_Tag_Relations_ibfk_1 FOREIGN KEY (id_tag) REFERENCES tags (id_tag) ON DELETE NO ACTION ON UPDATE NO ACTION; =================================================================================== Following is the exact query (this includes classes also - tutors can create classes and search terms are matched with classes created by tutors):- select count(distinct(od.id_od)) as tutor_popularity, CASE WHEN (IF((wc.id_wc 0), ( wc.wc_api_status = 1 AND wc.wc_type = 0 AND wc.class_date '2010-06-01 22:00:56' AND wccp.status = 1 AND (wccp.country_code='IE' or wccp.country_code IN ('INT'))), 0)) THEN 1 ELSE 0 END as 'classes_published', CASE WHEN (IF((lp.id_lp 0), (lp.id_status = 1 AND lp.published = 1 AND lpcp.status = 1 AND (lpcp.country_code='IE' or lpcp.country_code IN ('INT'))),0)) THEN 1 ELSE 0 END as 'packs_published', td . * , u . * from Tutor_Details AS td JOIN Users as u on u.id_user = td.id_user LEFT JOIN Learning_Packs_Tag_Relations AS lptagrels ON td.id_tutor = lptagrels.id_tutor LEFT JOIN Learning_Packs AS lp ON lptagrels.id_lp = lp.id_lp LEFT JOIN Learning_Packs_Categories AS lpc ON lpc.id_lp_cat = lp.id_lp_cat LEFT JOIN Learning_Packs_Categories AS lpcp ON lpcp.id_lp_cat = lpc.id_parent LEFT JOIN Learning_Pack_Content as lpct on (lp.id_lp = lpct.id_lp) LEFT JOIN Webclasses_Tag_Relations AS wtagrels ON td.id_tutor = wtagrels.id_tutor LEFT JOIN WebClasses AS wc ON wtagrels.id_wc = wc.id_wc LEFT JOIN Learning_Packs_Categories AS wcc ON wcc.id_lp_cat = wc.id_wp_cat LEFT JOIN Learning_Packs_Categories AS wccp ON wccp.id_lp_cat = wcc.id_parent LEFT JOIN Order_Details as od on td.id_tutor = od.id_author LEFT JOIN Orders as o on od.id_order = o.id_order LEFT JOIN Tutors_Tag_Relations as ttagrels ON td.id_tutor = ttagrels.id_tutor JOIN Tags as t on (t.id_tag = ttagrels.id_tag) OR (t.id_tag = lptagrels.id_tag) OR (t.id_tag = wtagrels.id_tag) where (u.country='IE' or u.country IN ('INT')) AND CASE WHEN ((t.id_tag = lptagrels.id_tag) AND (lp.id_lp 0)) THEN lp.id_status = 1 AND lp.published = 1 AND lpcp.status = 1 AND (lpcp.country_code='IE' or lpcp.country_code IN ('INT')) ELSE 1 END AND CASE WHEN ((t.id_tag = wtagrels.id_tag) AND (wc.id_wc 0)) THEN wc.wc_api_status = 1 AND wc.wc_type = 0 AND wc.class_date '2010-06-01 22:00:56' AND wccp.status = 1 AND (wccp.country_code='IE' or wccp.country_code IN ('INT')) ELSE 1 END AND CASE WHEN (od.id_od0) THEN od.id_author = td.id_tutor and o.order_status = 'paid' and CASE WHEN (od.id_wc 0) THEN od.can_attend_class=1 ELSE 1 END ELSE 1 END AND 1 group by td.id_tutor order by tutor_popularity desc, u.surname asc, u.name asc limit 0,20 Please note - The provided database structure does not show all the fields and tables as in this query

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• How to know if the client has terminated in sockets

  - by shadyabhi

  Suppose, I have a connected socket after writing this code.. if ((sd = accept(socket_d, (struct sockaddr *)&client_addr, &alen)) < 0) { perror("accept failed\n"); exit(1); } How can I know at the server side that client has exited. My whole program actually does the following.. Accepts a connection from client Starts a new thread that reads messages from that particular client and then broadcast this message to all the connected clients. If you want to see the whole code... In this whole code. I am also struggling with one more problem that whenever I kill a client with Ctrl+C, my server terminates abruptly.. It would be nice if anyone could suggest what the problem is.. #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <netdb.h> #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <signal.h> #include <errno.h> #include <pthread.h> /*CONSTANTS*/ #define DEFAULT_PORT 10000 #define LISTEN_QUEUE_LIMIT 6 #define TOTAL_CLIENTS 10 #define CHAR_BUFFER 256 /*GLOBAL VARIABLE*/ int current_client = 0; int connected_clients[TOTAL_CLIENTS]; extern int errno; void *client_handler(void * socket_d); int main(int argc, char *argv[]) { struct sockaddr_in server_addr;/* structure to hold server's address*/ int socket_d; /* listening socket descriptor */ int port; /* protocol port number */ int option_value; /* needed for setsockopt */ pthread_t tid[TOTAL_CLIENTS]; port = (argc > 1)?atoi(argv[1]):DEFAULT_PORT; /* Socket Server address structure */ memset((char *)&server_addr, 0, sizeof(server_addr)); server_addr.sin_family = AF_INET; /* set family to Internet */ server_addr.sin_addr.s_addr = INADDR_ANY; /* set the local IP address */ server_addr.sin_port = htons((u_short)port); /* Set port */ /* Create socket */ if ( (socket_d = socket(PF_INET, SOCK_STREAM, 0)) < 0) { fprintf(stderr, "socket creation failed\n"); exit(1); } /* Make listening socket's port reusable */ if (setsockopt(socket_d, SOL_SOCKET, SO_REUSEADDR, (char *)&option_value, sizeof(option_value)) < 0) { fprintf(stderr, "setsockopt failure\n"); exit(1); } /* Bind a local address to the socket */ if (bind(socket_d, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) { fprintf(stderr, "bind failed\n"); exit(1); } /* Specify size of request queue */ if (listen(socket_d, LISTEN_QUEUE_LIMIT) < 0) { fprintf(stderr, "listen failed\n"); exit(1); } memset(connected_clients,0,sizeof(int)*TOTAL_CLIENTS); for (;;) { struct sockaddr_in client_addr; /* structure to hold client's address*/ int alen = sizeof(client_addr); /* length of address */ int sd; /* connected socket descriptor */ if ((sd = accept(socket_d, (struct sockaddr *)&client_addr, &alen)) < 0) { perror("accept failed\n"); exit(1); } else printf("\n I got a connection from (%s , %d)\n",inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port)); if (pthread_create(&tid[current_client],NULL,(void *)client_handler,(void *)sd) != 0) { perror("pthread_create error"); continue; } connected_clients[current_client]=sd; current_client++; /*Incrementing Client number*/ } return 0; } void *client_handler(void *connected_socket) { int sd; sd = (int)connected_socket; for ( ; ; ) { ssize_t n; char buffer[CHAR_BUFFER]; for ( ; ; ) { if (n = read(sd, buffer, sizeof(char)*CHAR_BUFFER) == -1) { perror("Error reading from client"); pthread_exit(1); } int i=0; for (i=0;i<current_client;i++) { if (write(connected_clients[i],buffer,sizeof(char)*CHAR_BUFFER) == -1) perror("Error sending messages to a client while multicasting"); } } } } My client side is this (Maye be irrelevant while answering my question) #include <stdio.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <netdb.h> #include <string.h> #include <stdlib.h> void error(char *msg) { perror(msg); exit(0); } void *listen_for_message(void * fd) { int sockfd = (int)fd; int n; char buffer[256]; bzero(buffer,256); printf("YOUR MESSAGE: "); fflush(stdout); while (1) { n = read(sockfd,buffer,256); if (n < 0) error("ERROR reading from socket"); if (n == 0) pthread_exit(1); printf("\nMESSAGE BROADCAST: %sYOUR MESSAGE: ",buffer); fflush(stdout); } } int main(int argc, char *argv[]) { int sockfd, portno, n; struct sockaddr_in serv_addr; struct hostent *server; pthread_t read_message; char buffer[256]; if (argc < 3) { fprintf(stderr,"usage %s hostname port\n", argv[0]); exit(0); } portno = atoi(argv[2]); sockfd = socket(AF_INET, SOCK_STREAM, 0); if (sockfd < 0) error("ERROR opening socket"); server = gethostbyname(argv[1]); if (server == NULL) { fprintf(stderr,"ERROR, no such host\n"); exit(0); } bzero((char *) &serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr, server->h_length); serv_addr.sin_port = htons(portno); if (connect(sockfd,&serv_addr,sizeof(serv_addr)) < 0) error("ERROR connecting"); bzero(buffer,256); if (pthread_create(&read_message,NULL,(void *)listen_for_message,(void *)sockfd) !=0 ) { perror("error creating thread"); } while (1) { fgets(buffer,255,stdin); n = write(sockfd,buffer,256); if (n < 0) error("ERROR writing to socket"); bzero(buffer,256); } return 0; }

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