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• Detect pointer arithmetics because of LARGEADDRESSAWARE

  - by Suma

  I would like to switch my application to LARGEADDRESSAWARE. One of issues to watch for is pointer arithmetic, as pointer difference can no longer be represented as signed 32b. Is there some way how to find automatically all instances of pointer subtraction in a large C++ project? If not, is there some "least effort" manual or semi-automatic method how to achieve this?

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• String manipulation of type String substitution in mathematical expression

  - by Peterstone

  Imagine something like exp(49/200)+(x-49/200) I want to pass as argument of the function "roundn" whatever operation that is not a addtion or a subtraction So my expresion became roundn(exp(roundn(49/200,n)),n)+(x - roundn(49/200,n) Well the expression I want to manipulate is this: exp(49/200)+exp(49/200)*(x-49/200)+1/2*exp(49/200)*(x-49/200)^2+1/6*exp(49/200)*(x- 49/200)^3+1/24*exp(49/200)*(x-49/200)^4+1/120*exp(49/200)*(x-49/200)^5+1/720*exp(49/200)*(x-49/200)^6+1/5040*exp(49/200)*(x-49/200)^7+1/40320*exp(49/200)*(x-49/200)^8+1/362880*exp(49/200)*(x-49/200)^9+1/3628800*exp(49/200)*(x-49/200)^10+1/39916800*exp(49/200)*(x-49/200)^11 I´m looking for a method (That include whatever program) not based in lenguage programming, as much batch or somithing like that... Thank you!

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• operator overloading of stream extraction operator in C++ help

  - by Crystal

  I'm having some trouble overloading my stream extraction operator in C++ for a hw assignment. I'm not really sure why I am getting these compile errors since I thought I was doing it right... Here is my code: Complex.h #ifndef COMPLEX_H #define COMPLEX_H class Complex { //friend ostream &operator<<(ostream &output, const Complex &complexObj) const; public: Complex(double = 0.0, double = 0.0); // constructor Complex operator+(const Complex &) const; // addition Complex operator-(const Complex &) const; // subtraction void print() const; // output private: double real; // real part double imaginary; // imaginary part }; #endif Complex.cpp #include <iostream> #include "Complex.h" using namespace std; // Constructor Complex::Complex(double realPart, double imaginaryPart) : real(realPart), imaginary(imaginaryPart) { } // addition operator Complex Complex::operator+(const Complex &operand2) const { return Complex(real + operand2.real, imaginary + operand2.imaginary); } // subtraction operator Complex Complex::operator-(const Complex &operand2) const { return Complex(real - operand2.real, imaginary - operand2.imaginary); } // Overload << operator ostream &Complex::operator<<(ostream &output, const Complex &complexObj) const { cout << '(' << complexObj.real << ", " << complexObj.imaginary << ')'; return output; // returning output allows chaining } // display a Complex object in the form: (a, b) void Complex::print() const { cout << '(' << real << ", " << imaginary << ')'; } main.cpp #include <iostream> #include "Complex.h" using namespace std; int main() { Complex x; Complex y(4.3, 8.2); Complex z(3.3, 1.1); cout << "x: "; x.print(); cout << "\ny: "; y.print(); cout << "\nz: "; z.print(); x = y + z; cout << "\n\nx = y + z: " << endl; x.print(); cout << " = "; y.print(); cout << " + "; z.print(); x = y - z; cout << "\n\nx = y - z: " << endl; x.print(); cout << " = "; y.print(); cout << " - "; z.print(); cout << endl; } Compile erros: complex.cpp(23) : error C2039: '<<' : is not a member of 'Complex' complex.h(5) : see declaration of 'Complex' complex.cpp(24) : error C2270: '<<' : modifiers not allowed on nonmember functions complex.cpp(25) : error C2248: 'Complex::real' : cannot access private member declared in class 'Complex' complex.h(13) : see declaration of 'Complex::real' complex.h(5) : see declaration of 'Complex' complex.cpp(25) : error C2248: 'Complex::imaginary' : cannot access private member declared in class 'Complex' complex.h(14) : see declaration of 'Complex::imaginary' complex.h(5) : see declaration of 'Complex' Thanks!

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• Points on lines where the two lines are the closest together

  - by James Bedford

  Hey guys, I'm trying to find the points on two lines where the two lines are the closest. I've implemented the following method (Points and Vectors are as you'd expect, and a Line consists of a Point on the line and a non-normalized direction Vector from that point): void CDClosestPointsOnTwoLines(Line line1, Line line2, Point* closestPoints) { closestPoints[0] = line1.pointOnLine; closestPoints[1] = line2.pointOnLine; Vector d1 = line1.direction; Vector d2 = line2.direction; float a = d1.dot(d1); float b = d1.dot(d2); float e = d2.dot(d2); float d = a*e - b*b; if (d != 0) // If the two lines are not parallel. { Vector r = Vector(line1.pointOnLine) - Vector(line2.pointOnLine); float c = d1.dot(r); float f = d2.dot(r); float s = (b*f - c*e) / d; float t = (a*f - b*c) / d; closestPoints[0] = line1.positionOnLine(s); closestPoints[1] = line2.positionOnLine(t); } else { printf("Lines were parallel.\n"); } } I'm using OpenGL to draw three lines that move around the world, the third of which should be the line that most closely connects the other two lines, the two end points of which are calculated using this function. The problem is that the first point of closestPoints after this function is called will lie on line1, but the second point won't lie on line2, let alone at the closest point on line2! I've checked over the function many times but I can't see where the mistake in my implementation is. I've checked my dot product function, scalar multiplication, subtraction, positionOnLine() etc. etc. So my assumption is that the problem is within this method implementation. If it helps to find the answer, this is function supposed to be an implementation of section 5.1.8 from 'Real-Time Collision Detection' by Christer Ericson. Many thanks for any help!

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• Correct For Loop Design

  - by Yttrill

  What is the correct design for a for loop? Felix currently uses if len a > 0 do for var i in 0 upto len a - 1 do println a.[i]; done done which is inclusive of the upper bound. This is necessary to support the full range of values of a typical integer type. However the for loop shown does not support zero length arrays, hence the special test, nor will the subtraction of 1 work convincingly if the length of the array is equal to the number of integers. (I say convincingly because it may be that 0 - 1 = maxval: this is true in C for unsigned int, but are you sure it is true for unsigned char without thinking carefully about integral promotions?) The actual implementation of the for loop by my compiler does correctly handle 0 but this requires two tests to implement the loop: continue: if not (i <= bound) goto break body if i == bound goto break ++i goto continue break: Throw in the hand coded zero check in the array example and three tests are needed. If the loop were exclusive it would handle zero properly, avoiding the special test, but there'd be no way to express the upper bound of an array with maximum size. Note the C way of doing this: for(i=0; predicate(i); increment(i)) has the same problem. The predicate is tested after the increment, but the terminating increment is not universally valid! There is a general argument that a simple exclusive loop is enough: promote the index to a large type to prevent overflow, and assume no one will ever loop to the maximum value of this type.. but I'm not entirely convinced: if you promoted to C's size_t and looped from the second largest value to the largest you'd get an infinite loop!

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• Programming as a minor

  - by Tomas Cokis

  Hello Everyone! I've never asked a question here at programmers, and for reasons which will become obvious later I've never answered one here, but I do poke around in short bursts. Anyway, I'm 15 right now, and I've been programming in C++ for 4 years, just working on my own projects that are aim so high as to never be finished. I've been working on a single project for the last year, and every 3 months, I add a new system into it. It might be a value tabling directory enabled log system, or a render system, or a class to load up xml files, whatever it is, I don't mind too much that the overall project (a 3d engine) isn't ever going to get finished, I just get some satisfaction from getting what I have done building and running. I don't know what I want to do when I grow up, although I suspect I'll go into some form of engineering, but I was interested in knowing if I do choose to go into a career as a developer, what kind of material I could look at to push myself up and get myself experience that might help my career later. I'm not talking about books in particular, I'm more interested in subjects areas that will get me access to good job opportunities, or that will give me a hand-up if I do computer science and software related courses at uni. One of the things I was thinking of doing was designing some of the logic gate components of a small computer - which I started briefly over the holidays, working out integer addition, subtraction and multiplication. That kind of stuff interests me, but is it really useful - or more useful then just more programming? But anyway, Any advice? Should I continue on my perpetual 3d engine? Are there any other projects or particular accomplishments that would help my education? Perhaps I should mention that I live in Perth, Australia, so local software companies are likely to be more scarce then usual.

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• What is the best way to "carve" a terrain created from a heightmap?

  - by tigrou

  I have a 3d landscape created from a heightmap. I'd like to "carve" some holes in that terrain. That will allow me to create bridges, caverns and tunnels inside it. That operation will be done in the game editor so it doesn't need to be realtime. In the end, rendering is done using traditional polygons. What would be the best/easiest way to do that ? I already think about several solutions : Solution 1 1) Create voxels from the heightmap (very easy). In other words, fill a 3D array like this : voxels[32][32][32] from the heightmap values. 2) Carve holes in the voxels as i want (easy too). 3) Convert voxels to polygons using some iso-surface extraction technique (like marching cubes). 4) Reduce (decimate) polygons created in 3). This technique seems to be the most promising for giving good results (untested). However the problem with marching cubes is that they tends to produce lots of polygons thus reducing them is mandatory. Implementing 4) also seems not trivial, i have read several papers on the web and it seems pretty complex. I was also unable to find an example, code snippet or something to start writing an algorithm for triangle mesh decimation. Maybe there is a special decimation algorithm (simpler) for meshes created from marching cubes ? Solution 2 1) Create some triangle mesh from the heighmap (easy). 2) Apply severals 3D boolean operation (eg: subtraction with a sphere) to carve the mesh. 3) apply some procedure to reduce polygons (optional). Operation 2) seems to be very complex and to be honest i have no idea how to do that. Also applying many boolean operation seems to be slow and will maybe degrade the triangle mesh every time a boolean operation is applied.

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• Quaternion LookAt for camera

  - by Homar

  I am using the following code to rotate entities to look at points. glm::vec3 forwardVector = glm::normalize(point - position); float dot = glm::dot(glm::vec3(0.0f, 0.0f, 1.0f), forwardVector); float rotationAngle = (float)acos(dot); glm::vec3 rotationAxis = glm::normalize(glm::cross(glm::vec3(0.0f, 0.0f, 1.0f), forwardVector)); rotation = glm::normalize(glm::quat(rotationAxis * rotationAngle)); This works fine for my usual entities. However, when I use this on my Camera entity, I get a black screen. If I flip the subtraction in the first line, so that I take the forward vector to be the direction from the point to my camera's position, then my camera works but naturally my entities rotate to look in the opposite direction of the point. I compute the transformation matrix for the camera and then take the inverse to be the View Matrix, which I pass to my OpenGL shaders: glm::mat4 viewMatrix = glm::inverse( cameraTransform->GetTransformationMatrix() ); The orthographic projection matrix is created using glm::ortho. What's going wrong?

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• How to handle monetary values in PHP and MySql?

  - by Songo

  I've inherited a huge pile of legacy code written in PHP on top of a MySQL database. The thing I noticed is that the application uses doubles for storage and manipulation of data. Now I came across of numerous posts mentioning how double are not suited for monetary operations because of the rounding errors. However, I have yet to come across a complete solution to how monetary values should be handled in PHP code and stored in a MySQL database. Is there a best practice when it comes to handling money specifically in PHP? Things I'm looking for are: How should the data be stored in the database? column type? size? How should the data be handling in normal addition, subtraction. multiplication or division? When should I round the values? How much rounding is acceptable if any? Is there a difference between handling large monetary values and low ones? Note: A VERY simplified sample code of how I might encounter money values in everyday life: $a= $_POST['price_in_dollars']; //-->(ex: 25.06) will be read as a string should it be cast to double? $b= $_POST['discount_rate'];//-->(ex: 0.35) value will always be less than 1 $valueToBeStored= $a * $b; //--> any hint here is welcomed $valueFromDatabase= $row['price']; //--> price column in database could be double, decimal,...etc. $priceToPrint=$valueFromDatabase * 0.25; //again cast needed or not? I hope you use this sample code as a means to bring out more use cases and not to take it literally of course. Bonus Question If I'm to use an ORM such as Doctrine or PROPEL, how different will it be to use money in my code.

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• How do I implement deceleration for the player character?

  - by tesselode

  Using delta time with addition and subtraction is easy. player.speed += 100 * dt However, multiplication and division complicate things a bit. For example, let's say I want the player to double his speed every second. player.speed = player.speed * 2 * dt I can't do this because it'll slow down the player (unless delta time is really high). Division is the same way, except it'll speed things way up. How can I handle multiplication and division with delta time? Edit: it looks like my question has confused everyone. I really just wanted to be able to implement deceleration without this horrible mass of code: else if speed > 0 then speed = speed - 20 * dt if speed < 0 then speed = 0 end end if speed < 0 then speed = speed + 20 * dt if speed > 0 then speed = 0 end end end Because that's way bigger than it needs to be. So far a better solution seems to be: speed = speed - speed * whatever_number * dt

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• Transforms in Box2D

  - by user1264811

  I'm attempting to implement a camera in my game. I had it working for regular objects, but I began using Box2D and obviously things changed a bit. I have a Body object that I want to draw at the center of the screen. Basically what I'm doing is subtracting the viewportX and viewportY to the Body. I use this code that currently is not working as it should: public void paint(Graphics2D g, int viewportX, int viewportY) { Transform xf = new Transform(); // m_body is the Body object xf.set(m_body.getTransform()); // Here what I attemp to do is take the transform and alter it // by the viewportX and Y, which is something like **-240, -150**. // Why is it negative? Because an object has coordinates 500, 300 would be displayed // at 160, 150 when the subtraction is done. // With the DrawUtils.toScale(), it's just how I convert the units from JBox2D units // to my units. Vec2 v = Transform.mulTrans(xf, new Vec2(DrawUtils.toScale(-viewportX), DrawUtils.toScale(-viewportY))); // Set the new transform to the new vector. Keep the old angle. xf.set(v, xf.q.getAngle()); g.setColor(Color.white); // I know for a fact that the following method works 100%. It correctly displays // my object, just that it doesn't follow it. for (Fixture f = m_body.getFixtureList(); f != null; f = f.getNext()) DrawUtils.drawShape(f, xf); } Hopefully I didn't over comment this and you understand my problem. I don't want to alter the actual physics position of the object, I just want to display it in the center.

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• the carry flag issue!

  - by Zia ur Rahman

  Suppose AX =FFFE and BX=1234 now if we write cmp ax,bx (bx will be subtracted from ax and the approprite flages will be updated) now the binary representation of the numbers in ax and bx is given by AX = 1111 1111 1111 1110 BX= 0001 0010 0011 0100 As bx will be subtracted from ax so we have to negate bx (as Result= ax+(-bx)) so the negated bx (2's complement of bx ) is given by. BX= 1110 1101 1100 1100 Now we add both ax and bx (as subtraction is implemented by addition in computer) AX= 1111 1111 1111 1110 BX= 1110 1101 1100 1100 ------------------------------------ 1 1110 1101 1100 1010 Now as you can see the result is of 17 bits now the 17th bit should go into carry flage, but when i checked it the carry flag is 0 that is CF=0 why?

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• flex and bison: wrong output

  - by user2972227

  I am doing a homework using flex and bison to make a complex number calculator. But my program cannot give a correct output. .lex file: %option noyywrap %{ #include<stdio.h> #include<stdlib.h> #include "complex_cal.h" #define YYSTYPE complex #include "complex_cal.tab.h" void RmWs(char* str); %} /* Add your Flex definitions here */ /* Some definitions are already provided to you*/ ws [ \t]+ digits [0-9] number (0|[1-9]+{digits}*)\.?{digits}* im [i] complexnum {ws}*[-]*{ws}*{number}{ws}*[+|-]{ws}*{number}{ws}*{im}{ws}* op [-+*/()] %% {complexnum} {RmWs(yytext); sscanf(yytext,"%lf %lf",&(yylval.real),&(yylval.img)); return CNUMBER;} {ws} /**/ {op} return *yytext; %% /* function provided to student to remove */ /* all the whitespaces from a string. */ void RmWs(char* str){ int i=0,j=0; char temp[strlen(str)+1]; strcpy(temp,str); while (temp[i]!='\0'){ while (temp[i]==' '){i++;} str[j]=temp[i]; i++; j++; } str[j]='\0'; } .y file: %{ #include <stdio.h> #include <stdlib.h> #include "complex_cal.h" /* prototypes of the provided functions */ complex complex_add (complex, complex); complex complex_sub (complex, complex); complex complex_mul (complex, complex); complex complex_div (complex, complex); /* prototypes of the provided functions */ int yylex(void); int yyerror(const char*); %} %token CNUMBER %left '+' '-' %left '*' '/' %nonassoc '(' ')' %% /* start: Add your grammar rules and actions here */ complexexp: complexexp '+' complexexpmultidiv {$$=complex_add($1, $3);} | complexexp '-' complexexpmultidiv {$$=complex_sub($1, $3);} | complexexpmultidiv {$$.real=$1.real;$$.img=$1.img;} ; complexexpmultidiv: complexexpmultidiv '*' complexsimple {$$=complex_mul($1, $3);} | complexexpmultidiv '/' complexsimple {$$=complex_div($1, $3);} | complexsimple {$$.real=$1.real;$$.img=$1.img;} ; complexsimple: '(' complexexp ')' {$$.real=$2.real;$$.img=$2.img;} | '(' CNUMBER ')' {$$.real=$2.real;$$.img=$2.img;} ; /* end: Add your grammar rules and actions here */ %% int main(){ return yyparse(); } int yyerror(const char* s){ printf("%s\n", s); return 0; } /* function provided to do complex addition */ /* input : complex numbers c1, c2 */ /* output: nothing */ /* side effect : none */ /* return value: result of addition in c3 */ complex complex_add (complex c1, complex c2){ /* c1 + c2 */ complex c3; c3.real = c1.real + c2.real; c3.img = c1.img + c2.img; return c3; } /* function provided to do complex subtraction */ /* input : complex numbers c1, c2 */ /* output: nothing */ /* side effect : none */ /* return value: result of subtraction in c3 */ complex complex_sub (complex c1, complex c2){ /* c1 - c2 */ complex c3; c3.real = c1.real - c2.real; c3.img = c1.img - c2.img; return c3; } /* function provided to do complex multiplication */ /* input : complex numbers c1, c2 */ /* output: nothing */ /* side effect : none */ /* return value: result of multiplication in c3 */ complex complex_mul (complex c1, complex c2){ /* c1 * c2 */ complex c3; c3.real = c1.real*c2.real - c1.img*c2.img; c3.img = c1.img*c2.real + c1.real*c2.img; return c3; } /* function provided to do complex division */ /* input : complex numbers c1, c2 */ /* output: nothing */ /* side effect : none */ /* return value: result of c1/c2 in c3 */ complex complex_div (complex c1, complex c2){ /* c1 / c2 (i.e. c1 divided by c2 ) */ complex c3; double d; /*divisor calculation using the conjugate of c2*/ d = c2.real*c2.real + c2.img*c2.img; c3.real = (c1.real*c2.real + c1.img*c2.img)/d; c3.img = (c1.img*c2.real - c1.real*c2.img)/d; return c3; } .h file: #include <string.h> /* struct for holding a complex number */ typedef struct { double real; double img; } complex; /* define the return type of FLEX */ #define YYSTYPE complex Script for compiling the file: bison -d -v complex_cal.y flex -ocomplex_cal.lex.yy.c complex_cal.lex gcc -o complex_cal complex_cal.lex.yy.c complex_cal.tab.c ./complex_cal Some correct sample run of the program: input:(5+6i)*(6+1i) output:24.000000+41.000000i input:(7+8i)/(-3-4i)*(5+7i) output:-11.720000-14.040000i input:(7+8i)/((-3-4i)*(5+7i)) output:-0.128108+0.211351i But when I run this program, the program only give an output which is identical to my input. For example, when I input (5+6i)(6+1i), it just gives (5+6i)(6+1i). Even if I input any other things, for example, input "abc" it just gives "abc" and is not syntax error. I don't know where the problem is and I hope to know how to solve it.

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• varchar comparison in SQL Server

  - by Ram

  I am looking for some SQL varchar comparison function like C# string.compare (we can ignore case for now, should return zero when the character expression are same and a non zero expression when they are different) Basically I have some alphanumeric column in one table which needs to be verified in another table. I cannot do select A.col1 - B.col1 from (query) as "-" operator cannot be applied on character expressions I cannot cast my expression as int (and then do a difference/subtraction) as it fails select cast ('ASXT000R' as int) Conversion failed when converting varchar 'ASXT000R' to int Soundex would not do it as soundex is same for 2 similar strings Difference would not do it as select difference('abc','ABC') = 4 (as per msdn, difference is the difference in the soundex of 2 character expressions and difference =4 implies least different) Is there any other way of doing it ?

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• Accessing E4X nodes having special characters in name without breaking binding chain in flex.

  - by Jonas

  I am using E4X to bind some values from xml in flex 3. There is a problem when xml tag's (or attribute's) name has special character in it: having xml content var xml:XML = <tag> <special-name att="val" /> </tag> special-name could not be accessed using xml.special-name.@att because it is interpreted as subtraction, on the other hand using square bracket notation xml['special-name'].@att breaks binding chain. Is there an elegant way to solve this (like special language syntax) without writing custom binding setters and listeners?

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• How do I use timezones with a datetime object in python?

  - by jidar

  How do I properly represent a different timezone in my timezone? The below example only works because I know that EDT is one hour ahead of me, so I can uncomment the subtraction of myTimeZone() import datetime, re from datetime import tzinfo class myTimeZone(tzinfo): """docstring for myTimeZone""" def utfoffset(self, dt): return timedelta(hours=1) def myDateHandler(aDateString): """u'Sat, 6 Sep 2008 21:16:33 EDT'""" _my_date_pattern = re.compile(r'\w+\,\s+(\d+)\s+(\w+)\s+(\d+)\s+(\d+)\:(\d+)\:(\d+)') day, month, year, hour, minute, second = _my_date_pattern.search(aDateString).groups() month = [ 'JAN', 'FEB', 'MAR', 'APR', 'MAY', 'JUN', 'JUL', 'AUG', 'SEP', 'OCT', 'NOV', 'DEC' ].index(month.upper()) + 1 dt = datetime.datetime( int(year), int(month), int(day), int(hour), int(minute), int(second) ) # dt = dt - datetime.timedelta(hours=1) # dt = dt - dt.tzinfo.utfoffset(myTimeZone()) return (dt.year, dt.month, dt.day, dt.hour, dt.minute, dt.second, 0, 0, 0) def main(): print myDateHandler("Sat, 6 Sep 2008 21:16:33 EDT") if __name__ == '__main__': main()

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• Fibonacci using SBN in OISC in Machine Language

  - by velociraptor

  Hello, I want to generate fibonacci series using SBN in an OISC architecture. My initial approach is to implement it in assembly language first and then convert it to machine language. The first steps involve storing 0 and 1 in 2 registers and then subtract 1 from 0 and repeatedly subtract 1 in the consequent steps. Everytime it will generate a negative number and since its negative, it branches off and fetches the absolute value finding instruction. Is my approach correct? My confusion in the meaning of OISC. Correct me if i'm wrong, if i perform a subtraction and then an absolute value finding, it means that that i'm using 2 instructions everytime. or is it that in the OISC processor both these instructions are done at the sametime which would mean that my approach is correct. Please help. thank you all

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• Can we manipulate (subtsract) the valueof height while template bidning?

  - by Subhen

  Hi, I am currently defining few grids as following: <Grid.RowDefinitions> <RowDefinition Height="{TemplateBinding Height-Height/5}"/> <RowDefinition Height="{TemplateBinding Height/15}"/> <RowDefinition Height="{TemplateBinding Height/20}"/> <RowDefinition Height="{TemplateBinding Height/6}"/> </Grid.RowDefinitions> While the division works fine , the subtraction isn't yielding the output. Ialso tried like following: <RowDefinition Height="{TemplateBinding Height-(Height/5)}"/> Still no result. Any suggestions plz. Thanks, Subhen

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• Code Golf: All +-*/ Combinations for 3 integers

  - by Flash84x

  Write a program that takes 3 integers separated by spaces and perform every single combination of addition, subtraction, multiplication and division operations possible and display the result with the operation combination used. Example: $./solution 1 2 3 Results in the following output 1+2+3 = 6 1-2-3 = -4 1*2*3 = 6 1/2/3 = 0 (integer answers only, round up at .5) 1*2-3 = -1 3*1+2 = 5 etc... Order of operation rules apply, assume there will be no parenthesis used i.e. (3-1)*2 = 4 is not a combination, although you could implement this for "extra credit" For results where a divide by 0 occurs simply return NaN

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• How do I do division on HH:MM:SS format time strings in C#?

  - by Jake

  I have a series of times that are coming to me as strings from a web service. The times are formated as HH:MM:SS:000 (3 milisecond digits). I need to compare two times to determine if one is more than twice as long as the other: if ( timeA / timeB > 2 ) What's the simplest way to work with the time strings? If I was writing in Python this would be the answer to my question: Difference between two time intervals in Python Edit: What I'm really looking for is a way to get the ratio of timeA to timeB, which requires division, not subtraction. Unfortunately, the DateTime structure doesn't appear to have a division operator. Updated the question title to reflect this.

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• PHP Datediff days involved

  - by user3549835

  I need to know how many days are involved in a date diff. \For example: <? $start = new DateTime('2014-06-29 14:00:00'); $ende = new DateTime('2014-07-02 05:45:00'); $diff = $start->diff($ende); echo $diff->format('%R'); echo $diff->days; ?> The above code echos +2 My desired result would be 4, because the 29th, 30th, 1st and 2nd of July are "touched". I have no idea to achieve that with the given functions. Coding a day-subtraction seems to bean open door for errors.

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• Problem removing a dynamic form field in jquery

  - by rshivers

  I'm trying to remove a dynamic form field by click a button. It will also subtract whatever values it had from the total amount from my calculation. This is the code: function removeFormField(id) { var id = $(id).attr("name"); $('#target1').text($("#total" + id).map(function() { var currentValue = parseFloat(document.getElementById("currentTotal").value); var newValue = parseFloat($("#total" + id).text()); var newTotal = currentValue - newValue; document.getElementById("currentTotal").value = newTotal; return newTotal; }).get().join()); $(id).remove(); } Okay, it will do the subtraction portion of the code with no problem, this issue is with the last line to remove the field. If I comment out the rest of the code it will work, but not with the rest of the code. I know this is something simple, yet I can't seem to wrap my mind around it. Can someone please help?

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• Can a Printer Print White?

  - by Jason Fitzpatrick

  The vast majority of the time we all print on white media: white paper, white cardstock, and other neutral white surfaces. But what about printing white? Can modern printers print white and if not, why not? Read on as we explore color theory, printer design choices, and why white is the foundation of the printing process. Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites. Image by Coiote O.; available as wallpaper here. The Question SuperUser reader Curious_Kid is well, curious, about printers. He writes: I was reading about different color models, when this question hit my mind. Can the CMYK color model generate white color? Printers use CMYK color mode. What will happen if I try to print a white colored image (rabbit) on a black paper with my printer? Will I get any image on the paper? Does the CMYK color model have room for white? The Answer SuperUser contributor Darth Android offers some insight into the CMYK process: You will not get anything on the paper with a basic CMYK inkjet or laser printer. The CMYK color mixing is subtractive, meaning that it requires the base that is being colored to have all colors (i.e., White) So that it can create color variation through subtraction: White - Cyan - Yellow = Green White - Yellow - Magenta = Red White - Cyan - Magenta = Blue White is represented as 0 cyan, 0 yellow, 0 magenta, and 0 black – effectively, 0 ink for a printer that simply has those four cartridges. This works great when you have white media, as “printing no ink” simply leaves the white exposed, but as you can imagine, this doesn’t work for non-white media. If you don’t have a base color to subtract from (i.e., Black), then it doesn’t matter what you subtract from it, you still have the color Black. [But], as others are pointing out, there are special printers which can operate in the CMYW color space, or otherwise have a white ink or toner. These can be used to print light colors on top of dark or otherwise non-white media. You might also find my answer to a different question about color spaces helpful or informative. Given that the majority of printer media in the world is white and printing pure white on non-white colors is a specialty process, it’s no surprise that home and (most) commercial printers alike have no provision for it. Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.     

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• Array Multiplication and Division

  - by Narfanator

  I came across a question that (eventually) landed me wondering about array arithmetic. I'm thinking specifically in Ruby, but I think the concepts are language independent. So, addition and subtraction are defined, in Ruby, as such: [1,6,8,3,6] + [5,6,7] == [1,6,8,3,6,5,6,7] # All the elements of the first, then all the elements of the second [1,6,8,3,6] - [5,6,7] == [1,8,3] # From the first, remove anything found in the second and array * scalar is defined: [1,2,3] * 2 == [1,2,3,1,2,3] But What, conceptually, should the following be? None of these are (as far as I can find) defined: Array x Array: [1,2,3] * [1,2,3] #=> ? Array / Scalar: [1,2,3,4,5] / 2 #=> ? Array / Scalar: [1,2,3,4,5] % 2 #=> ? Array / Array: [1,2,3,4,5] / [1,2] #=> ? Array / Array: [1,2,3,4,5] % [1,2] #=> ? I've found some mathematical descriptions of these operations for set theory, but I couldn't really follow them, and sets don't have duplicates (arrays do). Edit: Note, I do not mean vector (matrix) arithmetic, which is completely defined. Edit2: If this is the wrong stack exchange, tell me which is the right one and I'll move it. Edit 3: Add mod operators to the list. Edit 4: I figure array / scalar is derivable from array * scalar: a * b = c => a = b / c [1,2,3] * 3 = [1,2,3]+[1,2,3]+[1,2,3] = [1,2,3,1,2,3,1,2,3] => [1,2,3] = [1,2,3,1,2,3,1,2,3] / 3 Which, given that programmer's division ignore the remained and has modulus: [1,2,3,4,5] / 2 = [[1,2], [3,4]] [1,2,3,4,5] % 2 = [5] Except that these are pretty clearly non-reversible operations (not that modulus ever is), which is non-ideal. Edit: I asked a question over on Math that led me to Multisets. I think maybe extensible arrays are "multisets", but I'm not sure yet.

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• What Precalculus knowledge is required before learning Discrete Math Computer Science topics?

  - by Ein Doofus

  Below I've listed the chapters from a Precalculus book as well as the author recommended Computer Science chapters from a Discrete Mathematics book. Although these chapters are from two specific books on these subjects I believe the topics are generally the same between any Precalc or Discrete Math book. What Precalculus topics should one know before starting these Discrete Math Computer Science topics?: Discrete Mathematics CS Chapters 1.1 Propositional Logic 1.2 Propositional Equivalences 1.3 Predicates and Quantifiers 1.4 Nested Quantifiers 1.5 Rules of Inference 1.6 Introduction to Proofs 1.7 Proof Methods and Strategy 2.1 Sets 2.2 Set Operations 2.3 Functions 2.4 Sequences and Summations 3.1 Algorithms 3.2 The Growths of Functions 3.3 Complexity of Algorithms 3.4 The Integers and Division 3.5 Primes and Greatest Common Divisors 3.6 Integers and Algorithms 3.8 Matrices 4.1 Mathematical Induction 4.2 Strong Induction and Well-Ordering 4.3 Recursive Definitions and Structural Induction 4.4 Recursive Algorithms 4.5 Program Correctness 5.1 The Basics of Counting 5.2 The Pigeonhole Principle 5.3 Permutations and Combinations 5.6 Generating Permutations and Combinations 6.1 An Introduction to Discrete Probability 6.4 Expected Value and Variance 7.1 Recurrence Relations 7.3 Divide-and-Conquer Algorithms and Recurrence Relations 7.5 Inclusion-Exclusion 8.1 Relations and Their Properties 8.2 n-ary Relations and Their Applications 8.3 Representing Relations 8.5 Equivalence Relations 9.1 Graphs and Graph Models 9.2 Graph Terminology and Special Types of Graphs 9.3 Representing Graphs and Graph Isomorphism 9.4 Connectivity 9.5 Euler and Hamilton Ptahs 10.1 Introduction to Trees 10.2 Application of Trees 10.3 Tree Traversal 11.1 Boolean Functions 11.2 Representing Boolean Functions 11.3 Logic Gates 11.4 Minimization of Circuits 12.1 Language and Grammars 12.2 Finite-State Machines with Output 12.3 Finite-State Machines with No Output 12.4 Language Recognition 12.5 Turing Machines Precalculus Chapters R.1 The Real-Number System R.2 Integer Exponents, Scientific Notation, and Order of Operations R.3 Addition, Subtraction, and Multiplication of Polynomials R.4 Factoring R.5 Rational Expressions R.6 Radical Notation and Rational Exponents R.7 The Basics of Equation Solving 1.1 Functions, Graphs, Graphers 1.2 Linear Functions, Slope, and Applications 1.3 Modeling: Data Analysis, Curve Fitting, and Linear Regression 1.4 More on Functions 1.5 Symmetry and Transformations 1.6 Variation and Applications 1.7 Distance, Midpoints, and Circles 2.1 Zeros of Linear Functions and Models 2.2 The Complex Numbers 2.3 Zeros of Quadratic Functions and Models 2.4 Analyzing Graphs of Quadratic Functions 2.5 Modeling: Data Analysis, Curve Fitting, and Quadratic Regression 2.6 Zeros and More Equation Solving 2.7 Solving Inequalities 3.1 Polynomial Functions and Modeling 3.2 Polynomial Division; The Remainder and Factor Theorems 3.3 Theorems about Zeros of Polynomial Functions 3.4 Rational Functions 3.5 Polynomial and Rational Inequalities 4.1 Composite and Inverse Functions 4.2 Exponential Functions and Graphs 4.3 Logarithmic Functions and Graphs 4.4 Properties of Logarithmic Functions 4.5 Solving Exponential and Logarithmic Equations 4.6 Applications and Models: Growth and Decay 5.1 Systems of Equations in Two Variables 5.2 System of Equations in Three Variables 5.3 Matrices and Systems of Equations 5.4 Matrix Operations 5.5 Inverses of Matrices 5.6 System of Inequalities and Linear Programming 5.7 Partial Fractions 6.1 The Parabola 6.2 The Circle and Ellipse 6.3 The Hyperbola 6.4 Nonlinear Systems of Equations

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