DaniWeb Forum Index > Software Development > C++

C++ RSS

school's back, and so am i :D

Please support our C++ advertiser: Intel Parallel Studio Home

Last »

•

Join Date: Jun 2006

Posts: 1,169

Reputation: Duki has a spectacular aura about

Solved Threads: 9

Duki

Offline

Veteran Poster

school's back, and so am i :D

Aug 28th, 2007

Hey everyone, I'm back in C++ this semester; Last semester I went through Structured C++ (and passed with a 4.0; many thanks to all of you!) and this semester I'm in OOP.

I don't have sample code yet because I haven't started. But I was talking to a classmate, and one of our programming exercises wants us to write a function that will modify a point (i.e., (3, 2)) so that it will rotate it 90 degrees, clockwise. Is there an easier way to do this rather than 5 or 6 "If" statements?

Example scenario:

I input point x as 3 and point y as 2. I select the option to rotate the point by 90 degrees and should get x as 2 and y as -3.

Last edited by Duki; Aug 28th, 2007 at 5:41 pm.

It is practically impossible to teach good programming style to students that have had prior exposure to Basic; as potential programmers they are mentally mutilated beyond hope of regeneration.

-Edsger Dijkstra

•

Join Date: Jun 2007

Posts: 322

Reputation: Hamrick will become famous soon enough

Solved Threads: 33

Hamrick

Offline

Posting Whiz

Re: school's back, and so am i :D

Aug 28th, 2007

How do you rotate a point? A point is a point, there's no kind of transformation you can do until you have more than one.

The truth does not change according to our ability to stomach it.

•

Join Date: Dec 2005

Posts: 5,850

Reputation: Salem has a reputation beyond repute

Solved Threads: 749

Salem

Offline

Void main'ers are DOOMed

Re: school's back, and so am i :D

Aug 28th, 2007

Don't they teach simple geometry in schools any more?
http://mathworld.wolfram.com/RotationMatrix.html

•

Join Date: Feb 2002

Posts: 12,036

Reputation: cscgal is a glorious beacon of light

Solved Threads: 130

cscgal

Offline

The Queen of DaniWeb

Re: school's back, and so am i :D

Aug 28th, 2007

•

Originally Posted by Hamrick

How do you rotate a point? A point is a point, there's no kind of transformation you can do until you have more than one.

I haven't taken a math class in many, many years, but from what I can recall, you rotate a point by drawing a vector starting at the origin and passing through the point, and then rotate that vector 90 degrees, in this case.

Dani the Computer Science Gal

Follow my Twitter feed! twitter.com/daniweb

•

Join Date: Feb 2006

Posts: 486

Reputation: Bench has a spectacular aura about

Solved Threads: 48

Bench

Offline

Posting Pro in Training

Re: school's back, and so am i :D

Aug 28th, 2007

•

Originally Posted by cscgal

I haven't taken a math class in many, many years, but from what I can recall, you rotate a point by drawing a vector starting at the origin and passing through the point, and then rotate that vector 90 degrees, in this case.

Yes that's right, but it assumes you're rotating about the origin

Either way, the origin is a point, so, as hamrick said, you need two points in order to rotate something.

¿umop apisdn upside down?

•

Join Date: Apr 2004

Posts: 4,335

Reputation: Dave Sinkula has a brilliant future

Solved Threads: 236

Dave Sinkula Dave Sinkula is offline

Offline

long time no c

Re: school's back, and so am i :D

Aug 28th, 2007

I like to do problems that are new to me. I found a few lines of trigonometry did just dandy.

"One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary." --Ayn Rand

•

Join Date: Jun 2006

Posts: 1,169

Reputation: Duki has a spectacular aura about

Solved Threads: 9

Duki

Offline

Veteran Poster

Re: school's back, and so am i :D

Aug 28th, 2007

Thanks Dave; any tips as to which ones?

Hamrick: sorry I didn't clarify. There is an assumed point (i'm guessing) that is constant at (0,0).

•

Join Date: Jun 2006

Posts: 1,169

Reputation: Duki has a spectacular aura about

Solved Threads: 9

Duki

Offline

Veteran Poster

Re: school's back, and so am i :D

Aug 28th, 2007

x' = x * cosine(90) + y * sine(90)
y' = x * sine(90) - y * cosine(90)

that look right?

edit] i think these are the right ones:

rx = x * cos(90) + y * sin(90) ;
ry = y * cos(90) - x * sin(90) ;

Last edited by Duki; Aug 28th, 2007 at 10:46 pm.

•

Join Date: Apr 2004

Posts: 4,335

Reputation: Dave Sinkula has a brilliant future

Solved Threads: 236

Dave Sinkula Dave Sinkula is offline

Offline

long time no c

Re: school's back, and so am i :D

Aug 28th, 2007

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
   point(double x_ = 0, double y_ = 0)
   : x(x_), y(y_), 
   radius(std::sqrt(x * x + y * y)), 
   angle(std::atan(y / x))
   {
   }
   void rotate(double radians)
   {
      angle = std::fmod(angle + radians, 2 * pi);
      x = radius * cos(angle);
      y = radius * sin(angle);
   }
   point(double x_ = 0, double y_ = 0)
   : x(x_), y(y_), 
   radius(std::sqrt(x * x + y * y)), 
   angle(std::atan(y / x))
   {
   }
   void rotate(double radians)
   {
      angle = std::fmod(angle + radians, 2 * pi);
      x = radius * cos(angle);
      y = radius * sin(angle);
   }

•

Join Date: Jun 2006

Posts: 1,169

Reputation: Duki has a spectacular aura about

Solved Threads: 9

Duki

Offline

Veteran Poster

Re: school's back, and so am i :D

#10

Aug 28th, 2007

Ok, here's how I am doing it; is this wrong?

 Help with Code Tags 
(Toggle Plain Text)
 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
#include <cmath>
#include <iostream>
using namespace std ;
 
int main () 
{
    int x ;
    int y ;
    double angle ;
    int rx ;
    int ry ;
 
    angle = 90 ;
    x = 3 ;
    y = 2 ;
    rx = x * cos(angle) + y * sin(angle) ;
    ry = y * cos(angle) - x * sin(angle) ;
 
    cout << rx << " " << ry << endl ;
 
    return 0 ;
}
#include <cmath>
#include <iostream>
using namespace std ;

int main () 
{
    int x ;
    int y ;
    double angle ;
    int rx ;
    int ry ;

    angle = 90 ;
    x = 3 ;
    y = 2 ;
    rx = x * cos(angle) + y * sin(angle) ;
    ry = y * cos(angle) - x * sin(angle) ;

    cout << rx << " " << ry << endl ;

    return 0 ;
}
     Help with Code Tags   c++ Syntax (Toggle Plain Text)    #include <cmath>#include <iostream>using namespace std ; int main () {    int x ;    int y ;    double angle ;    int rx ;    int ry ;     angle = 90 ;    x = 3 ;    y = 2 ;    rx = x * cos(angle) + y * sin(angle) ;    ry = y * cos(angle) - x * sin(angle) ;     cout << rx << " " << ry << endl ;     return 0 ;} #include <cmath>
#include <iostream>
using namespace std ;

int main () 
{
    int x ;
    int y ;
    double angle ;
    int rx ;
    int ry ;

    angle = 90 ;
    x = 3 ;
    y = 2 ;
    rx = x * cos(angle) + y * sin(angle) ;
    ry = y * cos(angle) - x * sin(angle) ;

    cout << rx << " " << ry << endl ;

    return 0 ;
}  