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A challenge for all newbies

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Join Date: Jun 2005

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Rashakil Fol Rashakil Fol is offline

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Re: A challenge for all newbies

#21

Jul 8th, 2005

To swap Perl scalars without writing a third variable:

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($x, $y) = ($y, $x);

If you want to swap Perl arrays, well, you'd be better off having used array references and swapping those like above.

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Join Date: Feb 2005

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Paul.Esson Paul.Esson is offline

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Re: A challenge for all newbies

#22

Jul 14th, 2005

Interesting how this has been done in two different ways, one with exclusive or operator and one with addition and subtraction.

In java we could also use, XOR in the same way.

int a, b;

a ^= b;
b ^= a;
a ^= b;

Ok, so I have a little challange now. Bit of fun.

Today we are going to swap the nibbles around in a byte
so the byte 11101010 will turn into 10101110.

can use as many varibles as you wish, but there must be a varible at the end that contains the swapped byte.

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Join Date: Sep 2004

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Narue

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Re: A challenge for all newbies

#23

Jul 14th, 2005

>Today we are going to swap the nibbles around in a byte
Pfft, too easy. Do the shuffle: shift left shift right shift left OR shift right:

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#include <stdio.h>
#include <limits.h>

#define HEXIT ( CHAR_BIT / 2 )

unsigned char swap_nibble ( unsigned char x )
{
  return x << HEXIT >> HEXIT << HEXIT | x >> HEXIT;
}

int main ( void )
{
  unsigned char x = 0xEA;

  printf ( "Before: 0x%X\n", x );
  printf ( "After:  0x%X\n", swap_nibble ( x ) );

  return 0;
}

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Join Date: Apr 2004

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Dave Sinkula Dave Sinkula is offline

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long time no c

Re: A challenge for all newbies

#24

Jul 14th, 2005

>Do the shuffle: shift left shift right shift left OR shift right:

I'm too white and can't dance as well:

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#include <stdio.h>
#include <limits.h>

#define HEXIT ( CHAR_BIT / 2 )

unsigned char swap_nibble ( unsigned char x )
{
  return x << HEXIT | x >> HEXIT;
}

int main ( void )
{
  unsigned char x = 0xEA;

  printf ( "Before: 0x%X\n", x );
  printf ( "After:  0x%X\n", swap_nibble ( x ) );

  return 0;
}

/* my output
Before: 0xEA
After:  0xAE
*/

"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

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Join Date: Sep 2004

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Narue

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Re: A challenge for all newbies

#25

Jul 14th, 2005

>I'm too white and can't dance as well:
It's easy, just shake it, shake it, shake it. Then shake it, shake it, shake it again:

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#include <stdio.h>
#include <limits.h>

#define HEXIT ( CHAR_BIT / 2 )

unsigned char swap_nibble ( unsigned char x )
{
  return x << HEXIT >> HEXIT << HEXIT >> HEXIT << HEXIT >> HEXIT << HEXIT
    | x >> HEXIT << HEXIT >> HEXIT << HEXIT >> HEXIT << HEXIT >> HEXIT;
}

int main ( void )
{
  unsigned char x = 0xEA;

  printf ( "Before: 0x%X\n", x );
  printf ( "After:  0x%X\n", swap_nibble ( x ) );

  return 0;
}

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Join Date: Aug 2005

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a1eio

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Re: A challenge for all newbies

#26

Aug 9th, 2005

just use clean python:

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>>> a = 5
>>> b = 4
>>> a, b = b, a
>>> a
4
>>> b
5
>>> a = 'text1'
>>> b = 'text2'
>>> a, b = b, a
>>> a
'text2'
>>> b
'text1'
>>>

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Join Date: Jun 2005

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Rashakil Fol Rashakil Fol is offline

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Re: A challenge for all newbies

#27

Aug 9th, 2005

Bah, just use clean, erm, XSLT.

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<xsl:template name="blah">
    <xsl:param name="x" select="2"/>
    <xsl:param name="y" select="5"/>
    <xsl:param name="swapped" select="0"/>

    ...

    <xsl:choose>
        <xsl:when test="$swapped = 0">
            <!-- First we run this code. -->

            <!-- And say we want to swap x and y! -->

            <!-- Oh no, we can't change their values! Curse!  Recurse!!-->
            <xsl:call-template name="blah">
                <xsl:with-param name="x" select="$y"/>
                <xsl:with-param name="y" select="$x"/>
                <xsl:with-param name="swapped" select="1"/>
            </xsl:call-template>
        </xsl:when>

        <!-- In the spirit of XML, they picked the most verbose name
        out of the choices 'else', 'default', and 'otherwise.' -->
        <xsl:otherwise>
            <!-- Now x and y are swapped! -->

            ...
        </xsl:otherwise>
    </xsl:choose>
</xsl:template>

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Join Date: Apr 2005

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numerouno

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Re: A challenge for all newbies

#28

Aug 9th, 2005

STOP! My brain is hurting!

Career Diagnostics

http://www.careerdiagnostics.com
Home of "Best Foot Forward!" - a "how to" guide to writing your Resume or CV

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Join Date: Jul 2005

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egoleo

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Re: A challenge for all newbies

#29

Aug 11th, 2005

yeah. its really a great challenge for us. Just look at the way guys are sending in those codes. Man i am kinda of confused now. :mrgreen:

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Join Date: Aug 2005

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Daishi

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Re: A challenge for all newbies

#30

Aug 17th, 2005

Here we go. I decided to do it without using any of those dirty bitwise operators. It was fun. :o No, I don't actually code like this.

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#include <iostream>
#include <string>

using namespace std;

string printBinary(unsigned char aByte) {  //  prints aByte in binary.
  int moder=128;
  string ret;
  for (int i=0; i<8; i++) {
    if (aByte >= moder) {
      ret+='1';
      aByte-=moder;
    } else
      ret+='0';
    moder /= 2;
  }
  return ret;
}

unsigned char getFromBinary(string buffer) {
  unsigned char ret=0, moder=1;
  for (int i=buffer.length()-1; i>=0; i--) {
    if ((char)buffer[i] == '1')
      ret+=moder;
    moder*=2;
  }
  return ret;
}

unsigned char swapBit(unsigned char byte, int a, int b) {
  string str = printBinary(byte);
  char temp = str[a];
  str[a] = str[b];
  str[b] = temp;

  return getFromBinary(str);
}

int main(int argc, char **argv) {
  unsigned char a = getFromBinary("11101010");
  cout << "A is " <<  (int)a << "\t" << printBinary(a) << endl;

  a = swapBit(a, 4, 5);
  cout << "A is " << (int)a << "\t" << printBinary(a) << endl;

  a = swapBit(a, 2, 3);
  cout << "A is " << (int)a << "\t" << printBinary(a) << endl;

  a = swapBit(a, 3, 4);
  cout << "A is " << (int)a << "\t" << printBinary(a) << endl;

  a = swapBit(a, 1, 2);
  cout << "A is " << (int)a << "\t" << printBinary(a) << endl;

  return 0;
}

It's horrible, I know.

-Fredric