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Quicksort problems

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Join Date: Sep 2006

Posts: 12

Reputation: Lutzee is an unknown quantity at this point

Solved Threads: 0

Lutzee

Offline

Newbie Poster

Quicksort problems

Jun 10th, 2007

Hi there everyone. I wonder if you could help me with my code. It just seems to go into an infinite loop. I would greatly appreciate some help with this. Thanks

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include<iostream>
using namespace std;
 
int qsrt(int array[], int first, int last)
 
{
 
 
    int over = 0;
    over = first-last;
    int g=0;
 
    if(over==0)
    {
    return 0;
    }
 
    int c=0;
 
    int start = first;
    int end = last;
    int pivot = array[first];
    int temp =0;
 
     while(first != last)
     {
 
    while((array[last]>pivot)&&(first != last))
    {
        last--;
    }
 
    while((array[first]<pivot)&&(first != last))
    {
        first++;
    }
 
    temp = array[last];
    array[last] = array[first];
    array[first] = temp;
 
 
 
    c = last-first;
 
     if(c>1)
     {
         first++;
         last--;
     }
 
 }
 
      c= 0;
     c= first-1;
 
     qsrt(array,first,end);
     qsrt(array,start,(c));
 
   return 0;
}
 
int main (void)
 
{
    int anarray[9] = {4,5,3,8,5,6,2,8,9};
 
 
 
    qsrt(anarray,0,8);
    system("pause");
 
 
    return 0;
}
#include<iostream>
using namespace std;

int qsrt(int array[], int first, int last)

{
    

    int over = 0;
    over = first-last;
    int g=0;

    if(over==0)
    {
    return 0;
    }
    
    int c=0;
    
    int start = first;
    int end = last;
    int pivot = array[first];
    int temp =0;
    
     while(first != last)
     {

    while((array[last]>pivot)&&(first != last))
    {
        last--;
    }

    while((array[first]<pivot)&&(first != last))
    {
        first++;
    }
    
    temp = array[last];
    array[last] = array[first];
    array[first] = temp;

     

    c = last-first;

     if(c>1)
     {
         first++;
         last--;
     }
     
 }
     
      c= 0;
     c= first-1;
     
     qsrt(array,first,end);
     qsrt(array,start,(c));

   return 0;
}

int main (void)

{
    int anarray[9] = {4,5,3,8,5,6,2,8,9};
    
    
    
    qsrt(anarray,0,8);
    system("pause");
    

    return 0;
}

Thanks once again

•

Join Date: Oct 2006

Posts: 222

Reputation: JRM will become famous soon enough

Solved Threads: 14

JRM

Offline

Posting Whiz in Training

Re: Quicksort problems

Jun 10th, 2007

IF your intent is to sort a range of integers beginning at first and continuing to last, there are simpler ways to do it.
You don't need two loops or so many extra varaibles.

If you need to sort from both ends, shouldn't pivot be in the middle of the arrary rather than equal to array[first]?

•

Join Date: Mar 2007

Posts: 1,429

Reputation: Nichito is an unknown quantity at this point

Solved Threads: 29

Nichito

Offline

Nearly a Posting Virtuoso

Re: Quicksort problems

Jun 10th, 2007

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
#include<iostream>
using namespace std;
 
int qsrt(int array[], int first, int last){ 
    int over = 0;
    over = first-last;
    int g=0;
    if(over==0){
        return 0;
    }int c=0;
    int start = first;
    int end = last;
    int pivot = array[first];
    int temp =0;
    while(first != last){
        while((array[last]>pivot)&&(first != last)){
            last--;
        }while((array[first]<pivot)&&(first != last)){
            first++;
        }temp = array[last];
        array[last] = array[first];
        array[first] = temp;
        c = last-first;
        if(c>1){
            first++;
            last--;
        }
    }c= 0;
    c= first-1;
    qsrt(array,first,end);
    qsrt(array,start,(c));
    return 0;
}
 
int main (void){
    int anarray[9] = {4,5,3,8,5,6,2,8,9};
    qsrt(anarray,0,8);
    system("pause");
    return 0;
}
#include<iostream>
using namespace std;

int qsrt(int array[], int first, int last){ 
    int over = 0;
    over = first-last;
    int g=0;
    if(over==0){
        return 0;
    }int c=0;
    int start = first;
    int end = last;
    int pivot = array[first];
    int temp =0;
    while(first != last){
        while((array[last]>pivot)&&(first != last)){
            last--;
        }while((array[first]<pivot)&&(first != last)){
            first++;
        }temp = array[last];
        array[last] = array[first];
        array[first] = temp;
        c = last-first;
        if(c>1){
            first++;
            last--;
        }
    }c= 0;
    c= first-1;
    qsrt(array,first,end);
    qsrt(array,start,(c));
    return 0;
}

int main (void){
    int anarray[9] = {4,5,3,8,5,6,2,8,9};
    qsrt(anarray,0,8);
    system("pause");
    return 0;
}

first, you should learn how to format your code correctly...

second, saying this

Help with Code Tags

C++ Syntax (Toggle Plain Text)

int a=0;
a=b-c;

is the same thing as saying

Help with Code Tags

C++ Syntax (Toggle Plain Text)

int a=b-c;

when you have b and c declared...

third, what are you doing there? it seems like you are ordering numbers from least to greatest... but... JRM is right... you could do this with less variables...

Last edited by happygeek; Jun 11th, 2007 at 5:40 am. Reason: swears removed, keep it clean

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