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Jun 10th, 2007

Quicksort problems

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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

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

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Lutzee

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Jun 10th, 2007

Re: Quicksort problems

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]?

JRM

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Jun 10th, 2007

Re: Quicksort problems

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

C++ Syntax (Toggle Plain Text)

int a=0;
a=b-c;

is the same thing as saying

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

Nichito

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