Sorting problems
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Thread: Sorting problems

  1. #1
    Join Date
    Aug 2012
    Posts
    4

    Sorting problems

    HI I just started learning c++. Below is the bubble_sorting program I wrote. Complied no error under eclipse(Ubuntu). But the result is not right.

    What is happening is, no matter what input numbers I provided, after sorting, the smallest number would be set to zero. Please, can anyone point out where did I do wrong. Many thanks in advance!

    //start of the program
    //Bubble_sorting

    #include <iostream>
    using namespace std;

    void BubbleSort(int *list,int len)
    {
    int i,j,temp;
    for(i=0;i<len;i++)
    for(j=0;j<len-i;j++)
    {
    if(list[j]>list[j+1])
    {
    temp=list[j];
    list[j]=list[j+1];
    list[j+1]=temp;
    }
    }
    }

    int main ()
    {
    int len;
    cout<<"input the number of int to sort"<<endl;
    cin>>len;
    int *p = new int[len];

    cout<<"Input ten number:";
    for(int i=0;i<len;i++)
    cin>>p[i];
    cout<<endl;

    cout<<"Before sorting: ";
    for(int i=0;i<len;i++)
    cout<<p[i]<<" ";
    cout<<endl;

    BubbleSort(p,len);
    cout<<"After sorting: ";
    for(int i=0;i<len;i++)
    cout<<p[i]<<" ";

    cout<<endl;
    cout<<p[0]<<endl;
    cout<<endl;

    delete[] p;
    p = NULL;
    return 0;
    }

  2. #2
    Join Date
    Oct 2002
    Location
    Austria
    Posts
    1,284

    Re: Sorting problems

    You have bufferoverflows in your bubblesort.
    And please use CODE tags when posting code.
    Kurt

  3. #3
    Join Date
    Aug 2012
    Posts
    4

    Re: Sorting problems

    Thanks Kurt! Can you be more specific?

  4. #4
    Join Date
    Apr 1999
    Posts
    27,427

    Re: Sorting problems

    Quote Originally Posted by rocketjumper View Post
    Thanks Kurt! Can you be more specific?
    Code:
    for(j=0;j < len-i;j++ )
    Assume len is 10 and i happens to be 0. That loop translates to this:
    Code:
    for(j=0;j < 10; j++)
    So you will loop from 0 to 9. But your code has this:
    Code:
    if( list[j] > list[j+1])
    Which translates to this on the last iteration of the loop
    Code:
    if (list [9] > list[10])
    Do you see a problem? You're accessing an invalid array element (list[10]).

    Regards,

    Paul McKenzie

  5. #5
    Join Date
    Aug 2012
    Posts
    4

    Thumbs up Re: Sorting problems

    Thanks Paul! That makes sense now! Just modify the inner for loop as

    Code:
    for(j=0;j<len-i;j++)
    will solve the problem! Thanks for explaining this to me

  6. #6
    Join Date
    Aug 2012
    Posts
    4

    Re: Sorting problems

    I mean:

    Code:
    for(j=0;j<len-i-1;j++)

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