help about bubble sort

This is a discussion on help about bubble sort within the C++ Programming forums, part of the General Programming Boards category; Hi@all I'm learning the bubble sort from my textbook. I just wrote a small program but something is wrong about ...

  1. #1
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    Red face help about bubble sort

    Hi@all

    I'm learning the bubble sort from my textbook. I just wrote a small program but something is wrong about output. I couldn't see my mistake. Please help me to see what is wrong with it.

    Thanks


    Code:
    #include <iostream>
    using namespace std;
    
    const int size=5;
    
    int main()
    {
            int m=0;
            int array[size];
            int counter=0; 
            
            cout <<"Enter some integers "<<endl;
    
    
            cin >>array[m];
            while (!cin.eof())
            {
                    m++;
                    counter++;
                    cin>>array[m];
            }
    
            for(int m=0; m<counter-1; m++)
            {
                    int holder=0;
    
                    for (int i=0; i<counter-1; i++)
                    {
    
                            int j=i;
    
                            if (array[i]>array[j++])
                            {
    
                                    holder=array[j];
    
                                    array[i]=array[j];
    
                                    array[i]=holder;
                            }
                    }
            }
    
            for (int i=0; i<counter; i++)
                    cout <<array[i]<<" ";
    
        return 0;
    }

  2. #2
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    What is the actual problem with your output? What are you getting that you weren't expecting?

  3. #3
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    Quote Originally Posted by sean_mackrory
    What is the actual problem with your output? What are you getting that you weren't expecting?
    Assume I typed 5,6 and 1 as my input. My output should look like 1 5 6 but I get the same as what I typed.

    Thanks

  4. #4
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    I think your problem is in these two lines:

    int j=i;
    if (array[i]>array[j++])

    j++ means return j and then increment j by 1. Thus the conditional essentially measures array[i] against array[i] which will never cause the conditional to be true so no swapping will occur. change j++ to ++j or drop j altogether and use i + 1 in place of j++, and make appropriate adjustment in the swap section of the code
    You're only born perfect.

  5. #5
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    Quote Originally Posted by elad
    change j++ to ++j
    I think you are right. I changed j++ to ++j but still something is wrong because when I write 5 4 3 2 1, the output is 1 1 1 1. I am

  6. #6
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    holder=array[j];
    array[i]=array[j];
    array[i]=holder;

    Why do you assign both array[j] and holder to array[i]? Work out the appropriate logic, and I think it will work better.
    You're only born perfect.

  7. #7
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    As elad said, your swap is a little broken. You may find it easier to use the STL swap algorithm, since it avoids little mistakes like this.
    Code:
    #include <algorithm>
    ...
    /*
        holder=array[j];
        array[i]=array[j];
        array[i]=holder;
    */
        swap(array[i],array[j]);
    If I did your homework for you, then you might pass your class without learning how to write a program like this. Then you might graduate and get your degree without learning how to write a program like this. You might become a professional programmer without knowing how to write a program like this. Someday you might work on a project with me without knowing how to write a program like this. Then I would have to do you serious bodily harm. - Jack Klein

  8. #8
    former member Brain Cell's Avatar
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    - there's no reason to make size global.

    - you declared m twice.

    - you used :
    Code:
    while (!cin.eof())
            {
                    m++;
                    counter++;
                    cin>>array[m];
            }
    to input values when you can simply use a 'for' loop to do the same job in less code.

    - Check this link for a much much easier way to sort your array.


    Hope this helps..
    My Tutorials :
    - Bad programming practices in : C
    - C\C++ Tips
    (constrcutive criticism is very welcome)


    - Brain Cell

  9. #9
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    Hi Brain Cell;

    Quote Originally Posted by Brain Cell
    -there's no reason to make size global.
    Yes you are right. I think because of the eof. I don't need size. I use a counter to find out the size.

    Quote Originally Posted by Brain Cell
    - you declared m twice.
    I am not agree about it because one m is inside the for loop. I also didn't get any error because of it from g++. (I just started to learn c++ so I am not sure. )

    Quote Originally Posted by Brain Cell
    to input values when you can simply use a 'for' loop to do the same job in less code.
    I was reading from my book. It was saying that for loop is good when you know the size but here I don't know the capacity of my array. I guess you were cofiused because of const. It was my fault sorry.

    Quote Originally Posted by Brain Cell
    - Check this link for a much much easier way to sort your array.
    The tutorial was great. Thanks
    Not to know, not to learn is shame

  10. #10
    former member Brain Cell's Avatar
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    Quote Originally Posted by Apropos
    I am not agree about it because one m is inside the for loop. I also didn't get any error because of it from g++. (I just started to learn c++ so I am not sure. )
    I don't know about g++, but i use Visual C++ 6 and it won't let me compile it because of "error C2374: 'm' : redefinition; multiple initialization". It should be declared only once.

    Quote Originally Posted by Apropos
    I was reading from my book. It was saying that for loop is good when you know the size but here I don't know the capacity of my array.
    What do you mean you don't know the capacity of your array? you declared your array as :
    Code:
    int array[size];
    size equal 5 wich means your array can hold 5 integer values. You can simply replace that part of your code with :
    Code:
    for(m=0; m<size; m++)
       cin >> array[m];
    see how easy it is now?
    My Tutorials :
    - Bad programming practices in : C
    - C\C++ Tips
    (constrcutive criticism is very welcome)


    - Brain Cell

  11. #11
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    Quote Originally Posted by Brain Cell
    I don't know about g++, but i use Visual C++ 6 and it won't let me compile it because of "error C2374: 'm' : redefinition; multiple initialization". It should be declared only once.
    This is due to Microsoft's language extensions. You can disable them by going to your Project Settings under the C/C++ tab and selecting the Customize option. There you can check a box to disable language extensions. Don't expect the Microsoft implementation of STL to compile without them, though. =/
    If I did your homework for you, then you might pass your class without learning how to write a program like this. Then you might graduate and get your degree without learning how to write a program like this. You might become a professional programmer without knowing how to write a program like this. Someday you might work on a project with me without knowing how to write a program like this. Then I would have to do you serious bodily harm. - Jack Klein

  12. #12
    former member Brain Cell's Avatar
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    Multiple declaration still cause confusion though
    My Tutorials :
    - Bad programming practices in : C
    - C\C++ Tips
    (constrcutive criticism is very welcome)


    - Brain Cell

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