Sorting elements in a row in a 2 dimensional array using pointers

Question

I am trying to sort a row of 2 dimensional array. But I am unable to achieve it.

For eg:

to be like this:

Below is my code:

void sort(int *a,int num){
    int i,j,temp;
    for(i=0;i<num-1;i++){
        for (j=0;j<num-i-1;j++){
            if (*((a+i*3)+j)>*((a+i*3)+j+1)){
                temp=*((a+i*3)+j);
                *((a+i*3)+j)=*((a+i*3)+j+1);
                *((a+i*3)+j+1)=temp;
            }
        }
    }

    for(i=0;i<num;i++){
        for(j=0;j<3;j++)
            printf("%d ",*((a+i*3)+j));
        printf("\n");
        }
}

Output of the above code:

Can anyone tell what's the problem in the code? Thanks in advance. :D

EDIT: So should the above code look like this?

    void sort(int *a,int num){
    int i,j,temp;
    for(i=0;i<num-1;i++){
        for (j=0;j<num-i-1;j++){
            if (*(*(a+i)+j)>*(*(a+i)+j+1)){
               temp=*(*(a+i)+j);
               *(*(a+i)+j)=*(*(a+i)+j+1);
               *(*(a+m)+j+1)=temp;
            }
        }
    }
}

There is no 2D array. Just a pointer to int. Using a 2D array (resp. pointer to a 1D array) and the index-operatorwould make this mess halfway readable. — too honest for this site
– too honest for this site, Commented Jul 23, 2017 at 17:28

amol13 · Accepted Answer · 2017-07-23 17:39:57Z

2

There are two main problems:

1) the loops are not running for n times, Hence the condition in for loop should be changed to i < num instead of i < num - 1 which skips the last row

2) From your code it seems you want to use bubble sort technique. The sort is O(n^2) and that's why require the swapping if statement to run (n - 1)times for each element, hence you should include one more for loop inside the j-for loop.

edited Jul 23, 2017 at 17:39

answered Jul 23, 2017 at 17:34

amol13

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1 Comment

nimish642 Over a year ago

Oh! Thank you very much...didn't think for the another loop. Thx once again. :D

anatolyg · Accepted Answer · 2017-07-23 17:33:55Z

1

The code is too complicated, so you did many small mistakes in it.

You should separate sorting of each row somehow, like this:

for (row = 0; row < num; row++) {
    sort_row(a + row * 3);
}

The function sort_row sorts just one row, so it's going to be easier to write and test (BTW I replaced the nondescript name i by row).

The function sort_row should do normal bubble sort. You can even use the standard library qsort instead (for purposes of testing).

Note that standard bubble-sort algorithm is implemented with two nested loops. If you want to implement your code without a separate sort_row function call, you will need three nested loops.

answered Jul 23, 2017 at 17:33

anatolyg

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1 Comment

nimish642 Over a year ago

Thx, anatolyg I will keep in mind to use library function next time... :D

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