Bubblesort sorting method with dynamic allocation + pointer

Question

Hey there, guys. I’m trying to solve an exercise, by bubblesorte ordering method and dynamic allocation (No pointers and no dynamic allocation the exercise becomes easier, however, the teacher asked to do with AD). The exercise is simple, is to say how many times the problem will run, pass the number of numbers to be reordered and, play on screen. Follow the code:

#include<stdio.h>
#include<stdlib.h>
main(){
    int qt,n,i,j,aux;
    int *p;
    scanf("%d",&qt);

    while(qt!=0){
        scanf("%d",&n);
        p = (int *) calloc(n, sizeof(int));

          for(i=0; i<n; i++){
                scanf("%d",(p+i));

          }

         /* for(i=0; i<n; i++){
                printf("%d\n",*p); /* Neste for, estou testando se o ponteiro está pegando os números, e está */
                ++p;
          } */

          for(i=0; i<n-1; i++){
            for(j=n-1; j>i; j--){
                if(*p < *(p-1)){
                    aux = *p;
                    *p = *(p-1);
                    *(p-1) = aux;

                }
            }
          }
          for(i=0; i<n; i++){
            printf("%d ",*p);
            ++p;
          }
          printf("\n");

          free(p);




        qt--;
    }

}

Anyway, the error happens in the sorting method, when in the end, I print the reordered values, only garbage appears. I know I am wrong in the ordering method, I have tried to put a ++p or --p, but it has not helped. I believe that *(p-1) is wrong. Could anyone tell me the mistake? Grateful.

Answer 1

I found it easier to redo the program than explain the mistakes individually...

Points to be observed:

1) If you have int* p then *(p + i) is the same thing as p[i].

2) Comments /* */ do not nest, that is, /* ..... */ ... */ in general will build error (if you’re lucky)

3) care when typing, do not change i, 1, l (and other similar cases)

4) use more spaces, it is easier to visualize the code...for example, this is bad here: while(qt!=0), use while (qt != 0)

#include<stdio.h>
#include<stdlib.h>

int main()
{
   int *p;
   int qt, n, i, j, aux;

   printf("\nQuantas rodadas ? ");
   scanf("%d",&qt);

   while (qt != 0)
   {
      printf("\nQuantos numeros ? ");
      scanf("%d", &n);
      p = (int*)calloc(n, sizeof(int));

      // printf("Digites %d numeros e tecle ENTER: ", n);
      for (i = 0; i < n; i++)
      {
         printf("%d/%d: ", i+1, n);
         scanf("%d", (p+i));
      }

      for (i = 0; i < n-1; i++)
      {
         for (j = i+1; j < n; j++)
         {
            if (p[i] > p[j])
            {
               aux = p[i];
               p[i] = p[j];
               p[j] = aux;
             } // if
         } // for j
       } // for i

       for (i = 0; i < n; i++)
       {
          printf("%d ", p[i]);
       }

       printf("\n");

       free(p);

       qt--;

   } // while

}

That’s all for now Folks :)