i make a program of selection sort using dynamic array and pointers but after running this code i found that array is being sorted if we give the size input like 4 and 6 but does't sort properly if the size input is like 5 and 7 etc ...i also did bubble sort program before this using same technique of pointers and dynamic array but it gave perfect sorted array in all the condition , i also try to debuge the code but still don't understand why this is happening if anyone having idea about this then please help me out .

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

int main()
{
  int * ptr,temp,min;
  int size,i,j,s;
  printf("Enter the size of array:");
  scanf("%d",&size);

  ptr = (int *)(calloc (size,sizeof(int)));

  if(ptr == NULL)
    printf("No memory");

  else
  {
    printf("\n=== RANDOM ELEMENTS OF ARRAY ===\n");

    for(s=0;s<size;s  )
      *(ptr s) = rand()%100;

    for(s=0;s<size;s  )
      printf("\nElement [%d]  = %d ",s,*(ptr s));

// selection sort algorithm

  for(i=0;i< size-1;i  )
  {
    min = i;
    for(j=i 1;j<size;j  )
    {
      if(*(ptr j) < *(ptr min))
      {
        min = j;
      }
      temp = *(ptr i);
      *(ptr i) = *(ptr min);
      *(ptr min) = temp;
    }
  }

// End of algorithm

    printf("\n\n=======  SORTED ELEMENTS  =======\n\n");
      for(s=0;s<size;s  )
        printf("Element [%d]  = %d \n",s,*(ptr s));


  }

}

CodePudding user response：

Your Selection Sort algorithm seems to be wrong. You have to replace the element in the current index with the minimum after the inner for loop finishes iteration:

  for(i=0;i< size-1;i  )
  {
    min = i;
    for(j=i 1;j<size;j  )
    {
      if(*(ptr j) < *(ptr min))
      {
        min = j;
      }
    }
    temp = *(ptr i);
    *(ptr i) = *(ptr min);
    *(ptr min) = temp;
  }

Now, it should work for all input sizes.

CodePudding user response：

Clearing away a couple of unnecessary confusion factors...

*(ptr   index)

Is identical to

ptr[index]

But the second is much easier to read.

Next, in the following section the variable min is introduced,

  if(*(ptr j) < *(ptr min))
  {
       min = j;
  }

...but is not necessary for a simple sort. Just stick with i and j and the sort will proceed correctly for either even or odd sets of values. Finally, to eliminate the memory leak, call free(ptr); when ptr is no longer needed. Following is a cleaned up version, with corrections.

int main(void)//added void
{
  int * ptr,temp/*,min*/;
  int size,i,j,s;
  printf("Enter the size of array:");
  scanf("%d",&size);

  ptr = calloc (size,sizeof(int));//casting is required in C   
                                  //but unnecessary in C.
                                  //(and can be problematic)
  if(ptr == NULL)
  {
    printf("No memory");
  }
  else
  {
    printf("\n=== RANDOM ELEMENTS OF ARRAY ===\n");

    for(s=0;s<size;s  )
      ptr[s] = rand()%100;

    for(s=0;s<size;s  )
      printf("\nElement [%d]  = %d ",s,ptr[s]);

// selection sort algorithm

    for(i=0;i< size-1;i  )
    {
        for(j=i 1;j<size;j  )//removed if section introducing 'min'
        {
            if(ptr[j] < ptr[i])
            {
                temp = ptr[i];
                ptr[i] = ptr[j];
                ptr[j] = temp;
            }
        }
    }

// End of algorithm

    printf("\n\n=======  SORTED ELEMENTS  =======\n\n");
    for(s=0;s<size;s  )
        printf("Element [%d]  = %d \n",s,*(ptr s));

   free(ptr);
  }
  return 0;//added 
}

BTW, this was tested with size == 3 and

  ptr[0] = 3;
  ptr[1] = 2;
  ptr[2] = 1;

along with several other odd and even counts of random values