shellsort.c

/*
 *   C Program that uses pointers to sort an array
 *   in ascending order using Shell Sort
 */

#include <exec/types.h>
#include <dos/dos.h>

#include <proto/exec.h>
#include <proto/dos.h>

#include <stdio.h>

/* proto types */
void swap(int *a, int *b);
void shellsort(int arr[], int nums);


void swap(int *a, int *b)
{
    *a=*a + *b;
    *b=*a - *b;
    *a=*a - *b;

    return ;
}

// Function definition of sort array using shell sort
void shellsort(int arr[], int nums)
{
    int i = 0, j = 0, k = 0;

    // i -> gap/interval
    for (i = nums / 2; i > 0; i = i / 2)
    {
        // Traverse j till we reach the end of the sublist.
        for (j = i; j < nums; j++)
        {
            for(k = j - i; k >= 0; k = k - i)
            {
                if (arr[k+i] >= arr[k])
                {
                    break;
                }
                else
                {
                    swap(&arr[k], &arr[k+i]);
                }
            }
        }
    }

    return ;

}

int main()
{
    int nums = 0;
    int k = 0;

    #ifdef __SASC
        int arr[256];
    #else
        int arr[nums];
    #endif


    printf("Enter total no. of elements : ");
    #ifdef __SASC
        printf("(max. allowed array size is 256)");
    #endif
    scanf("%d", &nums);

    #ifdef __SASC
        if (nums > 256)
        {
            puts("Sorry, that's too much for me!");
            puts("Yours sincerely,\nSAS/C");
            return 0;
        }
    #endif

    printf("Enter the array: \n");

    //scan the array elements.
    for (k =  0 ; k < nums; k++)
    {
        scanf("%d", &arr[k]);
    }

    //Call the function of shell sort, bypassing the array base pointer to the first element.
    shellsort(arr, nums);

    // After the sorting the array is
    printf("Sorted array is:  \n");

    for (k = 0; k < nums; k++)
    {
        printf("%d ", arr[k]);
    }

    puts("\nThats it!\n");
    return 0;
}