This program implements shell sort. Shell sort is named after its discoverer D.L. Shell. It is also called diminishing-increment sort.  Here we first compare the keys that are far apart.  Afterwards, we sort the entries  which are closer together. 
                                  

shellsort( int a[], int n, int inc[], int ninc)
{
        int i, j, k, increment, x;
        i = 0;
        while ( i < ninc )
        {
                increment = inc [i];
                j = increment;
                
while (j < n)
                {
                        /* insert a[j] into its proper place within its subfile */
                        x = a[j];
                        for (k=j � increment; k>=0 && x > a[k]; k �= increment)
                                a[k + increment] = a[k];
                        a[k + increment] = x;
                        j ++;
                }/*end of inner while*/
                i++;
        }/*end of outer while*/
}/*end of routine*/