Page 248 - Programming Microcontrollers in C

Sorting Programs 233

as was done above, but also, you can swap pointers from an array of
pointers to order a set of data that would be difficult to swap. For
example, if you had a collection of words, you could use a srtcmp()
routine to determine whether one word was lexically larger than the
other and then write a swap routine that merely swapped the pointers
to these words rather than swapping the words themselves. This
approach to sorting a list of words is relatively simple. On the other
hand, it would be extremely difficult—nearly impossible, in fact—
to sort a list of words that are packed into memory.
The following program is used to test the performance of the
above sort routines. The program simply makes an array of 11 entries
and sorts the array by both the Shell sort and the quick sort. The
result of this program is printed out below.

#include <stdio.h>
main()
{
int v[]={81,99,23,808,3,77,18,27,128,360,550};
int i,k[11];
for (i=0;i<11;i++)
k[i]=v[i];
shell_sort(k,11);
for( i=0;i<11;i++)
printf (“%d “,k[i]);
printf(“\n”);
quick_sort(v, 0,11 -1);
for( i=0; i<11; i++)
printf(“%d “,v[i]);
printf(“\n”);
}

The original array is not printed out by the program, but the order of
the array is seen in the above listing. The two sort programs sort the
values correctly.

3 18 23 27 77 81 99 128 360 505 808
3 18 23 27 77 81 99 128 360 505 808
The quick sort routine is not the best example of recursive
programming. Usually, the use of recursion results in a program that
is significantly shorter than would be expected with conventional