// Multipurpose sorting program using function pointers.
#include <stdio.h>
#define SIZE 10
// prototypes
void bubble( int work[], size_t size, int (*compare)( int a, int b ) );
int ascending( int a, int b );
int descending( int a, int b );
int main( void )
{
int order; // 1 for ascending order or 2 for descending order
size_t counter; // counter
// initialize unordered array a
int a[ SIZE ] = { 2, 6, 4, 8, 10, 12, 89, 68, 45, 37 };
printf( "%s", "Enter 1 to sort in ascending order,\n"
"Enter 2 to sort in descending order: " );
scanf( "%d", &order );
puts( "\nData items in original order" );
// output original array
for ( counter = 0; counter < SIZE; ++counter ) {
printf( "%5d", a[ counter ] );
} // end for
// sort array in ascending order; pass function ascending as an
// argument to specify ascending sorting order
if ( order == 1 ) {
bubble( a, SIZE, ascending );
puts( "\nData items in ascending order" );
} // end if
else { // pass function descending
bubble( a, SIZE, descending );
puts( "\nData items in descending order" );
} // end else
// output sorted array
for ( counter = 0; counter < SIZE; ++counter ) {
printf( "%5d", a[ counter ] );
} // end for
puts( "\n" );
} // end main
// multipurpose bubble sort; parameter compare is a pointer to
// the comparison function that determines sorting order
void bubble( int work[], size_t size, int (*compare)( int a, int b ) )
{
unsigned int pass; // pass counter
size_t count; // comparison counter
void swap( int *element1Ptr, int *element2ptr ); // prototype
// loop to control passes
for ( pass = 1; pass < size; ++pass ) {
// loop to control number of comparisons per pass
for ( count = 0; count < size - 1; ++count ) {
// if adjacent elements are out of order, swap them
if ( (*compare)( work[ count ], work[ count + 1 ] ) ) {
swap( &work[ count ], &work[ count + 1 ] );
} // end if
} // end for
} // end for
} // end function bubble
// swap values at memory locations to which element1Ptr and
// element2Ptr point
void swap( int *element1Ptr, int *element2Ptr )
{
int hold; // temporary holding variable
hold = *element1Ptr;
*element1Ptr = *element2Ptr;
*element2Ptr = hold;
} // end function swap
// determine whether elements are out of order for an ascending
// order sort
int ascending( int a, int b )
{
return b < a; // should swap if b is less than a
} // end function ascending
// determine whether elements are out of order for a descending
// order sort
int descending( int a, int b )
{
return b > a; // should swap if b is greater than a
} // end function descending
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