/* Fig. 7.26: fig07_26.c
   Multipurpose sorting program using function pointers */
#include <stdio.h>
#define SIZE 10

/* prototypes */
void bubble( int work[], const int size, 
             int (*compare)( int a, int b ) );
int ascending( int a, int b );
int descending( int a, int b );

int main()
{
   int order;   /* 1 for ascending order or 2 for descending order */
   int counter; /* counter */

   /* initialize array a */
   int a[ SIZE ] = { 2, 6, 4, 8, 10, 12, 89, 68, 45, 37 };

   printf( "Enter 1 to sort in ascending order,\n" 
           "Enter 2 to sort in descending order: " );
   scanf( "%d",  &order );

   printf( "\nData items in original order\n" );
   
   /* 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 );
      printf( "\nData items in ascending order\n" );
   } /* end if */ 
   else { /* pass function descending */
      bubble( a, SIZE, descending );
      printf( "\nData items in descending order\n" );
   } /* end else */

   /* output sorted array */
   for ( counter = 0; counter < SIZE; counter++ ) {
      printf( "%5d", a[ counter ] );   
   } /* end for */

   printf( "\n" );

   return 0; /* indicates successful termination */

} /* end main */

/* multipurpose bubble sort; parameter compare is a pointer to
   the comparison function that determines sorting order */
void bubble( int work[], const int size, 
             int (*compare)( int a, int b ) )
{
   int pass;  /* pass counter */
   int 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;   /* 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;   /* swap if b is greater than a */

} /* end function descending */



/**************************************************************************
 * (C) Copyright 1992-2004 by Deitel & Associates, Inc. and               *
 * Pearson Education, Inc. All Rights Reserved.                           *
 *                                                                        *
 * DISCLAIMER: The authors and publisher of this book have used their     *
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 * development, research, and testing of the theories and programs        *
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