sort.c

C和指针非常好的一本书.里面的有许多代码可以借鉴.

/*
** Read, sort, and print a list of integer values.
*/
#include <stdlib.h>
#include <stdio.h>

/*
**	Function called by 'qsort' to compare integer values
*/
int
compare_integers( void const *a, void const *b )
{
	register int	const *pa = a;
	register int	const *pb = b;

	return *pa > *pb ? 1 : *pa < *pb ? -1 : 0;
}

int
main()
{
	int	*array;
	int	n_values;
	int	i;

	/*
	** See how many numbers there will be.
	*/
	printf( "How many values are there? " );
	if( scanf( "%d", &n_values ) != 1 || n_values <= 0 ){
		printf( "Illegal number of values.\n" );
		exit( EXIT_FAILURE );
	}

	/*
	** Get memory to store them.
	*/
	array = malloc( n_values * sizeof( int ) );
	if( array == NULL ){
		printf( "Can't get memory for that many values.\n" );
		exit( EXIT_FAILURE );
	}

	/*
	** Read the numbers.
	*/
	for( i = 0; i < n_values; i += 1 ){
		printf( "? " );
		if( scanf( "%d", array + i ) != 1 ){
			printf( "Error reading value #%d\n", i );
			exit( EXIT_FAILURE );
		}
	}

	/*
	** Sort the values.
	*/
	qsort( array, n_values, sizeof( int ), compare_integers );

	/*
	** Print them out.
	*/
	for( i = 0; i < n_values; i += 1 )
		printf( "%d\n", array[i] );

	/*
	** Free the memory and exit.
	*/
	free( array );
	return EXIT_SUCCESS;
}