qsort快速排序

#include<stdio.h>
#include<stdlib.h>

/*
 * qsort invoke this function
 */
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;  // cool !
}

int main( int argc, char *argv[] )
{
    int *array;
    int n_values;
    int i;

    /*
     * see how many values there
     */
    printf( "How many values there?\n" );
    if( scanf( "%d", &n_values) == EOF || n_values <= 0 ){
        printf( "Illegal number of values.\n" ); 
        exit( EXIT_FAILURE );
    }

    /*
     * allocate mem to store the values
     */
    array = malloc( n_values * sizeof( int ) );
    if( array == NULL ){
        printf( "can't get mem for that values!\n" );
        exit( EXIT_FAILURE );
    }

    /*
     * load these numbers
     */
    for( i = 0; i < n_values; ++i ){
        printf("? "); 
        if( scanf( "%d", array + i ) == EOF ){
            printf( "error reading value #%d\n", i ); 
            free( array );
            exit( EXIT_FAILURE );
        }
    }

    /*
     * sort for these values
     */
    qsort( array, n_values, sizeof( int ), compare_integers );

    /*
     * print the result
     */
    printf( "\nThe result is as follows:\n" );
    for( i = 0; i < n_values; ++i ){
        printf( "%d\n", array[i] ); 
    }
    
    free( array );

    exit( 0 );
}