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Date: Fri, 11 Nov 2011 20:27:22 -0500
From: pete <pfiland@mindspring.com>
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Subject: Re: qsort
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.c:13159

Bill Cunningham wrote:
 
> double prices[]={24.45,24,21};
> 
> I want to sort them from highest to lowest.
> Still not knowing C's semantics
> well enough there's probably a simpler way
> but what kind of function would I
> want to write to pass to that last parameter of qsort?

/* BEGIN output from new.c */

From highest to lowest:
24.450000
24.000000
21.000000

/* END output from new.c */



/* BEGIN new.c */

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

int 
price_comp(const void *a, const void *b)
{
    const double *aa = a;
    const double *bb = b;

    return *aa > *bb ? -1 : *aa != *bb;
}

int 
main(void)
{
    double prices[] = {24.45, 24, 21};
    double *ptr = prices;
    size_t n = sizeof prices / sizeof *prices;

    qsort(prices, n, sizeof *prices, price_comp);

    puts("\n/* BEGIN output from new.c */\n");
    puts("From highest to lowest:");
    while (n-- != 0) {
        printf("%f\n", *ptr);
        ++ptr;
    }
    puts("\n/* END output from new.c */");
    return 0;
}

/* END new.c */

-- 
pete