Which value is returned by isalpha() ?

gistfile1.txt

/*
 * Which value is returned by isalpha() ? by M-Systems, Inc.
 */

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

int
main(void)
{
        int c, i;

        for (i = 0 ; i < 26 ; i++) {
                c = 'a' + i;
                (void)printf("%d\n", isalpha(c));
        }

        exit(EXIT_SUCCESS);
}