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

typedef struct { char c; unsigned count; } charcount_t;

charcount_t *count_chars(char *s)
{
    charcount_t *counts = calloc(256, sizeof(charcount_t));
    for(int i = 0; i < 256; i++)
        counts[i].c = i;

    while(*s)
        counts[(unsigned)*s++].count++;

    return counts;
}

int int_pair_desc(const void *a, const void *b)
{
    return ((charcount_t *)b)->count - ((charcount_t *)a)->count;
}

int main()
{
    char msg[] = "I am a large brown bear who lives in the forest.  My diet consists primarily of honey and spaceships.";
    printf("string: '%s'\n", msg);
    charcount_t *counts = count_chars(msg);
    qsort(counts, 256, sizeof(charcount_t), int_pair_desc);
    for(int i = 0; i < 256; i++)
        if(counts[i].count > 0)
            printf("Rank[%d]: '%c' - %u\n", i + 1, counts[i].c, counts[i].count);

    free(counts);
    return 0;
}