Count bits

count_bits.c

#include <stdint.h>
#include <limits.h>

#define numbits(x)  (sizeof(x) * 8)

#define max_signed_value_of_type(t)                             \
        (INTMAX_MAX >> (numbits(intmax_t) - numbits(t)))

void count_bits(unsigned int num)
{
        size_t bits = numbits(num);
        unsigned int max = max_signed_value_of_type(num) + 1;
        int i;
        unsigned int t = num;
        int zeroes = 0, ones = 0;

        for (i = 0; i < bits; i++) {
                if (!!(num & max))
                        ones++;
                else
                        zeroes++;

                num = num << 1;
        }

        printf("%u has %d 0's and %d 1's in its binary representation.\n", t, zeroes, ones);
}