Count number of bits set

/*
    $> gcc -msse4.2 -Wall -Wextra
    http://stackoverflow.com/questions/109023/best-algorithm-to-count-the-number-of-set-bits-in-a-32-bit-integer
*/
#include <stdio.h>

int main()
{
    unsigned int number;
    int num_bits_set;

    scanf("%u", &number);
    num_bits_set = __builtin_popcount(number);

    printf("%d\n", num_bits_set);

    return 0;
}